Synalpheus riosi, Anker, Arthur & Tóth, Eva, 2008

Anker, Arthur & Tóth, Eva, 2008, A preliminary revision of the Synalpheus paraneptunus Coutière, 1909 species complex (Crustacea: Decapoda: Alpheidae), Zootaxa 1915, pp. 1-28 : 11-14

Synalpheus riosi n. sp.

( Figs. 6 , 7 )

Synalpheus paraneptunus (not Coutière, 1909) – Dardeau 1984: 92 (part.), figs. 47–50 (part., not 50j, k).

Type material. Dominica. Holotype, breeding female (queen), USNM 136272, Prince Rupert Bay, Smithsonian-Bredin Expedition sta. 62-56, depth 1.5 m, 28 Mar 1956. Paratypes: 139 colony members, USNM 1116697, same collection data as for holotype.

Diagnosis. Rostrum slightly lower than orbital hoods, rather narrow at base, not particularly slender, variously longer than orbital teeth, with subacute tip; orbital teeth triangular, broad at base, subacute; both rostrum and orbital teeth slightly up-turned distally; notches between orbital teeth and rostrum moderately deep, more U- than V-shaped. Antennular peduncles with second segment distinctly longer than wide; stylocerite length variable from falling well short of distal margin to just reaching distal margin of first segment. Antenna with basicerite bearing blunt, slightly projecting distodorsal tooth; scaphocerite without blade or with narrow blade, latter if present not reaching mid-length of scaphocerite or tip of distolateral tooth of basicerite. Third maxilliped with crown of five-six spine-like setae on tip of ultimate segment. Major chela palm about 2.5 times as long as fingers; distodorsal tooth on palm swollen, with descendant, short acute point. Second pereiopod carpus with five segments, first carpal segment about 3.5 times length of second. Third pereiopod with propodus bearing six spine-like setae (not including distal pair); dactylus stout. Uropodal exopod with three fixed teeth (including lateral tooth of diaeresis) and slender movable spine-like seta. Telson with longitudinal median depression and two pairs of moderately stout spine-like setae inserted anterior and posterior to midlength, respectively; posterior margin broad, about half-length of anterior width (see Figs. 6 , 7 ). For detailed description and additional figures see Dardeau (1984).

Etymology. This new species is named after Dr. Ruben Ríos for his important contributions to the taxonomy of alpheid shrimps, in particular in the Synalpheus gambarelloides group ( Ríos and Duffy, 2007).

Colour pattern. Unknown.

Size. Largest non-breeding specimen (colony member), CL 3.8 mm; breeding female, CL 4.5 mm (holotype).

Type locality. Prince Rupert Bay, Dominica.

Distribution. With certainty known only from Dominica.

Life history. The presence of only one reproductive female carrying embryos under the pleon among 139 smaller, non-breeding and juvenile-looking specimens strongly suggests eusocial life style ( Duffy 2003). Unfortunately, the host sponge was not identified.

Remarks. Synalpheus riosi n. sp. appears to be very closely related to S. paraneptunus and S. duffyi n. sp., but can be distinguished from both species by the shape of the distodorsal tooth on the palm of the major chela, in particular by the short descendant acute point ( Fig. 7 A, C); the stouter dactylus on the third to fifth pereiopods ( Fig. 6 D); and the scaphocerite having a shorter blade or no blade at all ( Fig. 6 A, G). It differs specifically from S. duffyi n. sp. by the larger size (CL of queens: 4.5 mm for S. riosi n. sp. vs. 3.5 mm in S. duffyi n. sp.), and the slightly longer first segment in the carpus of the second pereiopod ( Fig. 6 H).

Figures

FIGURE 6. Synalpheus riosi n. sp., holotype, breeding female from Prince Rupert Bay, Dominica (USNM 136272) [A – F]; paratype, non-breeding specimen (colony member) (USNM 1116697) [G, H]: A, frontal region, dorsal view; B, third maxilliped, lateral view; C, second pereiopod, lateral view; D, third pereiopod, lateral view; E, abdomen, lateral view; F, telson and uropods, dorsal view; G, frontal region, dorsal view; H, second pereiopod, lateral view. Scale bar: 0.5 mm (A – D, F – H), 1 mm (E).

FIGURE 7. Synalpheus riosi n. sp., holotype, breeding female from Prince Rupert Bay, Dominica (USNM 136272) [A – D]; paratype, non-breeding specimen (colony member) (USNM 1116697) [E – H]: A, major cheliped of queen, lateral view; B, same, mesial view; C, minor cheliped of queen, lateral view; D, same, chela and carpus, mesial view; E, major chela of paratype with opened fingers, lateral view; F, same, distodorsal tooth of palm, lateral view; G, minor chela of paratype with slightly opened fingers, mesial view; H, same, dorsomesial aspect. Scale bar: 0.5 mm (C – H), 1 mm (A, B).