Heteromesus oryktus, Cunha & Wilson, 2006

Cunha, Marina R. & Wilson, George D. F., 2006, The North Atlantic genus Heteromesus (Crustacea: Isopoda: Asellota: Ischnomesidae), Zootaxa 1192 (1192), pp. 1-76 : 51-54

Heteromesus oryktus sp. nov.

( Figs 24–25)

Etymology

Oryktos means "digger" (Greek, masculine) because this species was collected from mudstone burrows possibly made by the animals.

Material examined

Holotype: female (6.1 mm), North Atlantic : off West Greenland, canyon bordering the western margin of the Fylla Structural Complex, 63º14.1’N, 55º26.0’W, 18.Aug 2003, R / V Prof Logachev, TTR13 stn AT­457­GR, 2140 m ( ZMUC CRU­9872 )

Paratype: male (5.7 mm), same data as holotype ( ZMUC CRU­9873 ) .

Diagnosis

Pereonites 1–3 with anterolateral denticulate spines; pereonites 1–4 with median and paired lateral denticulate spines arranged in dorsal rows. Pereonite 1 of male with paired lateral rook spines. Pereonite 5 in female length 2.2 width, in male 4.1 width. Pleotelson posterolateral margin anterior to uropods without spines or tubercles. Antennula with 5 articles altogether; article 3 length similar to article 4. Uropods in male length 0.45 length of pleotelson.

Description

Body length in female 6.1 mm; granular. Head in female length 0.60 width, with 1–2 pairs of simple spines, cuticular structure fine spinous granulations, lobe on ventrolateral margin absent in lateral view. Pereonite 1 in female width 0.20 total body length; with median simple spine, 2–3 pairs of dorsal simple spines, 1 pair of anterolateral simple spines, 2 pairs of lateral simple spines. Pereonite 2 in female with median simple spine, 2 pairs of dorsal rook spines, 2 pairs of lateral simple spines. Pereonite 3 in female with median simple spine, 2–3 pairs of dorsal simple spines, 1 pair of lateral simple spines. Pereonite 4 length 0.65 width; with 2 pairs of dorsal simple spines. Pereonites 1–4 in female with spines stout to short, denticulate and topped by setae; anterolateral spines decreasing in length from pereonite 1 to pereonite 3, length distinctly less than length of pereonite 1. Pereonite 5 in female length 0.25 total body length. Pereonite 5 with lateral row of setae. Pleotelson in female length 1.5 width.

Antennula in female article 2 length 0.58 head width, with 4 elongate stiff ventromedial setae (and 2 distal shorter setae); article 3 short and tubular, length near width, terminal article shorter than penultimate article, aesthetascs absent. Antenna in female article 2 with 1 ventromedial spine (in female only); article 3 length 0.35 anterior body length, length 3.4 width, with 1 distomedial stout pedestal spine and 1 ventral long pedestal spine placed in proximal third of article.

Labrum knobs present, low, rounded, sharply denticulate.

Pereopod bases proximal shoulder with rook spines. Pereopod I carpu s palm length near proximal region length, with 2 robust setae on palm distal to elongate seta; propodus ventral margin with 1 robust seta. Pereopods II–VII bases granulate.

Uropods in female length 0.25–0.30 length of pleotelson.

Male specific characters. Body length 5.7 mm. Head length 0.70 width; cuticular structure with spinous granulations. Pereonite 1 width 0.15 total body length; with median simple spine, 2 pairs of dorsal simple spines, 1 pair of anterolateral simple spines, 2 pairs of lateral rook spines. Pereonite 2 with median simple spine, 1 pair of dorsal rook spines. Pereonite 3 with median simple spine, 1 pair of lateral rook spines. Pereonite 4 length 0.65 width; with 1 pair of dorsal rook spines, 2 pairs of posterolateral rook spines. Pereonites 1–4 simple spines stout to short, denticulate and topped by setae; anterolateral spines decreasing in length from pereonite 1 to pereonite 3, length distinctly less than length of pereonite 1. Pereonite 5 length 0.30 total body length. Pleotelson length 1.35 width. Antennula article 2 length 0.60 head width. Antenna length 1.8 anterior body length; article 3 length 0.46 anterior body length, length 3.9 width, with distomedial pedestal spine; article 5 length 0.28 anterior body length; article 6 length 0.38 anterior body length; flagellum length 0.30 total antennal length, flagellum with at least 17–18 articles. Pleopod I distal tip with lateral horns. Pleopod II protopod apex rounded; stylet thin with medial blade, extending beyond distal margin of protopod. Uropods much longer than in female; length 0.45 length of pleotelson.

Distribution

North Atlantic : west of Greenland, canyon bordering the western margin of the Fylla Structural Complex, 2140 m, in mudstones; only known from type locality .

Remarks

Heteromesus oryktus sp. nov. was found in mudstones collected from the slope of a canyon (female found inside tubular cavity). The mudstones were heavily bored into by sipunculids.

Heteromesus oryktus is similar to H. dentatus and H. greeni (characters already mentioned in the remarks on these species). The most distinctive features of H. oryktus are the anterolateral denticulate spines on pereonites 1–3 and median and paired lateral denticulate spines arranged in dorsal rows on pereonites1–4.