Heteromesus spinescens Richardson, 1908

Cunha, Marina R. & Wilson, George D. F., 2006, The North Atlantic genus Heteromesus (Crustacea: Isopoda: Asellota: Ischnomesidae), Zootaxa 1192 (1192), pp. 1-76 : 59-61

Heteromesus spinescens Richardson, 1908

( Figs 28–29)

Heteromesus spinescens Richardson 1908: 83–84 , fig. 19; Menzies 1962: 123, fig. 22E; Wolff 1962: 85, 265; Kussakin 1988: 480–481, fig. 393.

Material examined

Holotype: male, Northwest Atlantic , off New England, off Virginia, approximately 37°30’N 72°30’W, 1883, USFC Steamer Albatross, stn 2105, 2551 m (1395 fathoms) ( USNM 38970 ).

Remarks on type material. The holotype male had been severely damaged since Richardson’s (1908) description. The body was found to be broken in three parts, several pereonites and the head smashed, both the antennula and the antenna on the right side missing and on the left side the antenna broken at article 4, pereopods I– IV in both sides and pereopods VI and VII on the right side missing (only the basis of some remain). Other material labelled under this species was found to belong to other species.

Diagnosis (Male only)

Pereonite 5 length 3.3 width. Antennula with 5 articles altogether, article 3 elongate and tubular, much longer than wide. Pereopod bases proximal shoulder with no spines; pereopods II– VII bases denticulate, sometimes sharply toothed with simple spines.

Description (Male characters only)

Body granular. Head with 2 tubercles (low and unelaborated) on dorsal surface near posterior margin of head. Pereonite 1 width 0.20 total body length; with median simple spine, 6 pairs of dorsal simple spines, 1 pair of anterolateral simple spines, 1 pair of lateral simple spines. Pereonite 2 with median simple spine, 6 pairs of dorsal simple spines. Pereonite 3 with median simple spine, 6 pairs of dorsal simple spines. Pereonite 4 length 0.60 width; with 2 pairs of dorsal simple spines. Pereonites 1–4 dorsal spines short, arranged in two transverse rows, anterolateral spines stout, length distinctly less than pereonite 1 length. Pereonite 5 length 0.30 total body length. Pleotelson length 1.4 width; posterolateral margin anterior to uropods with pedestal stout spines topped by short robust seta.

Antennula article 2 length 0.42 head width, with 3 elongate stiff ventromedial setae; article 3 longer than article 4; terminal article shorter than penultimate article; aesthetascs absent. Antenna article 3 length 0.48 anterior body length, length 4.7 width, with distomedial and distolateral stout pedestal spines, 1 ventromedial and 1 dorsal pedestal spines placed midlength.

Labrum knobs present, low, rounded, denticulate.

Pereopods II– VII bases denticulate, sometimes sharply toothed, with simple spines, scattered, with tuberculate (shorter than broad) shape, with robust sensillate setae, on dorsal and ventral margin.

Pleopod II protopod apex rounded; stylet thin with medial blade (tiny), extending beyond distal margin of protopod. Uropods length 0.40 length of pleotelson.

Distribution

Northwest Atlantic, off Virginia, south of Martha’s Vineyard, south of Block Island, southeast of Georges Bank, 2155–3337 m.

Remarks

The pleotelson of Heteromesus spinescens Richardson was incompletely described by Richardson (1908). The holotype has a posterolateral pedestal spine on each side of pleotelson (inserted ventrally near the border of operculum). Three pairs of low tubercles on the dorsal surface of the pleotelson are arranged medially in two longitudinal rows. The uropods also have setae, not shown in Richardson’s description.

Our database for H. spinescens was partially scored using the original description of Richardson (1908: 83–84), because the holotype was in such poor condition. Other material, mostly females and juveniles from the US National Museum of Natural History labelled as H. spinescens by Richardson, includes a mixture of at least four species (including 1 H. granulatus ). Among these, one male has 4 long spines on the head and is clearly from an undescribed species. H. spinescens differs from other species of Heteromesus by having the shortest pereonite 5 (length only 3.3 width) in the adult male.