Heteromesus longiremis sensu 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 : 49-50

Heteromesus longiremis sensu Chardy, 1974

Heteromesus longiremis sensu Chardy 1974: 1549–1551 , fig. 8–9.

Material examined

None ; male measurements taken from Chardy (1974: 1549–1552; figs. 8–9). Reported localities from the North Atlantic , Atlantic Abyssal Plain , Campagne Noralante R / V Jean Charcot, August–October 1971: 1 male illustrated, stn 8, E03 (52°10.4’N 45°32.3’W, 4100 m); 1 female, stn 5, E02 (54º21.6’N 23º00.2’W, 3178 m), 1 damaged specimen, stn 16, E06 (58°47.7’N 52°56.5’W, 3610 m); 2 females, stn 21, E07 (38°28.2’N 43°03’W, no indication of depth) .

Diagnosis (Male only)

Pleotelson posterolateral margin anterior to uropods without spines or tubercles. Pereonite 5 length 4.6 width. Antennula with 5 articles altogether ( Chardy, 1974:1549), article 2 distal tip produced distally beyond insertion of next article, distal article inserting subapically, article 3 longer than article 4. Uropods length 0.50–0.55 length of pleotelson.

Description (Male characters only)

Body length 5.7 mm, granular. Head length 0.45 width, with 2 tubercles on dorsal surface posterior to antennulae, cuticular structure fine tubercular granulations. Pereonite 1 width 0.20 total body length; with median tubercle, 4–5 pairs of dorsal tubercles, 1 pair of anterolateral simple spines. Pereonite 2 with median tubercle, 4 pairs of dorsal tubercles, 1 pair of anterolateral simple spines. Pereonite 3 with median tubercle, 2 pairs of dorsal tubercles. Pereonite 4 length 0.65 width; with median tubercle, 2 pairs of dorsal tubercles. Pereonites 1–4 dorsal tubercles arranged in transverse row along anterior margin, pereonite 1 with 1 additional pair of dorsal tubercles close to anterolateral spine, anterolateral simple short spines decreasing in size from pereonite 1 to 2, length distinctly less than pereonite 1 length ( Chardy (1974, fig. 8) drew median tubercles as short spines, but in Hansen (1916, Pl. VI, fig. 2a) these were drawn in female as tubercles). Pereonite 5 length 0.30 total body length. Pleotelson length 1.3 width.

Antennula article 2 length 0.50 head width with 3 elongate stiff ventromedial setae (and one proximal shorter seta), distal tip produced distally beyond insertion of next article, distal article inserting subapically; article 3 squat, wider than long; terminal article shorter than penultimate article, aesthetascs absent. Antenna length 2.6 anterior body length; article 3 length 0.47 anterior body length, length 4.1 width, article 3 with distomedial spine; article 5 length 0.31 anterior body length; article 6 length 0.51 anterior body length; flagellum length 0.41 total antennal length, flagellum with 17 articles.

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 merus dorsal margin with 2 distinctly robust setae (short), placed distally; carpus palm length distinctly less than proximal region length, with 2 robust setae on palm distal to elongate seta, shorter setae directly adjacent to elongate seta on palm ventral margin; propodus ventral margin with 1 robust seta, placed proximally to elongate fine seta and distally to several fine setae and fine denticles on proximal margin.

Pleopod I distal tip without lateral horns. Pleopod II protopod apex rounded, stylet thick and blunt, heavily calcified (assumed), extending beyond distal margin of protopod.

Distribution North Atlantic: Atlantic Abyssal Plain, 3178–4100 m.

Remarks

Because the original types of H. longiremis Hansen, 1916 are missing, we cannot fully evaluate Hansen’s specimens of this species. We suspect that the specimens of Chardy (1974) may be a different species, but have not inspected them. Thus, we cannot reclassify Chardy’s specimens. The male scored from Chardy (1974) and measurements obtained from the illustrations (his figs. 8–9) are at variance with Hansen’s original. Pereonite 5 length to width ratio in the male is 4.6, which is distinctly smaller than Hansen’s (1916) male specimen, 6.2. The uropod is smaller (length 0.50–0.55 length of pleotelson in Chardy’s specimen and 0.65 in Hansen’s). Pereonite 4 has dorsal tubercles in Chardy’s male and Hansen’s female lacks them (Hansen’s male is a fragment lacking head and P1–4). The pleotelson length to width ratio, however, is similar. Chardy mentioned the collection of 1 male, 2 females and 1 mutilated specimen but described only the male. Given the large geographic spread of the reported specimens, we are also unsure whether Chardy’s (1974) specimens are all conspecific. Heteromesus longiremis sensu Chardy is similar to H. schmidtii but the two species can be identified using the number of antennular articles. Chardy (1974: 1549) reports that the antennula has 3 terminal articles, and his illustration (his fig. 8D) shows that the two distal articles are minute. Given the difficulties in interpreting these articles in other species by the original authors, some uncertainty remains on this point.