Pseudanthessius dentatus, 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 : 419-423

Pseudanthessius dentatus n. sp.

( Figures 32 ±34)

Material examined. Eight mm and four 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 (six mm, two ll) have been deposited in the US National Museum of Natural History , Smithsonian Institution. Dissected specimens (one m and three l) are kept in the collection of the author.

Female. Body (®gure 32A) narrow, 0.89 mm long. Greatest width 0.31 mm. Prosome ®ve-segmented, occupying 58% of body length, with weak segmentation between cephalosome and ®rst pedigerous somite. Fourth pedigerous somite tapering laterally, weakly notched at end. Urosome (®gure 32B) slender, tapering and ®vesegmented. Fifth pedigerous somite 125 mm wide, with membranous fringe on both sides of posterior margin. Genital double-somite 135Ö 96 mm, with weakly expanded anterior two-thirds and narrower, slightly tapering, posterior one-third. Genital area located laterally. Three abdominal somites 36 Ö54, 19 Ö48, and 42Ö 42 mm, respectively. Second abdominal somite very short. Anal somite as long as wide, more than twice as long as second abdominal somite. Caudal ramus elongate, 113Ö 16 mm (7.06:1), slightly broadened distally. Outer lateral seta of caudal ramus located at 75% length of caudal ramus. This and inner dorsal seta naked. Other setae plumose.

Rostrum narrow, much longer than wide, with rounded posterior tip. Antennule (®gure 32C) seven-segmented and 222 mm long. First two segments broader. Armature formula 4, 13, 6, 3, 4 +1 aesthetasc, 2 +1 aesthetasc, and 7 +1 aesthetasc. Terminal segment short, blunt, half as long as penultimate segment. All setae naked. Antenna (®gure 32D) slender and four-segmented. Armature formula 1, 1, 2 +1 claw, and 3 +4 claws. Second segment slightly broadened distally, with minute spinules on outer margin. Terminal segment about 50Ö 18 mm (2.78:1). Claws on third and terminal segments slender, setiform.

Labrum (®gure 32E) deeply incised, with relatively long and narrow lobes. Posterior margin of both lobes fringed with broad membrane. Mandible (®gure 32F) with one spiniform outer scale. Concave margin with three large teeth and several spinules. Lash blunt and terminally twisted. Maxillule (®gure 32G) with three terminal (one of them broad) and one lateral setae. Maxilla (®gure 32H) twosegmented. First segment unarmed. Second segment distally with four strong spines (one of them on outer surface) and terminating in a thin, spinulated lash, and with three setae; seta on outer margin minute; seta on concave margin thick and curved basally, with spinules; seta on outer surface characteristic, terminating in four spiniform processes and one setule. Maxilliped (®gure 33A) three-segmented. First segment longest, margins nearly parallel. Second segment with one spiniform seta based on elevation on inner margin and one remotely isolated seta. Third segment sharply tapering, pointed at end, proximally with one spiniform seta and one small seta, and ornamented with setules on outer margin.

Leg 1 (®gure 33B), leg 2 (®gure 33C) and leg 3 with three-segmented rami. Leg 4 (®gure 33E) with three-segmented exopod and one-segmented endopod. Endopod of leg 4 longer than combined ®rst two exopodal segments, with deep notch and process on outer margin; terminal two spines subequal. Armature formula of legs 1±4 as follows:

Leg 5 completely incorporated into ®fth pedigerous somite, leaving only one seta on dorsal surface near corner of somite, and one slightly curved spine, one naked seta and one spinule on corner of somite (®gure 33F). Terminal spine and seta identical in length. Leg 6 represented by 1 spine and 1 seta in genital area (®gure 33F).

Male. Body (®gure 34A) resembling that of female, 0.85 mm long. Greatest width 248 mm. Urosome six-segmented. Genital somite nearly quadrangular, slightly longer than wide. Caudal ramus 4.55 times as long as wide.

Antennule with two additional aesthetascs, each on second and fourth segments (indicated by dark dots in ®gure 32C). All aesthetascs extending beyond distal end of antennule. Antenna with two larger spinules in addition to minute spinules on outer margin of second segment.

Maxilliped (®gure 34B) composed of three segments and claw. First and third segments unarmed. Second segment with two longitudinal rows of spinules and two simple setae on inner surface. Claw very long, curved weakly and evenly, much longer than basal three segments combined, proximally with one spiniform process and one broad seta. Other mouth parts as in female.

Legs 1±4 as in female, without sexual dimorphism. Leg 5 as in female, but terminal spine nearly straight (®gure 34C).

Etymology. The speci®c name is derived from the Latin dentatus , meaning`toothed’, and alludes to the presence of large teeth on the blade of the mandible.

Remarks. The most distinctive feature of the new species is the mandible in which the convex side bears one scale (or tooth), and the concave side three large teeth. In other known species of Pseudanthessius , the maximum armature on the mandible is, as far as known, one scale (or tooth) on each convex and concave side as in P. limatus Humes, 1978 . Eleven other species bear only a single tooth on the mandible. Among these 12 species there are only two species, viz. P. de®ciens Stock, Humes and Gooding, 1964 and P. limatus Humes, 1978 both from the western Atlantic, in which the caudal ramus is long, more than six times as long as wide. Pseudanthessius de®ciens di ers from P. dentatus n. sp., as well as from all other known congeners, in bearing a four-segmented urosome. Pseudanthessius limatus di ers from the new species in its anal somite being slightly longer than the preanal somite (ratio 1.2:1, in contrast to 2.2: 1 in the new species), the lateral margins of the genital double-somite being straight and bearing processes, and the antenna with one distinct claw on the third segment but no claw on the terminal segment.

Pseudanthessius dentatus is very similar to P. aestheticus Stock, Humes and Gooding, 1964 . Both species have a similar body form, long caudal rami and anal somite, and same armature for the antenna. However, P. aestheticus has, unlike P. dentatus , an unarmed mandible, sexually dimorphic leg 1, and slender, simple endopod of leg 4 without notch or point.

Except for the characteristic mandible, a combination of the following diagnostic features of P. dentatus can be used to separate the Korean species from all of its congeners: (1) the caudal rami are very slender, with a ratio of length to width 7.06, (2) the anal somite is more than twice as long as the pre-anal somite, (3) the antenna carries four setiform claws on the terminal segment, in addition to setae, (4) the endopod of leg 4 has a notch and a point on the outer margin, and (5) there are one setiform claw and two setae on the inner distal corner of the third antennary segment.

Figures

FIG. 32. Pseudanthessius dentatus n. sp., female: (A) habitus, dorsal; (B) urosome, dorsal; (C) antennule; (D) antenna; (E) labrum; (F) mandible; (G) maxillule; (H) maxilla. Scales: A = 0.1 mm; B±D =0.05 mm; E±H = 0.02 mm.