Hedgpethia filamentus, Staples, 2019

Staples, David A., 2019, Pycnogonids (Arthropoda, Pycnogonida) from the Southwest Indian Ridge, Zootaxa 4567 (3), pp. 401-449 : 431-433

Hedgpethia filamentus sp. nov.

Figure 15 A–I; Plate 5E, F

Material examined. Holotype, sex undetermined ( NHMUK 2018.38 ), Southwest Indian Ocean, Atlantis Bank , 32° 42.86´S, 57° 16.34´E, ROV, 750 m, specimen JC066-4211C, stn 8.29, mooring site, on net containing whale bone, 14 December 2011.

Paratypes. Two specimens of undetermined sex and two smaller (subadult?) specimens ( NHMUK 2018.39 ), same collection details as holotype. One damaged specimen ( NHMUK 2018.40 ), 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. Holotype. Leg span 12 mm. A very fine, slender specimen. Trunk ( Figs 15A, B . Plate 5E, F ) segmented, smooth; lateral processes clearly separated by almost twice their basal width. Ocular tubercle placed on mid-region of cephalon, acuminate, height twice width at base, basal part broad, posterior surface inflated; four large eyes of equal size, posterior pair less pigmented compared to anterior pair.

Proboscis slightly longer than trunk, spindle-shaped, angled downwards from about one-third length, maximum width at about half length, tapering to rounded tip, narrow basal part about half width at tip.

Abdomen ( Fig. 15H ) articulated at base, very short, base broad, implanted between fourth lateral processes, directed ventrally, barely evident in dorsal view.

Chelifores absent.

Palp ten-segmented ( Fig. 15E ), segment 3 about 1.9 times longer than segment 5, segments 7 to10 slender and of about equal length.

Oviger ten-segmented ( Fig. 15C ), segment 6 longest, slightly longer than next longest segment 4, segments 7 to10 lined with four or five rows of spatulate spines, distal-most spines taller than proximal spines, claw short, broad, less than half length of segment 10 ( Fig. 15D ), cutting edge curved, blade-like.

Third leg ( Fig. 15F ) slender, femur slightly inflated in mid-region, maximum width twice that of either tibia, few scattered spines and longer dorsodistal spine; tibiae with numerous scattered spinules, tibia 1 longest segment; tibia 2 only slightly longer than femur, tibia 2 with long dorsodistal spine about 3 times width of segment, tarsus more than half as long as propodus ( Fig. 15G ), all spines fine, undifferentiated, 18 to 20 spines on ventral surface, propodus almost straight, heel without major heel spines,18 to 25 sole spines; terminal claw short, little less than half length of propodus, auxiliary claws absent. Cement glands not evident. Gonopores not evident.

Measurements of holotype (mm). Trunk length (frontal margin of cephalon to tip of 4 th lateral processes), 1.384; length of cephalon, 0.424; width across 2 nd lateral processes, 0.600; proboscis length (lateral), 1.616; greatest diameter proboscis, 0.360. Third leg: coxa 1, 0.184; coxa 2, 0.136; coxa 3, 0.136; femur,1.416; tibia1,1.736; tibia 2, 1.400; tarsus, 0.256; propodus, 0.440; claw, 0.192. Palp: seg. 1, 0.112; seg. 2, 0.048; seg. 3, 1.024; seg. 4, 0.153; seg. 5, 0.536, seg. 6, 0.104; seg. 7, 0.168; seg. 8, 0.160; seg. 9, 0.160; seg. 10, 0.160. Oviger: seg.1, 0.080; seg. 2, 0.120; seg. 3, 0.216; seg. 4, 0.680; seg. 5, 0.168; seg. 6, 0.688; seg. 7, 0.264; seg. 8, 0.108; seg. 9, 0.200; seg. 10, 0.136; claw, 0.072.

Etymology. The species name alludes to the filamentous habitus of the specimen.

Remarks. The holotype was chosen because it is the more complete of the two larger specimens. There is some variability in the shape of the ocular tubercle amongst these six specimens with the ocular tubercle of one paratype (JC066-4214) being particularly acute ( Fig. 15I ). Eyes are only evident in the larger specimens. The slightly smaller specimens are of a similar size to each other and have leg spans of 8 to10 mm. Apart from size other morphological difference are not evident and the size difference may indicate that they are males rather than an indication of their maturity. Gonopores are not apparent in any of the specimens.

Hedgpethia filamentus shares a similarly shaped ocular tubercle with H. calva Arango, 2009 and H. eleommata Child, 1998 but both those species have vastly longer propodal claws and in neither species are the lateral processes so widely spaced as in this species. Hedgpethia atlantica ( Stock, 1970) also possesses an acuminated ocular tubercle and shares a similar proboscis shape with H. filamentus but differs in the arrangement of oviger spines on segments 7 to10 which are in one or two rows as opposed to four or five rows in the new species and in the much longer, pointed oviger claw.

Figures

PLATE 5. Colossendeis sp. A, proboscis lateral; B, palp. Colossendeis melancholicus. C, specimen on rock wall. D, specimen with proboscis inserted into Isactinernus quadrilobatus. Hedgpethia filamentus sp. nov., holotype. E, trunk, lateral view; F, trunk, dorsal view. Hedgpethia shalei sp. nov., holotype. G, trunk, lateral view; H, trunk, dorsal view.

FIGURE 15. Hedgpethia filamentus sp. nov., holotype. A, trunk, dorsal view; B, trunk, lateral view; C, right oviger; D, right oviger claw; E, right palp; F, third leg; G, tarsus and propodus; H, abdomen, ventral view. Paratype, (JC066-4214). I, ocular tubercle.