Similipedia diarris, Błażewicz-Paszkowycz & Bamber, 2007

Błażewicz-Paszkowycz, M. & Bamber, R. N., 2007, New apseudomorph tanaidaceans (Crustacea: Peracarida: Tanaidacea) from eastern Australia: Apseudidae, Whiteleggiidae, Metapseudidae and Pagurapseudidae, Memoirs of Museum Victoria 64, pp. 107-148 : 146-147

Similipedia diarris sp. nov.

Figures 24–26

Material. Female, holotype ( NMV J47126 ), Australia, Victoria, eastern Bass Strait, 8 km S of South East Point, Wilsons Promontory (39°12.54'S, 146°27.18'E), 65 m, 18/11/1981, ( BSS 180 S), R.S. Wilson. Paratypes: 42 females (7 brooding), same locality as holotype ; paratypes ( NVM J55752 ), 2 dissected on slides ( NMV J55938 ), same locality as holotype .

Description of female. Body dorsoventrally flattened, holotype 3.2 mm long (tip of rostrum to posterior of pleotelson), 5.3 times as long as wide, narrower posteriorly. Cephalothorax subrectangular, slightly longer than wide, naked, swollen around branchial chambers; anterior margin with conspicuous v-shaped rostral excavation. Eyes present; eyelobes with apophyses directed anterolaterally. 6 free pereonites; pereonites 1 and 2 subequal, about one-third as long as cephalothorax, lateral margins uniformly convex; pereonite 1 with anterodorsal row of 7 spiniform apophyses. Pereonite 3 1.5 times as long as pereonite 1, with 4 anterodorsal spiniform apophyses, lateral pair appearing as anterolateral apophyses; pereonite 4 longest, 1.7 times as long as pereonite 1, with 4 anterodorsal spiniform apophyses, anterolateral spiniform apophyses, mid-lateral spiniform apophyses anterior to conspicuous posterolateral swelling over coxal attachment; pereonite 5 just longer than pereonite 1, with anterodorsal and mid-dorsal rows of spiniform apophyses and expanded posterolaterally at attachment of coxae; pereonite 6 as long as pereonite 1, laterally uniformly convex with anterodorsal and mid-dorsal rows of spiniform apophyses (all pereonites respectively 2.4, 2.3, 1.6, 1.2, 1.9 and 1.8 times as wide as long). Pleon twice as long as pereonite 5, of 5 free subequal pleonites bearing pleopods plus pleotelson; pleonites dorsally convex, some 6 times as wide as long, laterally expanded by spiniform apophyses and with paired mid-dorsal spines. Pleotelson as long as wide, as long as pleonites 2 to 5 inclusive, naked.

Antennule peduncle article 1 elongate, 6.7 times as long as wide, with conspicuous inner and outer spine-like marginal apophyses, distally with inner tooth-like apophysis and larger outer denticulate apophysis, as long as peduncle article 3 and bearing 2 setae; article 2 0.3 times as long as article 1, with distal expansion bearing 3 inner and 3 outer setae; article 3 three-quarters length of 2nd, article 4 one-third as long as 3rd, naked. Main flagellum of 6 segments, sparsely setose as figured; accessory flagellum of 4 segments.

Antenna peduncle article 1 simple with outer seta; article 2 naked, without squama; peduncle article 3 as long as wide, with 1 seta; articles 4 and 5 of equal length, and 3.3 times as long as article 3, each with distal penicillate setae. Flagellum of 1 segment with 2 distal setae.

Mouth parts. Labrum sparsely setose. Left mandible with distal outer margin bearing group of spinous apophyses; strong, bifurcate, crenulated pars incisiva, lacinia mobilis as long as pars incisiva, setiferous lobe with 1 simple and 3 longer, distally expanded and setulose setae, pars molaris elongate, blunt; mandibular palp of 3 articles, article 1 naked, article 2 twice as long as wide with inner row of 11 simple setae in distal half, article 3 as long as article 2 but more slender, 5 times as long as wide, with 12 inner simple setae increasing in length distally, and 2 longer distal setae, the longer 1.3 times as long as article. Right mandible as left but without lacinia mobilis. Maxillule inner endite with 5 midlaterally-setulate distal setae and outer marginal apophysis; outer endite with 11 distal spines, 1 shorter than the rest, outer margin finely setose, inner margin with microtrichia; palp absent. Maxilla with microtrichia on outer margin; outer lobe of moveable endite with 2 simple setae on outer margin and 4 simple distal setae; inner lobe of moveable endite distally with 7 simple outer and 5 plumose inner setae; outer lobe of fixed endite with marginal microtrichia, distally with 6 outer simple setae, 5 stouter blunt or bifurcate spines, and inner plumose seta; inner lobe of fixed endite with rostral row of 22 setae guarding 5 longer plumose setae, inner margin finely denticulate. Labium glabrous, palp marginally densely setose with single distal spine. Maxilliped basis with tuberculate inner margin, sparse short setae and 2 mid-distal setae; palp article 1 with single distal seta on outer margin, paired inner setae and 3 sharp denticulations on inner margin; palp article 2 longer than wide, with rows of numerous short tooth-like tuberculations on inner margin adjacent to row of small, simple setae, outer margin with 1 simple seta subdistally; palp article 3 as long as wide, with 5 simple setae on expanded inner margin; palp article 4 with 5 distally denticulate distal setae, and 1 longer and 1 shorter simple subdistal setae. Endite with simple, flagellate inner and outer caudodistal setae, blunt bifurcate or spatulate, distal spines, margin of dense fine distal setules and 4 coupling hooks. Epignath slender, marginally densely setose, with prominent proximal lobe and setose distal spine.

