Synalpheus trinitatis, Anker, Arthur, Tavares, Marcos & Mendonça, Joel B., 2016

Anker, Arthur, Tavares, Marcos & Mendonça, Joel B., 2016, Alpheid shrimps (Decapoda: Caridea) of the Trindade & Martin Vaz Archipelago, off Brazil, with new records, description of a new species of Synalpheus and remarks on zoogeographical patterns in the oceanic islands of the tropical southern Atlantic, Zootaxa 4138 (1), pp. 1-58 : 40-44

Synalpheus trinitatis sp. nov.

( Figs. 13–15 )

Type material. Brazil: Holotype: male (cl 3.4 mm), MZUSP 30089, Trindade Island, Enseada dos Portugueses, Praia da Calheta, 20°30’20.9”S – 29°18’43.7”W, depth: 11.6 m, coll. J.B. Mendonça, 18.vii.2012. Paratypes: 1 male (cl 2.7 mm), MZUSP 30090, same collection data as for holotype; 1 male (cl 3.4 mm), 1 ovig. female (cl 3.8 mm), MZUSP 33316, Trindade Island, Enseada dos Portugueses, off SECON / ECIT, 20°30’20.9”S – 29°18’43.7”W, depth: 11 m, coll. J.B. Mendonça, 11.xi.2014; 1 male (cl 4.1 mm), MZUSP 34504, Trindade Island, Enseada dos Portugueses, Rampa Nova, 20°30’17.7”S – 29°18’56.7”W, depth: 11.6 m, coll. J.B. Mendonça, 08.vii.2015; 1 male (cl 3.5 mm), 1 ovig. female (cl 4.0 mm), OUMNH.ZC. 2016.02.0 18, Trindade Island, Enseada dos Portugueses, Ponta da Calheta, 20°30’18.7”S – 29°18’31.6”W, depth: 16.9 m, coll. J.B. Mendonça, 25.vi.2015; 1 male (cl 2.4 mm), MZUSP 30091, Trindade Island, Enseada Orelhas, 20°29’40.2”S – 29°20’32.9”W, depth: 13.9 m, coll. J.B. Mendonça, 30.vi.2012; 1 male (cl 3.1, missing major cheliped), MZUSP 34125, Trindade Island, Enseada da Cachoeira, Farrilhões, 20°31’22.4”S – 29°19’52.0”W, depth: 10.7 m, coll. J.B. Mendonça, 25.x.2014; 1 male (cl 3.4 mm), 1 ovig. female (cl 3.7 mm), MNHN-IU-2014-12837, Trindade Island, Enseada do Príncipe, Ilha Sul, 20°31’34.32”S – 29°19’27.98”W, depth: 22.2 m, coll. J.B. Mendonça, 10.vii.2015.

Comparative material examined. Synalpheus brooksi Coutière, 1909 . Brazil: 1 male-looking ovig. specimen (see Anker et al. 2012 for possible explanation), MZUSP 31145, Ceará, Pecém, harbour jetty, in Ircinia sp., coll. L.E. Arruda Bezerra, 10.ix.2011 (specimen illustrated in Fig. 16 ).

Description. Small-sized species from Synalpheus brooksi complex (cl range 2.4–4.1 mm), with subcylindrical, non-compressed body. Carapace and pleon smooth, glabrous, without setae. Rostrum as long as or slightly longer than orbital teeth, distinctly narrower, subtriangular in dorsal view, slightly upturned in lateral view ( Fig. 13 A); postrostral area usually noticeably lower than orbital hoods. Orbital hoods forming broad, bluntly rounded, somewhat triangular teeth; margin between rostrum and orbital teeth in form of shallowly rounded sinus ( Fig. 13 A); orbito-rostral process not distinct. Pterygostomial angle anteriorly produced, blunt ( Fig. 13 B). Posterior margin of carapace with deep cardiac notch.

