Hemityphis Claus 1879

Genus Hemityphis Claus, 1879

(Figs 51–52)

Hemityphis Claus, 1879: 4 (key), 12.— Gerstaecker 1886: 482 –483.— Claus 1887: 31 (key), 38.— Stebbing 1888: 1471.— Spandl 1927: 227 (key), 233.— Pirlot 1929: 159.— Barnard 1940: 541 (key).— Hurley 1955: 187 (key), 188.— Bowman & Gruner 1973: 55 (incl. key).— Vinogradov et al. 1982: 439 (key), 446.— Shih & Chen 1995: 226 (key), 241.— Vinogradov 1999: 1200 (key), 1201.

Hemiscelus Stewart 1913: 259 –260.— Spandl 1927: 250 (key).— Vinogradov et al. 1982: 465 (key), 474–475.— Vinogradov 1999: 1199 (incl. key).

Type species. Hemityphis tenuimanus Claus, 1879 by page priority. Type material could not be found at the MFN, but the ZMH has one lot of 13 male specimens from the Atlantic (K 8764) with “ Schnehagen ” as the collector. This dates the material to the time of Claus, because Claus (1871) proposed the genus Schnehagenia for his species S. rapax (= Brachyscelus rapax). One of the specimens has been dissected from the right, which is consistent with the figures of Claus (1887). Thus, these specimens are most likely syntypes, although one cannot be certain in the absence of more conclusive information. The type locality is the South Atlantic, near the Cape of Good Hope.

Type species of synonyms. The type species of Hemiscelus is H. diplochelatus Stewart, 1913 by monotypy. The unique holotype female is in the NHM (1914.2.25.122), on one microscope slide with remains in spirit. This specimen has been examined and is indistinguishable from juvenile specimens of Hemityphis tenuimanus, thus confirming the above synonymy, proposed by Zeidler (1998). The type locality is the south-west Atlantic off Brazil, “near Bahaia ” [15°45.5’S 33°11.5’W], H.M.S. Discovery.

Diagnosis. Head round. Eyes occupying most of head surface; grouped in two fields on each side of head. Antennae 1 of males with 1-articulate peduncle; flagellum with large, crescent-shaped callynophore, with aesthetascs arranged in two-field brush medially, with three smaller articles inserted on antero-dorsal corner. Antennae 1 of females with 2-articulate peduncle; callynophore narrowly rectangular, with two smaller articles inserted terminally. Antennae 2 of males 5-articulate; strongly zig-zagged, with all articles folded back on each other; extending anteriorly under head and posteriorly between the gnathopoda and pereopoda to pereonite 4; basal article distinctly inflated, about half or less the length of following article; articles 2 & 3 sub-equal in length; terminal two articles of similar length, slightly shorter than preceding one; terminal article pointing anteriorly. Antennae 2 of females 5-articulate, with very small terminal article. Mandibular incisor relatively broad, straight with several teeth, with small distal lobe medially; in male orientated more or less parallel to palp. Maxillae 1 consisting of elongate plates with few robust setae distally on medial margin. Maxillae 2 consisting of curved, elongate, pointed lobes, with a distinctive rounded, medial bulge, armed with tiny denticles, or setae, terminally. Maxilliped with inner lobes completely fused; medial margin of outer lobes without fringe of setae or membranous fringe. Coxae 1–6 separate from pereonites; coxa 7 mostly fused with pereonite. Gnathopods 1 & 2 chelate; carpal process knife-shaped, armed with microscopic teeth or setae. Pereopods 3 & 4 distinctly shorter than pereopods 5 & 6. Pereopod 5; basis very broad, oval-shaped, width about 0.4 x length; articles 3–7 inserted terminally, or subterminally to basis. Pereopod 6; basis very broad, bean-shaped, with relatively straight distal margin, maximum width about 0.4 x maximum length, with very small fissure; articles 3–7 inserted sub-terminally on basis; merus with antero-distal corner slightly extended, overlapping carpus medially. Pereopod 7 reduced in size with large, elongate basis; with only 1–3 terminal articles. Uropods 1 & 2 with articulated exopoda and endopoda. Uropod 3; endopod fused with peduncle. Rami of all uropoda more or less lanceolate, usually with serrated margins. Gills all without folds.

Species. Hemityphis tenuimanus Claus, 1879.

Sexual dimorphism. The sexes are remarkably similar in general morphology, and except for the antennae and mandibles, there is no obvious sexual dimorphism.

Remarks. Hemityphis is currently considered to be monotypic (Zeidler 1998). In the past H. tenuimanus Claus, 1879 has been considered a junior synonym of Typhis rapax Milne-Edwards, 1830. However, the description of T. rapax by Milne-Edwards (1830, 1840) most likely refers to Parapronoe crustulum Claus,1879, and this has been confirmed by examination of type material in the MNHN (Zeidler 1996b). Thus, the type species of the genus is H. tenuimanus Claus, 1879.

Hemityphis bears some resemblance to Platyscelus, but is readily distinguished by the morphology of the gnathopoda, the very small fissure on the basis of pereopod 6, and by the male second antennae, which have the last two articles considerably longer than half the length of the preceding one. The first maxillae also differ from Platyscelus and Paratyphis in that they are armed with three tiny, stout setae, instead of bifid denticles. The second maxillae also have a more denticulate inner lobe than other genera of the family.

Vinogradov (1990) described a new species of Hemiscelus, H. setosus, from the tropical south-eastern Pacific, in the region of the Nasca Ridge, which is very similar to the juvenile of Platyscelus armatus described and illustrated by Zeidler (1992), and the validity of this species is questionable.

There are no records of a parasitoid relationship with gelatinous plankton although Harbison et al. (1977) found H. tenuimanus inside a gastroid of a colony of the siphonophore Forskalia tholoides. “It was not appreciably digested, and so may have been recently captured and ingested. This siphonophore was also feeding on Anchylomera blossevillei ” (Harbison et al. 1977).

Very little is known about the biology of H. tenuimanus. Limited biogeographical information is provided by Stephensen (1925) and Thurston (1976). It seems to be widespread in tropical and warm-temperate regions of the world’s oceans and, from the limited available data, appears to be mainly epipelagic in habit.