Macrostylis peteri Riehl sp. nov.

Materials

Type status: Holotype. Occurrence: occurrenceDetails: in sediment; catalogNumber: NMV J 60800; occurrenceRemarks: free-living; recordedBy: G. C. B. Poore; individualCount: 1; sex: female; lifeStage: adult; reproductiveCondition: non-ovigerous; preparations: whole animal (ETOH); disposition: in collection; occurrenceID: 101BB144-53A6-50F1-9725-E96107890E93; Taxon: scientificName: Macrostylis peteri Riehl; kingdom: Animalia; phylum: Arthropoda; class: Malacostraca; order: Isopoda; family: Macrostylidae; genus: Macrostylis; specificEpithet: peteri; taxonRank: species; scientificNameAuthorship: Riehl; vernacularName: Peter's Long-stalked Sea Slater; nomenclaturalCode: ICZN; Location: higherGeography: Indian Ocean; continent: Australia; stateProvince: Western Australia; county: Australia; municipality: Ningaloo South; locality: SS 07 / 2005 Station 23 T 1 700; verbatimDepth: 715.17; verbatimCoordinates: 22°3'46.44''S, 113°43'22.8''E; verbatimLatitude: 22°3'46.44''S; verbatimLongitude: 113°43'22.8''E; decimalLatitude: - 22.0629; decimalLongitude: 113.723; Identification: identifiedBy: Torben Riehl; dateIdentified: 2011; Event: samplingProtocol: R / V SOUTHERN SURVEYOR cruise SS 02 / 2005, Smith McIntyre Grab; eventDate: 24. 07. 2005; habitat: sediment; fieldNumber: SS 07 / 2005 23 T 1 700; Record Level: institutionID: http://grscicoll.org/institution/museum-victoria; institutionCode: NMV; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: occurrenceDetails: in sediment; catalogNumber: NMV J 46837; occurrenceRemarks: free-living; recordedBy: G. C. B. Poore; individualCount: 1; sex: female; lifeStage: adult; reproductiveCondition: non-ovigerous; preparations: whole animal (ETOH); disposition: in collection; occurrenceID: BB12D00E-7FBD-5784-A097-35387E727389; Taxon: scientificName: Macrostylis peteri Riehl; kingdom: Animalia; phylum: Arthropoda; class: Malacostraca; order: Isopoda; family: Macrostylidae; genus: Macrostylis; specificEpithet: peteri; taxonRank: species; scientificNameAuthorship: Riehl; vernacularName: Peter's Long-stalked Sea Slater; nomenclaturalCode: ICZN; Location: higherGeography: Indian Ocean; continent: Australia; stateProvince: Western Australia; county: Australia; municipality: Ningaloo South; locality: SS 07 / 2005 Station 23 T 1 700; verbatimDepth: 715.17; verbatimCoordinates: 22°3'46.44''S, 113°43'22.8''E; verbatimLatitude: 22°3'46.44''S; verbatimLongitude: 113°43'22.8''E; decimalLatitude: - 22.0629; decimalLongitude: 113.723; Identification: identifiedBy: Torben Riehl; dateIdentified: 2011; Event: samplingProtocol: R / V SOUTHERN SURVEYOR cruise SS 02 / 2005, Smith McIntyre Grab; eventDate: 24. 07. 2005; habitat: sediment; fieldNumber: SS 07 / 2005 23 T 1 700; Record Level: institutionID: http://grscicoll.org/institution/museum-victoria; institutionCode: NMV; basisOfRecord: PreservedSpecimen

