Synalpheus filidigitus Armstrong, 1949

Anker, Arthur, Pachelle, Paulo P. G., Grave, Sammy De & Hultgren, Kristin M., 2012, 3598, Zootaxa 3598 (1), pp. 1-96 : 40-41

Synalpheus filidigitus Armstrong, 1949

Synalpheus filidigitus Armstrong 1949: 15 , fig. 5; Chace 1972: 92; Dardeau 1984: 39; Duffy & Macdonald 1999: 284.; (?) Bezerra & Coelho 2006: 701.

Zuzalpheus filidigitus — Ríos and Duffy 2007: 29 , figs 11, 12, pl. 3.

Material examined. Panama: 1 colony member, USNM 1191704 , Bocas del Toro , Isla Colón, Boca del Drago , in unidentified white sponge ( Xestospongia sp. ?), 1–3 m depth, coll. K. Hultgren, 20.09.2008 [fcn P08-14601-1-2]; 5 colony members, USNM, same collection data [fcn P08-14601-1, 14601-3-6] (specimens currently used for molecular studies) .

Description. See Armstrong (1949) for original description and illustrations, with additional illustrations in Ríos & Duffy (2007).

Size range. Colony members, 1.4–2.4 mm cl; females, 1.8–2.9 mm cl.

Colour in life. Translucent with bright to pale yellow ovaries and developing embryos ( Ríos & Duffy (2007).

Type locality. Barahona, Dominican Republic .

Distribution. Western Atlantic: Caribbean Sea: Dominican Republic [Barahona], Belize [Carrie Bow Cay], Panama [Bocas del Toro] ( Armstrong 1949; Ríos & Duffy 2007; present study) (see map in Fig. 51 ); records from Brazil [Ceará] by Bezerra & Coelho (2006) are doubtful (see below).

Ecology. Shallow coral reefs and associated habitats rich in sponges; depth range 0.5–15 m; obligate symbiont of demosponges, primarily Xestospongia sp. and Oceanapia sp. , with some records from Hyattella intestinalis ( Ríos & Duffy 2007; present study); occurs in social groups of tens to several hundred individuals, with one or (rarely) a few reproductive females ( Ríos & Duffy 2007).

Remarks. Synalpheus filidigitus can be most easily recognised by the thread-like appearance of the fingers on the chela of the second pereiopod. This appearance is due to the presence of terminal tufts of setae on the fingertips, which are aligned along the finger’s long axis, thus “extending” the fingers and giving them a filiform appearance ( Ríos & Duffy 2007). Therefore, the drawings of the second pereiopod in Armstrong (1949) are incorrect.

This species belongs to the morphologically challenging S. rathbunae Coutière, 1909 species complex, which includes three other social species viz. S. rathbunae Coutière, 1909 , S. elizabethae (see above), and S. regalis (see below). The identification of the Panamanian specimens as S. filidigitus was confirmed by DNA barcoding. On the other hand, Bezerra & Coelho's (2006) record of this species from Ceará, northeastern Brazil, is rather questionable. One of us (PP) examined a series of specimens reported by Bezerra & Coelho (2006) and deposited in the Universidade Federal de Pernambuco in Recife, Brazil (UFPE). None of them was S. filidigitus . It is possible that Bezerra & Coelho's record of S. filidigitus was actually based on specimens of S. brooksi (P. Pachelle, pers. obs.).

Figures

FIGURE 51. Presently known geographic ranges of Synalpheus africanus Crosnier & Forest, 1965; S. cf. africanus (eastern and western Atlantic); S. agelas Pequegnat & Heard, 1979; S. anasimus Chace, 1972; S. antillensis Coutière, 1909; S. apioceros Coutière, 1909; S. bocas Anker & Tóth, 2008; S. bousfieldi Chace, 1972; S. brooksi Coutière, 1909; S. carpenteri Macdonald & Duffy, 2006; S. chacei Duffy, 1998; S. congoensis Crosnier & Forest, 1965; S. dardeaui (Ríos & Duffy, 2007); S. dominicensis Armstrong, 1949; S. elizabethae (Ríos & Duffy, 2007); S. filidigitus Armstrong, 1949; S. fritzmuelleri Coutière, 1909; S. goodei