Simorhynchotus Stebbing, 1888

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 : 53-56

Genus Simorhynchotus Stebbing, 1888

( Figs 21–22 )

Simorhynchus Claus 1871: 156 .— Claus 1879: 32 (key), 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: 381 (key), 390–391.— Nair 1995: 6 (key), 8.— Shih & Chen 1995: 212.— Vinogradov 1999: 1194 (key), 1195.

Type species. Simorhynchus antennarius Claus, 1871 by monotypy and subsequent designation by Stebbing. Stebbing (1888) changed the spelling of Simorhynchus because it was “preoccupied among birds”. Type material could not be found at the MFN or ZMH and is considered lost. However, the description and figures provided by Claus (1871, 1879, 1887) for this species, readily characterise this genus. No specific type locality is given; just “Grosses Ocean” (the Pacific).

Diagnosis. Body shape robust or globular. Head rounded with slight rostrum in males. Eyes occupying most of head surface; grouped in one field on each side of head. Antennae 1 of males with 2-articulate peduncle; flagellum with large, crescent-shaped callynophore, with small 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 and pereopoda to pereonite 7; basal article distinctly inflated, about half 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 male orientated more or less parallel to palp. Maxillae 1 & 2 absent. Maxilliped with inner lobes completely fused; medial margin of outer lobes with membranous fringe. Gnathopod 1 simple.

Gnathopod 2 sub-chelate; carpal process knife-shaped, armed with microscopic teeth or setae. Pereopods 3 & 4 distinctly shorter than pereopods 5 & 6. Pereopod 5; basis about 3 x as wide as merus, non-locking but may overlap with P6; articles 3–7 inserted terminally to basis. Pereopod 6; basis wider proximally, about 4 x as wide as merus, not operculate, does not overlap, or lock, with opposing pereopod; articles 3–7 inserted terminally to basis. Pereopod 7 reduced in size with large basis; all articles present; dactylus normal. Uropod 1 with articulated exopoda and endopoda. Uropods 2 & 3; endopoda fused with peduncle. Rami of all uropoda 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 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 gnathopod 2, Simorhynchotus resembles members of the family Lycaeidae . The pereopoda, 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 ( Laval 1980) and Liriope tetraphylla ( Gasca et al. 2014) , and Lima & Valentine (2001) record it in the siphonophore Sulculeolaria quadrivalvis , although this may be an accidental inclusion.

Simorhynchotus is widely distributed, with a preference for near-surface, tropical waters.

Figures

FIGURE 21. Simorhynchotus antennarius (Claus, 1871), male (5.7 mm—A) and female (3.9 mm—B), Coral Sea, SAMA C 3694 & C 3693; female (4.1 mm—A 1) and male (6.2 mm—A 1 & 2, mouthparts), Indian Ocean, off South Africa, SAMA C 5817. A, habitus of male, C 3694; B, head of female, C 3693. Scale bars = 1.0 mm (A, B), 0.2 mm (A 1 & 2 - m, Md), 0.1 mm (A 1 - f).

FIGURE 22. Simorhynchotus antennarius (Claus, 1871), male (5.7 mm), Coral Sea, SAMA C 3694. Scale bars = 0.1 mm (Mxp), 0.5 mm (remainder).