Stenotanais Bird & Holdich, 1984

Segadilha, Juliana Lopes, Bird, Graham & Tavares, Marcos, 2023, Stenotanais (Crustacea, Tanaidacea) from the Santos Basin: the first described species of the family Akanthophoreidae off the Brazilian coast, Zoosystematics and Evolution 99 (2), pp. 423-437 : 423

Genus Stenotanais Bird & Holdich, 1984

Diagnosis

(Modified from Larsen 2005, 2011). Female. Body elongate (11.5-13 × L:W). Pereonites longer than wide, with straight lateral edges. Pleon short (15-20% of TBL). Antennule shorter than carapace, four-articled. Antenna six-articled. Mandibular molar tapering, with terminal spines. Maxillule with eight to ten terminal spines. Maxilliped endite with rounded cusps, spiniform lateral corners and distal seta. Cheliped carpus robust with large distoventral shield; chela robust, fixed finger with two robust ventral spines. Pereopods 1-3 basis wider than on pereopods 4-6; merus and carpus with spine. Pereopods 4-6 without coxae. Pereopods 4-6 dactylus and unguis not fused; dactylus with double-row of small spines. Pleopods short and broad, with plumose or simple setae. Uropods prominent, often as long as antennae: endopod two-articled; exopod one- or two-articled; specialised setae with a wide and flat basis present on either exopod or endopod.

Male. Immature (preparatory) male with antennule thicker than in female, functional mouthparts present (see remarks on genus). Sexually mature ‘swimming’ type: cephalothorax as long as first three pereonites; pereon shorter than in female; pleon well developed, as long as pereon, caudally pointed; multi-articulate antennule with multiple aesthetascs, distal article longer than preceding article; no functional mouthparts; uropod biramous, endopod and exopod two-articled.

Type species.

Stenotanais crassiseta Bird & Holdich, 1984, by original designation. Gender: feminine.

Species included.

Stenotanais arenasi Larsen, 2011; S. crassiseta Bird & Holdich, 1984; S. hamicauda Bird & Holdich, 1984; S. macrodactylus Larsen, 2005; S. leonardoi sp. nov.; S. uropedon sp. nov.

Remarks.

The rather infrequently-recorded Stenotanais is similar to akanthophoreid genera such as Pseudakanthophoreus Lubinevsky, Tom & Bird, 2022 and Parakanthophoreus Larsen & Araújo-Silva, 2014, by having chelipeds without extensive surface ornamentation and the absence of spurs on pleonite-5, pleotelson and the uropod basal article or endopod article-1. However, Stenotanais can be distinguished mainly by having the basis of pereopods 1-3 thicker than the basis of pereopods 4-6 and the presence of specialised setae with a wide and flat basal attachment on the uropod ( Bird and Holdich 1984; Larsen 2011).

Larsen (2011) described S. arenasi , based on a single specimen and expressed uncertainty as to whether it really belongs to Stenotanais , so that its generic affiliation should be considered tentative. We agree that this species may belong to a different genus as its cheliped lacks a strong carpal shield, the shape of the antennule articles 3-4 does not conform to other Stenotanais species (article-3 not rectangular and article-4 minute, as long as wide; which can be a sexually dimorphic character) and the uropods are not ventrally deflexed (i.e. not folded back on themselves). Although not an impediment for supporting the exclusion of S. arenasi from Stenotanais , it is of note that it is so far the only species of the genus reported from the Pacific Ocean (Fig. 8 ). Despite these considerations, we adhere to the current classification until more evidence is available.

The single available specimen of S. arenasi may be a preparatory male, based on characters of the antennule articles 1-2 (as suggested by Larsen 2011) and has functional mouthparts. Here, we record the first sexually mature ‘swimming’ male of S. leonardoi sp. nov. (see below), the first to have been noticed in Stenotanais , although it would have been desirable to confirm the link between male and female forms of the same species using molecular analysis.

Another character in the original generic diagnosis of Bird and Holdich (1984) is the pereopods 1-3 propodus having a distinct convex inferior margin armed with small strong spinules. This needs further investigation as it is true for S. crassiseta , S. hamicauda and both new species described here, but not for S. arenasi and S. macrodactylus .

Figures

Figure 8. Geographic distribution of Stenotanais species based on the present study and literature data (Bird and Holdich 1984; Schmidt and Brandt 2001; Larsen 2005, 2011).