Type status: Other material. Occurrence: occurrenceDetails: in sediment; catalogNumber: NMV J 60803; occurrenceRemarks: free-living; recordedBy: G. C. B. Poore; individualCount: 1; sex: male; lifeStage: subadult; reproductiveCondition: immature; preparations: whole animal (ETOH); disposition: in collection; occurrenceID: 8F9890F4-961E-50E9-BCDA-BB1DC55F618C; Taxon: scientificName: Macrostylis cf. peteri Riehl; kingdom: Animalia; phylum: Arthropoda; class: Malacostraca; order: Isopoda; family: Macrostylidae; genus: Macrostylis; specificEpithet: cf. peteri; taxonRank: species; scientificNameAuthorship: Riehl; vernacularName: Peter's Long-stalked Sea Slater; nomenclaturalCode: ICZN; Location: higherGeography: Indian Ocean; continent: Australia; stateProvince: Western Australia; county: Australia; municipality: Ningaloo North; locality: SS 07 / 2005 Station 33 T 2 400; verbatimDepth: 429.392; verbatimCoordinates: 21°58'0.85''S, 113°47'20.4''E; verbatimLatitude: 21°58'0.85''S; verbatimLongitude: 113°47'20.4''E; decimalLatitude: - 21.9669; decimalLongitude: 113.789; Identification: identifiedBy: Torben Riehl; dateIdentified: 2011; identificationRemarks: species identity unclear due to juvenile stage and lack of genetic data; Event: samplingProtocol: R / V SOUTHERN SURVEYOR cruise SS 02 / 2005, Smith McIntyre Grab; eventDate: 24. 07. 2005; habitat: sediment; fieldNumber: SS 07 / 2005 33 T 2 400; Record Level: institutionID: http://grscicoll.org/institution/museum-victoria; institutionCode: NMV; basisOfRecord: PreservedSpecimen

Description

Description non-ovigerous (preparatory) female

Body (Figs 40, 41, 42) shape broadest in anterior half, narrowing posteriorly, subcylindrical; length 2.3–2.4 mm, 3.5–3.8 width, tergite and Plt surfaces hirsute, rest of body less setose. Ventral projections (Fig. 40 B, Fig. 41 B) present; Prn 1 spine acute and prominent; Prn 2 spine directed ventrally, acute, prominent, located medially; Prn 3 spine acute, prominent, medially positioned on; Prn 4 spine directed posteriorly, acute, prominent, closer to posterior segment border; Prn 5 spine acute, prominent, positioned closer to posterior segment border; Prn 6 spine acute, prominent, positioned closer to posterior segment border; Prn 7 spine prominent, acute; spines 3-7 directed posteroventrally. Ceph (Fig. 40 A, Fig. 41 C) length 0.45–0.66 width, 0.10–0.15 body length; frontal furrow present, laterally bent anteriorly, medially straight; posterolateral setae present, flexibly articulated. Fossosoma (Fig. 40 A) length 0.85–0.89 width, 0.24 body length; ventral surface without carina, lateral tergite margins confluent, posterolaterally setose. Prn 1-3 (Fig. 40 A, B) posterolaterally with simple seta respectively. Prn 4 (Fig. 40 A) width 1.1–1.2 pereonite 5 width, length 0.3–0.39 width; with well developed collum, medially widest, with relatively slightly projecting posterolateral margin; lateral margins sinuoid, narrowest anteriorly at collum, widest at coxal insertions, progressively narrowing towards posterolateral protrusions; posterior tergite margin setose, setae flexibly articulated, not extending beyond posterolateral margin; posterolateral margins projecting, contracting laterally, tapering; posterolateral setae robust, spine-like, articulating on pedestals. Prn 5 (Fig. 40 A) length 0.48–0.5 width, 1.0–1.4 Prn 4 length; posterior tergite margin setose, setae flexibly articulated, not extending beyond posterolateral margin; posterolateral margins rounded; posterolateral setae robust, spine-like, articulating on pedestals. Prn 6 (Fig. 40 A) length 0.53–0.57 width, 1.02–1.08 Prn 5 length; posterior tergite margin setose; setae flexibly articulated, not extending beyond posterolateral angles; posterolateral margin projecting, rounded; posterolateral setae robust, flexibly articulated. Prn 7 (Fig. 40 A) length 0.42–0.45 width; posterior tergite margin setose, setae flexibly articulated, not extending beyond posterolateral margin. Posterolateral margin projecting posteriorly, tapering, subangular; posterolateral setae robust, (149) flexibly articulated. Plt (Fig. 40) length 0.23–0.24 body length, 1.4 width, slightly narrower than Prn 7, near-elliptic; posterior margin at uropod insertions straight to convex; apex convex, spatulate, length 0.15–0.18 Plt length, with 12 pappose setae positioned on and around apex; pleopodal cavity width 0.76 Plt width; setal ridges visible in dorsal view; longitudinal trough width 0.41 Plt width; anal opening caudally in the trough, exposed and superficial, tilted posteriorly relative to frontal plane.

