Zuzalpheus filidigitus ( Armstrong, 1949 ) Ríos, Rubén & Duffy, J. Emmett, 2007

Ríos, Rubén & Duffy, J. Emmett, 2007, A review of the sponge‑dwelling snapping shrimp from Carrie Bow Cay, Belize, with description of Zuzalpheus, new genus, and six new species (Crustacea: Decapoda: Alpheidae), Zootaxa 1602 (1), pp. 1-89 : 29-32

Zuzalpheus filidigitus ( Armstrong, 1949) n. comb.

( Figs. 11–12 , Plate 3 )

Synalpheus filidigitus Armstrong 1949: 15 , fig. 5; Duffy 1996c; Duffy and Macdonald 1999: 284; Ríos 2003: 79, figures 2–10 and 2–11, plate II.

Material examined. (1) Holotype ♂ ( AMNH 9572 ), 2.4 mm, Barahona Harbor , Dominican Republic, 1932– 1933 . Paratypes: hundreds of specimens ( AMNH 9573 ), same data as holotype .

(2) 5 ♂ ( USNM 1019061, VIMS 01CBC0502), 2.3–2.4 mm, Curlew Ridge, Belize, 27 Apr 2001, from a colony of 88 ♂ and a single ovigerous ♀ (2.9 mm), in demosponge Xestospongia sp. growing among dead Madracis sp. , 15 m.

(3) 1 ovigerous ♀ ( VIMS 93 CBC0302), 2.2 mm, 18 ♂ ( VIMS 93 CBC0303–93CBC0320), 1.4–2.4 mm, outer ridge at Carrie Bow Cay , Belize, 18 March 1993, in Oceanapia sp. , 15 m.

(4) 1 ovigerous ♀ ( VIMS 93 CBC0702), 1.8 mm, 6 ♂ ( VIMS 93 CBC0703–93CBC0708), 1.4–1.6 mm, from a colony of 7 individuals, outer ridge at Carrie Bow Cay , Belize, 18 March 1993, in Xestospongia cf. proxima , 15 m.

(5) 11 ♂ ( VIMS 94 CBC2602–94CBC2612), 1.5–2.2 mm, from a colony of 13 individuals, outer ridge at Carrie Bow Cay , Belize, 23 August 1994, in Xestospongia cf. subtriangularis , 17 m .

Diagnosis. Body subcylindrical; carapace smooth, with pterygostomian corner obtusely angular, and posterior margin with cardiac notch distinct. Rostrum triangular, clearly narrower than and slightly surpassing ocular hoods, distally upturned and with ventral margin convex. Orbitorostral process absent. Ocular hoods dorsally convex; in dorsal view, broadly triangular, separated from rostrum by deep adrostral sinus. Ocular processes absent. Ocellary beak in lateral view rod-like. Stylocerite slender; tip acute; reaching about as far as distal margin of 1 st segment of antennular peduncle; this latter segment without ventromesial tooth, and with 2 very small basal ventral processes. Basicerite with sharp spine on dorsal margin not surpassing stylocerite, longer lateral spine reaching distal half of second segment of antennular peduncle. Scaphocerite blade absent, lateral spine robust, clearly overreaching antennular peduncle; mesial corner at base of scaphocerite obtuse. Carpocerite slightly surpassing scaphocerite. Ma xilliped 3 with distal circlet of spines on distal segment and without ventrodistal spine on antepenultimate segment.

Major pereopod 1 massive, fingers clearly not longer than half length of palm; fixed finger reduced, slightly shorter than dactyl; in ventral view, outer face of fixed finger without distinct protuberance. Palm of chela with distal superior margin produced into prominent blunt tubercle, latter with short secondary spine on ventral surface. Merus with extensor margin strongly convex, ending in obtuse angle, sometimes with a hint of shallow angular projection.

Minor pereopod 1 with palm clearly less than 2 times longer than high; fingers about as long as palm; dactyl with flexor surface excavate, with subdistal bump and tooth near apex; transverse dorsal setal combs on extensor surface of dactyl very conspicuous; fixed finger with flexor surface obliquely concave, and no hint of subdistal tooth. Extensor margin of merus convex, ending in obtuse angle.

Pereopod 2 chela distally tapering, dactyl and fixed finger terminating in sets of anteriorly directed stiff simple setae, giving fingers a produced or filiform appearance; carpus 4-segmented, about as long as merus.

Pereopod 3 slender; dactyl biunguiculate, with proximal tooth thicker than distal one; merus without movable spines on flexor margin; mesial lamella on coxa present. Pereopods 4 and 5 normal.

Pleura 1 of male with posteroventral corner produced into short broadly acute hook; posteroventral corner of male pleura 2 produced into obtuse angle. Pleopod 1 of male with 3 terminal setae on endopod; pleopod 2 of male with marginal setae on exopod originating near midpoint; appendix interna on male pleopods 2–5 present. Telson with space between posterior marginal spines about one-third width of posterior margin; marginal convex lobe absent; posterior corners adjacent to spines obtuse. Anal flaps, perianal setae, and postanal setal brush all absent. Uropods with 1–2 (occasionally 3) fixed teeth on outer margin of exopod anterior to movable spine.