Cheliped robust, basis twice as long as wide, dorsally with central and distal groups of 3 spine-like apophyses, ventrally with small marginal setae, paired ventrodistal setae and 4 denticulations along the distal half; exopodite absent. Merus subrectangular, ventrally and distally with sparse setae, ventrodistal shoulder with 2 spine-like apophyses. Carpus 2.4 times as long as wide, with small, simple setae proximally and distally on dorsal margin, ventrally with spine-like apophyses becoming smaller distally and sparse simple setae. Chela fingers shorter than palm; palm with sparse ventral (3) and dorsal (5) setae, fixed finger with 4 ventral and 4 dorsodistal setae around distinct distal claw, 3 setae near articulation of dactylus; cutting edge of fixed finger crenulate; dactylus with fine dorsal setae, proximal setae and distal apophyses on cutting edge, distal claw pointed.

Pereopods generally all similar.

Pereopod 1 coxa with spinous apophysis; basis slender, 6.4 times as long as wide, with simple setae along both margins and row of 12 spines along dorsal margin; exopodite absent. Ischium with single, simple ventrodistal and dorsodistal setae. Merus 0.3 times as long as basis, with rows of simple dorsal and ventral setae as figured. Carpus 1.8 times as long as merus, with sparse dorsal marginal setae, ventral margin with 10 spines interspersed with fine simple setae. Propodus shorter than carpus, 1.5 times as long as merus, with dorsodistal and distal simple setae, ventral margin with 7 spines interspersed with fine simple setae. Dactylus slender, one-third length of propodus, with fine inner and outer setae and slight ventrodistal expansion adjacent to unguis; unguis short, slender, half length of dactylus.

Pereopod 2 similar to pereopod 1, but basis 5.4 times as long as wide, dorsally with row of 7 unequal spine-like apophyses and no setae. Ventrodistal swelling on dactylus larger.

Pereopod 3 similar to pereopod 2, but dorsal margin of basis with fewer, smaller apophyses; propodus with mesial row of 5 setae.

Pereopod 4 similar to pereopod 2 but basis with dorsoproximal tuft of penicillate setae; merus half as long as subequal carpus or propodus; propodus with mid-dorsal penicillate seta, dorsodistal tuft of 6 finely denticulate setae; ventrodistal swelling on dactylus more pronounced.

Pereopod 5 as pereopod 4 but with only single penicillate seta on basis, mesial setae but only 2 simple distal setae on propodus.

Pereopod 6 similar to pereopod 5.

Pleopods all alike. Basis elongate, with single dorsal seta. Both rami slender, with 2 distal and 1 subdistal setae; endopod shorter than exopod.

Uropod basis with paired distal setae, endopod of 10 slender segments, exopod of 2 segments shorter than proximal 2 segments of endopod.

Etymology. From the Greek “ dia ” – asunder, and “ rhis ” – a snout, referring to the cleft rostral margin of the cephalon (noun in apposition).

Remarks. Within the subfamily Hodometricinae , only 3 genera, viz. Pagurapseudopsis Shiino, 1963 , Parapagurapseudopsis Silva Brum, 1974 (including Brumia Băcescu, 1981 ), and Similipedia Guţu, 1989 have a full 5 pairs of pleopods in the adult. Of these 3, Pagurapseudopsis is distinct in having an exopodite on pereopod 1, and the basis of this pereopod is substantially larger than that of the remaining legs; Parapagurapseudopsis has an exopodite on the cheliped (rudiment only in Pagurapseudopsis ); both of these genera have a palp on the maxillule. With no maxillule palp, pereopod 1 of similar morphology to the remaining pereopods, and exopodites missing from both the cheliped and pereopod 1, the present species accords with Similipedia .

The only previously described species of Similipedia is S. eminescui Guţu, 1989 , from the north-east Mozambique Channel at 6 m depth, to which much of the morphology of S. diarris sp. nov. (habitus, rostral concavity, antennular basis apophyses, pereopod and pleopod structure, ventrodistal swelling on the pereopod dactyli) is very similar. The present species is distinguished from S. eminescui by having no squama on the antenna (very reduced squama evident in S. eminescui ), no rostrum (small eminence in the centre of the rostral concavity in S. eminescui ), dorsal spiniform apophyses on the pereonites (only setae in S. eminescui ), more segments in the antennular flagella, 1 less segment in the antennal flagellum, more slender mandibular palp articles, and the more elaborate outer distal apophysis on the proximal antennule peduncle article.

None of the specimens of Similipedia eminescui had retained their chelipeds, so the description of the cheliped from S. diarris adds to our knowledge of this genus, particularly that the cheliped exopodite is absent. Guţu (1989) also gave no description of the maxilla of his species.