Acinoproskelos vermes Bamber & Błażewicz-Paszkowycz 2013, sp. nov.

Acinoproskelos vermes sp. nov.

(Figures 5, 6)

Holotype. 1 manca (MV J57791), Stn. BSS 638Q, Eastern Bass Strait, slope, 102 km southeast of Cape Conran, Victoria, 38 ◦ 29.30 ′ S, 149 ◦ 32.24 ′ E, 1630 m depth, “clayeysand”, 16 November 1981, pipe-dredge, coll. R. S. Wilson.

Body (Figure 5) 2 mm long, five times as long as wide. Cephalothorax rounded, narrower towards anterior, as long as wide, almost as long as pereonites 1 to 3 together, with slight rounded rostrum, naked; eyes absent.

Pereonites; pereonites 1 to 5 with convex lateral margins; pereonite 1 about onethird as long as cephalothorax, 2.8 times as wide as long; pereonites 2 and 3 subequal in length and just longer than pereonite 1; pereonites 4 and 5 longer, 1.5 times as long as pereonite 1; pereonite 6 short, without pereopods. Pleon of five free subequal naked pleonites without pleopods, each pleonite nearly six times as wide as long. Pleotelson pentagonal, short, three times as long as pleonite 5, 1.7 times as wide as long, with pair of midlateral setae (Figure 5B).

Antennule (Figure 6A) of four articles, proximal article 3.2 times as long as wide, with outer distal tuft of four penicillate setae and one simple seta; second article 1.8 times as long as wide, about half length of first, with outer distal tuft of three penicillate setae and one simple seta; third article 0.8 times as long as second, with one simple and penicillate distal seta; fourth article slender but hardly tapering, 1.5 times as long as third article, with five distal setae and single aesthetasc.

Antenna (Figure 6B) of six articles, articles 1 to 3 subequal in length, proximal article naked, second and third articles each with single dorsodistal seta; fourth article longest, longer than articles 1 to 3 together, with mesial penicillate seta, distally with one simple and numerous penicillate setae; fifth article half as long as fourth, with one distal seta; sixth article (flagellum) minute with four distal setae.

Labrum (Figure 6C) not laterally compressed, apically rounded, distally finely setose. Mandibles (Figure 6D) similar to each other, without lacinia mobilis, pars incisiva a distal denticulation, pars molaris absent. Labium not recovered. Maxillule (Figure 6E) with four mesially setulose distal spines and two subdistal setae, palp short with one distal seta. Maxilla not seen. Maxilliped (Figure 6F) endites with single inner-distal seta and smooth distal margin; palp first article naked, second article with three inner-distal setae, third article with six inner marginal setae and one submarginal seta; fourth article with four distal setae and one subdistal seta; basis naked. Epignath (Figure 6G) ribbon-like, naked.

Cheliped (Figure 6H) attached by pseudocoxa, basis overlapping inner face of pseudocoxa; basis 1.6 times as long as wide, naked; merus with one mid-ventral seta; carpus 1.7 times as long as wide with paired ventral setae, ventral margin slightly flattened; propodus longer than wide, fixed finger as long as palm of propodus, with crenulated cutting edge, one ventral and three inner setae, and rounded subdistal tubercle; dactylus with outer margin slightly crenulated, cutting edge with small rounded apophysis.

Pereopod 1 (Figure 6I), coxa simple with seta (see Figure 5B); basis slender, 5.2 times as long as wide; ischium compact with single seta; merus one-third as long as basis with single ventrodistal slender spine; carpus 1.3 times as long as merus, with three slender distal spines; propodus as long as carpus, with short, blunt ventrodistal spine and pointed dorsodistal apophysis; dactylus naked, 0.6 times as long as slender unguis, both together 1.3 times as long as propodus. Pereopods 2 and 3 generally similar to pereopod 1, pereopod 3 with conspicuous penicillate seta on basis (Figure 5B).

Pereopod 4 (Figure 6J) basis 4.4 times as long as wide with mid-ventral penicillate seta; ischium with one ventral seta; merus with two slender ventrodistal spines; carpus 1.5 times as long as merus, with three slender distal spines; propodus with one dorsodistal and two ventrodistal slender spines and pointed dorsodistal apophysis; dactylus half as long as slender, curved unguis, both together 0.9 times as long as propodus. Pereopod 5 as pereopod 4. Pereopod 6 absent.

Pleopods absent.

Uropod (Figure 6K) basis naked, fused exopod short, about one-third as long as proximal endopod segment, with two distal setae; endopod of two segments, proximal segment slender with one distal penicillate seta, distal segment half as long as proximal segment, with one subdistal and four distal setae.

Two nematodes are visible within the abdomen of the specimen, presumably endoparasitic.

Vermes is the Latin plural for “worms”, being both a reference to the parasitic nematodes within the type specimen, and also the acronym of the World Register for Marine Species (WoRMS).

The generic distinction of Acinoproskelos vermes sp. nov. is discussed above. Bird (2004) discussed potentially valuable phylogenetic characters within this family by which genera may be associated into subfamilial groups, although groupings were not consistent between characters. Of the described species of Anarthruridae, the present species is perhaps closest to species of Anathruropsis with regard to habitus, mandible structure and cheliped ornamentation, but is distinct in its labrum-type, and its maxillular and maxilliped setation, the latter, together with the spination of the anterior pereopods, being unique in the family. The cheliped morphology (but not ornamentation) is very similar to that of Thorkelius glacialis (Hansen, 1913) (see Bird 2004).

Endoparasitic nematodes have been recorded before in tanaidaceans, both as secondary hosts for fish parasites and as presumed obligate parasites filling the entire exoskeleton (Larsen 2005 and references therein).

Acinoproskelos vermes was only taken at 1630 m on the northern slope of the Bass Canyon.