A Review of the Stenetriidae (Crustacea: Isopoda: Asellota)

The current classification of the Stenetriidae includes five genera and 63 species, of which 57 species are contained in the genus Stenetrium Haswell, 1881. A history of the classification of the family Stenetriidae is reviewed and useful characters for defining stenetriid taxa and species are derived from the literature. A new diagnosis for the family is provided. Stenetrium is redefined and its composition reduced to 18 species. The type species of Stenetrium, S. armatum Haswell, 1881, is fully redescribed. A new species, Stenetrium adrianae, is described in this paper, highlighting morphological variation that can be useful for distinguishing stenetriid taxa. Three other named genera, Stenobermuda Schultz, 1979a (Stenetrigus Schultz, 1982 is a junior synonym), Protallocoxa Schultz, 1978, and Tenupedunculus Schultz, 1982, are redefined and their compositions adjusted. Four new genera, Tristenium, Hansenium, Liocoryphe, and Mizothenar, are erected to contain distinctive species groups not treated in the literature. Six species are poorly described and cannot be classified in this new arrangement for the family. Lists of species assigned to each group and a key to the genera are provided. SEROV, P.A. & G.D.F. WILSON, 1995. A review of the Stenetriidae (Crustacea: Isopoda: Asellota). Records of the Australian Museum 47(1): 39-82. The isopod family Stenetriidae Hansen, 1905 occupies a central role in the understanding of the suborder Asellota. The disagreement between Wagele (1982, 1989) and Wilson (1987) on stenetriid sister group relationships highlights this family's importance. Although the Stenetriidae shares apomorphies with more derived Asellota (Wilson, 1987), the Stenetriidae also contain important variation in the male pleopods, sometimes resembling members of two other asellote families, the Gnathostenetroididae Kussakin, 1967 and the Pseudojaniridae Wilson, 1986a. Unlike most non-janiroidean families of Asellota, the Stenetriidae range from tropical to polar shallow marine waters (Kussakin, 1973; Hessler et al., 1979), thus occupying possible ancestral habitats for the Asellota. Despite being a potentially rich source of phylogenetic information on asellote relationships, the Stenetriidae has received little revisionary attention. Our paper redresses this situation. After Hansen's (1905: 303) description of the family, Wolff (1962) provided the only comprehensive examination of stenetriid species, but encountered barriers to understanding their interrelationships. The overall similarity of most species made the division of stenetriid taxa difficult. Wolff (1962: 21) stated that "on the whole, Stenetrium is no doubt exceedingly homogenous." This apparent homogeneity, however, was often caused by "short, insufficiently detailed 40 Records of the Australian Museum (1995) Vol. 47 descriptions and illustrations by some authors" (Wolff, 1962: 22). Owing to these problems, Wolff (1962: 22) stated "that several species are very close to each other and some others are probably identical" even though the species are widely separated geographically. He encountered the greatest difficulty in separating the following species: Stenetrium armatum Haswell, 1881 (south-eastern Australia) and S. dalmeida Barnard, 1920; S. diazi Barnard, 1920 (South Africa); S. stebbingi Richardson, 1902 (Bermudas) and S. antillense Hansen, 1905 (West Indies); S. ch iltoni Stebbing, 1905 (Indian and Pacific Oceans) and S. glauerti Nicholls, 1929 (Western Australia); S. medipacificum Miller, 1941 (Pacific Ocean) and S. dagama Barnard, 1920 (South Africa). The synonymies proposed for stenetriids (see Wolff, 1962) exemplify the lack of understanding of their high species diversity and parochial distributions. Stenetrium armatum Haswell, 1881, is a classic example of these misconceptions. Stenetrium armatum was first described only from Port Jackson, Sydney, eastern Australia. Since that time, all similar specimens from south-eastern Australia have been identified as this species. The most recent redescription of S. armatum, stated that the species "is distributed in south-eastern Australia from at least Port Stephens, central New South Wales ... , to the Gulf of St Vincent, near Adelaide, South Australia" (Schultz, 1982). Our extensive examination of all specimens of Stenetrium held by the Australian Museum and the Museum of Victoria revealed that the above range encompasses as many as 20-30 species. Most previous synonomies, therefore, are in doubt. An ongoing revision of the Asellota (e.g., Wilson, 1994; Wilson & Wagele, 1994 for the janiroidean family Janiridae) will assess the phylogenetic position of the Stenetriidae within the suborder. This paper begins this work with a review of stenetriid morphology and taxonomy. We provide a brief overview of the history of stenetriid classification, and then discuss the distinguishing features of the Stenetriidae and their character variation. In the taxonomic section, we provide diagnoses and synonymies for existing genera and describe four new genera: Tristenium, Hansenium, Liocoryphe, and Mizothenar. Descriptions of the type species of Stenetrium, S. armatum Haswell, 1881 and a new species, S. adrianae, demonstrate useful species-level character variation. History of the Stenetriidae Haswell (1881) placed two species in his new genus Stenetrium, S. armatum and S. inerme, both collected from Port Jackson at Sydney, Australia. Stenetrium inerme was later referred by Stebbing (1905) to the janiroidean genus Notasellus Pfeffer, 1881 (= Iathrippa: see Wilson & Wagele, 1994). The first stenetriid species was described by Lucas (1849) as Jaera longicornis from Algeria, later found at Lesina in the Adriatic by HelIer (1866). Bovallius (1886) established the genus J amna for this species, noting marked differences of the included species J aera longicornis and Jaera filicornis Grube, 1861 with other species of Jaera. Beddard (1886) also suggested that Jaera longicornis had been incorrectly placed within Jaera, but did not give an alternative classification. The junior synonym for Stenetrium, Jamna, was used by Stebbing (1893) but later its species were referred by Richardson (1910) to Stenetrium. Between 1881 and 1910, 13 stenetriid species were described. Hansen (1905) published a summary and revision of Stenetrium and proposed the family Stenetriidae. Wolff (1962) summarised the knowledge on stenetriids, including their taxonomy and distribution, and created the superfamily Stenetrioidea. In the period since 1962, 27 stenetriid species have been described, along with 4 new genera. Protallocoxa Schultz, 1978, was presented as an example of a new superfamily, but was later shown to be a taxon consisting of female Stenetrium specimens (Wilson, 1980). Stenobermuda Schultz, 1979a and Stenetrigus Schultz, 1982, were created for species from Bermuda and South Africa respectively, although we find below that these two genera are synonymous. Tenupedunculus Schultz, 1982 is a blind deep water form that is related to southern hemisphere, shallow water Stenetrium (sensu lato) species. Informative Characters of the Stenetriidae The structures used to distinguish taxa, especially the pereopod I and male pleopod 11, have diagnostic potential and are possibly phylogenetically informative. Our findings concern within-stenetriid