Heteromesus ctenobasius, 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 : 21-28

Heteromesus ctenobasius sp. nov.

( Figs 7–12)

Etymology

The name pertains to the comb­like basis of the pereopods.

Material examined

Holotype: female (4.3 mm), North Atlantic , Mid­Atlantic Ridge , Lucky Strike, 37º17.4’N, 32º16.6’W, 10 Aug 2000, R / V Prof Logachev, TTR10 stn AT­265­GR, 1685 m ( ZMUC CRU­9874 ).

Paratypes: male (4.3 mm), same data as holotype ( ZMUC CRU­9875 ); 2 females , 1 fragment, same data as holotype ( AM P 72119) .

Other material: female, same locality as holotype, 37º17.3’N, 32º16.5’W, 8 Aug 2000, R / V Prof Logachev, TTR10 stn AT­250­GR, 1704 m ( SEM stub AW575, AM P 72120); 1 female , same locality, 37º17.5’N, 32º16.9’W, 10 Aug 2000, R / V Prof Logachev, TTR10 stn AT­262­GR, 1720 m ( DBUA 787 ) .

Remarks on type material. Male pereonites 2 and 3 damaged.

Diagnosis

Pereonite 1–3 median pedestal spines. Pereonites 4–5 in female with lateral pedestal spines. Pereonite 5 in female length 2.3 width, in male 4.1 width. Pleotelson terminal margin with pedestal spines. Antennula with 5 articles altogether. Pereopod II–VII bases and ischia with pedestal spines.

Description

Body length in female 4.3 mm; granular. Head in female length 0.75 width; lobe on ventrolateral margin present in lateral view; dorsal cuticle fine tubercular granulation. Pereonite 1 in female width 0.2 total body length; with median pedestal spine, 1 pair of dorsal pedestal spines, 1 pair of anterolateral pedestal spines, 1 pair of lateral pedestal spines. Pereonite 2 in female with median pedestal spine, 1 pair of dorsal pedestal spines, 1–2 pair of dorsal rook spines, 1 pair of anterolateral pedestal spines, 1 pair of lateral pedestal spines. Pereonite 3 in female with median pedestal spine, 3–4 pairs of dorsal rook spines, 1 pair of anterolateral rook spines, 1 pair of lateral rook spines. Pereonite 4 in female length 0.65 width; with 3–4 pair of dorsal rook spines, posterolateral margins with row of 4 long pedestal spines topped by stout robust setae. Pereonites 1–4 in female with pedestal spines stout to long topped by short robust setae decreasing in length from pereonite 1 to 3, anterolateral spines length distinctly less than length of pereonite 1, rook spines short to stout. Pereonite 5 in female length 0.25 total body length; with lateral row of 10–11 stout to long pedestal spines topped by stout to long robust seta. Pereonite 7 in female with 1 pair of short pedestal spines topped by simple seta. Pleotelson in female length 1.55 width; posterolateral margin anterior to uropods with 1 pair of posterolateral stout pedestal spines topped by short robust setae; terminal margin with one pair of distal short pedestal spines topped by stout robust setae.

Antennula in female article 1 with 1 penicillate seta; article 2 length 0.88 head width, with 5 elongate stiff ventromedial setae; article 3 length similar to article 4, squat, wider than long, terminal article shorter than penultimate article, aesthetascs absent. Antenna in female length 1.9 anterior body length; article 2 with 1 lateral pedestal spine and 1 ventromedial pedestal spine; article 3 length 0.33 anterior body length, length 5.5 width, with 1 distomedial pedestal spine and 1 short distolateral pedestal spine placed somewhat ventrally (not visible in dorsal view: antenna slightly rotated as shown) and 2–3 stout dorsal pedestal spines placed proximally and at midlength; article 5 length 0.31 anterior body length; article 6 length 0.42 anterior body length; flagellum with 14 articles, flagellum length 0.39 total antenna length.

Labrum knobs present, conical.

Pereopod bases proximal shoulder with bifid spines. Pereopod I carpus palm length distinctly less than proximal region length, with 4 robust setae on palm distal to elongate seta; propodus ventral margin with 3 robust setae. Pereopods II–VII bases granulate, with short pedestal spines, topped with long robust seta, on dorsal and ventral margins, 2–6 spines dorsally, 10–15 ventrally; ischia with 2–3 short pedestal spines topped with long robust seta, on dorsal margin only.

Uropods in female length 0.25–0.30 length of pleotelson.

Male specific characters. Body length 4.3 mm. Head length 0.65 width. Pereonite 1 width 0.20 total body length; with median pedestal spine, 1 pair of dorsal pedestal spines, 1 pair of anterolateral pedestal spines, 1 pair of lateral pedestal spines. Pereonite 2 with median pedestal spine, 1 pair of dorsal pedestal spines, 1–2 pairs of dorsal rook spines, 1 pair of anterolateral pedestal spines, 1 pair of lateral pedestal spines. Pereonite 3 with median pedestal spine, 1–2 pairs of dorsal rook spines, 1 pair of anterolateral rook spines, 1 pair of lateral rook spines. Pereonite 4 length 0.75 width; with 2 pairs of dorsal rook spines, 1 pair of anterolateral rook spines, posterolateral margins with 2 pedestal spines. Pereonite 1–4 pedestal spines stout to long topped by short robust setae, median and dorsal spines decreasing in length from pereonite 1 to 3, anterolateral spines length distinctly less than length of pereonite 1, rook spines short to stout. Pereonite 5 length 0.25 total body length; with row of approximately 8 simple setae (some topping short pedestal spines). Pleotelson length 1.35 width; posterolateral margin anterior to uropods with 1 pair of stout pedestal spines topped by short robust setae; terminal margin with 1 pair of distal short pedestal spines topped by stout robust setae. Antennula article 2 length 1.1 head width. Antenna length 1.9 anterior body length; article 3 length 0.33 anterior body length, length 5.5 width, with distomedial and distolateral pedestal spines and 1 dorsal pedestal spine placed at midlength; article 5 length 0.23 anterior body length; article 6 length 0.44 anterior body length; flagellum length 0.37 total antennal length, flagellum with 15 articles. Pleopod I distal tip without lateral horns. Pleopod II protopod apex rounded, stylet thick and blunt, heavily calcified, not extending to distal margin of protopod. Uropods length 0.35 length of pleotelson.

Distribution

North Atlantic: Mid­Atlantic Ridge, Lucky Strike hydrothermal field, 1685–1720 m, on volcanic rocks, close to active hydrothermal chimneys, known only from type locality.

Remarks

Heteromesus ctenobasius sp. nov. is similar to H. spinosus in the heavy ornamentation of the body (many spines) and pereopods by both pedestal and rook spines and in having posterolateral and distal spines on the pleotelson. Both species have 5 antennular articles altogether. The most distinctive feature of H. ctenobasius is the dorsal median pedestal spine on peronites 1–3. The female shows conspicuous pedestal spines arranged along the lateral margin of pereonites 4 and 5.