Hedgpethia filamentus

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

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Hedgpethia filamentus

sp. nov.

Hedgpethia filamentus  sp. nov.

Figure 15View FIGURE 15 A–I; Plate 5E, FView PLATE 5

Material examined. Holotype, sex undetermined ( NHMUK 2018.38View Materials), 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.GoogleMaps 

Paratypes. Two specimens of undetermined sex and two smaller (subadult?) specimens ( NHMUK 2018.39View Materials), same collection details as holotype. One damaged specimen ( NHMUK 2018.40View Materials), 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 2011GoogleMaps  .

Description. Holotype. Leg span 12 mm. A very fine, slender specimen. Trunk ( Figs 15A, BView FIGURE 15. Plate 5E, FView PLATE 5) 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. 15HView FIGURE 15) 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. 15EView FIGURE 15), segment 3 about 1.9 times longer than segment 5, segments 7 to10 slender and of about equal length.

Oviger ten-segmented ( Fig. 15CView FIGURE 15), 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. 15DView FIGURE 15), cutting edge curved, blade-like.

Third leg ( Fig. 15FView FIGURE 15) 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. 15GView FIGURE 15), 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. 15IView FIGURE 15). 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.














Hedgpethia filamentus

Staples, David A. 2019


Hedgpethia filamentus

Staples 2019


H. filamentus

Staples 2019


H. calva

Arango 2009


H. eleommata

Child 1998


Hedgpethia atlantica (

Stock 1970