relations; more detailed research will be required to place these taxa in a broader context of other lower Asellota (Aselloidea, Gnathostenetroidoidea, Protojaniroidea, Pseudojaniridae, Vermectiadidae). In the following, we discuss our observations on characters of stenetriid species, based both on specimens in our collections and from those described in the literature. In many cases, we have inspected types described in the literature. Table 1 provides a list of genera and species mentioned in this paper. The taxonomic section provides explicit diagnoses of all genera, including the four new ones. Comparative illustrations for the genera can be found in Figures 1-3. Pereopod I (Fig. 3). The subchelate, sexually dimorphic pereopod I is the most prominent feature of the Stenetriidae and the most commonly used character in defining species. The male pereopod I has a large, ovoid propodus opposed by an elongate dactylus. The propodal palm varies considerably by possessing either a row of denticulate setae and terminating spine-like seta defining the end of the palm, or various arrangements of blade-like spines or a combination of both. The female pereopod is generally much smaller, unornamented and similar throughout the family, making identification of species from females on this basis difficult. The length of the dactylus relative to the length of the propodal palm in males is useful: the dactylus is longer than the distal width of the propodus in Stenetrium armatum, S. diazi, S. vemae Kensley, 1980, S. esquartum Schultz, 1982, and S. bartholomei Barnard, 1940. The carpus, merus and ischium of the pereopod I are short and robust and vary considerably at the species level in the degree of setation and dorsal margin spination. Stenobermuda acutirostrata (Richardson, 1902) has the most unusual male pereopod I within the family owing to the following features: the small size of the propodus; the large terminal setae on the propodal palm; and elongate carpus, merus and ischium. The female pereopod I (Figs 8A,B, 20A,B) may be distinguished at the species level by setal type, arrangement and number on the opposing edges of the propodus and dactylus, and the setation of the carpus, merus and ischium. The remaining pereopods 11-VII do not differ significantly throughout the Stenetriidae, apart from setal patterns. Sternal spines or keels (Figs 4A,B, 15e). Another strong sexually dimorphic character of the Stenetriidae is the simple spinose projections along the midline of the sternum of some males. Wolff (1962: 25) refers to them as "hyposphenians" but here they will be termed sternal keels owing to

The isopod family Stenetriidae Hansen, 1905 occupies a central role in the understanding of the suborder Asellota.The disagreement between Wagele (1982Wagele ( , 1989) ) and Wilson (1987) on stenetriid sister group relationships highlights this family's importance.Although the Stenetriidae shares apomorphies with more derived Asellota (Wilson, 1987), the Stenetriidae also contain important variation in the male pleopods, sometimes resembling members of two other asellote families, the Gnathostenetroididae Kussakin, 1967 and the Pseudojaniridae Wilson, 1986a.Unlike most non-janiroidean families of Asellota, the Stenetriidae range from tropical to polar shallow marine waters (Kussakin, 1973;Hessler et ah, 1979), thus occupying possible ancestral habitats for the Asellota.Despite being a potentially rich source of phylogenetic information on asellote relationships, the Stenetriidae has received little revisionary attention.Our paper redresses this situation.
After Hansen's (1905: 303) description of the family, Wolff (1962) provided the only comprehensive examination of stenetriid species, but encountered barriers to understanding their interrelationships.The overall similarity of most species made the division of stenetriid taxa difficult.Wolff (1962: 21) stated that "on the whole, Stenetrium is no doubt exceedingly homogenous."This apparent homogeneity, however, was often caused by "short, insufficiently detailed descriptions and illustrations by some authors" (Wolff, 1962: 22).Owing to these problems, Wolff (1962: 22) stated "that several species are very close to each other and some others are probably identical" even though the species are widely separated geographically.He encountered the greatest difficulty in separating the following species: Stenetrium armatum Haswell, 1881 (south-eastern Australia) and S. dalmeida Barnard,192ft S. diazi Barnard, 1920 (South Africa); S. stebbingi Richardson, 1902 (Bermudas) and S. antiilense Hansen, 1905 (West Indies); S. chiltoni Stebbing, 1905 (Indian and Pacific Oceans) and S. glauerti Nicholls, 1929 (Western Australia); S. medipacificum Miller, 1941 (Pacific Ocean) and S. dagama Barnard, 1920 (South Africa).
The synonymies proposed for stenetriids (see Wolff, 1962) exemplify the lack of understanding of their high species diversity and parochial distributions.Stenetrium armatum Haswell, 1881, is a classic example of these misconceptions.Stenetrium armatum was first described only from Port Jackson, Sydney, eastern Australia.Since that time, all similar specimens from south-eastern Australia have been identified as this species.The most recent redescription of 5. armatum, stated that the species "is distributed in south-eastern Australia from at least Port Stephens, central New South Wales..., to the Gulf of St Vincent, near Adelaide, South Australia" (Schuitz, 1982).Our extensive examination of all specimens of Stenetrium held by the Australian Museum and the Museum of Victoria revealed that the above range encompasses as many as 20-30 species.Most previous synonomies, therefore, are in doubt.
An ongoing revision of the Asellota (e.g., Wilson, 1994;Wilson & Wagele, 1994 for the janiroidean family Janiridae) will assess the phylogenetic position of the Stenetriidae within the suborder.This paper begins this work with a review of stenetriid morphology and taxonomy.We provide a brief overview of the history of stenetriid classification, and then discuss the distinguishing features of the Stenetriidae and their character variation.In the taxonomic section, we provide diagnoses and synonymies for existing genera and describe four new genera: Tristenium, Hansenium, Liocoryphe, and Mizothenar.Descriptions of the type species of Stenetrium, S. armatum Haswell, 1881 and a new species, S. adrianae, demonstrate useful species-level character variation.

History of the Stenetriidae
Haswell (1881) placed two species in his new genus Stenetrium, S. armatum and S. inerme, both collected from Port Jackson at Sydney, Australia.Stenetrium inerme was later referred by Stebbing (1905) to the janiroidean genus Notasellus Pfeffer, 1881 (= lathrippa: see Wilson & Wagele, 1994).The first stenetriid species was described by Lucas (1849) as Jaera longicornis from Algeria, later found at Lesina in the Adriatic by Heller (1866).Bovallius (1886) established the genus Jamna for this species, noting marked differences of the included species Jaera longicornis and Jaera filicornis Grube, 1861 with other species of Jaera.Beddard (1886) also suggested that Jaera longicornis had been incorrectly placed within Jaera, but did not give an alternative classification.The junior synonym for Stenetrium, Jamna, was used by Stebbing (1893) but later its species were referred by Richardson (1910) to Stenetrium.
