Clausia lobata, 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 : 375-380

Clausia lobata n. sp.

( Figures 4 ±6)

Material examined. Thirty-six mm and three llcollected from the polychaete, Marphysa sanguinea (Montagu) , in the intertidal mud ¯at of Jakyak-do Island o Inchon, on 1 September 1996. Holotype (m), allotype, and 23 paratypes (22 mm and one l) will be deposited in the US National Museum of Natural History , Smithsonian Institution. Thirteen mm and one l(including two mm and one; l dissected) are kept in the collection of the author.

Female. Body (®gure 4A) small, 650 mm long. Greatest width 265 mm.

Ventrolateral sides of cephalothorax with many wavy adhesion ridges (®gure 5A).

Rostral area of cephalothorax projected, broad, truncate anteriorly, and demarcated by a faint line from remaining part of cepahlothorax. Third pedigerous somite narrower but distinctly longer than second pedigerous somite. Fourth pedigerous somite with characteristic lobate protuberance on each lateral side. Urosome (®gure 4B, C) six-segmented. Fifth pedigerous somite 103 mm wide, distinctly wider than genital somite. Genital somite 49Ö 83 mm, or 1.69 times wider than long, nearly quadrangular, wider posteriorly. Demarcation between genital and ®rst abdominal somites distinct dorsally but obscure ventrally. Abdomen slightly tapering. Four abdominal somites 43 Ö53, 38 Ö45, 28 Ö40, 25 Ö 39 mm, respectively. Anal somite with two pairs of membranous ¯aps, each proximally and distally on ventral surface.

Caudal rami divergent, 32 Ö 16 mm (2.0:1). Outer lateral seta located two-thirds length of ramus. Two mid-terminal setae weakly pinnate in distal half. Other four setae naked. Egg sac elongate, longer than urosome, 323Ö 105 mm, containing relatively large eggs.

Rostrum completely incorporated into cephalothorax, leaving only faint boundary (®gure 5A). Antennule (®gure 4D) six-segmented and 142 mm long, with armature formula 4, 9, 9, 4 +1 aesthetasc, 2 +1 aesthetasc, and 7 +1 aesthetasc. Plumose setae are one on both fourth and ®fth segments and three on terminal segment. First segment distinctly broader than long. Antenna (®gure 4E) three-segmented, with armature formula 1, 0, and 7. Second segment with three membranous ¯aps. Third segment slightly broadened distally, with one membranous ¯ap; outermost seta on terminal segment plumose, and longest. Innermost seta broadened, spiniform, with membrane on inner margin and tipped with minute spinule. Other ®ve setae naked.

Labrum reduced, not covering mouth parts, with narrow posterior margin (®gure 5B). Mandible (®gure 5C) small, armed terminally with two spiniform elements of di erent sizes. Maxillule with three setae terminally and protuberance on inner side; outer one of these setae plumose on outer side, but other two setae naked. Maxilla largest among mouth parts, one-segmented, with three membranous ¯aps posteroventrally and two sclerotized blades distally, without seta or spine.

Maxilliped (®gure 5D) three-segmented, blunt, and unarmed. Third segment short, distally truncate, blade-like and indistinctly marked from second segment.

Leg 1 (®gure 5E), leg 2 (®gure 5F) and leg 3 with three-segmented rami. Leg 4 (®gure 6A) with two-segmented rami. All spines on rami of these legs setiform. Inner spine on posterior margin of leg 1 thick but short. Membranous ¯aps seen on intercoxal plate, coxa, basis and segments of rami of legs 1±4. Outer seta on basis of leg 3 slender compared with that of leg 2, and that of leg 4 naked. Legs 3 and 4 without inner seta of coxa. Armature formula of legs 1±4 as follows:

Leg 5 two-segmented (®gure 4B, C). Both segments each with three membranous ¯aps. Basal segment well de®ned from ®fth pedigerous somite, with one outer distal seta mounted on digitiform elevation. Distal segment nearly quadrate, 25 Ö 20 mm, with four long, naked terminal setae. Leg 6 represented by one spinule in genital area.

