Pycnogonum spatium, Takahashi & Dick & Mawatari, 2007

Takahashi, Yoshie, Dick, Matthew H. & Mawatari, Shunsuke F., 2007, Sea spiders (Arthropoda: Pycnogonida) from waters adjacent to the Nansei Islands of Japan, Journal of Natural History 41 (1 - 4), pp. 61-79 : 73-75

Pycnogonum spatium sp. nov.

( Figure 5 )

Material examined. Holotype: female, ZIHU 03172 , 28 ° 09.20 9 N, 129 ° 31.50 9 E, southeast of Amami Island , Kagoshima, 25 May 2004, 332– 334 m depth; collected by beam trawl, Y. Takahashi collector.

Measurements of holotype (mm). Trunk length, 2.31; body width, 1.09; length of abdomen, 0.50; length of proboscis, 0.47; third leg, coxa 1, 0.30; coxa 2, 0.38; coxa 3, 0.30; femur, 1.00; tibia 1, 0.50; tibia 2, 0.37; tarsus, 0.13; propodus, 0.50; terminal claw, 0.27.

Etymology. The species name spatium (Latin, meaning interval) refers to the wide intervals between lateral processes.

Description. Body very small, elongate; colour vivid yellow. Trunk ( Figure 5A, B ) integument granular, third and fourth segments fused; anterior three segments each with flat-topped dorsal median tubercle at posterior margin, the tubercle slightly lower than its basal width. Lateral processes half as long as wide, separated from one another by almost two-thirds their basal width, more widely separated distally; each lateral process armed with a single low tubercle dorsodistally, one-quarter the height of dorsal median tubercles on trunk. Ocular tubercle placed on anterior end of trunk, angled slightly forward, about half as high as its basal width, slightly taller than dorsal median tubercles on trunk. Eyes pigmented, situated on base of ocular tubercle. Proboscis large, 1.8 times as long as its basal width, width equal to the trunk width, cylindrical, almost flat at lip, ventral side slightly longer than dorsal side; single median tubercle situated on dorsal surface one-third of total length from end, as tall as its basal width, rising sharply anteriorly, sloping posteriorly. Abdomen horizontal, articulated at base, cylindrical, moderately tapering at the tip, reaching distal end of second coxae, about three times as long as its basal width, with a pair of tiny setae dorsodistally.

Palps, chelifores and ovigers absent. Only the female is known.

Legs ( Figure 5C ) extremely stout; first coxa equal to third coxa in length, with a pair of dorsolateral tubercles distally ( Figure 5A ), anterior tubercle bearing a short seta only on fourth legs; a single seta ventrodistally on first coxa, several setae ventrally and laterally on third coxa; second coxa about 1.3 times as long as other coxae, with few setae; femur extremely stout, as long as three coxae combined, with a large, mid-dorsal projection bearing setae, and with a single long seta in the middle of distal half; femur width at projection more than the narrowest femur width; femur has two strong dorsodistal bosses (the larger bearing many strong tubercles distally) with a prominent notch between them; first tibia about three times as long as its basal width, with two dorsal tubercles each bearing a short seta, and with single distal tubercle lacking setae, but with single long seta proximal to it; second tibia 0.7 times as long as first tibia, narrower than first tibia, with a similar tuberculation pattern; tarsus short, rounded ventrally; propodus ( Figure 5D ) moderately curved, slightly shorter than first tibia, with several setae dorsally; all segments bearing short setae ventrally, these different from dorsal setae in having a rounded tip ( Figure 5E ); terminal claw more than half as long as propodus; auxiliary claw absent. Genital pores of female on dorsal side of second coxa on all legs.

Remarks. Pycnogonum spatium sp. nov. resembles P. moolenbeeki Stock, 1992 and P. tuberculatum Clark, 1963 in having a dorsal tubercle on the proboscis, basal articulation of the abdomen, and a stout femur with strong bosses. Pycnogonum spatium , however, differs from P. moolenbeeki in having much stronger mid-dorsal tubercles on the trunk, a cylindrical proboscis with a flat lip, longer intervals between lateral processes, and a longer first tibia with ventral setae having a round tip. Pycnogonum spatium differs from P. tuberculatum as follows (characters of P. tuberculatum in parentheses): cylindrical proboscis with flat lip (gradually tapering towards tip, with rounded lip), wide intervals between the lateral process (relatively narrow), large trunk to proboscis length ratio (small), short first tibia (long), much stronger tubercles on femur and tibiae (strong). No other species in this genus has such wide intervals between the lateral processes as P. spatium . Each of the three species above is known only from its type locality: P. spatium from Okinawa, P. moolenbeeki from Oman, P. tuberculatum from southeastern Australia. Only females of these species have been collected; there is no information on males.

Distribution. Known only from the type locality, southeast of Amami Island, Okinawa.

Figures

Figure 5. Pycnogonum spatium sp. nov., holotype, female: (A) trunk, dorsal view; (B) trunk, lateral view; (C) third leg; (D) distal segments of third leg, by SEM; (E) endal setae of third leg, by SEM. Scale bars: 1 mm (A–C); 0.1 mm (D); 0.01 mm (E).