Austrodecus, Hodgson, 1907

Staples, David A., 2019, Pycnogonids (Arthropoda, Pycnogonida) from the Southwest Indian Ridge, Zootaxa 4567 (3), pp. 401-449 : 422-423

Austrodecus sp. C

Figure 12 A–D; Plate 4 B–D

Material examined. Male, Southwest Indian Ocean, Middle of What Seamount, 37 ° 57.42´S, 50° 26.34´E, ROV, 1148 m, specimen JC066-2743, coral rubble and sediment, 1 December 2011.

Description. Male holotype. Trunk segmented ( Fig. 12A, B ), segments 1 to 4 with finger-like dorsomedian tubercles ( Plate 4B ), height at least as tall as the depth of trunk, margins of tubercles uneven, otherwise without spines or processes; lateral processes smooth, separated by less than their own basal width; diverging distally ( Plate 4C ). Ocular tubercle tall, height almost equal to half length of trunk, inclined forward, over-reaching proboscis base, tapering from broad base to narrow truncate apical surface; four eyes, unpigmented, evidenced by four white areas ( Plate 4D ).

Proboscis typical of genus, down-curved, annulated distally, basal part inflated, smooth; jaws vertically bilateral.

Abdomen unarticulated at base, length about 25% of trunk length, carried horizontally, tapering slightly distally.

Chelifores absent.

Palp five-segmented, attached to lateral extension of cephalon, segment 1 longest, segment 3 next longest, less than half length segment 1.

Oviger probably four-segmented, details of segments unclear, distal-most segment appears to be longest.

Third leg ( Fig. 12C ) bearing short, scattered setae, femur longest segment, with long dorsodistal hair-like spine on low process, tibia 2 longer than tibia 1, tibiae with single long dorsodistal hair-like spine, distal spine on tibia 2 placed short distance back from distal margin, first coxae of all legs with prominent dorsodistal digitiform tubercles in the order of 1:2:2:1, each tubercle much shorter than corresponding trunk median tubercle, coxa 2 longer than coxae 1 or 3, third coxa with single, short, dorsal digitiform process, propodus gently curved, long, about threequarters length tibia 2, heel absent, sole lined with 7 to10 short spines, terminal claw about one-quarter length of propodus. Single, conical femoral cement gland duct on mid-ventral surface of legs 3 and 4 only ( Fig.12C ), height little more than corresponding width of femur. Auxiliary claws possibly absent. Gonopores not observed.

Remarks. Unfortunately the solitary specimen was lost before observations were fully documented and before photography was completed. This specimen is undoubtedly new to science and considering the importance of extending our knowledge of the biodiversity of this remote collection area I have described the species to a level where it can be readily identified. In as much as the palps and ovigers are not known in sufficient detail, the description is incomplete and accordingly the species is not named. The specimen was not measured but the relative proportions of segments are evident in the images taken. The femora of legs 1 and 2 are more slender and longer than those on legs 3 & 4 ( Figs 12C, D ).

This species shares the arrangement of dorsodistal digitiform tubercles on the first and third coxa, the position of a femoral ventral cement gland cone on legs 3 & 4, five-segmented palps and probably four-segmented ovigers with Austrodecus taylorae . The auxiliary claws could be tiny rather than absent. Differences are most evident in the taller and more-slender mid-dorsal tubercles which are at least as tall as the depth of the trunk, the much taller cement gland cones, the proportions of tibia 1 and 2, and the absence of prominent auxiliary claws.

Figures

PLATE 4. Austrodecus taylorae sp. nov., holotype, male. A, trunk, lateral view. Austrodecus sp. male. B, trunk, dorsal; C, trunk ventral; D, ocular tubercle. Rhynchothorax swir sp. nov., holotype, female. E, trunk, dorsal view; F, trunk, lateral view. Rhynchothorax coralensis sp. nov., holotype. G, trunk, lateral view; H, trunk, dorsal view.

FIGURE 12. Austrodecus sp. C. A, trunk, lateral view; B, trunk, dorsal view; C, third leg; D, fourth leg.