Between 1881 and 1910, 13 stenetriid species were described.Hansen (1905) published a summary and revision of Stenetrium and proposed the family Stenetriidae.Wolff (1962) summarised the knowledge on stenetriids, including their taxonomy and distribution, and created the superfamily Stenetrioidea.In the period since 1962, 27 stenetriid species have been described, along with 4 new genera.Protallocoxa Schuitz, 1978, was presented as an example of a new superfamily, but was later shown to be a taxon consisting of female Stenetrium specimens (Wilson, 1980).Stenobermuda Schuitz, 1979a andStenetrigus Schuitz, 1982, were created for species from Bermuda and South Africa respectively, although we find below that these two genera are synonymous.Tenupedunculus Schuitz, 1982 is a blind deep water form that is related to southern hemisphere, shallow water Stenetrium (sensu lato) species.

Informative Characters of the Stenetriidae
The structures used to distinguish taxa, especially the pereopod I and male pleopod II, have diagnostic potential and are possibly phylogenetically informative.Our findings concern within-stenetriid relations; more detailed research will be required to place these taxa in a broader context of other lower Asellota (Aselloidea, Gnathostenetroidoidea, Protojaniroidea, Pseudojaniridae, Vermectiadidae).In the following, we discuss our observations on characters of stenetriid species, based both on specimens in our collections and from those described in the literature.In many cases, we have inspected types described in the literature.Table 1 provides a list of genera and species mentioned in this paper.The taxonomic section provides explicit diagnoses of all genera, including the four new ones.Comparative illustrations for the genera can be found in Figures 1-3.
Pereopod I (Fig. 3).The subchelate, sexually dimorphic pereopod I is the most prominent feature of the Stenetriidae and the most commonly used character in defining species.The male pereopod I has a large, ovoid propodus opposed by an elongate dactylus.The propodal palm varies considerably by possessing either a row of denticulate setae and terminating spine-like seta defining the end of the palm, or various arrangements of blade-like spines or a combination of both.The female pereopod is generally much smaller, unornamented and similar throughout the family, making identification of species from females on this basis difficult.
The length of the dactylus relative to the length of the propodal palm in males is useful: the dactylus is longer than the distal width of the propodus in Stenetrium armatum, S. diazi, S. vemae Kensley, 1980, S. esquartum Schultz, 1982, and 5. bartholomei Barnard, 1940.The carpus, merus and ischium of the pereopod I are short and robust and vary considerably at the species level in the degree of setation and dorsal margin spination.Stenobermuda acutirostrata (Richardson, 1902) has the most unusual male pereopod I within the family owing to the following features: the small size of the propodus; the large terminal setae on the propodal palm; and elongate carpus, merus and ischium.
The female pereopod I (Figs 8A,B, 20A,B) may be distinguished at the species level by setal type, arrangement and number on the opposing edges of the propodus and dactylus, and the setation of the carpus, merus and ischium.The remaining pereopods II-VII do not differ significantly throughout the Stenetriidae, apart from setal patterns.
Sternal spines or keels (Figs 4A,B,15C).Another strong sexually dimorphic character of the Stenetriidae is the simple spinose projections along the midline of the sternum of some males.Wolff (1962: 25) refers to them as "hyposphenians" but here they will be termed sternal keels owing to their laterally flattened shape.The presence of the keels as well as their absence (e.g., in Stenetrium abyssale Wolff, 1962) has been mentioned by authors as far back as Hansen (1905), although no taxonomic significance was given to this feature.The keels have been illustrated in only Stenetrium maharepa MUller, 1991a, andStenetrium macrochirum Nicholls, 1929 (p. 362, his fig. 1).Size, shape, direction of individual keels may vary.The keels are usually directed anteriorly on pereonites 1-4 and posteriorly on pereonites 5-7.This arrangement is unique to Stenetriidae.Other Asellota have sternal keels on only one segment (Rapaniscus, Nannoniscus, laniropsis and Storthyngura) or on all pereonites such as Macrostylis.These spines differ, however, in direction and position on the pereonites from those seen in the Stenetriidae.The degree to which keels can be used diagnostically is yet to be determined, as they have not been illustrated extensively in the literature.
Eyes (Figs 1,2).Eye morphology varies considerably in the stenetriids by shape, size, number of ocelli and position on the cephalon.The most common eye form of the Stenetriidae is the anterolateral reniform shape containing about 20 ocelli, as seen in Stenetrium sensu stricto, Tenupeduncuius Schultz, 1982, and Hansenium n.gen.The remaining species possess either eyes of as few as 4 ocelli (e.g., Liocoryphe n.gen.and Stenobermuda Schultz, 1979a), or small groups of about 8-10 ocelli (e.g., Stenetrium patulipalma Kensley, 1984a andS. acutirostrum Muller, 1991b).We do not recognise Tenupeduncuius as a genus using the absence of eyes alone as was done by Schultz (1982).Although genera cannot be distinguished by the presence or absence of eyes, the consistency of eye form within the proposed new genera suggests that eyes may be used to distinguish species and genera.
Caution is required when using eyes as a feature owing to ontogenetic variation.Early mancas of some species have a circle of few ocelli similar to Stenetrium minocule, which develop into the characteristic reniform shape eye by the subsequent addition of ocelli anteromedially.Heterochrony, therefore, may be important in the ontogeny and phylogeny of the stenetriids.
Cephalon Projections.The cephalic projections (spines) and the mouthparts may offer important diagnostic features of the cephalon.Cephalic projections include lateral and antennal spines and the rostrum.The antennal spine is defined as a spinelike extension of the anterior margin of the cephalon between the antennula and the antenna.The lateral spines, then, are the spine-like extensions lateral to the antennule.The Stenetriidae and related families (Gnathostenetroididae, Pseudojaniridae) differ in this regard in that they either lack one or the other of these spines.The lateral spines are large and robust while the antennal spines are missing in Pseudojaniridae.In the Gnathostenetroididae, the antennal spines are reduced and the lateral spines are absent.
The rostrum is defined as any anterior extension from the frons or vertex of the cephalon.Shape and armature varies between species, although rostral sizes do not.Schultz (1982) stated that the rostrum of Stenetrium armatum varies from broadly rounded to produced independently of sex, although our research shows he was comparing several species.The serrations on the rostrum in S. armatum and S. adrianae n.sp.are not sexually dimorphic and do not vary ontogenetically except the serrations (when present) are more pronounced in larger animals.
Antennula (Figs 5C, 16D,E) and antenna (Figs 19A-C).These limbs vary in size and shape of the peduncular articles, the number and size of flagellar articles, and number and position of aesthetascs and setae on the flagellar articles.The number of flagellar articles also varies ontogenetically making this feature less useful at the generic level.A large lateral spine on the antennular article 1 is a distinctive feature of the Stenetrium sensu stricto.
Mouthparts (Figs 6,7,18,.The mouthparts are relatively constant throughout the family.The mandible shows principally species distinguishing setal numbers and arrangements on the second article of the palp, the number of spines in the spine row, the denticles and setae around the molar process.Observed differences in size, shape and number of denticles of the grinding surface of the molar process is of undetermined taxonomic significance, Wolff (1962) stated that the maxillula and the maxilla do not vary greatly during the postmarsupial develop-ment.Throughout the Stenetriidae, various setal types of both structures differ in number and size.Exact setal counts for each structure are difficult to determine owing to the poor illustrations of many species.These structures may yield useful information.
