Caligus triabdominalis Byrnes, 1987

Boxshall, Geoff, 2018, The sea lice (Copepoda: Caligidae) of Moreton Bay (Queensland, Australia), with descriptions of thirteen new species, Zootaxa 4398 (1), pp. 1-172 : 127

Caligus triabdominalis Byrnes, 1987

( Fig. 59 )

Material examined. 1♀ from Pomatomus saltatrix (Linnaeus, 1766) (TC17696) 28 June 2016, QM Reg. No. W63113.

Site on host. Roof of mouth.

Differential diagnosis. Cephalothorax dorsoventrally flattened with well-developed marginal membranes along lateral zones of dorsal cephalothoracic shield; frontal plates with lunules. Genital complex with constricted anterior neck region; complex 1.35 times longer than wide with rounded posterolateral corners; abdomen elongate, 2.5 times longer than wide; shorter than genital complex ( Fig. 59A ). Antenna with small, blunt posterior process on proximal segment ( Fig. 59B ). Post-antennal process with weakly curved tine; associated papillae bisensillate ( Fig. 59B ). Maxillule with simple tine on posterior process. Maxilliped of female with slight expansion on myxal margin. Sternal furca with slender, diverging tines ( Fig. 59C ). Distal exopodal segment of leg 1 with 3 plumose setae on posterior margin, basal setules on margin of plumose setae nearest apex unusually stout; distal spine 1 simple, longer than spines 2 and 3, each armed with accessory process; seta 4 about twice as long as spines and about as long as segment. Leg 2 with strong denticles along outer margin of endopodal segment 2 ( Fig. 59D ); outer spines on exopodal segments 1 and 2 lying obliquely across axis of ramus; proximal outer spine on segment 3 tiny, much shorter than distal spine ( Fig. 59E ). Leg 3 with 3-segmented exopod ( Fig. 59F ); first segment bearing small slightly curved spine, lacking inner seta; second segment with outer spine and inner seta; third segment with 3 long spines, plus 4 plumose setae; distal endopodal segment with swollen lateral margin. Leg 4 uniramous, 3- segmented; exopodal segments 1 and 2 with I and IV spines, respectively ( Fig. 59G ). Body length 3.81 mm.

Remarks. The original description of C. triabdominalis was based on material of both sexes collected from Acanthopagrus latus caught off Broome, Western Australia (Byrnes, 1987). When establishing it as a new species, Byrnes (1987) only made detailed comparisons with C. omissus , therefore some additional comparisons with other related species are included here. The distinctive features of C. triabdominalis are its long genital complex and long abdomen combined with the presence of stout denticles along the outer margins of endopodal segment 2 of leg 2 and the 2-segmented exopod of leg 4 bearing 4 spines on the distal segment. It shares these characteristics with a group of congeners including: C. asperimanus , C. biseriodentatus , C. bonito , C. hoplognathi , C. malabaricus , C. mutabilis , and C. tenuifurcatus Wilson, 1937 . Caligus bonito , C. mutabilis and C. omissus all possess patches of fine spinules posteriorly on the ventral surface of the abdomen, which are absent in C. triabdominalis . In C. biseriodentatus the posterior margin setae on the distal exopodal segment of leg 1 are all very reduced in size, whereas they are well developed in C. triabdominalis . In C. malabaricus the female genital complex is wider than long and the first somite of the abdomen is twice as wide as the second, while in C. triabdominalis the genital complex is longer than wide and the two abdominal somites are similar in width. Caligus triabdominalis is similar to C. asperimanus as redescribed by Cressey (1991) in body proportions but differs in the size and shape of the tines of the sternal furca and in having a more slender distal exopodal segment on leg 4 with spines that differ in relative length. In female C. hoplognathi the abdomen is twice as long as wide, compared to 2.5 times longer in C. triabdominalis and the sternal furca is flanked by a pair of accessory processes ( Yamaguti & Yamamsu, 1959). Finally, C. tenuifurcatus , as the name suggests, has long slender tines on the sternal furca that are longer than the box ( Wilson, 1937b) whereas those of C. triabdominalis are shorter than the box of the furca.

The females in the type material had a body length ranging from 4.00 to 4.18 mm (Byrnes, 1987). The sole female collected in Moreton Bay was found in the mouth of a new host, Pomatomus saltatrix , and was a little smaller, with a body length of 3.81 mm. This is the first record of C. triabdominalis from Queensland.

Figures

FIGURE59. Caligus triabdominalis Byrnes, 1987, female. A, habitus, dorsal; B, antenna, post-antennal processand maxillule drawn in situ; C, sternal furca; D, endopod of leg 2; E, outer margin spines on exopodof leg2; F, exopodof leg 3; G, exopodof leg 4. Scale bars:1.0 mm on A, 100 µm on B, C, 50 µm on D–F, 200 µm on G.