Heterotanoides Sieg 1977

Genus Heterotanoides Sieg, 1977

Sieg (1977a): 203 [diagnosis]; Sieg (1983): 442–443 [bibliography]; Sieg (1986a): 47 [new diagnosis, key to species]; Bamber & Bird (1997): 117, 120 [comparison of species]; Bamber (1998): 101, fig. 8 [distribution map of species]; Larsen & Wilson (2002): 13 [classification]; Bird & Larsen (2009): 156 [classification].

Diagnosis. (Modified from Sieg 1986a). Leptochelioid, with pleonites 1–4 with or without delicate plumose epimeral setae. Antennule three-articled, with or without small cap-like terminal segment [‘article-4’]; article-3 with one or more groups of subterminal aesthetascs. Antenna seven-articled; article-2 larger than article-3, both with stiff superodistal seta; article -4 with long setae on mesial border. Labium with two pairs of lobes, outer pair dominant. Mandible molar nodulose, without ridges. Maxillule endite with ten or eleven short terminal spines, palp with two long setae. Maxilliped bases not fused; with one long distal seta; endite with 2–4 spines (acute and digitiform); palp article-2 without lateral seta. Cheliped sclerite triangular, dorsally inserted into basis, posterior margin confluent with rear of carapace; basis posterior lobe reaching pereonite-1; carpus with up to four superior setae; propodus weakly or distinctly flared; palm and fixed finger with three or more inferior setae; fixed finger incisive margin with or without small distal teeth. Pereopods 1–3 merus, carpus and propodus with simple setae only. Pereopods 4–6 carpus with two or three setal loci [typically as two spines and superior seta]; propodus superodistal spines similar to inferodistal. Pleopod peduncle with seta; endopod inner margin with seta. Uropod peduncle with seta; endopod three-segmented; exopod two-segmented, segment-1 much shorter than segment-2. Male similar to female but antennule more elongate, with or without additional aesthetasc bundles; cheliped larger and more robust; mouthparts functional, as in female.

Type species. Heterotanoides capensis (Vanhöffen, 1914).

Composition. Heterotanoides capensis: Simons Bay, South Africa,?m, littoral?; H. cognatus Bamber & Bird 1997: Hong Kong, 4–14.5 m; H. muimui n.sp ; H. meridionalis Sieg, 1986a: Isla de los Estados (Argentina) and Tierra del Fuego, 13–44 m; H. ornatus Kudinova-Pasternak, 1976: Japan Trench,> 7200 m (possibly sample contamination?).

Remarks. The principal characters that distinguish Heterotanoides from all other leptochelioids are the presence of both subdistal antennular aesthetascs and a seven-articled antenna. Also, compared to genera such as Leptochelia Dana, Pseudoleptochelia Lang, and Heterotanais G.O. Sars (the last in the subfamily Heterotanaidinae), sexual dimorphism is also only moderate in Heterotanoides, restricted to relatively small differences in cephalothorax, pereon and cheliped proportions, with antennular aesthetascs being only slightly more numerous in males. Other characters could help define the genus, but are variable in the literature, but it is unclear if this is due to oversights or is real; examples include the setation of the maxilliped palp articles 2–4. The propodal spines of pereopods 4–6 are also similar in both superior distal and inferior distal groups, a feature possibly useful for diagnoses and phylogenetic studies.

In his redescription of H. capensis Sieg (1977a) used a ‘female without oostegites’ but the pereonite proportions do not match those shown by Vanhöffen (1914) for an ovigerous female; they more closely resemble the short pereonites of male H. muimui n. sp. [see below]. In addition, the aesthetasc pattern (Fig. 5 G) of two subterminal bundles corresponds to that of male H. muimui; these two observations suggest that Sieg’s figures of H. capensis are of a male. For similar reasons, and based on the relative stout cheliped, it is possible that the description of H. ornatus by Kudinova-Pasternak (1976) was also based on a male specimen.

If the extent and details of sexual dimorphism in Heterotanoides are confused, it is also possible that the genus is polyphyletic. Of the five species, H. meridionalis appears as an outlier because of the setation of the propodus on pereopods 4–6 and the aesthetasc distribution (Figs 5 E, J). If the inferences about sexual dimorphism are correct (see above), the female antennule is exceptional in having two bundles of subterminal aesthetascs: one is proximal on article-3, and the more distal bundle has three aesthetascs.