Pseudocheles falsapinca, Anker, 2012

Anker, Arthur, 2012, The shrimp family Pseudochelidae De Grave & Moosa, 2004 (Crustacea, Decapoda, Caridea) in Brazil, with the description of a new species, Zootaxa 3544, pp. 79-87 : 80-85

Pseudocheles falsapinca sp. nov.

Figs. 1–5

Type material. Holotype: ovigerous female, pocl 2.60 mm, cl 3.55 mm, MZUSP 25345 , Brazil, off Espírito Santo, REVIZEE - Comissão Central , sta. D-41, 19º41” S 38º14 ”W, depth 68–71 m, leg. M. Tavares, 29 February 1996 . Paratype: ovigerous female, pocl 2.73 mm, cl 3.71 mm, MZUSP 25967 , same collection data as for holotype .

Description. Rostrum moderately slender, barely reaching distal margin of first article of antennular peduncle, with five sharp, anteriorly directed, dorsal teeth of about equal size; most-posterior dorsal tooth situated anterior to post-orbital margin; ventral margin with one small, sharp, anteriorly directed, subdistal tooth ( Fig. 2a–c, m). Carapace slightly compressed laterally, finely pitted, non-setose, almost straight dorsally, strongly convex ventrally, mid-dorsal line with small anterior tubercle or notch situated behind most-posterior rostral tooth, without posterior low tubercle; infra-orbital lobe with very small to obsolete antennal tooth; pterygostomial angle rounded ( Fig. 2b, c, m). Thoracic sternites unarmed.

Abdomen (of females) with first and second pleura broadened ventrally; third somite narrower ventrally, posterior dorsal margin projecting and distinctly overhanging most–proximal portion of fourth somite, forming short hump; fifth pleuron with sharp, posteroventrally curved tooth on posterior margin; sixth somite elongate, almost twice as long as high, with sharply projecting tooth near base of telson ( Figs. 1, 2d, e).

Telson slender, almost four times as long as wide proximally, tapering posteriorly; dorsal surface with two pairs of spiniform setae inserted slightly posterior to 0.4 and at 0.7 telson length, respectively, at some distance from lateral margin; posterior margin ending in sharp triangular point, with four pairs of spiniform setae: one pair of short lateral spiniform setae situated most anteriorly; one pair of thicker sublateral spiniform setae, inserted slightly more posteriorly, much longer than lateral spiniform setae and with row of setules along mesial margin; one pair of short, distinctly more posterior submedian spiniform setae; and one pair of long median spiniform setae flanking median point of posterior margin, shorter and more slender than sublateral spiniform setae ( Fig. 2f, g).

Eyestalks divergent, with large, globular eyes; corneas well pigmented, occupying most of eyestalk’s terminal portion ( Fig. 2a, b).

Antennular peduncle not reaching distal margin of scaphocerite; first article with small stylocerite ending in acute point, latter not reaching distal margin of first article; third article longer than second article; lateral flagellum without distinct accessory ramus, with tufts of long aesthetascs starting from first article; mesial flagellum shorter than lateral ( Fig. 2a, b, h). Antenna with relatively small basicerite, ventrolateral margin ending in blunt tooth; scaphocerite elongate, with slightly convex lateral margin and broadly convex mesial margin, distolateral tooth small, not reaching beyond anterior margin of blade; carpocerite reaching to about end of antennular peduncle, not reaching end of scaphocerite; flagellum longer than antennular flagella ( Figs. 1, 2a, b, i, j).

Mouthparts typical for genus. Mandible with molar and incisor processes partly fused; molar process very small, with short setae along mesioventral margin; incisor process with several large, triangular, distally sharp teeth, divided into two series: ventral series with five teeth gradually increasing in size from ventral-most tooth to dorsal-most tooth, and dorsal series with five teeth alternating in size, including two largest incisor teeth; palp with two articles ( Fig. 3a, b). Maxillule with bilobed endopod, each lobe with slender seta; dorsal endite with row of stout spiniform seta on distal margin; ventral endite with long flexible setae dorsally and stouter, shorter setae ventrally ( Fig. 3c). Maxilla with scaphognathite much broader dorsally than ventrally; endopod apparently with two articles (subdivision very subtle), distal with long seta; dorsal endite elongate, narrow, furnished with long setae distally; ventral endite short, with long setae ( Fig. 3d). First maxilliped with large, broadly subtriangular epipod; exopod with large caridean lobe, distally truncate (without lash); endopod simple; dorsal and ventral endites furnished with rows or groups of long setae on distal surface ( Fig. 3e). Second maxilliped with narrow, earshaped epipod; exopod narrow, overreaching third (carpal) article of endopod; endopod with five articles, first two subequal in length, third (carpal) article distinctly shorter than second; fourth (propodal) article broader and much broader than third; fifth (dactylar) article short, armed with four very stout spiniform setae on apex ( Fig. 3f).

