Salmoneus rocas, Anker, Arthur, 2007

Anker, Arthur, 2007, New species and records of alpheid shrimps, genera Salmoneus Holthuis and Parabetaeus Coutière, from the tropical western Atlantic (Decapoda, Caridea), Zootaxa 1653, pp. 21-39 : 29-30

Salmoneus rocas n. sp.

Fig. 4

Material examined: Holotype: ovig. female, MNRJ 20216, Brazil, Atol das Rocas , east of Laguna Interna, in calcareous alga, depth 1 m, coll. F.B. Pitombo and R. Barroso, 18 Oct 2000 [dissected].

Description: Carapace not setose, with numerous minute pits ( Fig. 4 a–d). Rostrum much longer than broad; slightly overreaching distal margin of second segment of antennular peduncle ( Fig. 4 a, b); lateral margins slightly convace proximally; ventral margin unarmed ( Fig. 4 b, c); rostral carina distinct, reaching beyond eyes posteriorly ( Fig. 4 a). Orbital spines large, acute, slightly mesially directed ( Fig. 4 a). Pterygostomial margin slightly protruding anteriorly, broadly rounded ( Fig. 4 b–d). Eyes covered in dorsal view, visible in lateral view ( Fig. 4 a–d). Antennule with stylocerite distinctly overreaching distal margin of second segment of antennular peduncle, with acute tip; second segment about 0.7 times as long as wide ( Fig. 4 a). Antenna with basicerite bearing subacute distoventral spine ( Fig. 4 b); scaphocerite ovate, distolateral spine small, subacute ( Fig. 4 a). Third maxilliped with rounded lateral plate; ultimate segment with tapering tip, without distinct spiniform setae ( Fig. 4 j). Chelipeds strongly asymmetrical in shape, unequal in size ( Fig. 4 k–m). Major cheliped ( Fig. 4 k, l) with unarmed ischium; merus not inflated distally, ventral surface somewhat depressed; carpus cupshaped, ventrally not depressed, distally with rounded lobes ( Fig. 4 k); chela mostly smooth, subcylindrical, not depressed ventrally, not flattened mesially, with deep groove proximoventrally ( Fig. 4 k); fingers subequal to palm, cutting edges serrated, with 11 subtriangular-rounded teeth, distal teeth larger ( Fig. 4 l). Minor cheliped ( Fig. 4 m) with ischium subequal to merus, both unarmed; carpus slightly shorter than merus; chela small, simple, with fingers subequal to palm. Second pereiopod Fig. 4 n) with unarmed ischium; carpus bearing five segments, first segment subequal to sum of other four segments. Third pereiopod ( Fig. 4 o, p) with ischium bearing one ventrolateral spiniform seta; merus about four times as long as wide; carpus distally with small ventral spiniform seta; propodus with four small ventral spiniform setae, including distal seta; dactylus simple, conical, moderately slender, less than half length of propodus. Fifth abdominal somite with subacute posteroventral angle ( Fig. 4 e). Sixth abdominal somite without distinct articulated plate, with acute posteroventral projection ( Fig. 4 e); preanal plate acutely produced towards telson ( Fig. 4 f). Second pleopod with appendix masculina shorter than appendix interna, furnished with slender spiniform setae on apex and along outer margin ( Fig. 4 h). Uropod with with sinuous diaersis and relatively stout distolateral spiniform seta ( Fig. 4 e). Telson about 1.7 times as long as wide proximally, tapering posteriorly, with two pairs of dorsal spines, inserted at about mid-length and 2/3 telson length, respectively ( Fig. 4 g); posterior margin with subtriangular median notch and two pairs of spiniform setae at posterolateral angles, mesial setae distinctly longer than lateral setae ( Fig. 4 g). Gill/exopod formula typical for genus (see under S. ortmanni ).

Colour: Unknown.

Size: Holotype: CL 3.8 mm, TL 11.6 mm.

Etymology: The new species is named after the type locality, Atol das Rocas off the northeastern coast of Brazil.

Ecology: The holotype was found in a crust of calcareous algae, in 1 m deep water.

Type locality: Atol das Rocas , Brazil.

Distribution: Western Atlantic: presently known only from the type locality, Atol das Rocas .

Remarks: The new species appears to be related to S. arubae ( Schmitt, 1936) from the western Atlantic; S. teres Manning & Chace, 1990 , S. setosus Manning & Chace, 1990 , both from the western and central Atlantic (see below); and S. serratidigitus (Coutière, 1896) from the Indo-Pacific. It can be separated from S. arubae and S. teres by the very different shape of the frontal margin of the carapace (cf. Schmitt, 1936: fig 2a; Manning & Chace, 1990: fig. 10b); from S. arubae by the presence of a posteromedian notch on the telson (absent in S. arubae ; cf. Schmitt, 1936: fig. 2g); from S. setosus by the absence of conspicuous thickened setae on the carapace, abdomen and telson (a diagnostic feature of S. setosus ; cf. Manning & Chace, 1990: fig. 9a, b; see also Fig. 6 a, b); from S. serratidigitus by the ischium of the third pereiopod bearing one spiniform seta (vs. two or three setae in S. serratidigitus ), and the subtriangular median notch on the posterior margin of the telson (vs. U-shaped in S. serratidigitus ; cf. Banner & Banner, 1981: fig. 8). The present evidence suggests that S. rocas n. sp. is most closely related to S. serratidigitus from the Indo-Pacific and may represent the S. serratidigitus species complex in the western Atlantic.

The minute pits on the carapace are present in S. rocas n. sp., but also in S. cf. arubae (cf. Holthuis, 1990) and S. teres (R. Lemaitre, pers. comm.; see also below), and may be an important taxonomic and phylogenetic character within the S. serratidigutus species group ( Anker & Marin, 2006).

Figures

FIGURE 4. Salmoneus rocas n. sp., holotype, ovigerous female from Atol das Rocas, Brazil (MNRJ 201216): a—frontal region, dorsal view; b—same, lateral view (right side); c—same, more detailed (left side); d—carapace, lateral view; e—posterior abdominal somites and tail fan, lateral view; f—preanal plate of sixth abdominal somite, ventral view; gtelson, dorsal view; h – endopod of second pleopod, mesial view; i — egg; j—penultimate and ultimate segments of third maxilliped, lateral view; k—major cheliped, “ lateral ” view; l—same, chela fingers; m—minor cheliped, lateral view; n—second pereiopod, lateral view; o—third pereiopod, lateral view. Scale bars = 1 mm.

FIGURE 6. Salmoneus setosus Manning & Chace, 1990: ovigerous female from Atol das Rocas, Brazil (MNRJ 17890): a—frontal region, dorsal view; b—same, lateral view; c—major cheliped, lateral view; d—same, chela, mesial view; esame, detail of carpus, mesial view; f—minor cheliped, lateral view; g— second pereiopod, lateral view; h—third pereiopod, lateral view; i—uropod, dorsal view, dorsal view; j—telson, dorsal view; k—egg. Scale bars = 1 mm.