Leptocotis Streets, 1877

Zeidler, Wolfgang, 2016, A review of the families and genera of the superfamily PLATYSCELOIDEA Bowman & Gruner, 1973 (Crustacea: Amphipoda: Hyperiidea), together with keys to the families, genera and species, Zootaxa 4192 (1), pp. 1-136 : 80-83

Genus Leptocotis Streets, 1877

( Figs 37–38 )

Leptocotis Streets, 1877: 136 –137.— Streets 1879: 283.— Stebbing 1888: 1593.— Bovallius 1890: 47 (key), 110.— Spandl 1927: 179 (key), 204.— Pirlot 1929: 168.— Hurley 1955: 182 (incl. key).— Yoo 1971: 63 (key).— Bowman & Gruner 1973: 49 (key), 52.— Zeidler 1978: 30 (incl. key).— Vinogradov et al. 1982: 404 (key), 421.— Nair 1995: 6 (key), 14– 15.— Shih & Chen 1995: 190 (key), 203–204.— Vinogradov 1999: 1195 (key), 1196.

Oxycephalus (part)— Claus 1879: 48.— Claus 1887: 71.

Dorycephalus Bovallius, 1890: 46 (key), 75.— Spandl 1927: 179 (key), 203.

Type species. Leptocotis spinifera Streets, 1877 by monotypy. Type material could not be found at any major North American museum and is considered lost. However, Leptocotis is a very distinctive genus, unlikely to be confused with any other of the family Oxycephalidae . The type locality is the North Pacific , north of Hawaii [29°N 157°W], North Pacific Surveying Expedition , 16 June 1873 .

Leptocotis spinifera is currently considered to be a junior synonym of Oxycephalus tenuirostris Claus, 1871 . The type locality is the “ Gilolo Passage ” (= Halmahera), Indonesia, collected by Captain Schnehagen.

Type species of synonyms. The type species of Dorycephalus is Leptocotis lindstroemi Bovallius, 1887 by page priority. Type material could not be found at the NRS, ZMUC or in Upsala and is considered lost. However, there is no doubt that it is synonymous with Leptocotis , although the validity of species attributed to this genus by Bovallius (1890) warrants further investigation. It is likely that the sexual dimorphism of uropod 2 may account for some of the confusion, as Bovallius separated the two genera on the basis of the morphology of the urosome and uropoda. Bovallius (1887, 1890) only provides a general locality, “tropical parts of Atlantic ”.

Diagnosis. Body shape elongate and narrow. Head oval. Rostrum distinctly elongate. Eyes occupying most of head surface except for rostrum, grouped in one field on each side of head. Antennae 1 of males with 2-articulate peduncle; flagellum with large, elongate, crescent-shaped callynophore, with relatively large antero-distal lobe, with aesthetascs arranged in two-field brush medially; with three smaller articles inserted below antero-dorsal corner. Antennae 1 of females with 2-articulate peduncle; callynophore narrowly rectangular; with two smaller articles inserted terminally. Antennae 2 absent in females. Antennae 2 of males 5-articulate; strongly zig-zagged, with most articles folded back on each other; extending anteriorly under head and posteriorly between the gnathopoda to pereonite 1; basal article elongate, sub-equal in length to following article; terminal article very short, not folded, pointing posteriorly. Mandibular palp 3-articulate in males. Mandibular incisor relatively broad, with several teeth, with small distal lobe medially; in male orientated more or less parallel to palp. Maxillae 1 consisting of rounded plates. Maxillae 2 absent. Maxilliped with inner lobes completely fused; medial margin of outer lobes with membranous fringe. Coxae not fused with pereonites. Gnathopod 1 sub-chelate; carpal process knife-shaped, armed with prominent teeth and setae. Gnathopod 2 more or less chelate; carpal process knifeshaped, armed with prominent teeth and setae. Pereopods 3 & 4 sub-equal in length to pereopods 5 & 6. Pereopod 5; basis very broad proximally, postero-distal corner rounded, partly overlapping ischium; following articles relatively slender, inserted terminally to basis. Pereopod 6 with very broad basis, postero-distal corner rounded, produced to limit of ischium; articles 3–7 relatively slender, inserted terminally to basis. Pereopod 7 reduced in size with large basis; all articles present; dactylus normal. Uropod 1 with endopod reduced but articulated with peduncle. Uropod 2; endopod articulated with peduncle in male; fused with peduncle in female. Uropod 3; endopod fused with peduncle. Rami of all uropoda lanceolate, usually with serrated margins. Telson fused with double urosomite. Oostegites on pereonites 2–5. Gills on pereonites 2–6; all without folds.

Species. Leptocotis tenuirostris ( Claus, 1871) .

Sexual dimorphism. This genus is unusual in the sexual dimorphism of uropod 2. In females the endopod is fused with the peduncle, while in males it is articulated with the peduncle, and the denticles on the outer margin are finely serrated. In addition, the head of females is more bulbous around the eyes, and in mature males the head is characteristically indented on the dorsal surface, above the eyes, anterior to the neck. The double urosomite is also relatively longer in males.

Remarks. This genus is readily distinguished by the morphology of the rostrum, gnathopoda and urosome.

Leptocotis is similar to Calamorhynchus and Oxycephalus in general habit, and in the morphology of the pereopoda, and the first antennae of females. The first antennae of males, with an antero-distal ‘horn’ on the callynophore, resemble those of Calamorhynchus , Cranocephalus , Streetsia and Tullbergella . The second antennae of males are like those of Glossocephalus and Rhabdosoma , in that the juncture of articles 3/4 extend forward of the juncture of articles 1/2. The first maxillae consist of small, rounded lobes as is found in all other genera of Oxycephalidae except for Oxycephalus and Rhabdosoma . The maxilliped is most similar to that of Calamorhynchus . In having coxae not fused with the pereonites it resembles Glossocephalus , Streetsia and Tullbergella , although in the former genus the seventh coxae are fused with the pereonite.

The fifth pereopoda of Leptocotis have a relatively long, spinose structure on the medial surface of the coxae, which is analogous to similar structures found in most genera of Platysceloidea, allowing for the proximal articulation with the sixth pereopoda. However, in Leptocotis the pereopoda are sufficiently separated on the pereon so that articulation between pereopods 5 and 6 seems unlikely. Thus, the function of this spinose process is unclear. A similar structure is found in Streetsia .

Fage (1960) provides some information on the biology of Leptocotis tenuirostris , but there are no records of associations with gelatinous plankton. It seems to be epipelagic in habit, and is widely distributed in all of the world’s oceans, with a preference for tropical waters, although it is apparently absent from the west coast of Africa, and the Mediterranean and Red Seas ( Fage 1960).

Figures

FIGURE 37. Leptocotis tenuirostris (Claus, 1871), female (10.3 mm) and male (10.6 mm), Tasman Sea, SAMA C 5308 & C 5310. A, habitus of female; B, lateral view of head of male. All appendages except Mxp from female (P 3 deformed). Scale bars = 1.0 mm (A, B), 0.5 mm (Us), 0.2 mm (G 1 – P 7), 0.05 mm (Mxp).

FIGURE 38. Leptocotis tenuirostris (Claus, 1871), female (10.3 mm) and male (10.6 mm), Tasman Sea, SAMA C 5308 & C 5310. Scale bars = 0.5 mm (A 2, Md), 0.1 mm (A 1, G 1 & 2), 0.025 mm (Mx 1).