Simorhynchotus Stebbing, 1888

Zeidler, Wolfgang, 2021, Review of the hyperiidean amphipod family Lycaeidae Claus, 1879 (Crustacea: Amphipoda: Hyperiidea), Zootaxa 5081 (1), pp. 1-59 : 46-47

Genus Simorhynchotus Stebbing, 1888

Simorhynchus Claus 1871: 156 .— Claus 1879: 178 (32) (key), 188–189 (42–43).— Gerstaecker 1886: 486.— Claus 1887: 56 (key), 65.

Simorhynchotus Stebbing, 1888: 1572 .— Bovallius 1890: 46 (key), 48.— Spandl 1927: 178 (key).— Pirlot 1929: 161.— Hurley 1955: 182 (incl. key).— Yoo 1971: 63 (key).— Bowman & Gruner 1973: 53.— Zeidler 1978: 30 (key), 31.— Vinogradov et al. 1982 /1996: 381/471 (key), 390–391/482–483.— Shih & Chen 1995: 212.— Nair 1995: 6 (key), 8.— Vinogradov 1999: 1194 (key), 1195.— Zeidler 2016: 48 (key), 53–56.

Type species. Simorhynchus antennarius Claus, 1871 by monotypy. Type material could not be found in any major European institution and is considered lost. However, the description and figures provided by Claus (1871, 1879, 1887) for this species, readily characterise this genus.

Diagnosis. Body shape robust or globular.Head rounded in females, with slight rostrum in males. Eyes occupying most of head surface, except for rostrum; grouped in one field on each side of head. A1 of males with 2-articulate peduncle; flagellum with large, crescent-shaped callynophore, with aesthetascs arranged in two-field brush medially, with distinct antero-distal lobe and small, rounded postero-distal corner over-lapping following article; with three smaller articles inserted distally. A1 of females with 2-articulate peduncle; callynophore narrowly rectangular, with two smaller articles inserted terminally. A2 absent in females. A2 of males 5-articulate; strongly zig-zagged, with most articles folded back on each other; extending anteriorly under head and posteriorly between the gnathopods and pereopods to pereonite 7; basal article distinctly inflated, about 0.5 x or less the length of following article; following three articles of similar length; terminal article very short, not folded, pointing posteriorly. Mandibular incisor relatively broad, with several teeth, with small distal lobe medially; in males orientated more or less parallel to palp. Maxillae both absent. Maxilliped with inner lobes completely fused; medial margin of outer lobes with membranous fringe. G1 simple. G2 sub-chelate; carpal process knife-shaped, armed with microscopic teeth or setae. P3 and P4 distinctly shorter than P5 and P6. P5 distinctly longer than P6 basis slightly inflated, about 2 x as long as wide; articles 3–7 inserted terminally on basis. P6 basis wider proximally in males, about 1.5 x as long as wide; articles 3–7 inserted terminally on basis. P7 reduced in size with large basis; all articles present; dactylus hookshaped. U1 with articulated rami. U2 and U3; endopod fused with peduncle. Rami of all uropods lanceolate, usually with serrated margins.

Species. Simorhynchotus antennarius ( Claus, 1871) .

Sexual dimorphism. Apart from the morphology of the mandibles and the antennae, females are more robust than males, especially in the pereon, as is found in Lycaea . In addition, the head of males is produced into a short, slightly pointed rostrum.

Remarks. In the past Simorhynchotus has often been placed in the family Oxycephalidae based on the absence of maxillae (discussed earlier) and the slightly pointed head of males. However, the length of the rostrum is no greater than that found in males of the families Pronoidae or Brachyscelidae , and in general body shape, and especially in the form of G2, Simorhynchotus resembles members of the family Lycaeidae . The pereopods, coxae and urosome are also more like Lycaeids than Oxycephalids. Thus, this genus is a link between the families Lycaeidae and Oxycephalidae .

Very little is known about the biology of this genus. It has been recorded from the medusae Geryonia proboscidalis (Forsskål, 1775) ( Laval 1980) and Liriope tetraphylla ( Gasca et al. 2014) , and Lima & Valentine (2001) recorded it in the siphonophore Sulculeolaria quadrivalvis de Blainville, 1830 , although this may be an accidental inclusion.

The only species of Simorhynchotus , S. antennarius is widely distributed, with a preference for near-surface, tropical waters.