The most useful characters on the maxilliped are the epipod, the palp articles, and the fan setae on the distal margin of the endite.The distal tip of the stenetriid epipod typically extends to or beyond palp article 3 and varies principally in marginal setation and distal tip shape.The epipod shape ranges from a typically pointed, tapered tip with an angular coiner on the lateral margin (e.g., Stenetrium armatum), to a rounded tip (e.g., Stenetrium abyssale), or to an epipod with smooth lateral margins (e.g., Stenobermuda acutirostrata).
The maxillipedal endite distal margin has a complex arrangement of 3 rows of differing setae, with the middle row consisting of principally broad, fan shaped setae that vary in number and size between species and may be important at higher taxonomic levels.Unfortunately, most illustrations in the literature do not show these setae in sufficient detail.
Female Genitalia (Figs 13C,D, 26D,E).The external copulatory structure of Stenetrium dagama consists of an external cuticular pocket or broad groove on the anteromedial edge of pereonite 5.The groove possesses a short funnel-like depression and the posteromedial opening of the spermathecal duct ("culicular organ").The spermathecal duct extends posteriorly to the posterior edge of the spermatheca, which passes to the ovary via the lumen of the oviduct.This structure differs from Asellus by being attached to the ventral cuticle and the spermathecal duct.This stenetriid form is similar in many respects to that of the Pseudojaniridae (Wilson, 1986a;Poore & Just, 1990), with the exception that Stenetrium dagama and Stenetrium armatum (Fig. 13C,D) have only a shallow pocket, and the deep stylet receptacle of the Pseudojaniridae is lacking.The presence of a well-defined stylet receptacle in Stenetrium adrtanae n.sp.(Fig. 26D,E) suggests a closer relationship between the stenetriids and the pseudojanirids.The presence or absence of a stylet-like appendix masculina and its accompanying stylet receptacle may be a useful defining character for stenetriid genera.Owing to the variability in shape and length of the male stylet (in those species that possess a needle-like tip), a cor-  Kensley, 1984a, fig. 37b).D, Liocoryphe n.gen.(after Kensley, 1984a, fig. 32).E, Mizothenar n.gen.(after Kensley, 1984a, fig. 33h).F, Protallocoxa Schultz (after Wolff, 1962, fig. 4a).G, Stenobermuda Schultz (after Kensley, 1994, fig. 9a).H, Tenupedunculus Schultz (after Schultz, 1982, fig. 22a).responding species specific variability may be found in the female stylet receptacles.Generalisations concerning the stylet receptacle in the stenetriids must wait until many more species are inspected for this feature.
Pleotelson (Fig. 11, 24A).Three regions are diagnostic on the terminal segment of the body, the posterolateral spines, which are shared with the Gnathostenetroidoidea and the Pseudojaniroidea and some members of the Janiroidea; the telsonic region posterior to the spines may be evenly rounded or have various projections; and the lateral margins anterior to the spines that may be either smooth or serrate.These characters are reliable generic indicators.
Pleopods (Figs 11,12,13A,B,25,.The complex morphology of the pleopods, in particular, male pleopod II may be the most important, yet underused feature in the stenetriid classification.Hansen (1905) first proposed a division of the Asellota using the morphology of the pleopods and Wolff (1962) stated that the first and second male pleopods have offered excellent characters for distinguishing species.
The male pleopod I of the Stenetriidae is unique among the Asellota in having a large, rectangular sympod with two, unfused uniarticulated rami that are less than half the length of the pleotelson and are subequal in length to pleopod II.The rami are unornamented (i.e.do not have a stylet guide extension as is found in Pseudojaniroidea), but vary in shape and setation.This feature varies most at the species level.
The size of the fused sympod of the male first pleopod may be a useful dividing feature among some stenetriid taxa.In a majority of species, the sympod is large, rectangular and well illustrated, but in some species, such as those in Tristenium n.gen., in Mizothenar n.gen.and in Stenobermuda, the sympod is markedly reduced resulting in most authors neglecting to illustrate it.Schultz (1982) described the male pleopod I as without a fused sympod but questions whether it was absent or just not visible.In many of the above species, the sympod is present but reduced and is indicated in the illustrations by the proximal beginning of the sperm canal being above the connection of the pleopod to the sternum.This structure requires a detailed re-examination and may prove to be diagnostically significant.
The literature on asellotan relationships (Amar, 1957;Fresi et at., 1980;Hessler et ai, 1979;Magniez, 1974;Wagele, 1983Wagele, , 1989) ) suggests that the pleopods are homogeneous at the family level in the Stenetriidae.That this was not the case is apparent in our study of the male pleopod II, which was typically presented as having a blunt club-shaped appendix masculina.In fact, the stenetriid male pleopod II appendix masculina includes a broad variety of endopodal structures ranging from the blunt, club form to a stylet-like structure similar to that seen in the Janiroidea or some Aselloidea.Despite this great variety, a single theme emerges from our study.The characteristic features of the stenetriid appendix masculina include a ventrolateral sperm groove on the appendix masculina that is proximally broad, with a median bowl-shaped sperm pocket.The sperm groove narrows distally with an overlapping distolateral margin, and with small distally directed cuticular hairs inside the groove.The appendix masculina of most species also have a subapical, lateral arc or ridge of anteriorly directed cuticular hairs or spines.These features are well demonstrated by the type species, Stenetrium armatum.Variation to the above form includes a solid, narrow, laterallydirected stylet having a row of fine denticles or barbs near the tip, as in Stenetrium adrianae n.sp.Stenobermuda acutirostraia and Stenobermuda syzygus have complex and uniquely shaped male pleopod II, although these may be modifications of the features described above.
The female pleopod II is typically triangular with or without an apical notch and varies in the shape of the lateral margins, the depth of the apical notch (when present) and setal arrangements on the lateral margins.
The remaining three sets of pleopods have been ignored in many classifications.In many instances, pleopod IV and the uniramous pleopod V have been left out completely.The diagnostic features of pleopods III-V morphology should be based on the length/width dimensions, shape, relative size to the other rami (when present) and setal arrangements.The most marked variation of these pleopods occurs in Stenetrium patulipalma and Stenetrium maharepa where pleopod IV exopod is shorter than the endopod and is styliform in shape.This pleopod appears to be an intermediate form between the Stenetriidae and the Gnathostenetroididae. Pseudojanirid pleopods II-V are almost identical to some Stenetriidae, again indicating a close relationship between the two families.
Uropoda (Figs 12F, 24B,C).The uropods are typically short and do not vary significantly throughout the Stenetriidae.They are best used as species-specific features and vary only in setal types and arrangements.

Generic level taxa of the Stenetriidae
At present, the Stenetriidae contains 62 described species and 5 genera, many of which are poorly defined.Our review of stenetriid species has identified 8 distinctive groupings, which we define below as genera.Existing and new genera are diagnosed below, and all genera are delineated with new synonymies.

