Nymphon rogersi, Staples, 2019

Staples, David A., 2019, Pycnogonids (Arthropoda, Pycnogonida) from the Southwest Indian Ridge, Zootaxa 4567 (3), pp. 401-449 : 404-406

Nymphon rogersi sp. nov.

Figure 2 A–K; Plate 1A, B

Material examined. Holotype, female ( NHMUK 2018.2 ), Southwest Indian Ocean, Coral Seamount, ROV, 1300 m, specimen JC066-4197, stn 4.2, coral framework/rubble, 12 November 2011.

Paratype. One subadult ( NHMUK 2018.3 ), Southwest Indian Ocean, Coral Seamount, 41˚22.31'S, 42˚54.57'E, stn 4.38, 732 m, specimen JC066-908, parent 1276, mooring site, on net containing Mango wood, 20 November 2011 .

Other material. One subadult female, one damaged juvenile (NHMUK 2018.4), Southwest Indian Ocean, Coral Seamount, 41° 21.76´S, 42° 54.90´E, ROV, 686 m, specimen JC066-4288, stn 4.37, coral framework/rubble, 20 November 2011. One subadult ( NHMUK 2018.5 ), Southwest Indian Ocean, Coral Seamount, 41° 21.76´S, 42° 54.90´E, ROV, 686 m, specimen JC066-1296, stn 4.37, 20 November 2011 .

Description. Female holotype. Trunk ( Fig. 2A, B . Plate 1A, B ) smooth, fully segmented, neck forward of oviger bases about as wide as trunk; lateral processes longer than basal width, separated by about twice diameter at base. Ocular tubercle ( Fig. 2C ) not as high as basal width, placed mid-way between first lateral processes and bases of ovigers, two small, prominent dorsolateral papillae; four eyes, unpigmented in preserved specimen.

Proboscis tapering slightly to rounded tip.

Chelifore scape over-reaching proboscis, chela fingers curved inwards, crossing at tips, 14–16 needle-like teeth of uniform size on each finger, several setae present at bases of fingers ( Fig. 2D ).

Abdomen ( Fig. 2J, K ) narrowing distally, tip strongly cleft, length over three times greatest width, reaching slightly beyond first coxae of fourth legs, carried almost horizontally, structure of base unclear, basal suture line appears to be preceded by wide articulation membrane or collar.

Palp ( Fig. 2I ) five-segmented, segment 2 longest, almost 1.5 times next longest segment 3, segment 4 about half length of segment 5.

Oviger ( Fig. 2E ) ten-segmented, base implanted well forward of the first lateral processes, segment 5 longest, slightly longer than segment 4, segment 4 with gland opening on prominent mound on posterior surface, compound spine formula 8:5:3:5, spines slender, with three pair of lateral teeth, claw long, with nine sharp teeth, on inner margin.

Third leg ( Fig. 2G ), second coxa about 2.5 times length of coxae 1 or 2, coxa 1 and 2 subequal; femur with few long setae on dorsal surface up to 2.5 times width of segment, tibiae with scattered, fine setae, single long setae on dorsodistal surface of femur and tibia 2, tibia 2 longest segment, tibia 1 much longer than femur, propodus greater than twice length of tarsus, inner margin of tarsus lined with about eight spines of similar size to those on propodal sole, heel absent, sole lined with fifteen spines, claw less than one-third length of propodus, auxiliary claws absent. Gonopores not evident.

Measurements of holotype (mm). Length trunk (frontal margin of cephalic segment to tip of 4 th lateral process), 2.368; length cephalon, 1.336; width across 2 nd lateral processes, 1.440; proboscis length (lateral), 0.800; greatest diameter proboscis, 0.312; length abdomen (lateral), 0.352. Palp: seg. 1, 0.096; seg. 2, 0.424; seg. 3, 0.320; seg. 4, 0.160; seg. 5, 0.192. Oviger: seg. 1, 0.056; seg. 2, 0.120; seg. 3, 0.176; seg. 4, 0.624; seg. 5, 0.760; seg. 6, 0.288; seg.7, 240; seg. 8, 0.184; seg. 9, 0. 200; seg. 10, 0.160; claw, 0.144. Third leg: coxa 1, 0.240; coxa 2, 0.624; coxa 3, 0.240; femur, 1.320; tibia 1, 1.696; tibia 2, 2.968; tarsus, 0.264; propodus, 0.592; claw, 0.224.

Etymology. This species is named for Prof. Alex Rogers, Principal Scientific Officer for the expedition in recognition of his excellent leadership under sometimes difficult circumstances and for his outstanding advocacy for the marine environment.

Remarks. The larger size of the holotype and complete segmentation of the ovigers suggests that it is a more mature specimen than others in this collection, but it does not possess convincing characteristics of either sex. Cement gland ducts are not present nor does the specimen have an elongate, club-shaped oviger segment 5 indicative of a male. On this basis it is presumed to be a female. Gonopores are not apparent. In comparison to the smaller specimens there are more spines on oviger segments 7 to 10 and on the oviger claw. Spination of legs between specimens is slightly variable.

In addition to the three species described in this paper, only two uniunguiculate species have well developed eyes and the ocular tubercle placed midway between the widely separated first lateral processes and the bases of the ovigers. These species are N. longicoxa Hoek, 1881 and N. prolatum Fage, 1942 which belong to ‘species group 5a’ of Stock’s (1965) analysis of uniunguiculate Nymphon . The new species does not have the characteristic long second coxae of N. longicoxa nor the extraordinarily long ocular tubercle and abdomen of N. prolatum .

Figures

PLATE 1. Nymphon rogersi sp. nov., holotype, female. A, trunk lateral; B, trunk dorsal. Nymphon serpettiae sp. nov., holotype, female, C, trunk dorsal; D, trunk lateral; E, cephalon ventral. Nymphon dentatum sp. nov., holotype, male. F, trunk lateral; G, trunk dorsal; H, cement gland duct.

FIGURE 2. Nymphon rogersi sp. nov., holotype female. A, trunk, dorsal view; B, trunk, lateral view; C, ocular tubercle (arrow indicating anterior); D, right chela, inner; E, left oviger, segments 2–10; F, oviger claw; G, third leg; H, tarsus, propodus; I, right palp; J, abdomen, dorsal view K, abdomen, lateral view.