Heteromesus spinosus ( Beddard, 1886 )

Cunha, Marina R. & Wilson, George D. F., 2006, The North Atlantic genus Heteromesus (Crustacea: Isopoda: Asellota: Ischnomesidae), Zootaxa 1192 (1192), pp. 1-76 : 62-64

Heteromesus spinosus ( Beddard, 1886)

( Fig. 30)

Ischnosoma spinosum Beddard 1886: 40–42 , pl. VI, fig. 1–5.

Heteromesus spinosus .– Richardson 1908: 81.

Material examined

Holotype: female (4.3 mm), North Atlantic : off the Azores, 37º26’N, 25º13’W, 10 Jul 1873, R / V Challenger stn. 78, 1829 m ( NHM 89.4.27.52).

Remarks on type material. A single whole preparatory female mounted in Canada balsam, smashed, long spines broken, but otherwise complete with the exception of one or two of the pereopods. The female specimen measures "approximately 6mm, with short immature ovigerous lamellae upon the first four thoracic segments" (remarks by Beddard 1886: 40).

Diagnosis (Female only)

Pereonite 1 with 5 pairs of dorsal rook spines; pereonites 1–3 with long anterolateral and lateral pedestal spines; pereonites 6–7 with dorsal rook spines. Pereonite 5 length 2.3 width. Pleonite 1 region with lateral rook spines. Antennula with 5 articles altogether.

Description (Female characters only)

Body length 4.3 mm; granular. Head length 0.55 width; dorsal cuticle fine spinous granulation. Pereonite 1 width 0.25 total body length; with 1 median rook spine, 5 pairs of dorsal rook spines, 1 pair of anterolateral pedestal spines, 2 pairs of lateral pedestal spines. Pereonite 2 with 1 median rook spine, 2–3 pairs of dorsal rook spines, 2 pairs of lateral pedestal spines. Pereonite 3 with 1 median rook spine, 3 pairs of dorsal rook spines, 2 pairs of lateral pedestal spines. Pereonite 4 length 0.50 width; with 1 pair of anterolateral simple spines and 2 paired posterolateral rook spines short to stout. Pereonites 1–4 dorsal rook spines stout to long arranged in transverse rows, anterolateral pedestal spines long topped by short robust seta, decreasing in length from pereonite 1 to 3, length near pereonite 1 length, pereonite 4 anterolateral spine broad and short, length distinctly less than length of pereonite 1. Pereonite 5 length 0.30 total body length; with lateral row of 7–8 short pedestal spines topped with simple seta. Pereonites 6–7 only with 1 pair of short dorsal rook spines. Pleonite 1 region of pleotelson with 1–2 pairs short to stout dorsal rook spines and 3 pairs of stout to long lateral rook spines. Pleotelson length 1.3 width; with 7–8 stout to long rook spines arranged in two longitudinal median rows and 2 additional dorsal pairs on the lateral fields; posterolateral margin anterior to uropods with 1 pair of posterolateral pedestal spines, stout topped by simple seta; terminal margin with 1 pair of pedestal spines short topped by stout robust setae.

Antennula article 2 length 0.55 head width, with 3 elongate stiff ventromedial setae, distal tip produced distally beyond insertion of next article, distal article inserting subapically; article 3 length similar to article 4, elongate and tubular, much longer than wide; terminal article shorter than penultimate article, aesthetascs absent. Antenna article 2 with 2 medial and 1 ventral long pedestal spines; article 3 length 0.27 anterior body length, length 3.8 width, with 1 short distomedial pedestal spine, 1 elongate distolateral pedestal spine, 1 elongate ventromedial pedestal spine placed midlength and 2 long dorsal pedestal spines placed midlength and proximally on article; article 5 length 0.26 anterior body length; article 6 length 0.41 anterior body length.

Labrum knobs present, rounded, distally with sharp denticles.

Pereopod bases proximal shoulder with rook spines. 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 granulate, with stout to long pedestal spines topped by stout to long robust seta on dorsal and ventral margins of bases; ischia with 1 elongate pedestal spine on dorsal margin.

Uropods length 0.40 length of pleotelson.

Distribution North Atlantic: off the Azores, 1829 m, volcanic mud.

Remarks

Heteromesus spinosus (Beddard) was scored partially using original description because some parts were deformed or obscured in the mounted holotype. This species was not listed in Kussakin (1988).

This species is similar to H. ctenobasius , but its most distinctive features are the long anterolateral and lateral pedestal spines on pereonites 1–3.