Apseudopsis opisthoscolops, Bamber, Roger N, Chatterjee, Tapas & Marshall, David J, 2012

Bamber, Roger N, Chatterjee, Tapas & Marshall, David J, 2012, Inshore apseudomorph tanaidaceans (Crustacea: Peracarida) from Brunei: new records and new species, Zootaxa 3520, pp. 71-88 : 72-79

Apseudopsis opisthoscolops sp. nov.

( Figs 1–4 )

Material examined: Ƥ holotype with oostegites ( BMNH.2012.1055), 3 allotype ( BMNH. 2012.1056), 1 brooding Ƥ, 2433, 26Ƥ, 1 subadult, paratypes ( BMNH.2012.1057–1066), Brunei Darussalam, 0 4°40.5ʹN 114°26.5ʹE, sand, 2–8 m depth, March 2009. 533, paratypes ( BMNH.2012.1067–1071), 1 Ƥ with oostegites (dissected), paratype, Sungai Besar, Sungai Brunei Estuary and Bay, Brunei Darussalam, 4º56'N, 115º1'E, mud flat and algae covering the pneumatophores of Avicennia marina , coll T Chatterjee and David J Marshall, 10 March 2011.

Description of female: Body ( Fig. 1 A) tapering towards posterior, holotype 2.9 mm long, 4.6 times as long as wide. Cephalothorax with convex lateral margins, glabrous, as long as wide, as long as pereonites 3 and 4 together, with rounded rostrum bearing central point ( Fig. 1 B); eyelobes demarcated from carapace, with conspicuous anterior spine-like apophysis ( Fig. 1 B); eyes present, pigmented (pink in preserved material). Pereonites 1 and 2 naked, with convex lateral margins; pereonites 3 to 6 with lateral indentations at mid-length but without apophyses, with row of fine setae at anterolateral corners and single midlateral setae. Pereonite 1 shortest, pereonites 2, 3 and 6 subequal in length, 1.2 times as long as pereonite 1; pereonites 4 and 5 subequal in length, 1.4 times as long as pereonite 1 (all pereonites respectively 3, 2.4, 2.3, 1.7, 1.6 and 1.7 times as wide as long). Hyposphenia present between chelipeds and on pereonite 2, the former blade-like and blunt. Pereonite 6 with mid-ventral tubercle with distal spine. Pleonites about five times as wide as long; each pleonite with extended, triangular epimera terminating in a spine and bearing dorsal simple setae ( Fig. 4 A); pleonite 1 with backwardly-directed, pointed, blade-like hyposphenium. Pleotelson subpentangular, pointed mid-distally, nearly four times as long as each pleonite, 1.2 times as long as wide, with midlateral tubercle nearing four simple setae, distally with six simple and two penicillate setae as in Fig. 1 C.

Antennule ( Fig. 1 D) longer than cephalothorax, proximal peduncle article 3.5 times as long as wide without marginal tuberculation, inner margin with numerous simple setae, outer margin with both simple and penicillate setae; second article 2.5 times as long as wide, 0.4 times as long as first article, with inner and outer tufts of simple setae; third article half length of second, with inner and outer simple distal setae; distal peduncle article one-third as long as third article, with one distal seta. Main flagellum of seven segments, single aesthetascs on segments 4 and 6; accessory (inner) flagellum of three segments.

Antenna ( Fig. 1 E) proximal peduncle article with inner triangular apophysis bearing two marginal setae; second article 1.5 times as long as first, with two inner and two outer simple setae, squama a narrow oval bearing numerous marginal and few submarginal simple setae; third peduncle article short, with two inner-distal setae; fourth article half as long as second, with one outer simple seta; fifth article 1.6 times as long as fourth with paired inner and outer simple setae and four distal penicillate setae. Flagellum of seven segments, mostly sparsely setose, but first flagellum segment with outer comb-like array of eight simple setae, mostly three times as long as segment, third flagellum segment with two inner-distal setae as long as last four flagellar segments.

