Caligus biseriodentatus Shen, 1957

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 : 46-48

Caligus biseriodentatus Shen, 1957

( Fig. 20 )

Syns: Caligus obovatus Heegaard, 1962 Caligus proboscidatus Heegaard, 1962

Material examined. 1♂, 2 chalimus from Scomberomorus queenslandicus Munro, 1943 , (TC17388), 21 January 2016, NHMUK Reg. No. 2017.236; 2♀♀ from Auxis thazard (Lacepède, 1800) (TC 18122), 21 October 2016, 1♀ QM Reg. No. W53057 ; 1♀ NHMUK Reg. No. 2017.235.

Site on host. Body surface.

Differential diagnosis. Cephalothorax dorsoventrally flattened with well-developed marginal membranes; frontal plates with lunules. Genital complex 1.14 times longer than wide (measured along dorsal midline) with small posterolateral lobes; abdomen elongate, about 3.2 times longer than maximum width; just shorter than genital complex ( Fig. 20A ). Antenna with small, blunt posterior process. Post-antennal process with slender, weaklycurved tine; associated papillae each bisensillate. Posterior process of maxillule slender. Maxilla with smooth distal margin on brachium. Maxilliped of female with slight expansion on myxal margin. Sternal furca with broad, truncate, slightly diverging tines, with lateral flanges ( Fig. 20B ). Leg 1 with ornamentation of large spinules on sympod; distal exopodal segment ( Fig. 20C ) with 3 short plumose setae on posterior margin, basal setules on margin of plumose setae nearest apex unusually stout; distal spine 1 simple, longer than spine 2, spine 2 longer than spine 3, each armed with accessory process and serrated membrane; seta 4 about twice as long as spine 1 and just longer than segment. Leg 2 with strong denticles along outer margins of endopodal segments 1 and 2 ( Fig. 20D ); plumose setae on distal segments of both rami modified, with enlarged spinules basally ( Fig. 20E ); outer spines on exopodal segments 1 and 2 lying obliquely across axis of ramus. Leg 3 with 3-segmented exopod; first exopodal segment bearing slightly curved outer spine, lacking inner seta; second segment with outer spine and inner seta; third segment with 3 naked spines, plus 4 plumose setae. Leg 4 uniramous, 3-segmented; first and second exopodal segments with I and IV spines, respectively ( Fig. 20F ); apical spine on distal margin distinctly longer than adjacent middle spine; first exopodal segment ornamented with conspicuous denticles along outer margin. Body lengths of adult females 4.58 and 5.04 mm.

Male ( Fig. 20G ) with cephalothorax just longer than wide. Genital complex slender with weakly convex margins, about 1.26 times longer than wide. Abdomen 2-segmented; first and second somites subequal; abdomen about 2.6 times longer than wide, and about as long as genital complex. Fifth legs located ventrolaterally near lateral margin at about two thirds length of genital complex. Post-antennal process very large and more strongly recurved than in female; associated papillae multisensillate. Maxilliped ( Fig. 20H ) with conspicuous trifid process on myxal margin opposing tip of subchela. Sternal furca with strongly divergent tapering tines. Distal exopodal segment of leg 1 with 2 small plumose setae on posterior margin plus very small distal seta ( Fig. 20I ). