Leiochone Grube 1868

Genus Leiochone Grube, 1868, emended

Type species. Clymene leiopygos Grube, 1860:91, herein by subsequent designation [explicit designation following implicit in Arwidsson 1906:144]

Leiocephalus Quatrefages, 1866 [in part], non Gray, 1827 [homonym in Reptilia] Clymenura (Clymenura) sensu Imajima & Shiraki, 1982, non Verrill, 1900

Diagnosis. Body of 19 to 29 chaetigers, followed by up to five achaetous preanal segments. Cephalic plate and rim absent, or weakly defined plate edge present adjacent cephalic keel. Nuchal organs straight, length variable, palpode tip bluntly oval. Cephalic ocelli usually present. Eighth chaetiger with a large ventral glandular shield. Notochaetae winged capillaries only, or also with weakly ornamented forms. Neurochaetae single rows of rostrate manubriavicular uncini throughout, reduced in number, dentition, and subrostral bristle development on first two or three chaetigers. Pygidium with anal funnel absent, with anal cone prominent, basally rimmed with three cirri, or cirri absent, with anal valve peg usually present.

Remarks. Leiochone includes seven nominal taxa, of which six are valid, listed below under their original combinations, ordered by date of description (* = junior synonym), with character states as enumerated in Table 1. The next group of seven names are nomina dubia that have been included in Leiochone in the past, but which mostly now appear to be indeterminable.

Clymene leiopygos Grube, 1860, Adriatic. Type of Leiochone, with holotype at Zoologisches Museum, Berlin, Verm. Q.4641 (Hartwich 1993:112).

* Leiochone clypeata Saint-Joseph, 1894, Brittany, France. Synonym of L. leiopygos fide Arwidsson (1906, 1922) and Garwood (2007). Treated as valid by Fauvel (1927:188) although he listed several possible senior synonyms.

Leiochone johnstoni McIntosh, 1915, British Isles.

Leiochone tenuis Day, 1957, South Africa.

Leiochone tricirrata Bellan & Reys, 1967, Mediterranean France.

Clymenura annulata Mohammad, 1980, Kuwait. New combination herein as Leiochone annulata.

Clymenura (Clymenura) japonica Imajima & Shiraki, 1982, Japan. New combination herein as Leiochone japonica.

Nomina dubia

Clymene ebiensis Milne Edwards, 1843, plate 22, fig. 4, in Milne Edwards (1837 [1837 –1848]) (publication date fide Cowan (1976:61), see also Quatrefages (1866:243), McIntosh (1892:103; 1913:98), and Arwidsson (1922:8)), Brittany, France. Incompletely figured and no text description published, except characterised in the figure caption by “…la forme pyramidale de la tête et l'absence de dentelures autour de l'anus”. Placed in Leiochone subsequently, although presence of ventral shield unknown. Indeterminable to species (fide Arwidsson 1922), and holotype untraced.

Clymene urceolata Leidy, 1855 (as C. urceolatus), New Jersey, USA. Inadequate description, type missing (Light 1974:181). Placed in Leiochone by Grube (1868), but perhaps an indeterminable Asychis sp. (fide Arwidsson 1906).

Leiocephalus parvus Quatrefages, 1866, France? Inadequate description from anterior fragment, with no mention of ventral shield. Included in Leiochone by Arwidsson (1906:145). Holotype at Muséum national d’Histoire naturelle, Paris. Indeterminable to species?

Praxilla simplex Claparède, 1870, Italy. Inadequate description, with no mention of ventral shield, but has anal cirri. Tentative inclusion in Leiochone by Arwidsson (1906:145), and tentative synonymy into L. clypeata by Fauvel (1927:188). Types not retained, and indeterminable to species.

Leiochone singularis Gravier, 1907, Antarctica. Inadequate description, with no mention of ventral shield. Holotype at Muséum national d’Histoire naturelle, Paris. Not Leiochonini?

Leiochone polaris acirrata Zachs, 1923 (& Derjugin 1927), as var. acirrata. White Sea, Russia. Nomen nudum.

Leiochone tropica Mesnil & Fauvel, 1939, Indonesia. Inadequate description from broken specimen, with no mention of ventral shield, and holotype untraced. Not Leiochonini, and indeterminable to species?

Grube (1868) defined Leiochone simply on the basis of (in translation) a “terminal funnel smooth-edged and destitute of teeth [cirri]”. He did this for two existing species, his own Clymene leiopygos Grube, 1860 from Cherso (= Cres), an Adriatic island off Croatia, and C. urceolata Leidy, 1855 from New Jersey, USA, which together simply “might form a particular group (Leiochone)”. Clymene urceolata is a nomen dubium in Asychis (fide Light 1974:181), with an inadequate and un-illustrated original description, and a missing type. In essence, the original description indicated a species of 26 segments, with pygidium urceolate (pitcher shaped), head with a thin cephalic rim, and uncini from the second segment. C. leiopygos is the better-described of Grube’s species pair, and has an existing holotype, although it is fragmented. The original text inadequately indicates character states but is accompanied with anterior and posterior body figures.

Arwidsson (1906 footnote p.145, p.249) made statements that at the time eliminated C. urceolata from relevance to Leiochone (treating it as an Asychis on p.249), and treated C. leiopygos as the type of Leiochone. His statement that “… Clymene urceolata Leidy vermutlich eine Maldane - oder Asychis -Art ist. Der Name Leiochone ist auf das Vorderende von Clymene leiopygos zu beziehen, das verhältnismäßig gut bekannt ist und dessen Übereinstimmung mit dem z. B. von Clymene ebiensis und Leiochone clypeata augenfällig ist.” is indicative for the requirements of ICZN Article 69.1 on subsequent type designation (International Commission on Zoological Nomenclature 1999), and no conflicting designation exists (see below). However, Arwidsson’s indication may not be sufficiently categorical under Art. 67.5, and accordingly C. leiopygos has been designated as type of Leiochone above. Arwidsson (1922) later redescribed L. leiopygos at length, based on specimens from Devon, and included L. clypeata as a synonym. L. clypeata was at that time known as a common species on the Bay of Biscay coast (Joyet- Lavergne 1910). The species concept of L. leiopygos is in current use, but either under the combination Clymenura leiopygos, or more often still under Cly. clypeata (for L. clypeata) (e.g., Capaccioni et al. 1993; Martin et al. 2000; MarBEF 2004 distribution records, including from Adriatic; Hausen & Bleidorn 2006; Garwood 2007).

Arwidsson (1906:144) gave a loosely worded diagnosis of Leiochone, significantly mentioning the presence of a ventral glandular shield (also the diagnostic character in his p.5 key), that the cephalic plate and rim can be poorly developed, the presence of few anal cirri, and that anterior uncini had reduced dentition. Nevertheless, he included Verrill’s then monotypic Clymenura as a synonym (along with Leiocephalus Quatrefages, 1866) because of the glandular shield in Clymenura cirrata, although aware this species has a well-developed cephalic rim as figured in the original description. Arwidsson (1906:147) also indicated a possible future restructuring of Leiochone might again split off Clymenura when more was known of the group, and might also split off a new genus for L. polaris (Théel) (= Cly. polaris), a species with a cephalic plate, but almost no rim. After these preliminary analyses Arwidsson (1906) described a new species, L. borealis from Norway, an unnamed Leiochone (perhaps L. johnstoni McIntosh, fide Arwidsson 1922:16), and redescribed L. polaris.

McIntosh (1915) gave his own Leiochone diagnosis, noting a reduced cephalic plate, reduced dentition of anterior uncini, and few anal cirri, but did not include a clear statement on the significance of the 8th chaetiger glandular shield, although mentioning or figuring it for some of the four European Leiochone he included, including his new species L. johnstoni. Arwidsson (1922) did not include another formal diagnosis of the genus, but redescribed L. johnstoni, and was critical of McIntosh’s reports on the other nominal taxa, inter alia suggesting that McIntosh’s “ L. ebiensis ” description was of L. leiopygos. Four further Leiochone species and one subspecies were added to Leiochone by other authors between 1923 and 1967, with subsequently only a further subspecies added by Averincev (1990).

Hartman (1959:458) followed Arwidsson (1906) in placing C. urceolata in Asychis in her catalogue, but treated Leiochone as an orphan genus “ ex auctore ” without valid membership. She incorrectly stated that it was “erected for C. urceolatus ”, and disregarded C. leiopygos, the other possible type species. The use of “erected for” does not qualify as a type designation and was contrary to her usual practice of clearly indicating type species. She dealt with C. leiopygos circuitously, first under Clymene (Hartman 1959:453) by tentatively referring it to the junior taxon L. clypeata, and then referring L. clypeata and all other Leiochone to Clymenura, except for L. johnstoni which is not in her catalogue. Hartman’s entries may have been influential in the subsequent disregard of Leiochone in favour of Clymenura by some authors (e.g., Fauchald 1977:41). However, Bellan & Reys (1967:199) continued Leiochone, stating, “Nonobstant l'opinion de Hartman (1959), nous avons préféré conserver le taxon générique de Leiochone au lieu de celui de Clymenura Verrill 1900 … ", and “Nous donnons au genre Leiochone le sens le plus restreint que lui attribue Arwidsson et admettons le bien fondé de son argumentation sur la validité du genre proposé par Grube … ”.

The six valid Leiochone species have very similar morphology (Table 1). All lack cephalic plate rims and have reduced dentition in first chaetiger uncini, all have anal cones with three pygidial cirri (or cirri are absent in one species), and all except one have prostomial ocelli. They currently appear to be limited to temperate to tropical Eastern Hemisphere waters (Europe, Asia, Africa). Four are known as shore species (at least from the original description occurrences), and two may occupy inshore depths, although one of those (L. japonica) has been more often found in deepwater (Table 1).

TABLE 1, part one TABLE 1. Valid species in Leiochone and Clymenura, with differentiating character states. Character states taken from original descriptions, except redescriptions as indicated. States for the junior synonym L. clypeata (= L. leiopygos) are included separately for comparison.

Anal valve peg = a small projection or flap-like structure at the anal opening; ‘long’ pygidial cirri = cirri length longer than the anal cone. Abbreviations: y, n,? = yes, no, uncertain; L, W = length, width; lat, dor = lateral, dorsal; na = not applicable; af = anterior fragment.)

Genus Clymenura Verrill, 1900, emended

Type species. Clymene cirrata Ehlers, 1887:182, by monotypy

Clymenura (Cephalata) Imajima & Shiraki, 1982 [= nominotypical Clymenura]

Diagnosis. Body of 18 to 19 chaetigers, followed by up to six achaetous preanal segments. Cephalic plate present, strongly developed, with cephalic rim prominently raised or, exceptionally, present but indistinct. Nuchal organs straight, length variable, palpode tip bluntly oval. Cephalic ocelli present or absent. Eighth chaetiger with a large ventral glandular shield. Notochaetae winged capillaries only, or also with weakly ornamented forms.

Neurochaetae single rows of rostrate manubriavicular uncini similar on all chaetigers, or reduced in number, dentition, and subrostral bristle development on first two or three chaetigers, or acicular on first chaetigers. Pygidium with or without a deep funnel, if without then with prominent anal cone. Pygidial rim or funnel edge with one to numerous anal cirri, of short, long, or alternating length, with anal valve peg present or absent.

Remarks. Clymenura includes nine valid taxa which are listed immediately below under their original combinations, ordered by date of description, with character states as enumerated in Table 1. It excludes Clymenura gracilis Hartman, 1969, a species of uncertain placement which may need to be redescribed.

Praxilla polaris Théel, 1879, Novaya Zemlya. Included in Leiochone by Arwidsson (1906:150 redescription), included in Clymenura by Hartman (1959) and Imajima & Shiraki (1982).

Praxilla lankesteri McIntosh, 1885, Japan. Incomplete original description from anterior fragment. Redescribed in part from holotype by Imajima & Shiraki, 1982, and newly included in Clymenura by them as type of subgenus Cly. (Cephalata) Imajima & Shiraki.

Clymene cirrata Ehlers, 1887, Florida, offshore. Type of Clymenura. Holotype fragmented, possibly incomplete, also damaged fide Hartman (1938:15).

Leiochone borealis Arwidsson, 1906, Norway. Included in Clymenura by Hartman (1959). Treated as distinct herein, but possible synonym of Cly. lankesteri fide Imajima & Shiraki (1982).

Leiochone columbiana Berkeley, 1929, Canadian Pacific. Included in Clymenura by Hartman (1959) and Imajima & Shiraki (1982).

Clymenura (Cephalata) longicaudata Imajima & Shiraki, 1982, Japan.

Clymenura (Cephalata) aciculata Imajima & Shiraki, 1982, Japan. Incomplete original description from anterior fragments.

Leiochone polaris lena Averincev, 1990, Laptev Sea, Arctic Ocean. New combination herein as Clymenura polaris lena.

Clymenura snaiko sp. nov. New Zealand.

Incertae sedis

Clymenura gracilis Hartman, 1969, California. No ventral shield in holotype, LACM-AHF POLY 400, or in other specimens at Los Angeles County Museum of Natural History, pers. comm. Leslie Harris. Not Clymenura, not Leiochonini.

Clymenura was monotypic when introduced by Verrill (1900:654) for Clymene cirrata Ehlers, 1887 from 642 m depth off Carysfort Reef, off Key Largo, Florida. Verrill gave the following diagnosis in a footnote:

“Head as in Euclymene. Anal segment elongated, with a circular rim, bearing 4 long cirri. Uncini remarkable for having, above the large tooth, two transverse rows of numerous small hooklets, the first row containing about 9 larger ones, the 2d many more. The 2d, 3d and 4th setigerous segments are elongated, and each has a narrow anterior collar.”

Ehlers’ original description and figures from three fragments probably suffice to recognise new specimens of the Clymenura type species when obtained, but its total number of chaetigers remains uncertain, especially as Hartman (1938:15) reported that the type specimen had since become dry and considerably fragmented. Two species were added directly to Clymenura between 1969 and 1980 (Hartman 1969; Mohammad 1980), then Imajima & Shiraki (1982) added a further three species, and produced an emended Clymenura diagnosis with two subgenera. They included species first described in Leiochone, but without stating why they disregarded Leiochone as a name.

None of the features in the quotation from Verrill above remain in the diagnosis of Clymenura by Imajima & Shiraki (1982). Rather they considered that Clymenura united all maldanids with a ventral glandular shield on chaetiger eight. The seven species Imajima & Shiraki (1982:15) placed in a new subgenus Cly. (Cephalata) were supposedly those having a well-defined cephalic plate with flaring rim. The species remaining in the nominotypical subgenus, Cly. (Clymenura), were not listed by Imajima & Shiraki, but they intended to retain species where the plate is poorly defined and plate borders “are situated close to the keel,” thus paradoxically matching Arwidsson’s Leiochone concept if it excluded Clymenura.

Imajima & Shiraki (1982:12) are incorrect in stating that the nominotypical Clymenura species Cly. cirrata has a “rudimentary cephalic plate” as it is very well developed (see Ehlers 1887, pl. 46, fig.12). Imajima & Shiraki’s subgeneric split is thus anomalous, with both the Cly. (Clymenura) type, and the type species of the new subgenus, Cly. lankesteri, having very well-defined plates and rims. Further, both bear some very long anal cirri around an anal cone. Consequently the respective types of the two subgenera appear to be more closely allied to each other than to their intended fellow subgroup members, and subgeneric partitioning of Clymenura on the foundation set by Imajima & Shiraki is unworkable.

Imajima & Shiraki (1982) described one new species, Cly. (Cly.) japonica, in the nominal subgenus, and compared it to (current names) Leiochone johnstoni and L. tenuis. It seems logical from those comments, and is also apparent from Table 1 character states, that Cly. japonica is a Leiochone.

Clymenura is here restricted to members of Leiochonini with a well-developed cephalic plate and rim, with the addition of Cly. polaris, which has a wide cephalic plate, but lacks a cephalic rim. The separation from Leiochone is not so distinct in other important characters, and overall the members are more varied in morphology than Leiochone, with, for example, some Clymenura possessing similar pygidial features to members of Leiochone (such as a prominent anal cone), while others have the anal funnels similar to several other euclymenin genera. The synonymy of Leiochone borealis from Norway with Cly. lankesteri from Japan seas as suggested by Imajima and Shiraki (1982) is not confirmed; although both belong in Clymenura and they are very similar, the former has ocelli, and appears to differ in pygidial structure from the latter (Table 1).

The nine valid Clymenura are mostly species from high North European latitudes and the northern Pacific region, with the interesting geographic exceptions of Cly. cirrata from offshore Florida, and the New Zealand shore species. The geographic range was not previously known to extend to the Southern Hemisphere. Most are subtidal, with four of the species having depth distributions from inshore or continental shelf depths out to deep water (Table 1, variously to 590–1850 m).

Contrary to a suggestion of Jiménez-Cueto & Salazar-Vallejo (1997), the deep-water southern Indian Ocean maldanid, Axiothella crozetensis Gillet, 1989, cannot be placed in Clymenura, despite its tricirrate pygidial morphology and prominent anal cone (more typical of Leiochone), as Gillet (1989) originally reported it lacks a ventral glandular shield on chaetiger eight.