Heteromesus wolffi Chardy, 1974

Cunha, Marina R. & Wilson, George D. F., 2006, The North Atlantic genus Heteromesus (Crustacea: Isopoda: Asellota: Ischnomesidae), Zootaxa 1192 (1192), pp. 1-76 : 64-65

Heteromesus wolffi Chardy, 1974

Heteromesus wolffi Chardy 1974: 1543–1546 , figs. 4–5; Kussakin 1988: 475–476, figs. 388–389.

Material examined

Holotype: male (6.2 mm), North Atlantic, Labrador Basin, 55º52.5’N 49º53.4’W, R / V Jean Charcot , Campagne Noratlante stn 10 prl E 04, 3465 m (MNHN IS­3361 ).

Remarks on type material. The holotype was dissected by Chardy. Some dissected parts were found loose in the vial.

Diagnosis (Male only)

Head with squat anterolateral projections supporting antennae, projection width exceeding length;. Pereonites 1–3 with median dorsal and anterolateral simple spines. Pereonite 5 length 8.6 width. Pleonite 1 region with dorsal tubercles. Pleotelson with dorsal tubercles; posterolateral margin anterior to uropods without spines or tubercles. Antennula with 4 articles altogether.

Description (Male characters only)

Body length 6.2 mm, granular. Head length 0.65 width; dorsal surface with pair of cephalic bullae, cuticular structure coarse tubercular granulation; lobe on ventrolateral margin absent in lateral view. Pereonite 1 width 0.15 total body length; with median simple spine, 1 pair of anterolateral simple spines and 1 pair of lateral tubercles (indistinctly illustrated). Pereonite 2 with median simple spine, 1 pair of lateral simple spines. Pereonite 3 with median simple spine, 1 pair of lateral simple spines. Pereonites 1–3 long simple spines decreasing in length from pereonite 1 to 3, length near pereonite 1 length. Pereonite 4 length 0.60 width. Pereonite 5 length 0.40 total body length. Pleonite 1 region of pleotelson with 1 pair of median tubercles and 2 pairs of dorsal tubercles. Pleotelson length 1.25 width; medially indented, bilobed posteriorly with 1 pair of dorsal tubercles on lateral fields above incision of lateral margin.

Antennula article 2 length 0.9 head width, with 3 elongate stiff ventromedial setae (possibly 4); article 3 length similar to article 4, article 3 short and tubular, length near width, aesthetascs absent. Antenna article 3 length 0.64 anterior body length, 6.5 width, with distomedial spine (indistinctly illustrated).

Labrum knobs low. Maxillula medial lobe without robust dentate setae. Maxilla with 2 long (approximately as long as lateral lobes) medially­projecting pectinate seta on medial lobe.

Pereopod I carpus palm length near proximal region length, with 4 robust setae on palm distal to elongate seta; propodus ventral margin with 2 robust setae.

Pleopod I distal tip with lateral horns. Pleopod II protopod apex narrow, tapering; stylet tapering and pointed, not heavily calcified, not extending to distal margin of protopod. Uropods length 0.50 length of pleotelson.

Distribution

North Atlantic: Labrador Basin (55º52.5’N, 49º53.4’W) , south of Reykjanes Ridge (54º21.6’N, 27º06.0’W) and south of the Azores (36º48.5’N, 49º53.4’W), 3178–3663m .

Remarks

H. wolffi differs from other Heteromesus species in having the most elongated pereonite 5, long median dorsal and anterolateral simple spines on pereonites 1–3 and by its peculiar shape of the head and pleotelson. In particular, the antennae are born on squat projections that are shorter than the robust projections seen in Stylomesus . The long spines and the shape of head and pleotelson resemble some Haplomesus species , although the generic differences serve to separate these species. The holotype male of Heteromesus wolffi Chardy was scored according to Chardy (1974: 1543–1546, figs. 4–5) that also provided the following additional information on sexual dimorphism: “pereonite 5 [in female] proportionally wider and shorter; spine­like tubercles on cephalon developed into spines” (in the description of the male holotype Chardy placed the pair of “spine­like” tubercles laterally on pereonite 1).