Heteromesus drachi 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 : 33-34

Heteromesus drachi Chardy, 1974

Heteromesus drachi Chardy 1974: 1546–1549 , figs. 6–7.

Material examined

Holotype: male (5.6 mm), North Atlantic : off Ivory coast, 4º21.2’N, 4º35.2’E, 1971, R / V Jean Charcot, Campagne Walda stn 36 DS 28, 1261 m, ( MNHN IS­3362 ).

Remarks on type material. The holotype was dissected (apparently by Chardy), and some parts were found loose in the vial.

Diagnosis (Male only)

Pereon without rook spines. Pereonite 5 length 4.7 width. Pleotelson pleonite 1 region with low dorsal tubercles. Pleotelson with low dorsal tubercles; posterolateral margin anterior to uropods without spines or tubercles. Antennula with 4 articles altogether; article 3 short and tubular, length near width.

Description (Male characters only)

Body length 5.6 mm, granular. Head length 0.70 width, dorsal cuticle tubercular granulation, lobe on ventrolateral margin present in lateral view. Pereonite 1 width 0.20 total body length; with one median simple spine, 1 pair of anterolateral simple spines and 1 pair of lateral simple spines. Pereonite 2 with one median simple spine and 1 pair of anterolateral simple spines. Pereonite 3 with one median simple spine, 1 pair of anterolateral simple spines. Pereonites 1–3 median spines stout, anterolateral spines long to short, decreasing in size from pereonite 1 to 3, length distinctly less than pereonite 1 length, additional lateral spines short. Pereonite 4 length 0.60 width. Pereonite 5 length 0.35 total body length. Pleonite 1 region of pleotelson with 1 median and 2 dorsal pairs of tubercles. Pleotelson length 1.35 width, with 2 pairs of dorsal tubercles.

Antennula article 2 length 1.2 head width, with 4 elongate stiff ventromedial setae; article 3 longer than article 4; terminal article shorter than penultimate article, aesthetascs absent. Antenna length 2.0 anterior body length; article 2 with 1 ventromedial spine; article 3 length 0.39 anterior body length, length 5.0 width, with distomedial spine and 1 ventral stout spine; article 5 length 0.32 anterior body length; article 6 length 0.41 anterior body length; flagellum length 0.37 total antennal length, flagellum with 18 articles.

Labrum knobs absent. Maxillula medial lobe without robust dentate setae. Maxilla without long medially­projecting pectinate setae on medial lobe.

Pereopod bases proximal shoulder with simple spines only. 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.

Pleopod I distal tip with lateral horns. Pleopod II protopod apex rounded; stylet thick and blunt, extending beyond distal margin of protopod (with hook­like lateral curve under posterior margin of protopod). Uropods length 0.30 length of pleotelson.

Distribution North Atlantic, off Ivory Coast, 1261–3109 m.

Remarks

Chardy (1974) did not describe the female of H. drachi and made no comments on sexual dimorphism for this species. A pleotelson with a few paired tubercles (and nowhere else on the body) is the most distinctive feature of Heteromesus drachi . H. spinosus and H. dentatus also have rook spines on the pleotelson but they are arranged in longitudinal rows. It also differs from the former in having midline spines on the anterior pereonites. The elongate, curved appendix masculina has not been seen in other members of Heteromesus . With regard to the distal articles in the antennula, Chardy (1974: 1546) stated “Flagellum … constitué de 3 segments” as illustrated in his fig. 6 but our examination of the holotype finds only 2 distal articles.