Pseudomacrochiron urostenum, Kim, 2000

Kim, Il-Hoi, 2000, Poecilostomatoid Copepods from an Intertidal Mud Flat in the Yellow Sea, Journal of Natural History 34 (3), pp. 367-432 : 415-419

Pseudomacrochiron urostenum n. sp.

( Figures 29 ±31)

Material examined. Seven mm and ®ve llcollected from stagnant water on the intertidal mud ¯at at Jakyak-do Island o Inchon, on 29 September 1996. Holotype (m), Allotype (l), and eight paratypes (®ve mm, three ll) have been deposited in the US National Museum of Natural History , Smithsonian Institution. Dissected specimens (one m and one l) are kept in the collection of the author .

Female. Body (®gure 29A) slender, 1.03 mm long. Prosome ®ve-segmented. Segmentation between cephalosome and ®rst pedigerous somite distinct. Lateral margins of second pedigerous somite almost straight, its posterior corners pointed. Lateral margins of third and fourth pedigerous somites with narrow membranous fringe. Urosome (®gure 29C) slender and ®ve-segmented. Fifth pedigerous somite 97 mm wide. Genital double-somite 132Ö 98 mm, with moderately expanded anterior part and narrower posterior part; genital area located at area of maximum width in expanded anterior part. Three abdominal somites 33 Ö56, 27 Ö53, and 67Ö 51 mm, respectively. Anal somite distinctly longer than wide, longer than combined preceding two abdominal somites, with minute spinules on posteroventral margin. Caudal ramus elongate, 120Ö 19 mm (6.32:1), with six setae. Outer lateral seta located at 61% length of caudal ramus.

Rostrum (®gure 29B) longer than wide, tapering, with angular posterior tip. Antennule seven-segmented, 259 mm long, with armature formula 4, 13, 6, 3, 4 +1 aesthetasc, 2 +1 aesthetasc, and 7 +1 aesthetasc. All setae naked. Antenna (®gure 29E) slender and four-segmented, with armature formula 1, 1, 2 +1 claw, and 5 +2 claws. Claws on third and fourth segments slender, setiform. Fourth segment about 55 Ö 18 mm (3.06:1).

Labrum (®gure 29F) widely incised; posterior margins of both lobes fringed with narrow membrane. Mandible (®gure 29G) with deep proximal notch; terminal lash long, slender, spinulated, and well de®ned proximally; inner margin with one row of spinules; outer margin with proximal row of spinules and continued to serrate margin. Maxillule (®gure 29H) tapering, with three terminal and one subterminal setae. Maxilla (®gure 29I) two-segmented. First segment unarmed. Second segment drawn out into relatively short lash bearing spines on convex margin and one spiniform process on concave margin, with two setae and one proximal setule; seta on concave margin small and plumose. Maxilliped (®gure 30A) three-segmented. First segment longest and unarmed. Second segment with two identical setae on inner margin proximal to middle. Third segment tapering and terminating in sharp point, with two proximal (one being spiniform) and two distal setae.

Leg 1 (®gure 30B), leg 2 (®gure 30C) and leg 3 with three-segmented rami. Leg 4 (®gure 30D) with three-segmented exopod and one-segmented endopod. Endopod of leg 4 shorter than combined ®rst two segments of exopod, 52 Ö 19 mm, with small spiniform process on outer margin; both margins with hairs; two terminal spines subequal. Armature formula of legs 1±4 as follows:

Leg 5 consisting of one seta on ®fth pedigerous somite and free segment (®gure 30E). Free segment small, lobate, 26Ö 16 mm (1.63:1), with several setules on convex inner margin and terminally with one long spine (65 mm), one seta (45 mm) and one spiniform process. Leg 6 represented by one seta and two spinules in genital area (®gure 30E).

Male. Body (®gure 31A) 0.67 mm long. Greatest width 0.20 mm. Lateral margins of prosome nearly parallel. Urosome (®gure 31B) two-segmented. Fifth pedigerous somite 62 mm wide. Genital somite 107Ö 93 mm. Four abdominal somites 21 Ö44, 22 Ö38, 19 Ö36, 33 Ö 34 mm, respectively. Caudal ramus 63Ö 22 mm (2.86:1). Outermost terminal seta transformed, basally thickened.

Antennule with three additional aesthetascs: two on second and one on third (opposite to dark dots in ®gure 29D). All aesthetascs large, extending beyond end of antennule. Antenna spinulated on inner surface of second segment, otherwise, identical to that of female.

Maxilliped (®gure 31C) with unarmed ®rst and third segments. Second segment proximally narrow and distally expanded, with one longitudinal row of spinules and two setae on inner side; the latter two located proximal to middle of segment, and one of them slightly expanded in proximal two-thirds. Claw long, weakly curved, as long as proximal three segments combined, with proximally one seta and one setule.

Leg 1 with terminal endopodal segment bearing two spines and four setae (II, 4; instead of I, 5 as in female) (®gure 31D). Legs 2±4 as in female. Free segment of leg 5 (®gure 31E) ovoid, 19Ö 12 mm (1.58:1), both margins convex. Terminal spine 32 mm, and seta 37 mm. Leg 6 represented by two setae and one spiniform process on genital ¯ap (®gure 31B).

Etymology. The speci®c name urostenum is derived from the Greek oura (= tail) and stenos (= narrow), alluding to the narrow urosome of this species.

Remarks. The genus Pseudomacrochiron consists of ®ve incompletely described species: P. fucicolum (T. Scott, 1912) ; P. malayense ( Sewell, 1949) ; P. ornatum (Krishnaswamy, 1952) ; P. parvum (A. Scott, 1908) ; P. stocki Reddiah, 1969 .

Pseudomacrochiron urostenum n. sp. can be distinguished from those ®ve species by the structure of the caudal rami and female leg 5. The new species has long caudal rami with a length to width ratio of 6.32 in contrast to less than 4 in the other ®ve species. The free segment of leg 5 of the new species is very short, with the ratio of length to width being 1.63, while this ratio in the other known species is more than 3.

Figures

FIG. 29. Pseudomacrochiron urostenum n. sp., female: (A) habitus, dorsal; (B) rostrum; (C) urosome, dorsal; (D) antennule; (E) antenna; (F) labrum; (G) mandible; (H) maxillule; (I) maxilla. Scales: A =0.1 mm; B±E= 0.05 mm; F±I= 0.02 mm.