Labrum ( Fig. 1 F) apically rounded, setose. Left mandible ( Fig. 1 G) with four rounded teeth on pars incisiva, lacinia mobilis elongate with three distal teeth, spiniferous lobe bearing four uni- or bi-dentate spines; right mandible ( Fig. 1 H) similar but without lacinia mobilis, spiniferous lobe bearing five spines; pars molaris robust with rugose distal face; first article of mandibular palp bearing 11 distal and mesial simple setae; second article 1.4 times as long as first, six longer ventral to distal setae and six shorter submarginal spinules; third article just longer than first, with four subdistal shorter and four distal longer setae. Labium ( Fig. 1 I) distally finely setose, outerdistal margin with fine denticulations and setules; palp without apophyses, marginally setose and with three distal spines. Maxillule ( Fig. 2 A) outer endite with ten distal spines and two subdistal setae, inner endite with four plumose distal setae and outer subdistal apophysis; palp of two articles, distally with four shorter and two longer setae. Maxilla ( Fig. 1 J) with smooth outer margin; outer lobe of moveable endite with two simple subdistal setae and four distally-denticulate distal setae; inner lobe of moveable endite with five simple setae; outer lobe of inner endite distally with three bifurcate, one trifurcate and three simple spines, and four outer simple setae; inner lobe of fixed endite with rostral row of 15 setae guarding three longer finely denticulate setae. Maxilliped ( Fig. 2 B) basis naked; endites with two coupling hooks, eight outer fusiform setae, distal margin with a mixture of spatulate spines and fine setae, caudo-distal inner seta simple, stout, finely pointed; palp first article with fine outer-distal spine, paired inner-distal setae as long as or longer than second palp article; second article with outer distal stout spine, inner margin with about ten shorter curved setae in two rows and five longer straight setae; third article also with inner submarginal short, curved setae and inner marginal longer straight setae; fourth article reflexed, with two subdistal outer setae and five distal setae. Epignath ( Fig. 2 C) wide, lobate, distal spine finely setulose.

Cheliped ( Fig. 2 D) slender, basis 2.25 times as long as wide, dorsally with proximal tuft of fine setae, ventrally with two subdistal simple setae and one at mid-length; exopodite with four plumose setae on distal article; merus subrectangular, with mesial rows of inner and marginal setae and tuft of numerous setae on ventrodistal “shoulder”; carpus 3.8 times as long as wide, with proximal submarginal array of seven setae, one fine dorsodistal seta and numerous simple setae along ventral margin; propodus just longer than wide, sparsely setose but with two dorsodistal setae and one stronger and two finer setae in junction of fingers; fixed finger shorter than palm of propodus, with five fine distal setae and row of fine setules along cutting edge, terminal spine distinct; dactylus with three distal setae and fine spinules along cutting edge; neither cutting edge with denticulations or apophyses.

Pereopod 1 ( Fig. 2 E) robust, coxa with large, narrow apophysis bearing five setae; basis stout, twice as long as wide, with marginal rows of dorsal and ventral setae in proximal half, one ventrodistal spine and accompanying seta; exopodite with six plumose setae on distal article; ischium compact with three ventrodistal setae; merus 0.7 times as long as basis, with ventroproximal tuft of setae, and single dorsodistal and ventrodistal spines, each with associated tufts of simple setae; carpus 0.7 times as long as merus, with two ventral spines interspersed with simple setae, one dorsodistal spine amongst marginal row of setae, and mesial subdistal row of six simple setae; propodus 1.4 times as long as carpus, ventrally with four spines interspersed with simple setae, dorsally with one penicillate seta, eight simple setae in distal half and two distal setae, small bidenticulate spine adjacent to dactylus attachment; dactylus three times as long as unguis, both together two-thirds as long as propodus, dactylus with two ventral denticulations, single mid-dorsal and dorsodistal setae.

