Thamneus Bovallius, 1887

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 : 61-64

Genus Thamneus Bovallius, 1887

( Figs 26–27 )

Thamneus Bovallius, 1887: 31 .— Stebbing 1888: 1558.— Schellenberg 1927: 648 (key), 650.— Bowman & Gruner 1973: 46 (key), 48.— Shih & Chen 1995: 170 (key), 185.

Euthamneus Bovallius, 1890: 19 .— Pirlot 1929: 153.— Vinogradov et al. 1982: 395 (key), 401.— Vinogradov 1999: 1193 (key), 1194.

Dairinia (part)— Bate 1862: 309.— Bovallius 1885: 9.

Type species. Thamneus rostratus Bovallius, 1887 by monotypy. Type material could not be located at the NRS, ZMUC or in Upsala and is considered lost. However, Thamneus is a very distinctive genus. The type locality is the South Atlantic, off the Cape of Good Hope .

Diagnosis. Body shape robust or globular. Head rounded. Rostrum present in both sexes; short and rounded in females; duck-like in males. Eyes occupying most of head surface, except rostrum; grouped in one field on each side of head. Antennae 1 of males with 1-articulate peduncle; flagellum with large, crescent-shaped callynophore, with aesthetascs arranged in one-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 absent in females. Antennae 2 of males 4-articulate; loosely bent or L-shaped, without any articles folded back on each other; only extending anteriorly under head. Mandibular incisor relatively broad, with several, very small, teeth; in male orientated at right angles to palp. Maxillae 1 & 2 consisting of small, rounded lobes. Maxilliped with inner lobes completely fused; medial margin of outer lobes with membranous fringe. Gnathopods 1 & 2 sub-chelate; carpal process knife-shaped, armed with prominent teeth. Pereopods 3 & 4 distinctly shorter than pereopods 5 & 6. Pereopods 5 & 6 with slightly enlarged basis, only slightly wider than twice merus, not overlapping with other pereopoda; articles 3–7 inserted terminally to basis. Pereopod 7 reduced in size with large basis; all articles present; dactylus hook-shaped, overlapped laterally by triangular article attached to distal margin of propodus. Uropoda all with articulated exopoda and endopoda, all lanceolate, usually with serrated margins. Telson oval-shaped, constricted slightly at base.

Species. Thamneus rostratus Bovallius, 1887 .

Sexual dimorphism. Apart from the morphology of the antennae and mandibles, females are considerably more plump and wider than males, and the rostrum is much shorter and rounded, with an almost single, dorsal depression between the eyes.

Remarks. This is a very distinctive genus, easily distinguished by the morphology of the head, body, pereopoda and the second antennae of males.

Thamneus rostratus been recorded in association with medusae ( Stephensen 1925), and in particular Pelagia noctiluca (Harbison et al. 1977, Laval 1980, Gasca & Haddock 2004), Aequoria coerulescens ( Gasca & Haddock 2004) and Solmissus incisa ( Gasca et al. 2006) . Otherwise very little is known about its biology. It is relatively uncommon, but widely distributed, known from records in tropical and temperate regions of the world’s oceans ( Dick, 1970).

Figures

FIGURE 26. Thamneus rostratus Bovallius, 1887, female (6.2 mm) and male (6.8 mm), Philippines, SAMA C 5805. A, habitus of male; B, dorsal view of head of male; C, dorsal view of female; D, ventral view of Mx 1 & 2 lying on top of mandibles (male). Scale bars = 1.0 mm (A – C), 0.1 mm (D), 0.2 mm (remainder).

FIGURE 27. Thamneus rostratus Bovallius, 1887, male (6.8 mm), Philippines, SAMA C 5805. Scale bars = 0.2 mm.