Thorkelius glacialis ( Hansen, 1913 ) Hansen, 1913

Bird, Graham, 2004, Tanaidacea (Crustacea) of the Northeast Atlantic: non­filiform species of Anarthruridae Lang from the Atlantic Margin, Zootaxa 471, pp. 1-44 : 27-30

Thorkelius glacialis ( Hansen, 1913) comb. nov. ( Figs. 11–12 )

Leptognathia glacialis: Hansen, 1913: 102 , plate X figure 3a–3b.

Diagnosis. Fairly stout Thorkelius with all pereonites distinctly shorter than broad. Pleotelson short and conical. Cheliped fixed finger conical, 2.5 times longer than broad, with long shallow convexity.

Material examined. BIOICE Stn 2629, one neuter; Stn 2652, one prep. male.

Redescription. Neuter/non­ovigerous female. Large, body ( Fig. 11 A) fairly stout, 5.1 times longer than broad. Length 2.8–3.5 mm. Cephalothorax almost round and as long as broad, but tapering rostrally; rostrum with round apex. Pereonites 1–2 narrower caudally, all pereonites shorter than broad and laterally rounded; pereonites 1–4 with two dorsorostral setae. Pleon 21% of body length. Pleotelson ( Fig. 11 B) as long as one and a half pleonites, conical but only 0.43 times as long as broad, with lateral, dorsocaudal and terminal setae.

Antennule (see Fig. 11 A) just longer than cephalothorax, similar to that of T. latiremis . Antenna similar to preparatory male.

Mouthparts as for preparatory male (as far as can be seen in whole specimen).

Cheliped ( Fig. 11 K) surfaces with numerous microtrichia; pseudocoxa large, twice as long as basis; basis conical, with lateral seta; merus subtriangular, with strong ventral seta; carpus 1.4 times longer than broad, with two relatively long dorsal setae and two unequal setae near ventral protuberance; propodus without lateral fold, with group of three anterior spiniform setae ( Fig. 12 D); fixed finger cylindrical, with two ventral setae, one seta near dactylus and a close group of three spiniform seta near incisive margin; incisive margin convex, proximal half with low crenulations, distal ( Fig. 12 C) with four subtriangular teeth; terminal spine conical; dactylus curved, with strong anterior spiniform seta and two small spines on incisive margin.

Pereopods and pleopods similar to preparatory male.

Uropod ( Fig. 12 M) exopod shorter than basal article, with three unequal distal setae; endopod 1­articled, 5.5 times longer than broad, with one sensory seta and five terminal setae.

Preparatory male. Body similar to neuter but pleon larger, 26% of body length. Length 3.4 mm. Antennule ( Fig. 11 C) articles broader than in neuter. Antenna ( Fig. 11 D) similar to that of T. latiremis . Labrum ( Fig. 11 E) broadly conical. Mandible ( Figs. 11 F–G) with long conical incisor. Maxilla ( Fig. 11 H) pear shaped. Maxillule endite ( Fig. 11 H) with one short and six long terminal spiniform setae. Maxilliped basis with seta near palp; palp ( Fig. 12 A) article­2 with three setae; article­3 with four medial setae and one other seta; article­4 with five distal setae, all setae smooth or only minutely pinnate; endite ( Fig. 12 B) rectangular, with strong incurved medial seta. Cheliped as neuter, distal teeth of fixed finger better defined (possibly less abraded?).

Pereopod­1 ( Fig. 12 E) coxa with seta; basis about five times longer than broad, with proximal seta; ischium with one seta; merus 2.6 times longer than broad, with distoventral seta; carpus subrectangular, three times longer than broad, with three distal setae; propodus 1.4 times longer than carpus, with distoventral seta; dactylus and unguis together about as long as propodus, dactylus with accessory seta.

Pereopod­2 ( Fig. 12 F) similar to pereopod­1 but basis and merus slightly shorter and stouter; carpus twice as long as broad; propodus about 0.8 times length of pereopod­1 article. Pereopod­3 ( Fig. 12 G) similar to pereopod­2 but basis and carpus shorter; propodus longer than carpus.

Pereopod­4 ( Fig. 12 H) basis stout, 2.5 times longer than broad, with two sensory setae; ischium with two setae; merus curved, twice as long as broad, with two spiniform setae bearing bifid tips; carpus subrectangular, twice as long as broad, with three spiniform setae bearing complex tips and a simple seta; propodus as long as carpus, with three long, spiniform, and complex setae; dactylus and unguis 0.7 times length of propodus, unguis short.

Pereopod­5 ( Fig. 12 J) similar to pereopod­4, ischium with two setae. Pereopod­6 ( Fig. 12 K) similar to pereopod­5, but basis shorter and propodus with four distal spiniform setae.

Pleopod ( Fig. 12 L) rami well developed, endopod and exopod with about ten and thirteen finely plumose setae respectively.

Uropod as in neuter/non­ovigerous female.

Remarks. This species, not extensively figured by Hansen, can easily be accommodated in the same genus as T. latiremis , sharing very similar maxilliped, mandible, pereopod and uropod morphology. It is best distinguished by its shorter pereonites and more elongate cheliped dactylus and fixed finger.

Apart from the type locality in Fleming Inlet, East Greenland, 216 m ( Hansen 1913) it has been recorded from two BIOICE stations on the Iceland Plateau, 603–913 m, with mean bottom temperature –1o C, and silt substrate.

Figures

FIGURE 11. Thorkelius glacialis. Non­ovigerous female A, dorsal; B, pleotelson; preparatory male C, antennule, lateral view, setae omitted; D, antenna; E, labrum, ventral view; F – G mandibles; H, maxillule and maxilla; J, epignath; non­ovigerous female K, cheliped. Scale bar 2 mm (A), 1 mm (B), 0.67 mm (C – D, K), 0.33 mm (E – J).

FIGURE 12. Thorkelius glacialis. Preparatory male A, maxilliped palp; B, maxilliped endite; C, cheliped fixed finger, detail; D, anterior setae of cheliped propodus; E – G, pereopods 1 – 3 respectively; H – K, pereopods 4 – 6 respectively, with enlargements of complex spiniform setae; L, pleopod; non­ovigerous female M, uropod. Scale bar 0.67 mm (E – L), 0.5 mm (M), 0.33 mm (A – D).