Austrodecus taylorae, Staples, 2019

Staples, David A., 2019, Pycnogonids (Arthropoda, Pycnogonida) from the Southwest Indian Ridge, Zootaxa 4567 (3), pp. 401-449 : 420-422

Austrodecus taylorae sp. nov.

Figure 11 A–I; Plates 3H ; 4A

Material examined. Holotype, male ( NHMUK 2018.24 ), Southwest Indian Ocean, Atlantis Bank , 32° 42.86´S, 57° 16.34´E, ROV, 750 m, specimen JC066-4213C, stn 8.29, mooring site, on net containing Mango wood, 14 December 2011.

Paratype. One male ( NHMUK 2018.25 ), same collection details as for holotype. Two males ( NHMUK 2018.26 ), Southwest Indian Ocean, Atlantis Bank , 32° 42.86´S, 57° 16.34´E, ROV, 750 m, specimen JC066- 4214C, stn 8.29, mooring site, on net containing Mango wood, 14 December 2011 .

Description. Male holotype. Trunk ( Fig.11A, B . Plates 3H , 4B ) papillose, quite transparent, segments 1 to 4 with dorsomedian tubercles, height each little more than half depth of trunk, those on segments 2 and 4 slightly shorter than those on segments 1 and 3, margins of tubercles uneven; lateral processes smooth, separated by about half basal width, diverging distally. Ocular tubercle tall, height almost equal to 60% of trunk length, inclined forward, over-reaching base of proboscis, tapering from broad base to narrow truncate tip, surface of basal part coarsely rugose; four eyes, unpigmented.

Proboscis 30% longer than trunk, typical of genus, down-curved, annulated distally, basal part inflated, smooth, jaws vertically bilateral.

Abdomen ( Fig. 11C ) unarticulated at base, surface coarsely rugose, length about 35% of trunk length, carried horizontally, tapering slightly distally.

Chelifores absent.

Palp ( Fig. 11E ) five-segmented, attached to lateral extension of cephalon, segment 1 longest segment, with 1 or 2 strong inward-facing curved spines, segment 3 next longest, greater than half length segment 1, with six inwardfacing curved spines of similar shape and size.

Oviger ( Fig. 11F ) four-segmented, attached to ventral extension of cephalon, second segment with strong recurved spine on distal margin, segment 4 longest, constricted at tip and accompanied by several spines.

Third leg: ( Fig. 11D ) femur widest and longest segment, single mid-ventral femoral cement gland duct legs 3 and 4 only, conical, height little more than one-third width of femur, tibia 1 longer than tibia 2, tibia 2 more setose ventrally than other segments, femur with single long dorsodistal hair-like spine on low process, first coxae with prominent dorsodistal digitiform tubercles in the order of 1:2:2:1, coxa 2 longer that coxae 1 or 3, third coxa with a distinctly bifurcate tubercle about one-third the height of those on coxa 1 ( Fig. 11I ), tarsus short, with several median spines and two longer dorsolateral spines, propodus gently curved, heel absent, sole lined with about ten short spines, without major heel spines, terminal claw about 40 percent of propodus length, auxiliary claws almost half length main claw, flared outward. Gonopores not evident.

Measurements of holotype (mm). Trunk length (frontal margin of cephalic segment to tip of 4 th lateral process), 0.784; width across 2 nd lateral processes, 0.400; proboscis length (dorsal), 1.016; abdomen length (lateral), 0.280; height ocular tubercle (lateral), 0.456. Third leg: coxa 1, 0.120; coxa 2, 0.128; coxa 3, 0.088; femur, 0.480; tibia 1, 0.440; tibia 2, 0.368; tarsus, 0.048; propodus, 0.280; claw, 0.112; auxiliary claws, 0.048. Palp: seg. 1, 0.576; seg 2, 0.080; seg. 3, 0.304; seg. 4, 0.040; seg. 5, 0.032. Oviger: seg. 1, 0.032; seg. 2, 0.040; seg. 3, 0.032; seg. 4, 0.088.

Etymology. Named for Dr Michelle Taylor, whose drive, direction and organization of all biological aspects contributed significantly to the efficient operation of the voyage.

Remarks. The basal part of ocular tubercle surface is particularly rugose with tiny pyramid-shaped projections. There is variability in the shape of oviger segment 4 which may be age dependent. In the holotype there is a strong constriction near the tip accompanied by one or two small spines ( Fig. 11F ) whereas oviger segment 4 of one paratype is without apparent constriction ( Fig. 11G ) but spination is similar. The fourth oviger segment of one smaller (less mature?) male is shorter, slightly ovate and without distal constriction ( Fig. 11H ).

Austrodecus taylorae sp. nov. is one of seven species in which males possess cement glands on legs 3 and 4 only. The other species are A. acone Hedgpeth and McCain, 1971 , A. bathyale Stock, 1991 , A. excelcum Stock, 1991 , Austrodecus sp. C (below), A. latum Stock, 1991 and A. tuberculatum Stock, 1991 . The cement gland in all these species except A. acone opens through a long tube on the posterior surface on the distal end of the femur; in A. acone the gland opens through a basal cone with apical tube on the ventral surface of the femur. Austrodecus taylorae and the unnamed species ‘C’ described herein are the only species in which the cement gland opens through a ventral cone lacking an apical tube. Three species are known from female specimens only and accordingly the shape, number and position of the cement glands are unknown. These species are A. elegans Stock, 1957 , A. frigorifugum Stock, 1954 and A. macrum Child, 1994b . Austrodecus elegans differs primarily from the new species in having very low mid-dorsal tubercles and tiny auxiliary claws. Austrodecus frigorifugum differs in possessing very tall tubercles on the mid-dorsal surface of the trunk, no auxiliary claws and a very much shorter proboscis. Austrodecus macrum is a far more elongate species with mid-dorsal tubercles low to absent. Cement gland ducts have also not been recorded in A. varum Child, 1994b and A. palauense Child, 1983 however the descriptions of both species were based on juveniles. Austrodecus varum is distinguished from the new species by low or non-existent mid-dorsal tubercles and an exceptionally long dorsodistal process on coxa 1. Austrodecus palauense can be distinguished from A. taylorae by more widely spaced lateral processes and the absence of auxiliary claws.

Compared to A. bamberi , A. taylorae is more compact and differs most noticeably in the shorter ocular tubercle and in the lesser number of femoral cement glands.

Figures

PLATE 3. Tanystylum tiara sp. nov., holotype male. A, trunk lateral; B, trunk, dorsal; C, trunk anterior view. Sericosura species indeterminate. D, trunk dorsal; E, trunk, lateral. Austrodecus bamberi. F, trunk dorsal; G, trunk, lateral. Austrodecus taylorae sp. nov., holotype, male. H, trunk dorsal.

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 11. Austrodecus taylorae sp. nov., holotype male. A, trunk, lateral view; B, trunk, dorsal view; C, abdomen, lateral view; D, third leg; E, right palp; F, oviger. Paratype male (JC066-4213). G, oviger; H, oviger (juvenile?); I, coxa 1, 2 and 3 showing dorsal tubercles.