Leptognathia microcephala Kudinova-Pasternak, 1977

Figures 17–18

Leptognathia microcephala Kudinova-Pasternak, 1977: 122 –124, figs 4–5. Larsen & Shimomura, 2007: 15.

Material examined. 1 preparatory male, two mancae-III, station XR12, 41°37.67’– 41°37.08’N, 146°54.19’– 146°52.72’E. 5473–5484 metres, 22–23 September 2001.

Remarks. The three specimens from the present study agree with Kudinova-Pasternak’s description of L. microcephala, rather than L. birsteini (see above) especially with regard to cephalothorax and pereonite proportions (Fig. 17 A) and the shape of the pleotelson (Fig. 17 B). The species (and its probable ‘congeners’) appears to be one of the most morphologically complex tanaidomorphans, with possible exception of the paratanaid genus Bathytanais Beddard, 1886 . Of particular interest, the antennule is distinctly five-articled, with a small terminal article that could have been overlooked in previous studies. This is not homologous with the Paraleptognathia-Chauliopleona-Akanthophoreus configuration and is not linked to sexual development: although the preparatory male (length 3.48 mm) (Fig. 17 A) has stout and broad antennules (Fig. 17 C), the two mancae (1.92–2.18 mm) (Fig. 17 E) also have five-articled antennules, which are slender (Fig. 17 F). Unusual sensory setae on article 1 of antennule (Fig. 17 D) have a pedestal and articulated basal element.

Other notable characters include: the pleotelson (Fig. 17 B) with slightly tapering lateral margins and with long apical process; the cheliped (Fig. 18 A) carpus has a large free posterio-dorsal margin, so that the appearance of the cheliped is almost malleolate; the cheliped fixed-finger spine, incisive margin and dactylus are heavily sclerotised; all pereopods, especially pereopod 1 (Fig 18 C) are very slender and elongate; the pereopod 1 carpus has a small spatulate seta (Fig. 18 D); the uropods (Fig. 18 E) are slender, both articles are twoarticled, the exopod reaching half length of endopod article 2.

To confirm the true generic position of this species, and that of L. birsteini, it is desirable that material of Latitanais beklemishevi Kudinova-Pasternak, 1987 (type-locality Madagascar Basin, 5040–5069 metres) is obtained to check the number of antennule articles. In addition, new and irrefutable specimens of L. birsteini would help clarify distinctions between it and L. microcephala .

Distribution. Recorded from the Izu-Ogasawara Trench, 6330 metres (Kudinova-Pasternak 1978) and the Kurile-Kamchatka Trench, 5473–5484 metres in the present study.