Third maxilliped very slender, pediform; coxa with acutely produced lateral plate and rounded epipod-like structure (see under remarks); exopod well developed, reaching distal margin of penultimate article in full extension; antepenultimate article slightly twisted, about as long as penultimate article, both articles with long, stiff, curving setae on dorsal margin and numerous more straight setae on ventral margin; ultimate article longer than penultimate, with transverse rows of serrulate setae, tip rod-shaped, with several long, stout setae ( Fig. 3g –i).

First pereiopod (= first cheliped) with coxa robust, bearing bluntly projecting ventral lobe; basis with several groups of long, stiff setae; exopod well developed, reaching far beyond carpus; ischiomerus somewhat angular in cross-section, elongate, distally widening, ventrally setose; carpus very short, plate-shape, much wider than long; chela moderately swollen, with palm smooth, subcylindrical, more or less rounded in cross-section, ventrolateral surface with some stiff setae; fingers about 0.4 times as long as palm, slightly gaping, with smoothly curving, crossing tips; cutting edge of dactylus with small, rounded teeth; cutting edge of pollex with small, irregularly shaped teeth ( Fig. 4a–c).

Second pereiopod (= second cheliped) about the same length as first, but conspicuously more slender; coxa not projecting ventrally; basis with slender spiniform seta on ventral surface; exopod well developed, reaching to midlength of carpus; ischiomerus slender, elongate, not widening distally, ventrolateral margin with long setae and one stout spiniform seta at about 0.8 ischiomerus length; carpus short, cup-shaped; chela feebly swollen, with palm smooth, subcylindrical, rounded in cross-section, ventrolateral surface with three long, stiff setae; fingers slightly more than half as long as palm, slightly gaping, with curving, crossing tips; cutting edge of both dactylus and pollex pectinate from about 0.2 to 0.9 of cutting edge length, with size of teeth gradually increasing distally ( Fig. 4d, e).

Third pereiopod longest of all pereiopods, reaching far beyond antennular peduncles and scaphocerite when fully extended; coxa slightly projecting ventrally; basis short, with stiff setae ventrally; exopod reaching to about 0.3 merus length; ischium with stout spiniform seta on ventrolateral surface; merus long, at least seven times as long as greatest width, ventrolateral surface with four stout spiniform setae; carpus short, vase-shaped, distally widening, with stout spiniform seta on ventrolateral surface, and small spiniform seta on distomesial margin; chela slender, with palm smooth, cylindrical, rounded in cross-section, ventrolateral surface with two spiniform setae, first at about mid-length of palm, second subdistal; distoventral margin of palm with three spiniform setae of different length and thickness; ventral spiniform seta elongate, reaching to crossing with dactylus tip (cf. Figs. 1, 5e; seta broken at about 0.8 length on the right side in the holotype, cf. Fig. 5a–d), thick, with row of setules along mesial margin, setules stopping at about half-length of (complete) seta; first ventrolateral spiniform seta distinctly more slender and shorter, reaching to about mid-length of dactylus, with row of minute setules; second ventrolateral spiniform seta about half as long as first ventrolateral spiniform seta; dactylus elongate, as long as palm, slender, curving towards tip, with cutting edge finely pectinate from dactylar base to about 0.9 dactylar length ( Fig. 5a–e).

Fourth pereiopod generally similar to third pereiopod, although somewhat shorter and more slender; armature on basis, ischium and merus identical to that of third pereiopod; merus about 7.5 times as long as greatest width; chela with palm and fingers shorter than in third pereiopod, otherwise very similar ( Fig. 5f, g).

Fifth pereiopod shorter than third and fourth pereiopods; exopod reaching half-length of merus; ischium with two spiniform setae on ventrolateral surface; merus about 6.7 times as long as greatest width, with four spiniform setae on ventrolateral surface; carpus vase-shaped, with stout spiniform seta on ventrolateral surface, and small spiniform seta on distomesial margin; chela generally similar to that of fourth pereiopod, with slightly more slender palm ( Fig. 5h, i).