Diagnosis.
Cephalon with anterolateral and frontal projection lengths subequal to rostrum length; antennal insertions closely spaced laterally with broad interantennular space.Pereon with sternal keels in males anteriorly directed on pereonites 1-4 and posteriorly on 6-7.Antennula as long as width of cephalon; male antennula with 16 articles.Coxal lobes visible in dorsal view on lateral margins of pereonites 2-5 in males and 3-5 in females, Pleotelson with weakly notched lateral margins.Mandibular incisor process with 4 distinct cusps; left spine row with 6 members.Male pereopod I with dactylus longer than width of propodal palm; propodal palm of males with 1 large terminating tooth, 2 connected medial teeth and 1 small, round proximal tooth; carpus length shorter than width in males.Female pereopod I dactylus ventral margin with up to 14 denticulate setae; ischium with prominent spine on anterodorsal corner.Male pleopod I protopod with 1 distal robust seta on each side of medial depression, rami of male narrow, evenly rounded on lateral margins; male pleopod II protopod distal tip sharply produced, appendix masculina with dorsal groove open posteriorly with spine-fringed dome on lateral side of groove.Female pleopod II with apical notch.Uropodal endopod with 3 transverse rings of sensillate setae, 2 distal penicillate setae and apical setal tufts shorter than endopod and exopod.
Head (Figs 5A,B, 6A,B), Large lateral spines and smaller antennal spines subequal in length to rostrum, medial length 0.6 width, 1,15 height.Cephalon freely articulated with pereonite 1. Eyes anterolateral, reniform with up to 18 ocelli depending on stage of development.Rostrum broadly rounded, margin denticulate or smooth, not sexually dimorphic.Dorsal surface medially convex with anterolateral flattened projections.Antennal insertions closely spaced laterally.Frons concave.Labrum evenly rounded, as long as broad, with fine setae fringing the anterior edge.Labrum projects 0.05 body lengths past the rostrum.Clypeus rounded, length 0,125 width, as broad as space between antennal insertions.
Pleon (Figs 4,11).Two free somites.Pleotelson length 1.07 width; length 0.26 body length; lateral margins weakly notched, with 2 elongate simple setae projecting posteriorly from each notch; posterolateral posteriorly directed spine 0.66 along length of pleotelson; small denticle posterior to spine; broadly rounded telson with rounded posterolateral margin.Pleotelson dorsal surface sparsely setose, with rounded longitudinal medial ridge with broad mildly convex lateral fields to each side.
Antennula (Figs 5C,D).Slightly shorter than cephalon width, length 0.36 body length.Male antennula with 16 articles, 13 articles in flagellum with one aesthetasc per article distally; 2 aesthetascs on final article.Article 1 length 1.2 width.One large penicillate seta on lateral margin and a row of 5 small penicillate setae on medial margin.Article 2 length 1.43 width with 2 distal groups of three simple setae.Article 3 medial length 3.7 width, with 2 groups of 3 simple setae.Remnant of second flagellum poorly defined on mediodistal side of article 3, with 2 projecting simple setae and one aesthetasc anterior to scale.
Maxillula (Fig. 6E).Lateral lobe with 9 robust spinose setae, anterior medial setae with posteriorly directed teeth and posterior setae with anteriorly directed teeth.Lateral lobe length 0.15 body length, medial lobe width 0.54 lateral lobe width, medial lobe length 0.83 lateral lobe length.Medial lobe with 3 large, densely setulate setae.Lobe margins and medial lobe distal end with fine hair-like setae.
Pereopod I (Figs 8A-E).Subchelate, sexually dimorphic, males larger with bladed extensions of propodal palm; total length 0.8 body length in males and 0.45 in females.
Males: dactylus length 1.2 propodal width; ventral edge of dactylus with alternating long and short spinulose setae, short setae terminating in bifid denticles, single, broad unguis on distal tip with accessory seta; surface of dactylus sparsely covered in simple setae.Propodus robust, length 1.3 width, densely covered in long simple setae; palm with 1 large ventral tooth, 2 mediodistal teeth and single dorsal tooth.Carpus short, length 0.7 width, medial margin densely covered in simple setae.Merus, short, trapezoidal, with numerous setae, dorsal margin with rounded distal extensions.Ischium and basis length 1.3, 2.6 width, respectively.Basis length 0.23 total pereopod length.
Female: dactylus length 1.1 propodal palm width; ventral margin of dactylus with 10 denticulate setae; distal tip with single claw, Propodus elongate, length 1.7 width; palm with 9 comb setae and 5 long simple setae, terminating in 1 long, robust spinose seta; ventrolateral margin with numerous long, plumose and simple setae.Carpus length 1.2 width, with dense row of plumose setae on ventral margin.Merus as long as wide with prominent distal spine on dorsal margin; numerous simple setae along ventral margin.Ischium dorsal margin with large, robust spine.Basis length 3.4 width, length 0.3 total pereopod length.
Female Genitalia (Figs 13C,D).The female specimen was not treated with KOH because only 1 brooding female was in the collection.Female oopore is a broad, posteriorly directed groove on anterior ventromedial margin of pereonite 5. Sperm athecal duct (cuticular organ) of brooding female opens externally at anterior of oopore, and anteromedially adjacent to a cuticular fold that continues posteriorly into a shallow depression or stylet pocket.Opening of spermathecal duct is surrounded by thickened wall that narrows as organ extends posteriorly.A short tube connects orifice to posterior edge of the spermatheca.Spermatheca is an unexpanded, thin-walled sac that is attached to ventral cuticle and spermathecal duct.Spermatheca extending posteromedially into ovary via a thin-walled, expandable oviduct.
Male Pleopod I (Figs 11B, 12A).Length 0.5 pleotelson length; width 0.1 pleotelson length; protopod length 0.6 width, fused medially producing a central depression between rami with 1 robust seta on each side.Rami lateral margin evenly rounded with simple setae on distal and lateral margin.Pleopod I covering pleopod II; length of pleopod I 1.3 length of pleopod II.
Male Pleopod II (Figs 13A,B).Protopod longer than wide, length 2.8 width, with distal tip sharply produced.Exopod length 1.4 width, positioned distolaterally on protopod.Endopod inserting 0.77 protopod length on medial margin.Endopod length 1.2 protopod length; appendix masculina length 1.6 length of proximal segment.Proximal segment with groove length 0.42 proximal segment length.Appendix masculina groove on dorsal surface, extending from mid length to distal tip, groove fringed by long fine cuticular spines and posteriorly directed fine cuticular hairs.Domed ridge dorsal to groove with fringe of anteriorly directed short spines.
