Heteromesus greeni ( Tattersall, 1905 )

Cunha, Marina R. & Wilson, George D. F., 2006, The North Atlantic genus Heteromesus (Crustacea: Isopoda: Asellota: Ischnomesidae), Zootaxa 1192 (1192), pp. 1-76 : 40-42

Heteromesus greeni ( Tattersall, 1905)

( Fig. 18)

Ischnosoma greeni Tattersall 1905: 20–22 , 72, pl. IV, figs. 1–6.

Heteromesus greeni (Tattersall) .– Richardson 1908: 81; Wolff 1962: 86, 217, 260, 274; Kussakin 1988: 483–485, fig. 397.

Material examined

Holotype: preparatory female (4.2 mm), North Atlantic : off west coast of Ireland, west of Achill Head, approximately 54ºN, 11ºW, Aug 1901, R / V Helga, 698 m ( NHM 1911.11.8.9599).

Remarks on type material. Holotype female was in almost perfect condition.

Diagnosis (Female only)

Pereonites 1–3 with median rook spines, but with no paired dorsal spines or tubercles. Pereonite 5 length 2.2 width. Pleotelson posterolateral margin anterior to uropods without spines or tubercles. Antennula with 5 articles altogether, article 2 distal tip not produced distally, next article inserting apically; article 3 longer than article 4, squat, wider than long. Antenna article 2 with 1 ventromedial spine. Labrum knobs present. Pereopod bases proximal shoulder with rook spines.

Description (Female characters only)

Body length 4.2 mm; granular. Head length 0.7 width; dorsal surface with pair of cephalic bullae; dorsal cuticle coarse spinous granulation. Pereonite 1 width 0.20 total body length; with median rook spine, 1 pair of anterolateral pedestal spines, 1 pair of lateral simple spines. Pereonite 2 with median rook spine. Pereonite 3 with median rook spine. Pereonites 1–3 rook spines short, pereonite 1 pedestal spines stout topped by short robust seta, length distinctly less than length of pereonite 1. Pereonite 4 length 0.60 width. Pereonite 5 length 2.2 width, 0.25 total body length. Pleotelson length 1.2 width.

Antennula article 2 length 0.56 head width, with 4 elongate stiff ventromedial setae; article 3 longer than article 4, squat, wider than long; terminal article shorter than penultimate article. Antenna length 2 anterior body length; article 2 with 1 ventromedial stout pedestal spine terminated with fine seta; article 3 length 0.42 anterior body length, length 5 width, with 1 ventral stout pedestal spine; article 5 length 0.32 anterior body length; article 6 length 0.32 anterior body length; flagellum with 15 articles, flagellum length 0.37 total antenna length.

Labrum knobs present, strongly asymmetric, right side conical, left side rounded, both denticulate.

Pereopod bases proximal shoulder with rook spines. Pereopod I carpus palm length near proximal region length, with 2 robust setae on palm distal to elongate seta; propodus ventral margin with 2 robust setae. Pereopods II– VII bases denticulate, sometimes sharply toothed.

Uropods medial margin denticulate; length 0.45–0.50 length of pleotelson.

Distribution North Atlantic, off North Ireland, 364– 700 m.

Remarks

Heteromesus greeni is similar to H. dentatus and H. oryktus in having spinous granulation of the body, 5 antennular articles altogether and inconspicuous ornamentation of the pereopods showing only rook spines on the proximal "shoulders" of the bases. It is distinctive in its having one rook spine on the dorsal midline of pereonites 1–3.