Paraergasilus dichotomus, El-Rashidy & Boxshall, 2001

El-Rashidy, Hoda & Boxshall, Geoffrey A., 2001, Biogeography and phylogeny of Paraergasilus Markevich, 1937 (Copepoda: Ergasilidae) with descriptions of two new species from the gills of grey mullet, Journal of Natural History 35 (12), pp. 1807-1819 : 1808-1811

Paraergasilus dichotomus n. sp.

(®gures 1± 3)

Type material. Female holotype ( BMNH Reg. No. 1999.154 0); 10 female paratypes ( BMNH Reg. Nos 1999.1541 ±1550) .

Type locality. New South Wales, Australia .

Type host. Mugil cephalus Linn.

Site of infection. Gill rakers.

Etymology. The speci®c name refers to the dichotomously branched claw on the antenna.

Description of female

Body small, cephalothorax irregularly oval-shaped, without lateral stylets, mean body length 0.47 Ô 0.03 mm, mean body width 0.20 Ô 0.02 mm (n 57). First pedigerous somite incorporated into cephalothorax. Free pedigerous somites decreasing in width posteriorly (®gure 1A). Genital double-somite barrel-shaped, nearly as long as wide (®gure 1B), and nearly as long as three free abdominal somites combined; ventral surface ornamented with seven rows of spinules plus posterior margin row. First and second free abdominal somites nearly equal in length; anal somite slightly shorter than preceding somite; each somite ornamented with single ventral spinule row along posterior margin. Caudal rami slightly longer than anal somite; row of spinules present posteriorly; armed with large plumose medial seta, three other setae increasing in length laterally.

Antennule ®ve-segmented (®gure 2A), ®rst segment largest; setal formula as follows: 16, 51 ae, 41 ae, 21 ae, 71 ae; several setae plumose. Aesthetasc on terminal segment sharing common base with adjacent seta, as typical for members of family. Antenna four-segmented with three curved terminal claws (®gure 2B). Coxobasis long, widest proximally, with inner distal seta. First endopodal segment about 3.5 times longer than average width; armed with bi®d spine near middle of medial margin. Second endopodal segment about twice as long as wide, bearing one small spinule proximally and one distally on concave margin: third endopodal segment small; second and third segments together constituting nearly half of ®rst endopodal segment length. Third endopodal segment bearing six setal elements, including three terminal claws. Inner claw longest, bi®d, constituting about 1.5 times length of second and third segments combined; median claw shortest, slightly less than second and third endopodal segments combined; outer claw about 1.2 times length of these segments, additional armature comprising one blunt element on inner margin and two small spinules, one each at base of outer and medial claws (®gure 2C).

Mandible unsegmented, bearing anterior, mid and posterior blades: anterior blade with teeth on anterior margin; middle blade with spinules anteriorly and strong teeth posteriorly; posterior blade with teeth on posterior margin. Maxillule lobate bearing two outer setae and minute process medially. Maxilla consisting of large syncoxa tapering distally and small spatulate basis, armed anteriorly with rows of sharp teeth (®gure 1C).

Swimming legs 1±4 (®gure 3A±C) with rami three-segmented, except twosegmented exopod of leg 4. Outer seta on posterior surface of basis in all legs. Basis of leg 1 with distal spinule row. Setules present on inner margins of ®rst exopodal segments of all legs. Posterior margin of interpodal plates lacking ornamentation. Exopod of leg 1 modi®ed, ¯attened; second and third exopodal segments particularly broad, and with thickened cuticle along outer margin (®gure 3A). Endopod of leg 1 with lateral row of large spinules on ®rst segment, plus rows of ®ne spinules on second and third segments. Spine and seta formula in table 1.

Fifth leg (®gure 3D) small, with protopodal segment fused to somite; outer basal seta located dorsally; free exopodal segment armed with two long terminal setae and small lateral seta.

Remarks

The new species can be grouped with those Paraergasilus species that lack a pair of posterolateral stylets on the cephalothorax; this group comprises the following seven species: P. remulus , P. lagoonaris , P. minutus , P. in X atus, P. reductus , P. dentatus and P. acanthopagri . It diOEers from these and from all previously described Paraergasilus species in the presence of a bi®d claw on the antenna (see below).