Nymphon falcatum Utinomi, 1955

Takahashi, Yoshie, Kajihara, Hiroshi & Mawatari, Shunsuke F., 2012, Sea spiders of the genus Nymphon (Arthropoda: Pycnogonida) from waters around the Nansei Islands, Japan, Journal of Natural History 46 (21 - 22), pp. 1337-1358 : 1340-1343

Nymphon falcatum Utinomi, 1955

( Figures 2 , 3 )

Nymphon falcatum Utinomi, 1955, p. 15 , fig. 9.

Nymphon falcatum: Stock 1956, p. 94 , fig. 15; 1965, p. 21 [list, key]; Utinomi 1971, p. 321; Nakamura and Child 1991, p. 47.

Material examined

ZIHU 4088 (one male with eggs) , ZIHU 4089 (one male without eggs) , ZIHU 4090 (one female) , ZIHU 4091 (six juveniles), 26 ◦ 48.23 ′ N, 127 ◦ 52.18 ′ E, northeast of Ie Island , Okinawa, 26 May 2002, 337– 340 m depth, beam trawl, Y. Takahashi . ZIHU 4092 (one female), 31 ◦ 18.80 ′ N, 131 ◦ 28.00 ′ E, Toi Cape, south of Kyushu , 20 May 2003, 164 m depth, beam trawl, Y. Takahashi .

Description

Trunk ( Figures 2A,B , 3A,B ) slender, elongate, completely segmented, without median processes or other protuberances. Lateral processes about four times as long as wide, separated distally by more than twice their width, with several setae dorsally and laterally. Neck narrow, longer than four times its width. Ocular tubercle in midline, in line with anterior margin of first lateral processes, height less than or equal to basal diameter; round, well pigmented eyes situated just below top. Ocular tubercle lower and wider in material from Okinawa than in material from Kyushu. Abdomen long, reaching middle of first coxa of fourth leg, straight, horizontal, with one to four pairs of tiny setae on posterior half. Proboscis short, about half as long as neck, cylindrical, rounded at tip.

Chelifore scapes ( Figures 2A,B , 3A,B ) about five times as long as wide, directed outwards at 50 ◦ –70 ◦, with several lateral setae. Chelae strongly bent inwards, slender, about 1.5 times as long as scape. Fingers ( Figures 2C , 3C ) slender, about 1.5 times as long as palm, with 25–30 strong teeth endally on movable fingers and 34–40 on immovable fingers, the latter with several setae at equal intervals; movable finger shorter than fixed finger in all material from Okinawa.

Palps ( Figures 2D , 3D ) slender, five-segmented; second segment longest, with several setae laterally; third and fifth segments almost equal, shorter than fourth; fourth segment slightly curved, densely covered with fairly long setae ventrally and laterally; fifth segment with sparse short setae.

Ovigers 10-segmented. In male ( Figure 2E,F ), fifth segment longest, curved inwards, with short setae at equal intervals on ectal side and with a small, distinct apophysis bearing three setae (not visible in Figure 2E ). Fourth segment about twothirds as long as fifth segment, with small ectal protuberance in middle of proximal half, with sparse tiny spines over entire surface. Sixth segment with numerous long setae ventrally and laterally, setae longer than leg width. Distal four segments each with a single dorsodistal seta and with compound endal spines ( Figure 2F ) having three denticles per side; terminal claw with six widely spaced serrations, spine formula 6: 5: 4: 4 :: 6. In female ( Figure 3E,F ), fifth segment longest, straight, with some short setae ectally and laterally. Fourth segment four-fifths the length of fifth segment, with a few setae. Sixth segment with several short setae in a line ectally and a single short seta endally. Distal four segments each with one or two dorsodistal setae and with compound endal spines having three denticles per side, terminal segment shortest; terminal claw with seven serrations, spine formula 6: 6: 5: 5 :: 7.

Legs ( Figures 2G , 3G ) long, slender, with many tiny setae. Second coxa about twice as long as first coxa, about three times as long as third coxa; femur shorter than tibiae; first tibia longest segment. Cement gland pores ( Figure 2G ) with slightly elevated opening on ventral side of both femur and tibia 1; mid-ventral line of two to 10 pores on femur, 15–43 pores extending for proximal two-thirds of first tibia length; number of pores increases with leg length. Tarsus shorter than two-thirds of propodus length. Main claw slender, longer than half propodus length, longer than tarsus. Auxiliary claws absent.

Remarks

Nymphon falcatum is a distinctive species recognized by its long neck and lateral processes. According to Utinomi (1955) and Stock (1956), N. falcatum has a propodus more than 1.5 times the length of the tarsus, and a main claw longer than the propodus in both sexes. Utinomi (1955) noted that “this species differs from N. hedgpethi in the relative length of the distal segments of legs”. However, our material shows variation in the relative lengths of the three distal leg segments, irrespective of sex or habitat. Specifically, the length ratio of tarsus to propodus varies from 1: 1 to 1: 2, and that of main claw to propodus from 1.3: 1 to 2: 1. Further variation is evident in the length ratio of movable to immovable fingers of the chelae and in the height of the ocular tubercle. The female specimen from southern Kyushu (ZIHU 4092) agrees well with the original description ( Utinomi 1955); however, although in all specimens from Okinawa the lower ocular tubercle agrees with the original description, the movable finger is shorter than the immovable one. Although no previous authors have reported N. falcatum to have cement glands, our material has many pores of cement glands on both the femur and tibia 1. The number of pores varies with leg length, ranging from two to 10 per femur and from 15 to 43 per tibia 1. Nymphon falcatum is similar to N. hedgpethi Stock, 1953 , except for two characters (state of N. hedgpethi in parentheses): the lateral processes have short (versus fairly long) distal setae, and the palps have the third segment slightly shorter (versus longer) than the fourth.

Figures

Figure 2. Nymphon falcatum Utinomi, 1955, ZIHU 4088, non-type, male. (A) Trunk, dorsal view; (B) trunk, lateral view; (C) chelifore; (D) palp; (E) oviger; (F) enlargement of distal segments of oviger; (G) third leg. Scale bars: A–C, G, 1 mm; D, E, 0.25 mm; F, 0.1 mm.

Figure 3. Nymphon falcatum Utinomi, 1955, ZIHU 4092, non-type, female. (A) Trunk, dorsal view; (B) trunk, lateral view; (C) chelifore; (D) palp; (E) oviger; (F) enlargement of distal segments of oviger; (G) third leg; (H) enlargement of distal segments of third leg. Scale bars: A, B, G, H, 1 mm; C, E, 0.5 mm; D, F, 0.25 mm.