Cilunculus gracilis Nakamura & Child 1991

Cilunculus gracilis

MATERIAL EXAMINED.—HONSHU: Sanriku-oki, E of Otsuchi, 38°58.6′N, 142°56.7′E, 1430–1440 m, KT84-9, sta SR8, 11 Jul 1984 (l holotype, USNM 234470, 3, 1 juv, paratypes, USNM 234471); 39°12.4′N, 142°18.7′E, 700–736 m, KT84-9, sta SR5, 10 Jul 1984 (5, 4, paratypes, USNM 234472).

OTHER MATERIAL.—Same locality, 39°11.4′N, 142°11.5′E, 430–435 m, KT84-9, sta SR4, 12 Jul 1984 (9 with eggs, 17, 30, 3 juv); 39°13.3′N, 142°16.2′E, 562–563 m, KT85-11, sta SR15, 14 Aug 1985 (2, 1).

DESCRIPTION.—Size moderately small, leg span 17.3 mm. Trunk slender, segmentation lines barely discernible or missing, integument covered with tiny papillae or rugosities. Lateral processes long, over twice as long as segment diameter, separated by their diameters or less, each armed with very slender dorsodistal tubercle and 1 or 2 tiny papillae lateral to tubercles, tubercles longer than segment diameters on second and third pairs of lateral processes, shorter than their diameters on first and fourth pairs. Neck short shorter than anterior diameter, oviger implantation next to and partly hidden by first pair of lateral processes. Ocular tubercle tall, slender, over four times longer than basal diameter, eyes small, at tip of tubercle, unpigmented, apex with tiny tubercle. Proboscis moderately inflated, without proximal or distal suture lines, lips flat Abdomen long, straight, carried below horizontal, armed with 5 or 6 distal setae.

Chelifores long, slender, 0.6 length of proboscis, with 2-segmented scape, first segment armed with 2 long lateral setae, second segment 1.5 times longer than first, armed with 9 or 10 long lateral and distal setae, all at least twice segment diameter or longer. Chelae tiny, with vestigial finger buds and distal seta as long as scape setae.

Palp second segment longest, 0.2 longer than fourth. Third, fifth, and sixth segments subequal, distal 3 segments shorter, subequal, fifth through ninth armed with dense ventral setae as long as or longer than segment diameters.

Ovigers moderately short, slender, second segment only slightly shorter than fourth, both armed with few lateral and distal setae. Fifth segment 0.6 as long as fourth, armed with ectal row of 7 or 8 short setae. Strigilis segments short, sixth segment longest, swollen, armed with four rows of short recurved spines and setae, terminal 4 segments hardly longer than wide, armed with few ectal setae longer than segment diameters and endal denticulate spines, 1 on each segment except the tiny terminal segment, which has 2. Spines broad, with many lateral serrations.

Legs moderately long, robust, very setose with setae increasing in numbers distally, setae slightly longer to 3 times longer than segment diameters. First coxa with dorsodistal tubercle like those of lateral processes but shorter and 2 anterior and 2 posterior long lateral setae. Second coxa with 2 or 3 long lateral setae. Third coxa with several short ventral setae and fringe of longer ventrodistal setae. Femur with several proximoventral setae and 1 dorsodistal seta about as long as segment diameter and several distal setae twice segment diameter. Cement gland tube a single dorsodistal cone pointing distally, not as long as segment diameter. First tibia the longest segment, slightly longer than femur and about 0.2 longer than second tibia. Both tibiae armed with ventral, lateral and dorsal rows of long setae. Tarsus short, quadrangular, armed with dorsal seta and several ventral setae. Propodus slender, well curved, without prominent heel but with 3 heel spines, 7 or 8 shorter sole spines and several long lateral and dorsal setae. Claw slender, well curved, half propodus length, auxiliaries more slender, equal in length to main claw, slightly more curved.

Female slightly larger than male except for smaller and shorter oviger. Lateral process and coxae tubercles not as long as those of male.

MEASUREMENTS (holotype, in mm).—Trunk length (anterior rim of cephalic segment to tip 4th lateral processes), 2.14; trunk width (across 2nd lateral processes), 1.51; proboscis length, 1.63; abdomen length, 1.36; third leg, coxa 1, 0.49; coxa 2, 0.75; coxa 3, 0.5; femur 1.55; tibia 1, 1.75; tibia 2, 1.39; tarsus, 0.19; propodus, 0.84; claw, 0.42.

DISTRIBUTION.—Known only from the Sanriku-oki area, east of northern Honshu, in 430 to 1440 m.

ETYMOLOGY.—The species name is from the Latin gracilis (slender or thin), and refers to the generally slender habitus of the specimens and to the slender lateral processes in particular.

DISTRIBUTION.—This species was described from specimens taken from Sagami Bay in depths of 30–174 meters. These additional records extend its distribution to the south and into considerably deeper water at 416 meters. It should be noted that, at station 7, Cilunculus armatus and C. sekiguchii were also collected as were the latter species and C. galeritus at station 15. These four species apparently have a broad depth tolerance.

MATERIAL EXAMINED.—HONSHU: Suruga Bay, 34°54.0′N, 138°43.7′E, 337–355 m, KT74-14, sta B8, 23 Sep 1974 (1, 1). Kii Strait, 33°28.6′N, 135°42.1′E, 353–416 m, KT84-12, sta 7, 31 Aug 1984 (1); 33°28.6′N, 135°28.9′E, 353–354 m, KT84-12, sta 15, 1 Sep 1984 (1); 33°28.l′N 135°28.5′E, 455–492 m, KT84-12, sta 16, 1 Sep 1984 (1).

DISTRIBUTION.—This species was known only from its type series collected in Sagami and Suruga bays in depths from 30 to 300 meters. These specimens extend its distribution to the south at Kii Strait and to a maximum known depth of 492 meters. Besides the above species, C. armatus and C. haradai were also collected at station 7, while at station 15, C. galeritus, C. haradai, and C. sewelli were also trawled. It is possible that these collecting stations are at the depth preferred by these species.