Tanystylum tiara

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

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Tanystylum tiara

sp. nov.

Tanystylum tiara  sp. nov.

Figure 8View FIGURE 8 A–I; Plate 3View PLATE 3 A–C

Material examined. Holotype, female ( NHMUK 2018.18View Materials), 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, BView FIGURE 8. Plate 3A, BView PLATE 3) 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. 8CView FIGURE 8. Plate 3CView PLATE 3); 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. 8GView FIGURE 8) seven-segmented, segment 4 longest, almost 30% longer than segment 2, distal three segments with long ventral setae.

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

Third leg; ( Fig. 8EView FIGURE 8) 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. 8HView FIGURE 8). 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.