Pleopods without specific features; second to fifth pleopods with short appendix interna near base of endopod ( Fig. 2k). Uropod with stout protopod, its distolateral lobe ending in sharp tooth; endopod slender, tapering distally; exopod slender, not tapering; distolateral area with small tooth and adjacent, stout spiniform seta; diaeresis irregularly curved, as illustrated ( Fig. 2l).

Gill-exopod formula: 5 pleurobranchs (P1–5), 0 arthrobranch, 0 podobranch, 3 epipods (Mxp1–3, but see discussion below), 8 exopods (Mxp1–3, P1–5).

Colour in life unknown.

Etymology. Derived from two Portuguese words, falsa (feminine of falso) = false, and pinça = forceps, claw, referring to pseudochelate condition of the third to fifth pereiopods characteristic of the genus and the family; used as a noun in opposition.

Vernacular name proposed. Brazilian false-clawed shrimp (English), camarão falsa-pinça brasileiro (Portuguese).

Distribution. Presently known only from the type locality at the outer margin of the Brazilian continental shelf, about 160 km east of Rio Doce estuary, Espírito Santo, and just north of Vitória Seamount.

Habitat. Both type specimens of P. falsapinca sp. nov. were collected together in a dredge on a maerl-type bottom, consisting of fragments and nodules of calcareous algae, at a depth range of 68–71 m.

Remarks. All four presently known species of Pseudocheles are morphologically very similar and can be discriminated by the combination of two or three subtle characters rather than by conspicuous autapomorphies. Pseudocheles falsapinca sp. nov. differs from the only Atlantic congener, P. chacei , by the absence of spine-like mesial projections on the coxae of the third and fourth pereiopod; the absence of an acute mesial projection on the basis of the third pereiopod; a rostrum with fewer dorsal teeth (5 vs. 6–8 in P. chacei ), all of which are anterior to post-orbital margin (vs. 1 or 2 most-posterior teeth posterior to post-orbital margin in P. chacei ) (cf. Kensley 1983, figs. 18–22). The new species can also be distinguished from the two Indo-West Pacific species, e.g., from the type species, P. enigma , by the reduced antennal tooth (well developed in P. enigma ) and the presence of a sharp, ventroposteriorly directed tooth on the posterior margin of the fifth pleuron (absent in P. enigma ) (cf. Chace & Brown 1978, figs. 1–4); and from P. neutra by the presence of a very stout spiniform seta on the carpus of the third, fourth, and fifth pereiopods (absent in P. neutra ) (cf. De Grave & Moosa 2004, figs. 1–4). In addition, P. falsapinca sp. nov. has no trace of a low tooth on the posterior portion of the carapacial dorso-median line, which is present or at least indicated in P. chacei , P. enigma , and P. neutra . Noteworthy, the Brazilian species is also the deepest species of Pseudocheles reported so far, with the depth of 68–71 m at the type locality. The three other species have been found at much shallower depths of 1–15 m ( P. enigma ), ~ 10 m ( P. neutra ), and 6–28 m ( P. chacei ).

Kensley’s (1983) figure 18 of the habitus of P. chacei shows the third abdominal somite forming a cap over the fourth somite, but not overhanging it, as in all other species of the genus, including P. falsapinca sp. nov. ( Figs. 1, 2d). However, a photograph of the holotype of P. chacei made by Gustav Paulay at the author’s request clearly shows that the dorso-posterior margin of the third abominal somite projects posteriorly, forming a distinct hump overhanging the dorsal base of the fourth somite. Therefore, it seems that all species of Pseudocheles have this abdominal hump (see also Chace & Brown 1978, fig. 1; De Grave & Moosa 2004, fig. 1b).

The presence of an epipod on the third maxilliped in Pseudocheles has not been previously mentioned nor illustrated (cf. Chace & Brown 1978, fig. 3h; Kensley 1983, fig. 20b; De Grave & Moosa 2004, fig. 2f). In P. falsapinca sp. nov., there is a small, but rather conspicuous, rounded structure right below the acutely produced lateral plate on the coxa of the third maxilliped, in a position typically occupied by an epipod in many other carideans ( Fig. 3g, i). Importantly, this epipod-like structure is present in both examined specimens. It is here tentatively considered as a reduced epipod and is included as such in the gill-exopod formula above. Whether the epipod on the third maxilliped is truly absent or perhaps overlooked in the other species of Pseudocheles warrants further study.

The four currently known species of Pseudocheles can be separated using the following key.