Neoacrenhydrosoma zhangi, Gee & Mu, 2000

Gee, J. M. & Mu, F-H., 2000, A new genus of Cletodidae (Copepoda; Harpacticoida) from the Bohai Sea, China, Journal of Natural History 34 (6), pp. 809-822 : 811-819

Neoacrenhydrosom a zhangi sp. nov.

(®gures 1±6)

Material examined

HOLOTYPE: adult female (dissected on to three slides) from muddy sand at 19 m depth in Bohai Bay , NHM Reg. No. 1999.675 . PARATYPES: one male (dissected on to three slides) and two whole and one partial female, spirit preserved, NHM Reg. Nos 1999.676 ±679.

Description of female

Body (®gure 1). Length 0.47±0.51 mm (mean5 0.49 mm, n 5 3) semi-cylindrical, tapering posteriorly from posterior border of cephalothorax, without clear distinction between prosome and urosome. Cephalothorax almost square with pattern of subcuticular ribs and sensilla as in ®gure 1; posterior border smooth with six small sensillum-bearing socles. Free prosomites and urosomites with pattern of subcuticular ribs in anterior region of somite as in ®gure 1A; presence of tube pores not discerned because of dirt on specimens; dorsal and lateral posterior borders smooth, with four to eight sensillum-bearing socles, four of which particularly prominent and spinulose on each urosomite (®gure 2B); dorsal socles on preanal somite with tube pores rather than sensilla. Ventral border of urosomites minutely spinulose (®gure 2A) and, on urosomites 3±4, with two strongly spinulose, sensillum-bearing socles (®gure 2D). Urosomites 2±3 fused to form genital double-somite, line of fusion marked dorsally and laterally by presence of socles, and ventrally by subcuticular rib. Anal operculum in posterior half of anal somite (®gure 2B), semi-circular, minutely dentate, bordered by pair of small sensillum-bearing socles. Caudal rami (®gures 1C, 2B) elongate, cylindrical, tapering posteriorly, approximatel y ®ve times longer than basal width, setae I and II implanted at 25%, setae III and VII at 34% of ramus length, distal seta IV small, fused at base to well-developed, minutely pinnate seta V, seta VI very small; outer margin with two tube pores, one proximal to seta I, the other distal to seta III but variable in position.

Rostrum (®gure 2C). Fused to cephalothorax, recurved dorsally, triangular with slightly bi®d tip, pair of lateral sensilla and median ventral pore.

Antennule (®gure 3A). Short, stout, ®ve-segmented with one to four pinnate or pectinate setae on all segments except segment 4; segment 1 with four rows of spinules; segment 2 with a ¯exible penicillate seta; segment 3 with aesthetasc fused at base to one seta; segment 4 small, segment 5 with distal trithek of two smooth setae and a small aesthetasc. Setal formula as follows: 1[1], 2[8], 3 [6 1 (1 1 a)], 4 [1]. 5[9 1 (2 1 a)].

Antenna (®gure 4A). Coxa well developed with three rows of spinules. Allobasis with partial suture on dorsal surface in region of exopod, with a proximal pectinate seta and distal group of strong spinules on abexopodal margin. Exopod onesegmented bearing two large setae, distal seta with small, closely set pinnules, lateral seta with widely spaced, long pinnules. Free endopod with two rows of strong spinules on outer margin, and rows of smaller spinules on distal and inner margin; subdistal armature consisting of two large, strongly spinulose, spines and a small seta; distal margin armed with two pectinate spines, a smooth spine, two geniculate setae and a tube pore and small seta fused to base of inner spine.

Labrum (®gure 4B). Fused to form a single plate, with group of long spinules on anterior face and three rows of small spinules on distal margin.

Mandible (®gure 4C). Coxa relatively slender, with row of spinules on outer margin. Gnathobase with three bicuspid and one unicuspid teeth and a pinnate seta at dorsal corner. Palp one-segmented with two rows of long spinules and three pinnate setae (one basal and two endopodal).