Male (in amplexus). Body (®gure 6B) distinctly tapering, very small. Length 0.37 mm. Greatest width 177 mm. Urosome (®gure 6C) six-segmented. Fifth pedigerous somite wider than genital somite. Genital somite 30Ö 52 mm, dorsally well marked from, but ventrally fused with, ®fth pedigerous somite. Genital ¯ap not seen. Four abdominal somites 26 Ö42, 21 Ö35, 18 Ö30, and 18Ö 28 mm, respectively. Anal somite with membranous ¯ap on each side of ventral surface. Caudal ramus 18 Ö 11 mm (1.64:1).

Maxilliped (®gure 6D) three-segmented. First segment very short and unarmed. Second segment with seven small tubercles on inner surface. Third segment the longest, tapering and claw-like, with one tubercle proximally and one curved row of small bead-like spinules. Other mouth organs as those of female.

Endopod of leg 1 two-segmented. First segment with one inner seta. Second segment with four setae. Legs 2±4 with armature formula identical to that of female.

Basal segment of leg 5 completely incorporated into ®fth pedigerous somite, leaving one long seta near base of free segment. Free segment small, lobate, 7.7 Ö 4.6 mm (1.67:1), with four setae. Leg 6 not observed.

Etymology. The speci®c name lobata alludes to the large, lobate lateral processes on the fourth pedigerous somite.

Remarks. Copepods of the Clausiidae may be divided into two groups based on the body form. One group, containing Pherma Wilson, 1923 , Rhodinincola Levinsen, 1878 (= Seridium Giesbrecht, 1895 ), and Stockia Sebastian and Pillai, 1974 , displays a vermiform body or displays reduced tagmosis. The other group, consisting of Clausia ClapareÁde, 1863 , Indoclausia Sebastian and Pillai, 1974 , Megaclausia O’Reilly, 1995 , Mesnilia Canu, 1897 , Pseudoclausia Bocquet and Stock, 1960 , and Pontoclausia BaÏcescu and Por, 1959 , show the normal body form. The latter group, to which Clausia lobata n. sp. belongs, shows various reductions in the leg segmentation. This reduction in leg segmentation proceeds anteriorly from the fourth to the ®rst legs. A complete leg segmentation is present in the genus Pontoclausia , the intermediate state in Megaclausia , Mesnilia and Pseudoclausia , and the most reduced leg segmentation in Clausia . Gooding (1963) rejected this classi®cation due to the overlap in various characters between these genera. Gooding’s classi®cation is preferred in the present report, particularly because Clausia lobata n. sp. is another example demonstrating this morphocline. Indoclausia Sebastian and Pillai, 1974 shows no signi®cant di erence from the Clausia s. str. and therefore is incorporated into Clausia .

Clausia lobata shows completely segmented rami on leg 3 and two-segmented rami on leg 4. In this respect this species appears intermediate between the Pontoclausia -group and the Mesnilia -group. At present the `Pontoclausia -group’ comprises Clausia tomis (BaÏcescu and Por, 1959) and the unpublished C. wilsoni Gooding, 1963 , and the `Mesnilia- group’ consists of C. cluthae T. and A. Scott, 1896, C. martinensis (Canu, 1898) and C. mirabilis (O’Reilly, 1995) . Clausia lobata di ers from these ®ve species, respectively, in the small body (only 0.65 mm long), the relatively broad prosome (not harpacticiform), a pair of prominent lobate processes on the fourth pedigerous somite, and no claw-like element on the terminal segment of the antenna.

Although C. lobata di ers from the `Clausia s. str. -group’ in the morphology of the legs and other appendages, it shows some a nities with the latter group in the four-segmented female urosome, a well-developed female leg 5, a three-segmented antenna, and sexual dimorphism in the segmentation of the endopod of leg 1.

Most species of Clausia were described on the basis of few specimens and it has been assumed that at least some members are associated with annelids ( Gooding, 1963). Therefore, the association of C. lobata with Marphysa sanguinea seems to be the ®rst unambiguous host record for the genus Clausia .

Figures

FIG. 4. Clausia lobata n. sp., female: (A) habitus, dorsal; (B) urosome, dorsal; (C) same, ventral; (D) antennule; (E) antenna. Scales: A = 0.1 mm; B±C= 0.05 mm; D = 0.02 mm; E= 0.01 mm.