Heteromesus granulatus 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 : 38-40

Heteromesus granulatus Richardson, 1908

( Fig. 17)

Heteromesus granulatus Richardson 1908: 82 , figs. 14–18; Menzies 1962: 121–123, fig. 22D; Wolff 1962: 86, 262, 274–275; Kussakin 1988: 485–487, fig. 400.

Heteromesus granulatis . – Kussakin 1988: fig. 399 [lapsus calami].

Material examined

Holotype: female (3.2 mm), Northwest Atlantic: off Massachusetts, south of Martha’s Vineyard, approximately 39ºN, 70º30’W, 1885, USFC Steamer Albatross , stn 2547, 713 m (390 fathoms) ( USNM 38969 ).

Remarks on type material. The holotype, an ovigerous female, was in almost perfect condition, the antennae are broken at article 4 (described by Richardson but not found in the vial) and all pereopods are intact except for pereopod VI (both in the left and right sides). The body is more slender than described by Richardson (1908: 82, fig. 14): "Body of female about three and a half times longer than wide", although we measure the body length as 4.2 pereonite 1 width. The antennulae have long setae on article 2 as is typical for members of this genus. Paratypes, determined from Richardson (1908: 83) as 40 additional females and 4 males from the same sample, were not examined.

Diagnosis

Pereonite 5 length in female 1.6 width, in male 3.7 width. Antennula with 3 articles altogether; article 2 distal tip produced distally beyond insertion of next article, distal article inserting subapically. Pereopods II– VII bases denticulate, sometimes sharply toothed, with simple spines. Uropods length in female 0.25–0.30, in male 0.40 length of pleotelson.

Description

Body length in female 3.2 mm; granular. Head in female length 0.35 width; dorsal cuticle coarse tubercular granulation. Pereonite 1 in female width 0.20 total body length; with 1 pair of dorsal tubercles, 1 pair of anterolateral simple spines, short, length distinctly less than length of pereonite 1. Pereonite 4 in female length 0.55 width. Pereonite 5 in female length 0.20 total body length. Pleotelson in female length 1.35 width; posterolateral margin anterior to uropods with posterolateral tubercles inserted ventrally, not visible in dorsal view.

Antennula with 3 articles altogether; article 2 in female length 0.31 head width, with 4 elongate stiff ventromedial setae, distal tip produced distally beyond insertion of next article, distal article inserting subapically; article 3 terminal, squat, wider than long, aesthetascs absent. Antenna in female article 3 length 3.0 width, flagellum with 14 articles ( Richardson 1908).

Labrum knobs present, distally rounded, denticulate, strongly asymmetrical. Maxillula medial lobe with 1 robust medially­projecting dentate seta.

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

Male specific characters. Pereonite 5 length 3.7 width. Pleotelson length 1.55 width. Antenna flagellum with 16 articles.

Distribution

Northwest Atlantic, south of Martha’s Vineyard, southeast of Georges Bank, south of Block Island, 713–3235 m.

Remarks

The male of Heteromesus granulatus was scored according to information from original description (pereonite 5 and pleotelson illustrated). Richardson (1908) mentioned collection of abundant material (males and females) from different locations off New England, USA. Given the depth range of the reported localities, these should be examined to test whether they are all conspecific.

H. granulatus is similar to H. inaffectus , H. schmidtii and the female of H. frigidus in having 3 antennular articles altogether, and in its nearly complete absence of large spines, denticles or tubercles on the dorsal and lateral surfaces except for short anterolateral spines on the first pereonite. Although Richardson (1908) called attention to the granulation of the cuticle, we find that this is common for many of the species of Heteromesus . The most distinctive feature of this species is its compact body shape with a short pereonite 5 (L/W much less than 2.0) and short uropods.