Maxillule (®gure 4D). Praecoxa with row of spinules; arthrite with one subdistal seta, and three spines and two pinnate setae on distal margin. Coxa partially fused to basis, bearing two setae (one naked and one pinnate) on distal margin. Basis and rami completely fused into one-segmented palp with six setae (one pinnate seta exopodal, one seta endopodal, and four setae basal, in origin).

Maxilla (®gure 2E). Syncoxa with two rows of spinules and two endites each with three elements, all naked except for pinnate spine on proximal endite. Allobasal endite with fused, slightly dentate spine and two naked setae. Endopod represented by two setae not fused at base.

Maxilliped (®gure 4E). Well developed, subchelate. Syncoxa with large pinnate seta on distal margin. Basis oval with row of spinules on palmar margin and two rows on outer margin. Endopod represented by a claw (much longer than basis) and a large accessory seta.

P1 (®gure 5A). Intercoxal sclerite narrow, straight and naked. Praecoxa narrow, triangular without setules. Coxa with row of surface spinules near inner, distal and outer margin. Basis with row of spinules on distal margin and at base of inner and outer stout pinnate setae. Exopod three-segmented, each segment with row of spinules on outer and distal margin and row of setules on inner margin; two setae on distal margin of exp-3 without comb tips and outer seta very short (only equal in length to distal outer spine). Endopod two-segmented, each with row of spinules on outer and row of setules on inner margins; enp-2 three times longer than enp-1, distal margin with inner naked seta, a large pinnate seta without comb tip, and a large pinnate outer seta.

P2±P4 (®gures 5B, 6A). Protopod as for P1 except praecoxa with row of setules, coxa with extra proximal row of spinules, basis without inner seta. Exopod two-segmented, each with row of spinules on outer and distal margin and row of setules on inner margin; exp-1 with two outer spines and hyaline frill at inner distal margin. Endopod two-segmented, ornamented as in P1 but enp-2 armed with only

two elements. Setal formula of swimming legs as follows:

Exopod Endopod

P1 0.0.022 0.021

P2 0.022 0.020

P3 0.122 0.020

P4 0.122 0.020

P5 (®gure 6B). A large, strongly chitinized uniramous structure projecting laterally from the body (as in ®gure 1A) and triangular in shape. Wide basal portion ¯attened with a socket-like structure to the inner and outer basal corners, a long penduncle bearing one seta and articulating near the median proximal margin; a row of spinules, a pinnate spine and a tube pore on inner proximal margin. Distal portion long, cylindrical, recurved distally, sparsely covered with small setules but with a row of strong, blunt teeth and two setae on the outer margin, and a tube pore medially on inner margin.

Genital ®eld (®gure 2D). Vestigial P6s forming small ¯aps over gonopores, with two rows of strong spinules on face, two naked setae on distal margin (outer one short), and row of setules on inner margin. Unclear as to whether gonopores open into common genital slit or whether this fused medially. Copulatory pore small, opening at ventral subcuticular rib marking line of fusion of genital double-somite; single copulatory duct leading to paired seminal receptacles.

Description of male

As in female except in urosome, antennule and P5.

Body. Slightly smaller than female, length 0.46 mm. Genital somite (®gure 3D) separate, vestigial P6 forming small asymmetrical plate ornamented with row of setules but without armature elements.

Antennule (®gure 2B, C). Short, stout, seven-segmented, sub-chirocer with principal articulation between segments 5 and 6. Segment 1 with two rows of spinules; segment 2 with ¯exible penicillate seta and ®ve pectinate setae; segment 4 minute; segment 5 markedly swollen with row of spinules on anterior face, palmar margin with a dentate spine and a chitinous hump, distal margin with aesthetasc fused at base to one seta; segment 6 small with a spine; segment 7 hook-shaped with distal trithek of two naked setae and a small aesthetasc. Setal formula as follows: 1 [1], 2 [9], 3[8], 4[2], 5[9 1 spine 1 (1 1 a)], 6[1 1 spine], 7[7 1 (2 1 a)].

P5 (®gure 6C). As in female except row of spinules and spine absent from inner proximal margin (but tube pore probably still present).

Etymology. The speci®c name is in honour of Professor Zhang Zhi-nan of the Ocean University, Qingdao, whose enthusiasm for meiofauna research initiated this project.