Sternostylidae, Baba, Ahyong & Schnabel, 2018

Baba, Keiji, Ahyong, Shane T. & Schnabel, Kareen E., 2018, Rediagnosis of the squat lobster genus Gastroptychus Caullery, 1896, with a new genus Sternostylus and a new family Sternostylidae (Crustacea: Decapoda: Anomura: Chirostyloidea), Zootaxa 4524 (1), pp. 77-86 : 81

Sternostylidae new family

Diagnosis. Carapace spinose, without transverse striae. Rostrum spiniform, supraocular spines absent. Sternite 3 confluent with sternites 1 and 2, without abrupt transverse step or demarcation at maxilliped 3 articulations; anteromedially produced and sloping anterodorsally, with pair of spines directly behind anterior margin. Sternal plastron concavely constricted between sternites 4–5 (often hourglass-shaped). Pleuron of abdominal somite 2 without anterolateral spine. Tailfan folded beneath preceding abdominal somite; telson divided into anterior and posterior lobes. Eyes well developed. Antennal acicle present or absent. Maxilliped 1 without epipod. Maxillipeds 3 close to each other. Pereopods 2–4 dactyli ending in fixed, corneous unguis, demarcation between unguis and remaining dactylus diffuse, ill-defined. Maxilliped 3 to pereopod 4 each with 2 arthrobranchs; pereopod 5 with 1 arthrobranch; pereopods 2–4 each with 1 pleurobranch. Male pleopods 1 and 2 present.

Type genus. Sternostylus new genus.

Remarks. Three major features, namely sternite 3 being anteromedially produced and evenly sloping anterodorsally with a pair of spines directly behind the anterior margin ( Fig. 2A ), the left and right maxillipeds 3 placed adjacent to each other ( Fig. 2A ), and the dactyli of the pereopods 2–4 ending in an indistinctly demarcated corneous spine, separate Sternostylidae from members of Chirostylidae . The last mentioned characer is shared by the Kiwaidae and Eumunididae and with most other Anomura, and is most parsimoniously interpreted as plesiomorphic. In members of the Kiwaidae , sternite 3 is strongly produced and sharply triangular, covering the mesial parts of closely adjacent bases of maxillipeds 3, whereas in Eumunididae , the anterior margin of sternite 3 is bifurcated and produced anteriorly, with the bases of maxillipeds 3 moderately separated rather than adjacent or appressed ( Fig. 2 B–D). Relationships among the four families within the Chirostyloidea are discussed below (see Discussion).

Figures

FIGURE 2. Anterior part of sternal plastron, with left and right maxillipeds 3, and left and right pereopod 1 coxae; maxillipeds 1 and 2 omitted. A, Sternostylus formosus (Filhol, 1884) n. comb., syntype, male, CL 16.7 mm, MNHN IU-2015-11878. B, Kiwa hirsuta Macpherson, Jones & Segonzac, 2005, holotype male, CL 51.5 mm, MNHN IU-2010-1683 (Ga 5310). C, Eumunida similior Baba, 1990, holotype, male, CL 33.1 mm, MNHN IU-2011-5516 (Ga 729). D, Pseudomunida fragilis Haig, 1979, female, CL 11.2 mm, NIWA 24583. Scales = 1 mm.