First pleura of male with posterior corner produced into small, ventrally directed hook; second pleura of male broadly rounded; third to fifth pleura of male progressively more acute ventrally ( Fig. 13 C). Telson tapering distally along its entire length, posterior margin being only one fourth length of anterior margin; dorsal surface with two pairs of stout spiniform setae, situated approximately at one third and two thirds of telson length, respectively; posterior margin with small median convexity and two stout spiniform setae, mesial much longer than lateral, posterolateral corners obtuse, not projecting ( Fig. 13 D).

Antennular peduncle with first article longest, widening distally; stylocerite with blunt tip and somewhat convex lateral margin, reaching to 0.4 length of first article of antennular peduncle; second article subquadrate in dorsal view, as long as wide; third article shortest, wider than long; lateral flagellum with distinct accessory branch ( Fig. 13 A, B). Antenna with basicerite armed with very long distoventral tooth, latter subequal to or slightly overreaching scaphocerite, and reaching almost to end of third article of antennular peduncle, dorsal margin of basicerite bluntly projecting, not forming conspicuous tooth; scaphocerite without blade; carpocerite robust, reaching far beyond end of antennule ( Fig. 13 A, B).

Mouthparts typical for genus. Third maxilliped with coxal lateral plate posteriorly curved, acute; antepenultimate article longest and most robust; penultimate article very short, subquadrate; ultimate article tapering distally, with distal circlet of at least five, relatively slender, spiniform setae; exopod not reaching distal margin of antepenultimate article; arthrobranch well developed ( Fig. 13 E, F).

Major cheliped with very short ischium; merus robust, with strongly convex dorsal margin and flattened ventral surface, unarmed distally; carpus very short, plate-shaped; chela ovoid, inflated, subcylindrical; palm smooth, with distodorsal protuberance relatively short, bluntly pointing forwards or slightly upwards; fingers about half-length of palm; pollex slightly shorter than dactylus ( Figs. 14 A–C, 15A, B).

Minor cheliped with short ischium; merus about 3.5 times as long as maximum width; carpus vase-shaped; palm subcylindrical, slightly compressed laterally, height slightly more than half of length; fingers clearly shorter than palm; dactylus with gambarelloid setae well developed, consisting of numerous transverse setal combs; cutting edges of dactylus and pollex sharp, blade-like, finger tips bifid, with one subdistal tooth and slightly larger terminal tooth ( Fig. 14 D, E).

Second pereiopod ( Fig. 13 G) with carpus consisting of five articles with ratio approximately equal to 3: 1: 1: 1: 1.8 and clearly longer than merus; chela simple, longer than proximal carpal article, finger tips subacute. Third pereiopod relatively stout; merus about 3.5 times as long as wide, not particularly inflated, margins not forming flange; carpus much more slender than merus, less than half-length of merus, distoventral margin with small spiniform seta; propodus shorter than merus, armed with seven spiniform setae on ventral margin and distal pair of spiniform setae adjacent to dactylus; dactylus biunguiculate, with accessory (flexor) unguis clearly thicker than terminal (extensor) unguis, margin between accessory and terminal ungui deep, V-shaped ( Fig. 13 H, I). Fourth pereiopod similar to third, more slender. Fifth pereiopod more slender than third and fourth, with much shorter merus; carpus unarmed distoventrally; propodus with three spiniform setae on ventral margin, distal pair of spiniform setae adjacent to dactylus, and three transverse combs of stiff cleaning setae, distolaterally ( Fig. 13 J).

Second to fifth pleopods with appendices internae. Uropod usually with two or three teeth, exceptionally with one tooth, on lateral margin of exopod, most distal tooth distinctly removed from sharp distolateral tooth and adjacent stout spiniform seta ( Figs. 13 K, 3C). Ovigerous females with less than 20 large eggs (diameter approximately 1.2 x 0.9 mm).

Colour in life not recorded.

Etymology. Derived from the type locality, Trindade Island ( Ilha da Trindade), Brazil; used as an adjective.

Distribution. Southwestern Atlantic: presently known only from Trindade Island, Espírito Santo, Brazil.