Remarks.The specimens marked as possible syntypes, held by the Australian Museum, had an uncertain origin.This material could not be shown to the same used by Haswell in his original descriptions.Has well (1881) did not designate types in his description nor did he label specimens as types (Springthorpe & Lowry, 1994).The specimens of this species from Port Jackson may be the original specimens but they could also have been collected after the date of publication by others such as Whitekgge, McCulloch or Hedley.Consequently the term 'possible syntype' was used by Springthorpe & Lowry (1994).Schultz (1982), the last revisor of this species did not designate them as types.Stenetrium armatum, however, is the type of its genus, so stability in the generic concept would be improved by establishing a name-bearing specimen for the species.Therefore, one male (AM P42112) is assigned to be the neotype for S. armatum from the "possible syntype" specimens.This specimen matches, as well as can be determined, Haswell's (1881) original description of the species.
Stenetrium armatum may be distinguished from other species of the genus by the armature of the large subchelate pereopod I and unique pleopodal structures.Male pereopod I possesses a distinct dactylus that extends past the propodal palm; the propodal palm has a large, elongate, terminal tooth followed by 3 smaller teeth, 2 of which are broadly joined at their bases.Pleopod I rami has short, robust setae at the base of each ramus.A unique appendix masculina of pleopod II has a subapical fringe of proximally directed, short setae around a lateral dome and a broad apical opening surrounded by long cuticular hairs.Large sternal spines are found on pereonites 1-4 and 6-7.The female can be distinguished by a large spur-like spine on the medial margin of the pereopod I ischium.The distolateral margin of pereonite 5 has a notch above the coxal lappets and no proximal notch on the distolateral margin of pereonite 6. Etymology.The species name 'adrianae' is dedicated to Adriana, the wife of the first author, for her continuous support and encouragement.
Diagnosis.Cephalon with anterolateral and antennal spines shorter than rostrum length, sternal keels in males anteriorly directed on pereonites 2-3 and posteriorly on pereonites 6-7; coxal spines visible in dorsal view on lateral margins of pereonites 4-5 in males and 3-6 in females.Pleotelson with weakly notched lateral margins.Antennula length half width of cephalon; male antennula with 9 articles.Mandibular incisor process with 4 distinct cusps and no denticles; left spine row of incisor process with 5 members.Maxilla lateral lobe with 7 short robust setae on medial margin.Maxilliped endite with 6 long spinulose setae on distal margin.Male pereopod I with dactylus same length as propodal palm width; propodal palm of pereopod I in males with small tooth on margin, 1 large sharply pointed tooth and 1 small rounded tooth adjacent to dactylus; carpus length equal to width in males; opposing margin of dactylus of female pereopod 1 with 16 denticulate setae.Pereopod II ischium with 3 large simple setae on dorsal margin.Male pleopod I broad rami subquadrangular with clipped corner on lateral distal margin.Male pleopod II protopod with broad base, truncated posteriorly with apex roundly produced; appendix masculina with posteromedial opening on lateral margin and long needle-like stylet, without setae or teeth.Female pleopod II without apical notch.Pleopod IV and V of both sexes with 7 and 9 plumose setae, respectively.Uropodal endopod with 2 rows of latitudinal sensillate setae and 6 distal penicillate setae, exopod and endopod with apical setal tufts almost twice as long as rami.
Head (Fig. 16A-C).Large anterolateral spines and smaller antennal spines shorter than length of rostrum.Cephalon dorsal length 0.6, 0.7 width females and males, respectively.Rostrum not sexually dimorphic, broadly rounded with either serrated or smooth tip.Eyes anterolateral, reniform with up to 20 ocelli.Labrum projects 0.15 cephalon lengths past the rostrum.Clypeus length 0.1 width, broader than space between antennule insertions.
Antennula (Fig. 16D,E).Length 0.75 width of cephalon.Male antennula with 9 articles, 6 articles in flagellum with one aesthetasc per article; 2 aesthetascs on terminal article.Article 1 length 1.6 width, small spinose setae on distal half.Article 2 length 0.8 width with 3 groups of simple setae on both sides of distal margin.Article 3 medial length 1.05 width; 2 groups of 2 setae on medial and lateral distal margins.Second flagellum remnant poorly defined on medial side of article 3, with 2 projecting simple setae.
Mandible (Figs 15A, 17B-F).Slender, length 0.66 cephalon length, with 4 distinct cusps on both incisor processes.Lacinia mobilis with 4 distinct cusps, no denticles on dorsal edge, several fine hair-like setae on proximomedial margin and six medially directed simple setae on dorsal base margin.Left spine row with 6 members; first spine separate and attached to base of lacinia mobilis.Right spine row with 12 members having fine setae along bases.Molar process length 0.27 mandibular body length; numerous pointed denticles around posterolateral margin; 9 large setose setae and simple setae below posterior margin; numerous overlapping lamellar setae on anterior margin.Triturating surface graded from coarse to fine granular denticles.Dorsal condyle smoothly rounded, length 0.2 mandibular body length.Palp equal in length to mandibular body length; palp second article length 0.4 mandibular body length, with 2 large setae positioned dorsodistally and mediodistally, with fine setation along upper 0.7 length.Row of 9 small spinose setae between large setae, extending anteriorly from mediodorsal setae.Article 3 with 2 rows of setae extending 0.7 along article length, Paragnath (Fig. 18B).Length 0.8 width; each side not bilobed; 2 rows of fine hair-like setae on distal and medial margins.Ventral surface with numerous cuticular combs.
Maxilla (Fig, 18C).Lobes slender.Lateral lobe with 5 large setae on distal tip and 7 small, short, robust setae on medial margin.Middle lobe with 4 large setulate setae on distal tip and 7 long robust setae on medial margin.Medial lobe distal surface and medial margin densely covered with 13 robust, setulate setae.
Maxilliped (Fig. 19D-F).Basis width 1.1 endite width.Endite with 5 coupling hooks, endite length 0.4 total basis length; distal tip with 6 robust fan setae on ventral margin, increasing in size laterally to seta 5, with seta 6 reduced to 0.9 length of setae 5. Extremely fine hair-like setae along distal lateral margin and posterodorsal margin to fan setae 6. Six large spinose setae between fan setae on ventral surface and undulating cuticular ridge on dorsal surface.Medial distal corner with one large robust, spine-like setae.Dorsal medial ridge of basal endite with 5 setulate setae, and with extremely fine hair-like setae along bases of large setae, grading into spinose setae covering distomedial part of dorsal surface.Palp article 2 same width as endite.Epipod length 3.1 width, length subequal to basis length, distal margins with 12 small simple setae, length 1.6 basis length.
