Sericosura dimorpha, Arango, Claudia P. & Linse, Katrin, 2015

Arango, Claudia P. & Linse, Katrin, 2015, New Sericosura (Pycnogonida: Ammotheidae) from deep-sea hydrothermal vents in the Southern Ocean, Zootaxa 3995 (1), pp. 37-50 : 42-45

Sericosura dimorpha sp. nov.

( Figs 4–5 )

Material examined. Holotype— male ( NHMUK 2015. 81), ex JC42-F-340, from Expedition JC42 RRS James Cook, Station JC 42-4-7 ISIS 140, 30January 2010, East Scotia Ridge, Site E9, Black & White, 60 2' 33.72" S, 29 58' 53.04" W, 2402 m.

Paratypes— ( NHMUK 2015. 82), ex JC42-F-340, from Expedition JC42 RRS James Cook, Station JC 42-4-7 ISIS 140, 30 January 2010, East Scotia Ridge, Site E9, Black & White, 60°2'33.72"S, 29°58'53.04"W, 2402 m, one female ( DNA voucher). ( NHMUK 2015. 83–92), ex JC42-F-340, from Expedition JC42 RRS James Cook, Station JC 42-4-7 ISIS 140, 30 January 2010, East Scotia Ridge, Site E9, Black & White, 60°2'33.72"S, 29°58'53.04"W, 2402 m, 14 specimens; (QM-S98775–6), same location, two specimens.

Diagnosis: Legs of male dimorphic, third and fourth pairs of legs with inflated propodi and strongly curved main claw; first and second pairs of male legs with slender propodi.

Description. Male holotype. Trunk fully segmented ( Fig. 4 A, B), with smooth dorsal ridges, glabrous except for few short setae on distal margin of lateral processes. Cephalon widest at its anterior margin, smooth, triangular, narrowing distally; ocular tubercle not evident in dorsal view, insignificant low protuberance in lateral view ( Fig. 4 D), eyes unpigmented, faint. Abdomen long, horizontal, articulated at base, reaching further than distal margin of first coxae, slightly inflated distally with three rows of long setae from midpoint to apex. Lateral processes wider than long, few short setae on distal margin. Proboscis long, horizontal, almost cylindrical, distal half bent slightly upwards when seen laterally ( Fig. 4 D). Chelifore peeking out under the cephalic hood, one-segmented scape, tiny knob as palm, fingers absent. Palp seven-segmented ( Fig. 4 D, 5A), P1 short, very wide, P2 near three times longer than P3 with setae, P4with dorsal and ventral setae, P5 longer than P7, P5–P7 covered in short thick setae. Oviger 10-segmented, O3 longest, O4 and O5 with ectal row of short, fine setae, O6 densely setose, O7 with fewer long setae, O8 with two bunches of long twisted setae distally, O9 with one long setae, O10 small, less than half length of O9, glabrous; oviger spines simple, not denticulate, formula 0:2:1:2, spines on O10 very close together (5B, C). Legs with dorsal, ventral and lateral rows of long setae, also on distal margin of each segment; coxa 2 longer than coxa 1 or 3; femur longest segment followed by tibia 1; tarsus very short. Propodi dimorphic, third and fourth pairs of legs with inflated, globular propodi with short, scattered setae, paler in colour compared to rest of the body; main claw almost as long as propodus, sharply curved; auxiliaries slender, about 0.5 main claw length ( Fig. 4 C, 5D). Propodi of first and second legs elongated, densely setose, distal setae longer, main claw gently curved, near 0.7 propodal length, auxiliaries strong, longer than half main claw length ( Fig. 4 F). Femoral cement gland not found. Female propodi not dimorphic, all propodi resembling those of males on first and second pairs of legs.

Measurements male holotype (in mm). Trunk length: 5.68; trunk width: 3.97: abdomen: 3.07; proboscis: 6.04; third leg coxa 1;1.09; coxa 2: 2.35; coxa 3:1.88; femur: 5.52; tibia 1: 4.95; tibia 2: 4.50; tarsus: 0.75; propodus: 3.59; main claw: 2.45; auxiliaries: 1.26.

Etymology. Referring to the dimorphism of the male propodi.

Remarks. Leg span about 60 mm. The holotype has three bracelets of egg masses attached to each oviger, the eggs are minute ( Fig. 4 E). Only Sericosura heteroscela Child & Segonzac, 1996 from the Mid-Atlantic Ridge is known to have the third and fourth legs with expanded propodi, but that species does not have the compact trunk with ridged, crowded segments and lateral processes touching as in S. dimorpha . The new species from the East Scotia Ridge has a very low ocular tubercle and the proboscis is slightly upturned distally, as opposed to a very tall ocular tubercle and slightly down-curved proboscis in S. heteroscela . Dimorphic propodi have been described in two Antarctic species of Ammothea , A. spinosa (Hodgson, 1907) and A. allopodes Fry and Hedgpeth 1969 , but in Ammothea the inflated propodi are on legs 1and 2.

Figures

FIGURE 4. Sericosura dimorpha sp. nov. Holotype male (NHMUK 2015. 81), A, dorsal view. Female paratype (NHMUK 2015. 82), B, dorsal view. Holotype male. C, legs 3 and 4 with diagnostic inflated propodi (arrows); D, lateral view of cephalon, proboscis (pr), palp (pa), chelifores (ch) and ocular tubercle (oc); E. male in ventral view showing egg masses (indicated by arrows) attached to the ovigers; paratype, female. F, propodi on legs 3 and 4.

FIGURE 5. SEM images. Sericosura dimorpha sp. nov., Paratype male (QM-S 98775), A, distal segments of palp; B, oviger with egg masses attached by bracelets, oviger segments 4 - 10; C, distal oviger segments, arrows indicating simple spines on distal segments; D, leg 3, propodus (pd), main claw (mc) andauxiliary claws (au) (claw in foreground broken off).