Pycnogonum (Pycnogonum) copleyi, 2019

Staples, David A., 2019, Pycnogonids (Arthropoda, Pycnogonida) from the Southwest Indian Ridge, Zootaxa 4567 (3), pp. 401-449 : 437-438

Pycnogonum (Pycnogonum) copleyi sp. nov.

Figure 18 A–E; Plate 6 C–E

Material examined. Holotype, male ( NHMUK 2018.46 ), Southwest Indian Ocean, Coral Seamount, ROV core, 740 m, specimen JC066-4288, stn 4.37, sand, 20 November 2011. Right oviger mounted in Euparal on glass slide.

Description. Male holotype. Trunk elongate, ( Fig. 18A, B . Plate 6C, D ) segmentation distinct, arthrodial membrane wide, surface finely granulate, without conspicuous processes or tubercles, posterior dorsal surface of segments 1, 2, 3 inflated, inflated part more conical on segments 3 and 4; lateral processes touching at bases, diverging to about one-quarter and one-third their width distally, each process shorter than width at base, with inconspicuous dorsodistal swellings on legs 2, 3 and 4. Ocular tubercle on anterior margin of cephalon, low, wider than tall; four eyes pigmented, of equal size.

Proboscis little less than half length of trunk, widest proximally, narrowing to a slight constriction at about one-third length before a slight inflation tapering to a rounded oral region, length little more than twice greatest width; arthrodial membrane at base of proboscis broad, distal margin dark, oral glands present.

Abdomen unarticulated at base, broad, length 2.2 times median width, cylindrical, angled slightly downwards tip, truncate, anal slit ventrodistal.

Oviger ( Fig. 18E ) nine-segmented, segments cylindrical, smooth, terminal claw strong, pointed, slightly curved, length slightly shorter than segment 10.

Third leg robust ( Fig. 18C . Plate 6E ), dorsal surfaces strongly granulate, first coxa short, much broader than long, coxa 2 more slender than coxa 1, longer than coxa 1 or 3, femur longest segment, proximal ventral half strongly inflated, tibia1 longer than tibia 2, each with long dorsodistal spine, propodus gently curved, no hint of heel, ventral margin of tarsus and propodal sole with about 15 slender, blunt-tipped spines, claw less than half length of propodus, auxiliary claws absent ( Fig. 18D ). Ecdysial line not evident. Gonopores not evident. Blisterlike coxal pellicula present on distodorsal surface of coxa 2 of all legs.

Measurements of holotype (mm). Trunk length (frontal margin of cephalic segment to tip of 4 th lateral process), 3.520; length cephalon, 0.984; width across 2 nd lateral processes, 1.600; proboscis length (ventral), 1.624; proboscis maximum diameter, 0.784; abdomen length, 0.792. Third leg: coxa 1, 0.344; coxa 2, 0.336; coxa 3, 0.360; femur, 0.848; tibia 1, 0.720; tibia 2, 0.680; tarsus, 0.176; propodus, 0.560; claw, 0.240.

Etymology. Named for Dr. Jon Copley, Principal Scientist of the Longqi/Dragon hydrothermal vent field survey (RRS James Cook Voyage JC067).

Remarks. This species can most easily be confused with P. crassirostrum Sars, 1888 , P. magellanicum Hoek, 1898 , P. magnirostrum Möbius, 1902 , P. microps Loman, 1904 and P. platylophum Loman, 1923 . These species have a similar habitus and share a combination of nine-segmented ovigers and the absence of auxiliary claws. Gordon (1932), Stock (1966b) and Arnaud (1970) have commented on probable synonymy within this group of species and a review of the type material is required.

The most conspicuous difference between this species and P. crassirostris is the proboscis which is described by Sars as short and thick. Based on Sars (1891, Pl. 1, Fig 2c ), the proboscis of P. crassirostris is squat and almost parallel-sided whereas the proboscis of P. copleyi is more-slender, length about twice its greatest width and with a slight constriction at about one-third its length before narrowing to a rounded tip. The irregular folds around the margins of the mouth mentioned by Sars are not evident in this species. The “obtuse protuberances” along the trunk of P. crassirostris figured by Sars (Sars 1891, Pl. 1, Figs 2, 2a ) appear to be more prominent and the abdomen longer than that of P. copleyi . The trunk length of the present specimen is considerably less than the type specimens of P. crassirostris which measure 10.0 mm and 6.5 mm respectively for the female and male. Stock, 1955 found that P. magnirostrum was too incompletely known for comparisons however based on Pushkin’s figures differences are evident in the shapes of the femur and tibiae ( Pushkin 1993, Fig. 317). The oviger claw is also illustrated as being longer than segment 10 compared to shorter in P. copleyi . Both P. micropes and P. platylophum differ from P. copleyi in the shapes of their abdomens. The abdomen of P. micropes is decidedly spatula-shaped and Loman described and illustrated the abdomen of P. platylophum as cuneiform (wedge-shaped) which in P. copleyi it is not. A post-ocular process in P. micropes serves as a further point of difference to distinguish that species. The ocular tubercle of P. platylophum is described as almost flat and whilst it is low in P. copleyi , it is never the less welldeveloped. Differences in the proboscis shape of both species are also apparent. Using Stock’s 1966 key this species can be followed down to couplet 38b at which point where it identifies as P. magellanicum Hoek, 1898 . Hoek described the body of P. magellicum as thick and square-set and with a rather large abdomen, descriptions which are inconsistent with the body shape of P. copleyi . The body shape of P. magellanicum is best illustrated by Pushkin (1993, Fig. 323). The body length of the P. magellanicum holotype is 9 mm; more than twice that of the P. copleyi holotype. None of these species appear to have the conspicuous, irregular and granulose surface of P. copleyi .

This species shares a granulate leg surface with P. sentus but from which it differs most noticeably in the absence of strong dorsal trunk cowls and in the shape of the ocular tubercle. This specimen appears to be mature but with gonopores possibly obscured by the rugose surface.

Figures

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.

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 18. Pycnogonum (Pycnogonum) copleyi sp. nov., holotype. A, trunk, lateral view; B, trunk, dorsal view; C, third leg; D, tarsus & propodus; E, oviger.