A 1 (Fig. 43 A, D) length 0.22 head width, 0.13 A 2 length, width 0.53 A 2 width; Art decreasing in size from proximal to distal, relative Art length ratios 1.0: 0.85: 0.55: 0.49: 0.33; Art L / W ratios 2.0, 2.9, 1.8, 1.9, 1.8; all Art longer than wide; Art 1 longest and widest; terminal article with 1 aesthetascs; aesthetasc with intermediate belt of constrictions. A 2 (Fig. 43 A, D) length 0.4 body length; C length shorter than width; basis length exceeding width, more than twice C length; ischium longer than C; merus and carpus each longer than C, basis and ischium combined; carpus shorter than merus length; (218) flag with 7 Art. Md (Fig. 44) with lateral setae; molar process length greater than incisor length; both incisor processes oligodentate with dorsal and ventral subdistal teeth that partly enclose lacinia, left Md incisor process with four cusps, lacinia mobilis robust, similar to incisor process, with four cusps; right Md incisior process with three cusps, lacinia mobilis spine-like, smaller than left lacinia.

Mxp (Fig. 43 F-H) basis length 4 width; endite distally with four fan setae, medioventrally setose; palp wider than endite, Art 2 wider than Art 1; ischium distomedially with one seta, shorter than Art 3, Art 4 distomedial extension present, Art 5 absent; epipod length 3.2 width, 1.0 coxa-basis length. P 1 (Fig. 45) length 0.46 body length; ischium dorsal margin with five simple setae; merus dorsal margin with six setae: five simple, long, one more robust, bifid apically, ventral margin with four medially biserrate, distally sensillate setae; carpus dorsally with three setae: one simple, long, one broom, one bifurcate; dactylus medially-subdistally with three sensillae, terminal claw length 0.28 dactylus length. P 2 (Fig. 45 B) length 0.42 body length. Ischium dorsally with 4-5 simple setae submarginally; merus dorsally with 4-5 simple, long setae submarginally and one bifurcate seta distodorsally, ventrally with four medially biserrate, distally sensillate setae, on ventral margin, with 1-2 minute, simple distomedially; carpus dorsally with 2-3 setae: 0-1 simple, one broom, one bifurcate, ventrally with 3-4 setae: 2-3 medially biserrate, distally sensillate, one slender, simple, asetulate; dactylus medially-subdistally with three sensillae. P 3 (Fig. 45 C) length 0.48 body length. Ischium dorsal lobe subtriangular; dorsal margin proximally with four asetulate setae; apex with one prominent, robust, sensillate, bifid, straight, flexibly articulated seta; distally with row of three asetulate setae; merus dorsally with six setae: four simple, slender, asetulate, one bifurcate, slender, one bifurcate, robust, ventrally with three medially biserrate, distally sensillate setae; carpus dorsally with five setae: one simple, slender, three bifurcate, slender, one broom; carpus ventrally with four setae: two medially biserrate, distally sensillate, two simple, asetulate; dactylus medial cuticle subdistally with three sensillae. P 4 (Fig. 46 B, Fig. 47 C) length 0.27 body length; carpus oval in cross section.

P 5 (Fig. 46 C, Fig. 47 B) length 0.47 body length. P 6 (Fig. 46, Fig. 47 C) length 0.63 body length. P 7 (Fig. 46 E, Fig. 47 D) length 0.63 body length; basis length 4.0 width, dorsal margin row of 16 elongate setae, exceeding beyond proximal half of article, setae longer basis width, ventral margin with row of six elongate setae, setae shorter basis width; ischium length 3.5 width, mediodorsally with three simple setae, medioventrally with three simple scattered setae, distoventrally with one simple seta; merus length 2.7 width, distodorsally with three simple setae, medioventrally with simple one seta, (343) distoventrally with two simple setae; carpus length 8.5 width, distodorsally with two setae: one simple, one broom, medioventrally with two simple setae, distoventrally with four setae; propodus length 7.3 width; dactylus length 3.0 width.

Op (Fig. 40 C, Fig. 41 E) elongate; length 2.0 width, 1.0 pleotelson dorsal length, completely covering anus; distally tapered; distal margin broad, apical width 0.52 operculum width; with rounded, edgeless keel; with lateral fringe consisting of 12–14 setae on either side, with lateral fringe separate from apical row of setae; with 16 short apical setae. Plp 3 endopod plumose setae shorter endopod; exopod monoarticulate, with one conspicuous subapical seta. Plp 4 distal pappose seta absent, exopod lateral fringe of setae present. Urp (Fig. 40 A, D) length 0.87 pleotelson length; protopod cylindrical, distal margin blunt, endopod insertion terminally; protopod length 10.8 width, 0.65 pleotelson length; endopod width at articulation subequal protopod width, length 6.2 width, 0.36 protopod length.

Macrostylis cf. peteri

Description juvenile male

Body (Fig. 48 A) more elongate than in female, length 1.84 mm, 4.0 width. Ventral projections relatively needle-shaped, slender and pointed; Prn 3-4 spines acute, prominent, located medially, directed posteroventrally; Prn 4 spine directed posteriorly, prominent; Prn 5-7 spines prominent, located closer to posterior segment border, directed posteroventrally. Cephalothorax (Fig. 48 A, C) length 0.62 width, 0.13 body length; frontal furrow present, with row of small setae, posterior tergum on either side with four setae in subtriangular arrangement, posterolateral setae present. Fossosoma (Fig. 48) length 0.87 width. Prn 3 posterolaterally with two asensillate, robust, flexibly articulated setae.

Prn 4 (Fig. 48) integration with other segments clearly distinct from both anterior and posterior pereonites: with well-developed collum, widest medially, relatively small posterolateral projections; lateral margins sinusoid; posterolateral margins tapering; posterolateral setae robust, sensillate, spine-like. Prn 5 posterolateral setae sensillate, robust, flexibly articulated.

Pln 1 (Fig. 48) tergal articulation with Plt present, clearly visible, laterally meeting with Prn 7 posterior margin resulting in a wedge-shaped appearance or pleonite 1; medially with pair of simple setae near posterior margin. Plt (Fig. 48) hourglass-shaped; length 1.4 width, 0.23 body length, slightly narrower than pereonite 7, posterior margin at uropod insertions straight; posterior apex convex, subtriangular, length 0.17 Plt length, with 10 setae on apex; pleopodal cavity width 0.83 Plt width, longitudinal trough width 0.40 Plt width.

A 1 (Fig. 48 B, C) length 0.8 head width; art 1, 2 and 5 elongate tubular; art 3–4 squat or noticeably shorter; aesthetascs with intermediate belt of constrictions; art 1, 2 elongate, of subsimilar length; art 3–4 squat, shorter than article 1; art 5 elongate, shorter than art 1. A 2 (Fig. 48 B, C) coxa squat; basis elongate, cylindrical along whole axis, longer than coxa; ischium elongate, cylindrical along whole axis.

P 1 (Fig. 49 A) ischium with dorsal setae submarginally. P 3 (Fig. 49 C) length 0.46 body length; dorsal lobe flat and rounded; proximally with three simple setae; apex with one prominent seta, apical seta robust, flexibly articulated, straight, bifid; distally with two simple setae; ischium dorsal margin with row of six setae: three simple, three bifurcate; merus ventrally with three setae, distally setulate; carpus dorsally with four setae in row along margin: one simple, three bifurcate; carpus ventrally with four setae: two medially submarginally, distally sensillate, one broom distally, one simple distally near carpo-propodal articulation.

P 6 (Fig. 50 B) length 0.64 body length; art L / W ratios 5.2, 3.3, 2.5, 7.0, 8.0, 2.0; relative art length ratios 1.0, 0.74, 0.48, 0.90, 0.52, 0.13. P 7 (Fig. 50 C) length 0.67 body length; relative article length ratios 1.0, 0.70, 0.42, 0.64, 0.67, 0.24; basis length 4.1 width; dorsal margin row of 11 elongate setae; ventral margin with row of five setae, setae shorter basis than width; ischium length 3.3 width, mediodorsally with two simple setae in row, medioventrally with three simple setae in row; distoventrally with two simple setae; merus length 2.8 width, distodorsally with four simple setae, medioventrally with one simple seta; distoventrally with three setae: one slender, simple laterodistally, one robust, bifurcate, one simple, slender mediodistally; carpus length 4.2 width, mediodorsally with two simple setae submarginally, distodorsally with two setae: one broom, one bifid, semi-robust, medioventrally with three simple setae in marginal row, distoventrally with two bifid, semi-robust setae; propodus length 7.3 width; dactylus length 4.0 width.

Plp 1 (Fig. 51 A, B, C) shorter Plp 2, with the latter projecting beyond Plp 1; medial lobes distally with five sensillae, ventrally with setae present; distally projecting ventrally beyond Plp 2 ventral margin. Plp 2 (Fig. 51 B) protopod apex tapering, distally enclosing Plp 1 and converging towards counterpart, with nine setae on proximolateral margin; with eight pappose setae distally.

Type material

Holotype (NMV J 60800), adult, non-ovigerous female; paratype (NMV J 46837), adult, non-ovigerous female.

Material examined

Macrostylis peteri sp. nov. Holotype (NMV J 60800) and paratype (NMV J 46837) and two additional specimens:

Macrostylis cf. peteri: one sub-adult male (NMV J 60803) from near the type locality, station SS 07 / 2005 Station 33 T 2 400, 21°58'0.85''S, 113°47'20.4''E, 429.4 m depth. Macrostylis sp 2: two adult, ovigerous females (NMV J 60820) from south-eastern Indian Ocean, Australian continental shelf, off Western Australia, Barrow region, 21°00'30.2"S, 114°22'51.6"E, 397 m depth. one adult, non-ovigerous female (NMV J 60801), one adult male (NMV J 46835) and two juveniles (NMV J 46836) from south-eastern Indian Ocean, Australian continental shelf, off Western Australia, Ningaloo Region, 22°01'26.0"S, 113°39'25.2"E, 1073 m depth.

Type locality

South-eastern Indian Ocean, Australian continental shelf, off Western Australia, Ningaloo Region, 22°3'46.44''S, 113°43'22.8''E, 715.2 m depth.

Diagnosis

Pleotelson posterior apex subtriangular; male pleonite 1 articulation with pleotelson expressed. Maxilliped dactylus reduced, absent. Pereopod 3 ischium dorsal lobe flat subtriangular, dorsal margin proximally with row of 3–4 asetulate setae; apex with one flexibly articulated, straight, prominent robust, setulate, bifid seta; distally with row of 2–3 asetulate setae. Operculum relatively large, ca. 0.8 pleotelson width, projecting caudally to near pleotelson apex, covering anal opening.

Etymology

The specific epithet honours the father of the describer, Claus-Peter Riehl.

Distribution

Only known from the type locality (Fig. 52).

Taxon discussion

On the assignment of a male

As the examined male specimen is not at the adult / copulatory stage, it has not been fully scored and evaluated in DELTA, particularly with respect to morphometric data. This omission is based on established evidence indicating that the morphology of males in many species undergoes significant changes during the terminal (adult) moult (Riehl et al. 2012, Bober et al. 2017). Nevertheless, the specimen exhibits distinct character states that unequivocally place it within the Macrostylis subinermis group of the Macrostylidae. Specifically, the antennula displays a characteristic sequence of length-to-width ratios that diverges from the plesiomorphic condition (see, for example, Riehl et al. (2012), Riehl et al. (2014 a)) and the arrangement of the first and second pleopods is diagnostic: distally, the first pleopods project posteroventrally from within the second pleopods, which envelop them at their distal region.

Sexual dimorphism can complicate the assignment of conspecific adult males and females. In the case of Macrostylis peteri Riehl, sp. nov., male and female specimens were collected from stations separated by several miles (km) and at slightly different depths. Although spatial co-occurrence alone would not definitively confirm conspecificity, it would provide supporting evidence. However, in this instance, the subadult male — typically morphologically similar to the female (Riehl et al. 2012, Riehl 2014) — exhibits several shared characteristics with the female that further substantiate the assumption of conspecificity. These include its slightly smaller body size relative to the female, a common trait in macrostylids (Bober et al. 2017), as well as general morphological similarities, such as the shape of pereonite 4, the distribution of posterolateral pereonal setae, the incomplete tergal separation between pereonites 1 and 2, the size and distribution of ventral spines and the extent of pleopod 2 (operculum), which projects nearly to the posterior pleotelson apex and partially covers the anus. Nevertheless, doubt remains about the conspecifity of the male and female specimens investigated due to the lack of molecular data and the juvenile stage of the male specimen. Hence, the male specimen cannot be allocated to Macrostylis peteri Riehl, sp. nov. with certainty.

Notes

First macrostylid from Australian waters

Macrostylis peteri Riehl, sp. nov. is the first species of the family Macrostylidae reported from Australian waters.

Oostegite development

For the first time, the internal development of the oostegites during the preparatory phase could be observed for the family Macrostylidae. This character state differentiates Macrostylidae from the Janiroidea families Munnopsidae and Desmosomatidae which have been discussed as potentially closely related to Macrostylidae. This internal development has been observed as well in Urstylis Riehl, Wilson & Malyutina, 2014 and was one of the arguments suggesting a sister-group relationship between Macrostylidae and Urstylidae (Riehl et al. 2014 a).

Methods

Samples were collected during the Australian R / V SOUTHERN SURVEYOR cruise SS 07-2005 (Williams et al. 2005). Sediment samples were obtained using a Smith-McIntyre grab (Smith and Mcintyre 1954).

Specimens were initially preserved in 70 % denatured ethanol. For taxonomic examination, they were subsequently transferred from 70 % ethanol into an ethanol-glycerine solution (1: 1) before being placed in glycerine. To facilitate morphological illustration, dissected appendages were temporarily mounted on slides following the methodology of Wilson (2008) and stained with methyl green. Permanent slide mounts of dissected appendages were prepared using Euparal, following Riehl and Kaiser (2012). Whole specimens and dissected parts were documented using stack photography with a Visionary Digital ™ system at the Australian Museum in Sydney.

Pencil drawings were produced from temporary slide mounts using a compound microscope, equipped with a camera lucida. Morphological character states were coded utilising the DELTA software (Dallwitz 1980, Dallwitz 1993, Dallwitz et al. 2010) and an updated DELTA database for Macrostylidae (Riehl et al. 2012, Riehl and De Smet 2020) which is publicly available via the Zenodo repository (Riehl 2024). Description texts and diagnoses were generated from this database. Linear measurements were derived from line drawings using the distance-measurement tool in Adobe Acrobat Professional, following the protocol outlined by Hessler (1970). Calibration was performed with a stage micrometer and ratios were reported in accordance with Wilson (1989). Line drawings were digitally rendered using Adobe Illustrator CS 5 and CS 6 (Coleman 2009, Bober and Riehl 2014) and subsequently arranged into figure plates in Adobe Illustrator CC.

Morphological terminology follows established conventions for Janiroidea (Wilson 1989, Riehl et al. 2014 a). Ratios described as ‘ near’ or ‘ subequal’ are defined as within ± 5 % of the comparative measurement, as per Kavanagh and Wilson (2007). Nomenclature for setae adheres to the classifications of Hessler (1970) and Riehl and Brandt (2010). To ensure consistency and comparability, this study employs nomenclature for the antennal podomeres rather than numerical designation, following Hansen (1893).

Repository: Specimens have been deposited in the collection of Museum Victoria, Australia (NMV).