Ecology. Subtidal hard bottom with rocks, calcareous algae and rock-algae-sponge conglomerates; possibly obligate associate of small sponges in crevices and boring holes of conglomerates; depth range: 10.7–16.9 m.

Remarks. Synalpheus trinitatis sp. nov. has all the characteristics of the Synalpheus gambarelloides ( Nardo, 1847) species group (= Zuzalpheus Ríos & Duffy, 2007 ) and within this large group belongs to the western Atlantic Synalpheus brooksi species complex, which also includes S. brooksi Coutière, 1909 , S. bousfieldi Chace, 1972 , S. chacei Duffy, 1998 , S. carpenteri Macdonald & Duffy, 2006 , S. ruetzleri Macdonald & Duffy, 2006 , S. idios ( Ríos & Duffy, 2007) , S. plumosetosus Macdonald, Hultgren & Duffy, 2009 , S. thele Macdonald, Hultgren & Duffy, 2009 , and S. corallinus Macdonald, Hultgren & Duffy, 2009 (see Coutière 1909; Chace 1972; Dardeau 1984; Duffy 1998; Macdonald & Duffy 2006; Ríos & Duffy 2007; Macdonald et al. 2009). The S. brooksi species complex was recovered as a monophyletic clade both in the multi-locus analysis of the western Atlantic members of Synalpheus ( Hultgren & Duffy 2011) and in the recent worldwide phylogeny of the genus ( Hultgren et al. 2014).

Synalpheus trinitatis sp. nov. may be separated from S. brooksi by the distodorsal protuberance of the major chela being shorter, less tapering and directed forwards (anteriorly), not slightly upwards (dorsally), as in S. brooksi (cf. Figs. 14 B, C, 15A, B, 16D), the less ventrally produced and pointed third and fourth pleura (cf. Figs. 13 C, 16B), and somewhat broader and blunter orbital teeth (cf. Figs. 13 A, 16A). Another difference between S. trinitatis sp. nov. and S. brooksi is the presence of usually two or three teeth on the distolateral margin of the uropodal exopod vs. usually one in S. brooksi , although some specimens of the former species have one tooth, whereas some specimens of the latter species may occasionally have two teeth, at least on one of the uropods ( Figs. 13 K, 15C, 16E, F; see also Christoffersen 1979, Dardeau 1984 and Ríos & Duffy 2007). The Brazilian material reported as S. brooksi by Christoffersen (1979) should be re-examined, in particular all specimens with two teeth on the distolateral margin of both uropodal exopods as they may belong to S. trinitatis sp. nov.

Synalpheus trinitatis sp. nov. differs from S. bousfieldi , S. idios and S. thele by the presence of usually two or three teeth on the distolateral margin of the uropodal exopod (vs. one in the other three species; however, this character is somewhat ambiguous as S. trinitatis sp. nov. may occasionally have only one tooth); from S. bousfieldi and S. idios by the less projecting distodorsal protuberance of the major chela; from S. idios by the shorter and blunter orbital teeth and the longer antennal scaphocerite and distoventral tooth of the basicerite, both reaching mid-length of the third article of the antennular peduncle vs. only slightly overreaching the distal margin of this article in S. idios ; from S. bousfieldi by the longer second to fourth carpal articles of the second pereiopod (illustrated as very short by both Chace 1972 and Dardeau 1984 for S. bousfieldi ) and narrower telson; from S. thele by the shorter stylocerite, not reaching half-length of the first article of the antennular peduncle vs. overreaching this margin in S. thele (cf. Figs. 13 A, K, 14B, C and Chace 1972: figs. 29, 30; Dardeau 1984: figs. 7–10, Ríos & Duffy 2007: figs. 13, 14; Macdonald et al. 2009: fig. 22, 23; Anker et al. 2012: fig. 14). It must be noted here that the specimen from Atol das Rocas , Brazil, reported as S. bousfieldi in Anker et al. (2012) , has a less pronounced distodorsal protuberance of the major chela compared to that of the holotype, approaching the configuration observed in S. trinitatis sp. nov. Anker et al. (2012) noted some other minor differences between the Atol das Rocas material and the material reported as S. bousfieldi by Dardeau (1984).

