Pycnogonum cheni, Staples, 2019

Staples, David A., 2019, Pycnogonids (Arthropoda, Pycnogonida) from the Southwest Indian Ridge, Zootaxa 4567 (3), pp. 401-449 : 439-440

Pycnogonum cheni sp. nov.

Figure 19 A–G; Plate 6 F–H

Material examined. Holotype, male ( NHMUK 2018.47 ), Southwest Indian Ocean , Middle of What Seamount, 37° 57.92´S, 50° 24.43´E, ROV net, 1003 m, specimen JC066-2740, stn 6.4, coral framework and sediment, 1 December 2011.

Paratype. One subadult specimen ( NHMUK 2018.48 ), Southwest Indian Ocean, Coral Seamount, 41° 21´36S, 42° 55.11´E, Box Core, 950 m, specimen JC066-138, stn 4.18, coral framework/rubble, 16 November 2011 .

Description. Male holotype. Trunk compact ( Fig. 19A, B . Plate 6F, G ), integument inconspicuously granulate, dorsal trunk segmentation complete; lateral processes and trunk separated by faint suture line, processes touching throughout length, without tubercles. Ocular tubercle placed on mid-region of cephalon, conical, shorter than basal width; four eyes unpigmented, anterior pair larger.

Proboscis ( Fig. 19C ) longer than trunk, tapering evenly to slightly less than half width at base, weevil-like.

Abdomen ( Fig. 19G ) articulated at base, length about twice median width, reaching to two-thirds length of coxa 2, down-curved.

Oviger terminal claw absent ( Fig. 19F ) right oviger missing entirely, distal three segments of left oviger bear strong spines.

Legs rather slender for genus, ( Fig. 19D . Plate 6H ) second coxae twice length of coxa 3, all legs with prominent distoventral process taller than segment width present on second coxae, process on first legs lower than remaining legs, no dorsal openings evident. Blister-like coxal pellicula on low mound on dorsal surface of coxa 2 of all legs at about two-thirds length. Tibia 2 longest, tibia 1 about half length of tibia 2 and shorter than femur, all longer segments with short, scattered spinules, femur with strong dorsodistal spine, broken off on most legs; tarsus short, with three strong spines on the ventral surface, propodal heel absent, sole with four to six robust spines, terminal claw strong, about half length of propodus, auxiliary claws absent ( Fig.19E ). Gonopores not evident but perhaps tiny and obscured by the granular integument;

Measurements of holotype (mm). Trunk length (frontal margin of cephalic segment to tip of 4 th lateral process), 2.768; length cephalon, 0.568; width across 2 nd lateral processes, 1.776; proboscis length (lateral), 2.784; proboscis diameter at base 0.664; abdomen length, 0.600. Third leg: coxa 1, 0.504; coxa 2, 0.960; coxa 3, 0.480; femur, 2.520; tibia 1, 2.280; tibia 2, 3.664; tarsus, 0.184; propodus, 1.120; claw, 0.520.

Etymology. Named for Dr Chong Chen scientist and fellow voyage companion.

Remarks. It is unclear whether the holotype is a fully mature specimen but at this stage of development the left oviger is four-segmented and lacks a terminal claw. If the oviger has reached its full complement of segments the species will belong in the subgenus Retroviger ( Stock 1968: 60) . The ovigers of the subadult paratype consist of single buds. The ecdysial line is present on the lateral margins of the trunk and on the dorsal and ventral margins of the legs.

A number of species share a long, tapered proboscis however all those species have mid-dorsal trunk processes and in this regard the new species is unique. Other unique characters are the robustness of the spines on the oviger and propodal sole. Should the holotype be immature these defining characters are unlikely to change with age.

Figures

PLATE 6. Pycnogonum (Retroviger?) sentus sp. nov., holotype. A, trunk, lateral view; B, trunk, dorsal view. Pycnogonum copleyi sp. nov., holotype. C, trunk, lateral view; D, trunk, dorsal view; E, leg 3. Pycnogonum cheni sp. nov., holotype, male. F, trunk lateral; G, trunk dorsal; H, third leg.

FIGURE 19. Pycnogonum cheni sp. nov., holotype. A, trunk, lateral view; B, trunk, dorsal view; C, proboscis, anterior view; D, third leg; E, tarsus & propodus leg 3; F, left oviger; G, abdomen, dorsal view.