Pereopod 2 ( Fig. 3 A) coxa with smaller apophysis than that of pereopod 1, basis 2.8 times as long as wide, with numerous dorsal and ventral marginal setae, and tuft of six ventrodistal setae; ischium with one dorsal and five ventrodistal setae; merus one-third as long as basis, with two ventrodistal and one dorsodistal slender spines, numerous ventral marginal setae, three dorsodistal setae and three mesial subdistal setae; carpus 1.6 times as long as merus, ventrally with two slender spines interspersed by simple setae and two submarginal hook-like spinules, diagonal row of setae from subdistal mid-line to dorsodistal corner; propodus just longer than carpus, ventrally with three slender spines interspersed by simple setae, two subproximal inner hook-like spinules, and two dorsodistal slender spines surrounding four or five simple setae; dactylus with one midventral denticulation, one mid-dorsal seta and two distal setae, dactylus and claw together as long as propodus. Pereopod 3 ( Fig. 3 B) similar to pereopod 2, but basis less setose, merus without dorsodistal spine, carpus less robust, propodus with three dorsodistal spines.

Pereopod 4 ( Fig. 3 C) basis three times as long as wide, with paired hook-like ventroproximal spines and one adjacent penicillate seta, three mid-dorsal penicillate setae and four ventrodistal setae; ischium with three ventrodistal setae; merus with dorsodistal seta, ventrally with numerous setae and two spines; carpus 1.8 times as long as merus, with six slender spines along ventral and onto distal margin, interspersed with setae; propodus threequarters as long as carpus with dorsoproximal penicillate seta, ventral and distal margins with numerous setae, dorsodistal margin with six finely-denticulate slender spines; dactylus with two mid-dorsal and two distal setules, together with unguis three-quarters as long as propodus. Pereopod 5 ( Fig. 3 D) similar to pereopod 4, but basis stouter and without dorsal penicillate setae, merus with three spines, propodus more elongate and without dorsodistal spines, dactylus with three mid-dorsal setules.

Pereopod 6 ( Fig. 3 E) basis without hook-like spines but with numerous marginal plumose setae dorsally and ventrally and three dorsoproximal penicillate setae; merus with three dorsal plumose setae; carpus with seven dorsal plumose setae; propodus with ventral to distal row of about fifteen lanceolate spines, single slender ventrodistal and dorsodistal spines in addition to numerous setae, dactylus with three mid-dorsal and three distal setules.

Pleopods ( Fig. 4 A) all alike, basis with four outer and five inner plumose marginal setae; rami subequal, slightly larger endopod with fifteen plumose setae around margins, exopod with sixteen marginal plumose setae but without setae on proximal inner margin.

Uropod ( Fig. 1 C) basis with small outer and distal setae, and conspicuous slender, pointed inner-distal apophysis two-thirds as long as basis; exopod of four segments, articulation occasionally obscure; endopod elongate, about half as long as total body length, with some 30 segments.

Description of male: Generally as female, including hyposphenia and penial tubercle on pereonite 6. Dimorphism shown by antennule and cheliped. Antennule ( Fig. 4 B) main flagellum of nine segments, with five aesthetascs on segments 2 and 3, four on segment 5 and two on segment 7. Cheliped ( Fig. 4 C) stouter than that of female, basis similar but without mid-ventral seta, merus with fewer proximal setae, carpus 1.8 times as long as wide, without proximal setae; propodus as long as carpus, with dense tuft of setae in junction of fingers, adjacent to tooth-like apophysis; larger tooth-like apophysis at proximal end of cutting edge of fixed finger; cutting edge of dactylus minutely crenulate, each crenulation bearing one spinule.

Etymology. From the Greek opisthen —behind, and skolops —a thorn, anything pointed: with reference to the inner-distal apophysis on the uropod basis.

