Caligus brevicaudus Pillai, 1963

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 : 51-52

Caligus brevicaudus Pillai, 1963

( Fig. 23 )

Material examined. 2♀♀, 1♂ from Caranx ignobilis (Forsskål, 1775) (TC17579) 25 June 2016; 1♀, 1♂ QM Reg. No. W53059 ; 1♀ NHMUK Reg. No. 2017.248.

Site on host. gill arches.

Differential diagnosis. Cephalothorax dorsoventrally flattened with well-developed marginal membranes along lateral zones; frontal plates with lunules ( Fig. 23A ); thoracic zone small, posterior margin about level with posterior margins of lateral zones. Genital complex about 1.1 to 1.2 times longer than wide; abdomen small, 1- segmented, wider than long; genital complex about 4.3 times longer than abdomen (including caudal rami). Antenna with well developed posterior process on proximal segment. Post-antennal process bifid ( Fig. 23B ), tine without marginal flange; associated papillae bisensillate, unisensillate papilla on adjacent cephalothoracic surface.

Posterior process of maxillule bifid ( Fig. 23C ); smaller outer tine arising near base of main (inner) tine. Maxilliped of female with bilobed swelling on surface and fold in myxal area; claw strongly recurved with striations along concave margin ( Fig. 23D ). Sternal furca with blunt tines bearing conspicuous flanges ( Fig. 23E ). Distal exopodal segment of leg 1 with 3 short plumose setae on posterior margin ( Fig. 21F ); distal spine 1 longer than other spines; spines 2 and 3 each with accessory process; seta 4 longer than spines 2 and 3, shorter than segment. Leg 2 with marginal setules on endopodal segments 2 and 3; outer spines on exopodal segments 1 and 2 aligned close to longitudinal axis of ramus. First exopodal segment of leg 3 with large recurved outer spine but lacking inner seta ( Fig. 23G ); apron with raised bifid rib-like process plus circular array of large denticles on ventral surface and corrugated adhesion pad on outer margin and adjacent dorsal surface. Leg 4 uniramous, 4-segmented; exopodal segments armed with I; I; III spines. Leg 5 comprising exopodal papilla bearing 2 setae, located adjacent to protopodal papilla bearing single seta ( Fig. 23H ). Body lengths of females 1.93 mm and 2.19 mm; length of male 1.66 mm.

Remarks. This is a distinctive but uncommon member of the Caligus confusus -group. It was originally described by Pillai (1963), based on material of both sexes collected from an unspecified species of Caranx Lacepède, 1801 caught off Trivandrum ( India). However, there have been no new records since the original description although it was widely cited, e.g. in reviews by Pillai (1967b, 1968) and in his monograph (1985). It is also interesting to note that this species has not been recorded from Taiwan, despite intensive study of Taiwanese waters by Ho & Lin (see Ho & Lin, 2004, 2007; Lin & Ho, 2007).

In Moreton Bay C. brevicaudus was found only on Caranx ignobilis , where it attached to the gill arches, the same microhabitat as C. confusus . At 1.93 to 2.19 mm the females found in Australian waters were only half the length of the Indian specimens, reported as 4.3 mm by Pillai (1963). Despite this marked size difference, no morphological differences were apparent.

Figures

FIGURE 21. Caligus bonito Wilson, 1905, female. A, habitus, dorsal; B, antenna, post-antennal process and maxillule drawn in situ; C, brachium of maxilla; D, maxilliped; E, sternal furca; F, leg 1; G, endopod of leg 2, showing denticulate ornamentation on lateral margin of first andsecond segments; H, outer spines on exopodof leg 2.Scale bars:1.0 mm on A, 200 µm on B–D, 100 µm on E–H.

FIGURE23.Caligus brevicaudus Pillai, 1963, female.A, habitus, dorsal; B, bifid post-antennal process; C, bifid maxillule;D, maxilliped; E, sternal furca; F, distal exopodal segment of leg 1; G, leg 3; H, leg 5. Scale bars: 1.0 mm on A, 200 µm on B, C, G, H, 100 µmon E, F, 50 µm on D.