Tanystylum tiara, Staples, 2019

Staples, David A., 2019, Pycnogonids (Arthropoda, Pycnogonida) from the Southwest Indian Ridge, Zootaxa 4567 (3), pp. 401-449 : 416

Tanystylum tiara sp. nov.

Figure 8 A–I; Plate 3 A–C

Material examined. Holotype, female ( NHMUK 2018.18 ), Southwest Indian Ocean, Coral Seamount, 41˚ 22.37'S, 42° 54.60'E, ROV, 745 m, specimen JC066-1068, stn 4.12, parent 736, 16 November 2011. Right palp and right oviger are mounted in Euparal on glass slides.

Description. Female holotype. Trunk ( Fig. 8A, B . Plate 3A, B ) discoid, unsegmented, cephalon with thickened anterior rim, prominent dorsolateral processes each coalesced into single flange divided into three spine-tipped peaks, each peak decreasing in size from inner to outer margin ( Fig. 8C . Plate 3C ); lateral processes touching, each with a distal anterior and posterior tubercle. Ocular tubercle taller than wide, apical one-third conical, circumscribed with an apparent suture line, lateral papillae about level with top of eyes; four eyes, large, pigmented.

Proboscis cylindrical, longer than trunk, stained black distally, truncate, oral surface recessed, rim irregular, bubbly.

Abdomen with low dorsal bulge at base, unarticulated, enlarged at about two thirds length, tapering distally to pointed tip, several distal spines.

Chelifore scapes separated at bases, each one-segmented, directed upwards, tapering from base towards tip, one very long terminal spine about half length of scape and two lesser spines, chelae absent.

Palp ( Fig. 8G ) seven-segmented, segment 4 longest, almost 30% longer than segment 2, distal three segments with long ventral setae.

Oviger ( Fig. 8I ) nine-segmented, segment 4 longest, segment 9 with two simple terminal spines.

Third leg; ( Fig. 8E ) femur with dorsodistal fringe of setae on low swelling, first tibia with two proximal spinetipped dorsal swellings; propodus gently curved, proximal half with four robust spines, tips blunt, rounded, distal half with field of much shorter, sharp spines; auxiliary claws slightly longer than half length terminal claw, flared outward from bases. Gonopore ventrodistal, coxa 2, all legs.

Measurements of holotype (mm). Trunk length (frontal margin of cephalic segment to tip of 4 th lateral process), 1.520; width across 2 nd lateral processes, 1.120; proboscis length (lateral), 1.840; greatest diameter proboscis, 0.736; abdomen length (lateral), 1.024. Palp: seg. 1, 0.160; seg. 2, 0.272; seg. 3, 0.144; seg. 4, 0.664; seg. 5, 0.160; seg. 6, 0248; seg. 7, 0.224.

Oviger: seg. 1, 0.120; seg. 2, 0.184; seg. 3, 0.184; seg. 4, 0.328; seg. 5, 0.280; seg. 6, 0.112; seg. 7, 0.104; seg. 8, 0.48; seg. 9, 0.80. Third leg: coxa 1, 0.400; coxa 2, 0.440; coxa 3, 0.280; femur, 0.520; tibia 1, 1.680; tibia 2, 2.528; tarsus, 0.120; propodus, 0.800; claw, 0.352; auxiliary claws 0.232.

Etymology. Tiara (Tiara–ornamental headband worn on front of head). Alluding to the ornate tiara-like flanges on the anterolateral margin of the cephalon; a noun in apposition.

Remarks. When viewed under high power the e ntire surface is seen to be covered in bifurcate setae. Tubercles on lateral process are mostly irregular in shape with minute spines on lateral margins ( Fig. 8H ). Whilst some Tanystylum have a thickened anterior rim on the cephalon, this species is unique in possessing a tiara-like flange on the anterolateral margins.

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.

FIGURE 8. Tanystylum tiara sp. nov., holotype, female. A, trunk, dorsal view; B, trunk, lateral view; C, cephalon, anterior view; D, trunk, ventral view; E, third leg; F, tarsus and propodus, third leg; G, right palp; H, dorsodistal tubercles on third lateral process (distal view); I, right oviger.