Pereopod I (Fig. 20).Subchelate, strongly sexually dimorphic, total length 0.7 body length in males and 0.4 in females.Strongly sexually dimorphic.Males: dactylus length subequal propodal width; opposing edge of dactylus with long and short simple setae; single claw on distal tip; surface of dactylus densely covered in long simple setae.Propodus robust, length 1.1 width, densely covered in long simple setae; palm with 1 small terminating tooth, one large, sharply pointed tooth and one smaller rounded tooth.Carpus length 0.9 width, ventral margin densely covered with simple setae.Merus length 1.4 width, trapezoidal, with numerous setae, dorsal margin sharply elongated distally.Ischium and basis length 1.4, 4.6 width, respectively.Basis length 0.32 total pereopod length.Female Pereopod I: dactylus length subequal to propodal palm width; opposing edge of dactylus with 16 denticulate setae, 4 long simple setae and single claw on distal tip.Propodus elongate, length 1.4 width; propodal palm with 11 comb setae, terminating in a long, robust seta; numerous long distally plumose setae and simple setae on ventral margin only.Carpus length 0.8 width, with dense row of distally plumose setae on distal part of ventral margin.A, female pereopod I, dactylus and propodus with enlargement of denticulate setae and lateral plumose setae.B, female pereopod I. C-E, holotype male (AM P.42283).C, male dactylus, distal tip.D, male dactylus, proximal joint.E, male pereopod I. Scale bar = 0.1 mm.Merus length 0.8 width, with prominent narrow distal extension of dorsal margin, almost parallel with lateral margin of carpus; medial and lateral margins with numerous iong, simple setae.Ischium length 1.3 width.Basis length 2.9 width, length 0.31 total pereopod length.
Female Genitalia (Fig. 26D,E).The female specimen was treated with KOH in order to clear the cuticle and remove muscle tissue.Female oopore is a broad, posteriorly directed groove on anterior ventromedial margin of pereonite 5. Spermathecal duct (cuticular organ) of brooding female opens externally at anterior of oopore, and anteromedially adjacent to a cuticular fold that continues posteriorly into a blind sac or stylet receptacle.Opening of spermatheca!duct surrounded by thickened wall that narrows as duct extends posteriorly.A short tube connects orifice to posterior edge of the spermatheca.Spermatheca is unexpanded, thin-walled sac that is attached to ventral cuticle and spermathecal duct.Spermatheca extends posteromedially into ovary via a thin-walled, expandable oviduct.
Male Pleopod 11 (Fig. 26A-C).Length 2.9 width.Protopod with broad base, pointed posteriorly with posterolateral corner rounded and produced with 5 simple setae on lateral margin.Exopod length 1.3 width.Endopod length 1.7 protopod length; appendix masculina length 2.3 proximal segment length.Proximal segment ventral groove length 0.5 proximal segment length; 5 sensillate setae on distoventral surface.Appendix masculina stylet-like with distal open groove on lateral side folding to closed tube distally; proximal groove with fine cuticular combs; distal tube thickened, rod-like, with internal striations and external denticles on medial margin.
Remarks.Stenetrium adrianae was originally identified as S. armatum in the collection of the Australian Museum.Although the two species are similar in body shape and dimensions, several morphological characters distinguish 5. adrianae from the latter species: the male pereopod I dactylus is equal in length to the propodal palm width, not extended past the palm as in S. armatum; the propodal palm has a small terminal tooth followed by two large, distinctly separate teeth; large sternal spines are present only on pereonites 2-3 and 6-7; the appendix masculina of pleopods II in males terminates in a long needle-like stylet.
Females can also be distinguished among other species: pleopod II lacking an apical notch, the shape of distolateral corners of pereonites 5-6 (i.e. the shape, depth and position of the coxal spines and notches on the peronites); the absence of large spur-like spines on the carpus, merus and ischium of pereopod I; the presence of a deep stylet receptacle, matching the elongate stylet of the male.

Species included. See Table 1.
Etymology.Tristenium is a re-arrangement and modification of Stenetrium, and is similar to the name of the second author's son.The gender is neuter.Diagnosis.Head frontal margin with weak lateral and antennal spines, antennal spines rounded and longer than blunt lateral spines.Eyes with circlet of few ocelli.Rostrum with broad base and narrow pointed tip.Antennular flagellum with 3 articles.Antennal article 1 without lateral spine.Maxilliped endopodite distal margin with 3 fan setae.Lateral margins of pereonites rounded; pereonites 1-4 sub equal in length, longer than remaining pereonites; most pereonites with only 1 coxal lobe or spine visible in dorsal view.Male pereopod I with broad, robust propodus with denticulate setae and broad blunt teeth on propodal palm; dactylus equal in length to propodal palm; propodal palm terminal seta with small accessory seta and serrate ventral margin.Pleopod II protopod distal tip rounded without distal extension; exopod and endopod positioned subapically on medial margin.Appendix masculina elongate, tapering to needle-like stylet with long setae on lateral margin.Pleotelson elongate, with 3 free reduced pleonites; posterolateral spines reduced; postanal region roundly triangular, without posterolateral extensions.
Remarks.The species of this genus all possess heads with reduced lateral and antennal spines, eyes with few ocelli, narrow triangular rostrums, and appendices masculinae with long needle-like stylets.Although a stylet similar to Stenetrium adrianae occurs in this genus, the long setae on the stylet tip and the differences in the body shape, cephalon shape and the shape of the remaining pleopods clearly distinguish this genus as a separate unit.

Species included. See Table 1.
Etymology.Hansenium is named in honor of H.J. Hansen, who provided the first definitive work on the Stenetriidae early in this century.The gender is neuter.

Remarks.
The genus Hansenium is most closely related to Stenetrium sensu stricto in overall morphology but can be distinguished most prominently by the large, pointed extended carpus that participates in grasping with an elongated dactylus.Hansenium also has large reniform eyes, reduced lateral spines and a broad short rostrum.A correction is made to the nomenclature of the species described as S. caicosensis Kensley & Heard, 1991 by changing it to H. caicosense, in order that the species name is consistent with the gender of the genus, i.e. neuter.
Species included.See Table 1.
Etymology.Liocoryphe is derived from the Greek words "lius" meaning smooth, and "coryphe" meaning crown of the head.The name refers to the smooth head of this genus which lacks spines or lateral fields.The gender is feminine.

Remarks.
Liocoryphe is closely related to Hansenium and is distinguished by the males having an extended carpus.This genus gains separate generic status by lacking lateral spines on the head, having a small round group of ocelli, a short blunt rostrum, and a large blunt extension on the carpus that does not participate in grasping with the dactylus.

Species included. See Table 1.
Etymology.Mizothenar is derived from the Greek words "mizon" meaning larger, and "thenar" meaning flat of the hand or palm.The name refers to the propodal palm of first pereopod, which is larger than in most stenetriids.The gender is neuter.