The remaining species of the S. brooksi complex are easier to distinguish from S. trinitatis sp. nov. For instance, S. carpenteri has a more pronounced rostrum, a shorter scaphocerite, and the distodorsal protuberance of the major chela usually ends in a small acute point, although this last feature is less consistent (cf. Figs. 13 A, 2B, C and Macdonald & Duffy 2006: figs. 1, 3, 6). In S. ruetzleri , the distodorsal protuberance of the major chela is slightly bulbous and tapering into a small point, whereas the antennal scaphocerite bears a small blade (cf. Figs. 13 A, 2B, C and Macdonald & Duffy 2006: figs. 8, 10). In S. chacei and S. corallinus , the gambarelloid setae of the minor chela are arranged into two rows (vs. one in S. trinitatis sp. nov.), whereas the exopodal uropod has only one fixed tooth on the distolateral margin (vs. typically two or three in S. trinitatis sp. nov.). In addition, in S. chacei , the distoventral tooth of the basicerite is distinctly shorter than the antennal scaphocerite (vs. subequal to the scaphocerite in S. trinitatis sp. nov.) (cf. Figs. 13 A, K, 2E and Duffy 1998: fig. 1; Macdonald et al. 2009: figs. 6, 7). The Caribbean S. plumosetosus is characterised by the plumose gambarelloid setae, which are simple in S. trinitatis sp. nov. (cf. Fig. 14 E and Macdonald et al. 2009: fig. 7).

Because of the subtleness of the morphological characters separating the species of the S. brooksi complex ( Macdonald & Duffy 2006; Ríos & Duffy 2007; Macdonald et al. 2009) and intraspecific variation observed in most species, thorough comparative analyses of the DNA (especially of the divergence in the barcoding segment of the COI gene) are becoming increasingly important. Therefore, S. trinitatis sp. nov. should be genetically compared to the other species of the S. brooksi complex, especially S. bousfieldi and S. brooksi ( Brazil, Gulf of Mexico, Caribbean Sea, Florida), but also S. idios (Caribbean Sea, Florida) and S. thele (Caribbean Sea) , to verify the validity of the new species and the morphology-based identifications of the Brazilian material of S. bousfieldi and S. brooksi .

Figures

FIGURE 13. Synalpheus trinitatis sp. nov., holotype, male from Enseada dos Portugueses, Trindade Island (MZUSP 30089): A — frontal region, dorsal view; B — same, lateral view; C — pleon, lateral view; D — telson, dorsal view; E — right third maxilliped, lateral view; F, same, tip of ultimate article, mesial view; G — right second pereiopod, lateral view; H — right third pereiopod, lateral view; I — same, distal portion of propodus and dactylus, lateral view; J — right fifth pereiopod, lateral view; K — right uropod, dorsal view.

FIGURE 14. Synalpheus trinitatis sp. nov., holotype, male from Enseada dos Portugueses, Trindade Island (MZUSP 30089): A — right (major) cheliped, lateral view; B — same, chela, mesial view; C — same, distal portion of chela, lateral view; D — left (minor) cheliped, lateral view; E — same, chela, mesial view.

FIGURE 15. Synalpheus trinitatis sp. nov., paratype, male from Trindade Island, Enseada dos Portugueses (MZUSP 33316): A — right (major) chela, lateral view; B — same, detail of distodorsal protuberance; C — left uropod, dorsal view.

FIGURE 16. Synalpheus brooksi Coutière, 1909, male-looking ovigerous specimen from Ceará, Brazil (MZUSP 31145): A — frontal region, dorsal view; B — pleon, lateral view; C — telson, dorsal view; D — right (major) chela, mesial view; E — left uropod, dorsal view, F — right uropod, dorsal view.