Color ( Plate 3 ). Translucent with pale to bright yellow ovaries and developing embryos; the digestive gland is a yellowish-salmon color.

Variations. The number of fixed teeth on the lateral margin of the uropodal exopod is almost always 2, with few smaller specimens having only one. Four specimens in the colony examined lack a rostrum, while the queen has an asymmetrical frontal border due to a broadened adrostral sinus on the right side. Two of the specimens (USNM 1019061) lack the protuberance overhanging the base of the dactyl on the major chela, just as Armstrong (1949) recorded in a few of his specimens. Among the hundreds of paratypes (AMNH 957), Armstrong (1949) separated 14 specimens and labeled them as “variations”; in this vial there is a detached small cheliped with a trifid dactyl, otherwise these shrimps seem to belong in Z. filidigitus . The female in the examined colony is a “large queen” ( Duffy and Macdonald 1999), well differentiated from the rest of the members by having a larger body size, broad abdominal pleura, and two minor chelipeds on the first pereopods.

Ecology. At Carrie Bow Cay Z. filidigitus seems to be restricted to the sponges Xestospongia spp. and Oceanapia sp. , with incidental records from Hyattella intestinalis , all growing among branches of coral, usually Madracis mirabilis . Like Z. regalis and Z. chacei , Z. filidigitus is a eusocial species forming colonies with one or rarely a few reproductive females and tens of males and juveniles ( Duffy and Macdonald 1999).

Distribution. Western Atlantic: Dominican Republic ( Armstrong 1949), Belize Barrier Reef (this study).

Remarks. Zuzalpheus filidigitus is one of a complex of four closely related species ( Duffy 1996c) that bear a sharp spine on the dorsal margin of the basicerite, lack any trace of a blade on the scaphocerite, and have only four segments in the carpus of the second chelae. The four species in the “ Zuzalpheus rathbunae complex” can be separated by a combination of consistent morphological characters ( Table 2). When Armstrong (1949) erected S. filidigitus , he noted the similarity of this species to Z. rathbunae and listed five characters to distinguish them: length of spine on dorsal margin of basicerite, tubercle overhanging base of major chela dactyl, merus of minor chela, fingers of second chelae, and merus of third pereopod. The name that Armstrong (1949) gave to the species comes from what he called "threadlike" fingers on the chela of the second pair of pereopods; as shown in his figure 5c. Dardeau (1984) concurred with Armstrong and described the fingers as filiform, without any further comments. Examination of several specimens from Belize under high magnification suggests that the threadlike appearance of the fingers is actually due to the presence of distal and subdistal brushes of stiff simple setae on both the dactyl and the fixed finger, which obscure the tips of the fingers and give them a filiform appearance. Additional observations are necessary to verify that those specimens without the filiform tips have not just lost them due to trauma.

Figures

PLATE 3. Zuzalpheus filidigitus, female (VIMS 01CBC0901) from Xestospongia cf. proxima, Curlew Reef, Belize. Zuzalpheus herricki, female (VIMS 05FK0602) from Hippospongia sp., Tavernier Key, Florida, USA. Zuzalpheus goodei, female (VIMS 03CBC3701) from Pachypellina podatypa, Sand Bores, Belize. Zuzalpheus goodei, male (VIMS 03CBC3702) from Pachypellina podatypa, Sand Bores, Belize. Zuzalpheus idios, female (VIMS 01CBC8001) from Hymeniacidon amphilecta, Carrie Bow Cay, Belize. Zuzalpheus kensleyi, female (VIMS 01CBC3802) from unidentified yellow sponge, Sand Bores, Belize.

FIGURE 11. Zuzalpheus filidigitus (Armstrong 1949). Male holotype 2.4 mm (AMNH 9572): a, anterior region of carapace and cephalic appendages, lateral view (right scaphocerite missing); b, same, dorsal view. Male 2.3 mm (USNM 1019061): c, left minor first pereopod (setal combs on dactyl omitted), lateral view; d, same, tip of dactyl, ventrolateral view; e, same, tip of fixed finger, lateral view; f, left second pereopod, lateral view; g, same, tip of chela with some setae removed, lateral view; h, left third pereopod, lateral view; i, same, detail of distal portion, lateral view. Scale bar = 1.3 mm for a, b, c, f; 1.0 mm for h; and 0.25 mm for d, e, i, g.

FIGURE 12. Zuzalpheus filidigitus (Armstrong 1949). Male 2.4 mm (USNM 1019061): a, abdomen, lateral view. Incomplete moult (VIMS 01CBC0502): b, first pleopod; c, telson and left uropod, dorsal view; d, distolateral corner of left uropod, dorsal view. Scale bar = 1.6 mm for a; 0.41 mm for b; 1.0 mm for c; and 0.31 mm for d.