Diagnosis.Small bodied (2-3 mm), elongate stenetriid.Head frontal margin with no lateral spines, antennal spines weak but longer than rostrum; rostrum much reduced and bilobed; eyes small, round, anterolateral groups of up to 10 ocelli set close to lateral margin.Antennular flagellum with 4 articles, second article longer than remaining articles.Antennal article 1 without lateral spine.Maxilliped endopodite distal margin with 3 fan setae.Pereonite lateral margins rounded; pereonite lengths subequal.Pereopod I not sexually dimorphic but extremely broad and rounded, larger than cephalon, as long as broad; dactylus as long as propodal palm.Female pleopod II shield shaped with deep, narrow apical notch.Male pleopod II appendix masculina elongate with blunt distal tip and subapical row of short, proximally directed cuticular hairs.Pleopod IV endopod styliform.Pleotelson strawberry shaped with weak posterolateral spines, with 3 reduced free pleonites.
Remarks.The two closely related species of Mizothenar are distinguished from the other genera by possessing a largely gnathostenetroidid habitus that includes the absence of lateral spines, reduced antennal spines, and bilobed, reduced rostrum on the cephalon; short appendix masculina, styliform exopod of pleopod 4; and small body size.The other pleopods, pereopod I and the presence of sternal keels along the ventral midline are, however, distinctly stenetrioid in form.A closer examination of these species may throw more light on the relationships between the two superfamilies, Stenetrioidea and Gnathostenetroidoidea.
Stenetrigus was created by Schultz (1982) for Stenetrium syzygus Barnard, 1940 using the following features: eyes of few ocelli; male pleopod II without fused sympod; possible hermaphroditism; no posterolateral notch on the pleotelson; long anterolateral and "antennal spines" and a long, acutely pointed rostrum; manus simple, toothed with plumose setae on ventral margin of propodus.This combination of features, although rare, is not unique among the stenetriids.Stenobermuda acutirostrata (Richardson, 1902) is similar to S. syzygus in many respects, particularly the ones used here to define Stenobermuda.The absence of the posterolateral notches on the pleotelson is the only difference between the two species, which is not a genus-level feature.As with the description of Stenobermuda, the structure of pleopods III-V and the male pleopod II of S. syzygus, which closely resembles that of Stenobermuda, were not mentioned in the original description of Schultz, 1982.Owing to the similarities of the two species mentioned above, both genera are synonymised, with the name Stenobermuda having priority.The possible hermaphroditism or similarity of the pleopods between the male and female alluded to by Schultz (1982: 58-59) cannot be evaluated further because Barnard's (1940) "female" specimen was not available to Schultz for inspection.
Diagnosis.Head angular, broader than long with elongate, acutely pointed lateral spines extending past rostrum.Rostrum small rounded, extending slightly past antennal spine.Eyes reniform of about 20 ocelli.Antennal article 1 without lateral spine, Antennular flagellum with 12-24 articles, Pereonites \-A with sharply produced anterolateral corners, double coxal lobes visible in dorsal view.Male pleopod II protopod with small, pointed apical extension; appendix masculina elongate, narrow, distal tip rounded laterally but weakly pointed on medial margin with subdistal lateral setal ridge; exopod and endopod subapical on medial margin.Female pleopod II with distal half narrowing sharply to rounded point.Pleotelson with 2 free pleonites.Pleotelson with weak posterolateral spines, prominent posterolateral and medial cuticular extensions.Uropods large.
Remarks.The unifying features of Tenupedunculus include the shape of the male pleopod I, the appendix masculina of pleopod II, the number of dorsally visible coxal lobes, and a head with large, robust lateral spines and reduced antennal spines.The degree of enlargement of the lateral spine and reduction of the antennal spine varies throughout the genus from the extreme cases as seen in Stenetrium acutum and Stenetrium inflectifrons to the more subdued forms of Stenetrium pulchrum and Stenetrium drakensis (nee Protallocoxd) S. drakensis was placed in this genus, even though no males were collected, because of its close resemblance with Stenetrium beddardi in the cephalon armature, the pleotelson shape and the presence of 2 coxal lobes on pereonite I. Schultz (1982) also noted a close resemblance between these two species.
The concept of Tenupedunculus Schultz, 1982 was based on lack of eyes in T. elongatus, a dubious diagnostic feature (cf.Wolff, 1962;Hessler & Wilson, 1983).All other features used in Schultz's (1982) description do not unequivocally define the new genus among all stenetriids, Schultz (1982) even states that the "male pleopod 2 and others [are] Stenetrium like".
The similarities to Stenetrium pulchrum and Stenetrium haswelli in the male pleopods, the pleotelson and the dorsally visible coxal lobes of T. elongatus, however, place this species within this genus.Although T. elongatus does not represent the typical form of this genus as seen in S. acutum and S. inflectifrons, the genus name is valid and has priority.Therefore Tenupedunculus is used as the name for this genus.Tenupedunculus may be further separated into two groups after closer examination of the types.

Biogeographical Distributions
The proposed generic groupings have resulted in three distinct geographical regions for the distribution of the Stenetriidae.Stenetrium sensu stricto is a shallow water group distributed from a region including New Zealand to the western side of South Africa, taking in all of southern Australia.The deep ocean component of this region contains members oiProtallocoxa.
Tenupedunculus is a deep ocean assemblage encompassing the second region, around the southern tip of South America to Antarctica.
The remaining five genera are circumtropical with considerable overlap between the genera.They inhabit the littoral and sublittoral zones, principally in coral reef biomes.In all stenetriid genera, body spinosity increases with increasing latitude in the southern hemisphere, although the reasons for this geographic pattern are not apparent.
present, dorsal.One or two free pleonites visible dorsally.Female spermathecal duct opens adjacent to oopore and posteriorly-directed pocket in ventral cuticle (stylet receptacle).Penes separate, emerging lateral to midline from posterior margin of pleonite 7 near medial side of coxa VII; penes tubular with non-overlapping rounded tips.Antennulae short, less than one-third body length.Antennal scale well developed, basally broad.Pereopod I sexually dimorphic, prehension between dactylus and propodus; propodus enlarged with strong comb setae (not bifid comb setae) on prehensile margin; carpus distinctly smaller than propodus, roughly trapezoidal.Pleopods I-II less than half length of pleotelson.Female pleopods II fused into single shield-like sympod, protopod absent.Male pleopod I with distinct protopod, fused medially; distal ramus clearly articulating with 99, Family diagnosis.Asellota with flattened body and subparallel lateral margins.Ventral surfaces of males with spine-like sternal keels (sometimes absent).Eyes Fig, 5. Stenetrium armatum Haswell.Neotype male (AM P.42112).A, dorsal view of cephalon.B, ventral view of cephalon.C, antennula with enlargement of penicillate setae on article 1. D, antennular second flageilura remnant on article 3. Scale bar = 0.5 mm.if protopod; rami without distal stylet guides.Male pleopod II protopod with small apical, laterallycurving extension; exopod uniarticulate, short and broad, with oval transverse terminal hook; proximal endopodal segment tubular, elongate and narrow, shorter than distal segment; appendix masculina with distal groove or tube with many cuticular hairs terminating in laterally directed stylet or broad opening.Pleopod III endopod with 3 or more plumose setae.Uropods generally short but with protopod extending beyond posterior margin of pleotelson.