Heteromesus schmidtii Hansen, 1916

Cunha, Marina R. & Wilson, George D. F., 2006, The North Atlantic genus Heteromesus (Crustacea: Isopoda: Asellota: Ischnomesidae), Zootaxa 1192 (1192), pp. 1-76 : 54-56

Heteromesus schmidtii Hansen, 1916

( Fig. 26)

Heteromesus schmidtii Hansen 1916: 69–70 , pl. VI, fig. 3a–e; Gurjanova 1932: 45, tabl. XV, 56, 1933: 411; Menzies 1962: 122; Wolff 1962: 85, 217, 260; Kussakin 1988: 477–478, fig. 390.

Material examined

Holotype: female (4.1 mm), North Atlantic : South of Iceland, 62º 57’N, 19º58’W, 14 Jul 190, R / V Thor, 3956m (508 Danish fathoms) ( ZMUC CRU­8027 ).

Remarks on type material. The holotype is a fragile preparatory female, with most pereopods broken; the left uropod and right pereopod I are also broken but in the vial.

Diagnosis (Female characters only)

Pereonite 1 with paired lateral spines; pereonite 4 with median tubercle and paired tubercles. Pereonite 5 length 1.9 width. Antennula with 3 articles altogether, article 2 distal tip produced distally beyond insertion of next article, distal article inserting subapically, article 3 terminal.

Description (Female characters only)

Body length 4.5 mm; granular. Head length 0.40 width; dorsal surface with pair of cephalic bullae; dorsal cuticle tubercular granulation. Pereonite 1 width 0.20 total body length; with median tubercle, 1 pair of dorsal tubercles, 1 pair of anterolateral simple spines, 1 pair of lateral simple spines. Pereonite 2 with median tubercle, 3–4 pairs of dorsal tubercles, 1 pair of lateral tubercles. Pereonite 3 with median tubercle, 3–4 pairs of dorsal tubercles. Pereonite 4 length 0.60 width; with median tubercle, 2–3 pairs of dorsal tubercles. Pereonites 1–4 tubercles arranged in row along anterior margin, anterolateral spines stout, length distinctly less than length of pereonite 1. Pereonite 5 length 0.25 total body length. Pleotelson length 1.3 width.

Antennula article 2 length 0.59 head width, with 3 elongate stiff ventromedial setae; article 3 terminal, squat, wider than long, aesthetascs absent. Antenna length 1.6 anterior body length; article 2 with 1 ventromedial spine; article 3 length 0.41 anterior body length, length 4 width, with 1 ventromedial short pedestal spine with thin curved simple seta; article 5 length 0.27 anterior body length; article 6 length 0.39 anterior body length; flagellum with 10 articles, flagellum length 0.22 total antenna length.

Labrum knobs present, rounded conical, with spinous granulation.

Pereopod bases proximal shoulder with simple spines only. Pereopod I carpus palm length distinctly less than proximal region length, with 1 robust seta on palm distal to elongate seta; propodus ventral margin with 2 robust setae. Pereopods II– VII bases granulate.

Uropods length 0.50 length of pleotelson.

Distribution North Atlantic, south of Iceland, 956 m.

Remarks

Hansen (1916: 69) described the antennulae of Heteromesus schmidtii as follows: "it has above near the distal end a small tubercle, which in closer examination is seen to consist of three extremely short joints (Pl. VI, fig. 3c)". We find only one reduced article with the proximal part of the long distal seta that is broken. Our drawing ( Fig. 26) is similar to Hansen’s but he clearly drew 3 articles and a distal seta. The situation with this species is similar to H. frigidus , which also has only one article, while Hansen (1916: 71) stated that it has 2 articles.

H. schmidtii is distinct from similar species of the genus ( H. granulatus , H. inaffectus and the female of H. frigidus ) because pereonite 1 has paired lateral spines and pereonite 5 has a different L/W ratio (longer than H. granulatus and shorter than H. frigidus and H. inaffectus ).