Genus Calamorhynchus Streets, 1878

(Figs 39–40)

Calamorhynchus Streets, 1878: 285.— Stebbing 1888: 1599.— Bovallius 1890: 46 (key), 72.— Spandl 1927: 179 (key), 197.— Pirlot 1929: 163.— Barnard 1940: 542 (key).— Hurley 1955: 181 (key), 182.— Yoo 1971: 63 (key).— Bowman & Gruner 1973: 49 (key), 50.— Vinogradov et al. 1982: 404 (key), 423.— Nair 1995: 6 (key), 16.— Shih & Chen 1995: 190 (key), 198.— Vinogradov 1999: 1195 (key), 1196.

Type species. Calamorhynchus pellucidus Streets, 1878 by monotypy. Type material could not be found at any major North American museum and is considered lost. However, Calamorhynchus is a very distinctive genus, unlikely to be confused with any other of the family Oxycephalidae. The type locality is the north-east Pacific [28°06’N 140°12’W], W.H. Jones, surface.

Diagnosis. Body shape elongate and narrow. Head oval. Rostrum distinctly elongate, pointed, with lateral flanges. 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, short, not folded, pointing posteriorly. Mandibular palp 3-articulate in males. Mandibular incisor relatively broad, with several teeth, without medial lobe; 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. Coxae all partly fused with pereonites. Gnathopod 1 sub-chelate, or almost chelate; carpal process knife-shaped, armed with prominent teeth and setae. Gnathopod 2 chelate; carpal process knife-shaped, 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, slightly produced; articles 3–7 relatively slender, inserted terminally to basis. Pereopod 7 sub-equal in length to P6, with large basis; all articles present; dactylus normal. Uropods 1 & 2 with articulated exopoda and endopoda. 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 with folds.

Species. Calamorhynchus pellucidus Streets, 1878.

Sexual dimorphism. The sexes differ mainly in the morphology of the antennae and mandibles. Also, in males the dorsal keel on the head is often more developed than in females, and the lateral flanges are relatively feeble compared to females.

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

Calamorhynchus most closely resembles Leptocotis in general habit, and in the morphology of the pereopoda, the first antennae of females, and the maxilliped. The first antennae of males resemble those of Leptocotis, Cranocephalus, Streetsia and Tullbergella. The second antennae of males are like those of Oxycephalus and Streetsia. The first maxillae consist of tiny, rounded lobes, similar to that found in all other genera of Oxycephalidae except Oxycephalus and Rhabdosoma. In having the coxae fused with the pereonites it resembles Oxycephalus, Cranocephalus and Rhabdosoma.

Fage (1960) provides some information on the biology of Calamorhynchus pellucidus, but there are no records of associations with gelatinous plankton. It seems to be epipelagic in habit, occurring mainly in depths of 0–300 m (Fage 1960). It appears to be relatively uncommon, but is widely distributed, mainly in tropical regions of the world’s oceans.