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).