Heteromesus calcar, 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 : 15-21

Heteromesus calcar sp. nov

( Figs 2–6)

Etymology Calcar means spur, and is used as a noun in apposition.

Material examined

Holotype: female (3.7 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 CRU­9878 ).

Paratypes: male (3.2 mm), same data as holotype ( ZMUC CRU­9879 ) ; 1 male (3.0 mm) same data as holotype, (dissected, mouthparts on slide AM P 72117) ; 3 females, 1 male, 1 intersex, 2 fragments (heads), same data as holotype ( AM P 72118) .

Other material: 1 female, same locality as holotype, 37º17.5’N, 32º16.9’W, 11 Aug 2000, R / V Prof Logachev, TTR10 stn AT­271­GR, 1712 m ( DBUA 786.01 ) ; 2 females, 1 manca, same locality as holotype, 37º17.4’N, 32º16.6’W, 11 Aug 2000, R / V Prof Logachev, TTR10 stn AT­273­GR, 1675 m ( DBUA 786.02 ) .

Diagnosis

Pereonites 1–3 with anterolateral spines. Pereonite 2 in female with no paired dorsal spines or tubercles. Pereonite 5 in female length 2.0 width, in male 6.3 width. Antennula with 3 articles altogether. Pereopods IV–V bases with pedestal spines; ischia with elongate pedestal spines.

Description

Body length in female 3.7 mm; granular. Head in female length 0.95 width; dorsal surface with pair of cephalic bullae; lobe on ventrolateral margin present in lateral view; dorsal cuticle tubercular granulation. Pereonite 1 in female width 0.2 total body length; with median tubercle, 1 pair of anterolateral simple spines, 1 pair of lateral simple spines. Pereonite 2 in female with median tubercle, 1 pair of anterolateral simple spines, 1 pair of lateral spines. Pereonite 3 in female with median tubercle, 1 pair of anterolateral simple spines. Female pereonites 1–3 anterolateral simple spines stout to long decreasing in length from pereonite 1 to 3, anterolateral spines length distinctly less than length of pereonite 1, lateral simple spines short. Pereonite 4 in female length 0.65 width. Pereonite 5 in female length 0.25 total body length. Pleotelson in female length 1.35 width; terminal margin without distal tubercles (only in male).

Antennula with 3 articles altogether; article 2 length in female 0.65 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. Antenna in female length 2.7 anterior body length; article 2 with 1 ventromedial pedestal spine; article 3 length 0.28 anterior body length, length 2.6 width, with distomedial and distolateral pedestal spines and 1 dorsal pedestal spine placed midlength; article 5 length 0.15 anterior body length; article 6 length 0.31 anterior body length; flagellum with 15 articles, flagellum length 0.37 total antenna length.

Labrum knobs low. Maxilliped palp article 2 wider than 3.

Pereopod bases proximal shoulder with simple spines only. Pereopod I merus dorsal margin with 2 distinctly robust setae, placed distally; carpus palm length near proximal region length, with 1 robust seta on palm distal to elongate seta; propodus ventral margin with 2 robust setae. Pedestal spines only on dorsal margin of bases and ischia of pereopods IV and V, 1–2 long pedestal spines topped by long robust seta on basis and 1 pedestal spine on ischium.

Uropods in female extending near posterior margin of pleotelson; length 0.25 length of pleotelson.

Male specific characters. Body length 3.2 mm. Head length 1.0 width; with 4 tubercles. Pereonite 1 width 0.20 total body length; with 1 pair of anterolateral simple spines, 1 pair of lateral simple spines. Pereonite 2 with median tubercle, 1 pair of anterolateral simple spines, 1 pair of lateral spines. Pereonite 3 with median tubercle, 1 pair of anterolateral simple spines. Pereonite 4 with 1 pair of dorsal tubercles. Pereonite 1–3 anterolateral simple spines stout to long decreasing in length from pereonite 1 to 3, lateral simple spines short. Pereonite 4 length 0.75 width. Pereonite 5 length 0.40 total body length. Pleotelson length 1.25 width; terminal margin with 1 pair of distal tubercles. Antennula article 2 length 0.47 head width. Antenna length 2.0 anterior body length; article 3 length 0.40 anterior body length, length 4.5 width, with distomedial and distolateral pedestal spines and 1 dorsal pedestal spine placed midlength; article 5 length 0.27 anterior body length; article 6 length 0.47 anterior body length; flagellum length 0.32 total antennal length, flagellum with 15 articles. Pleopod I distal tip with lateral horns. Pleopod II protopod apex rounded, stylet tapering and pointed, not heavily calcified, extending beyond distal margin of protopod. Uropods length 0.35 length of pleotelson.

Distribution

North Atlantic: Mid­Atlantic Ridge, Lucky Strike hydrothermal field, 1675–1712 m, on hydrothermal sulphide deposits, sulphide rubble and volcanic rocks, close to active hydrothermal chimneys, known only from type locality.

Remarks

Heteromesus calcar sp. nov. is similar to H. frigidus , H. granulatus , H. inaffectus and H. schmidti in having altogether 3 antennular articles, and by the tubercular granulation and inconspicuous ornamentation (few spines) of the body. It differs from these species in having anterolateral spines on pereonites 1–3. The most distinctive feature is the presence of long pedestal spines only on dorsal margin of the basis and ischium of pereopods IV and V (also seen in H. spinosus and H. ctenobasius ).