Remarks. Norman (1899) originally distinguished Apseudopsis from Apseudes Leach, 1814 on the basis of the distinct groove between the ocular tubercle and the carapace in the latter, absent in the former. Apseudopsis opisthoskolops sp. nov. does not have a “distinct groove”, but a subtle demarcation is present. Nevertheless, with no row of lanceolate spines along the propodus of pereopod 5, the present species cannot fit into Apseudes . Most of the morphology of the new species (e.g. the conformation of the antennule, the spination of the mouthparts including the complex setation-spination of the mandibular palp, the ornamentation of the pereopods, pereonites and pleon) agrees well with other species of Apseudopsis where sufficient description is available. The morphology of the antennule, including the array of setae on the proximal flagellar segment, is consistent with many species of the genus such as A. latreilli ( Milne-Edwards, 1828) (see Esquete et al. 2012a, for redescription of this species; see also Guţu 2002, for a number of species described therein as Apseudes ), while the pointed apophyses on the ocular tubercles are also found in the generotype A. acutifrons ( Sars, 1882) (see Sars 1886), in A. tridens ( Guţu, 2002) (q.v.) and in A. adami Esquete & Bamber (Esquete et al. 2012b) .

Apseudopsis opisthoskolops is immediately distinct from the known species of the genus owing to the slender, spine-like inner-distal apophysis on the basis of its uropods. This character is diagnostic of the apseudomorphan family Whiteleggiidae , but there can be no confusion between those taxa and the present species. Such an apophysis is also present in, for example, the metapseudid genus Synapseudes Miller, 1940 , wherein it shows intrageneric variation from a conspicuous “spike” in, for example, S. tomescui Guţu, 2006 , to a small swelling with a seta in S. erici Blazewicz-Paszkowycz et al., 2011 . The elaboration of plumose setae on the basis of pereopod 6 is also more excessive than has been recorded previously in the genus, most species having only the dorsal setae plumose (e.g. A. latreilli ), and others having very few ventral plumose setae (e.g. A. isochelatus Guţu, 2006 , q.v.) or being without ventral setae other than the distal tuft (e.g. A. acutifrons ; A. adami ) (unfortunately, for a number of the species described rather inadequately by Guţu, 2002, there is no useful mention of the morphology of the posterior pereopods). Neither of these features could be concieved to warrant generic separation.

The elaboration of aesthetascs on the male antennule does also appear to be unusual for species of Apseudopsis , as does the size of the tooth-like apophysis on the fixed finger of the male cheliped (in many species of the genus the male is undescribed). Both sexes of Apseudopsis opisthoskolops have a similar mid-ventral tubercle on pereonite 6, presumably a penial tubercle, suggesting simultaneous hermaphroditism (as is apparently common in the Apseudidae —see Guţu 2006; Larsen et al. 2011); the morphology of this tubercle is identical with that shown for males of A. latreilli and A. adami ( Esquete et al. 2012a, fig. 11a; 2012b, fig. 7c, respectively). Moult-to-moult survival of mature animals of such a species may be expected to be very low; however, there is evidence of iteroparity in Apseudopsis adami ( Esquete et al., 2012b). As the conformation of the cheliped and the antennule is radically different between “sexes”, in practice the species is likely to perform as a protogynous hermaphrodite; there is no significant difference in adult body size between the two “sexes”.

Figures

FIGURE 1. Apseudopsis opisthoskolops sp. nov., female: A, holotype, dorsal; B, anterior margin of cephalothorax; C, pleotelson and proximal part of uropods; D, antennule; E, antenna; F, labrum; G, left mandible; H, right mandible; I, labium; J, maxilla. Scale line = 1.0 mm for A, 0.3 mm for B – E, 0.2 mm for F to J.

FIGURE 2. Apseudopsis opisthoskolops sp. nov., female: A, maxillule; B, maxilliped and endite; C, epignath; D, cheliped; E, pereopod 1. Scale line = 0.2 mm for A – C, 0.3 mm for D and E.

FIGURE 3. Apseudopsis opisthoskolops sp. nov., A, pereonite 2; B, pereonite 3; C, pereonite 4; D, peeonite 5; S, pereonite 6. Scale line = 0.3 mm.

FIGURE 4. Apseudopsis opisthoskolops sp. nov., A, epimere and pleopod (most setae shown only by their bases); B, male antennule; C, male cheliped (exopod not shown). Scale line = 0.2 mm for A, 0.3 mm for B – C.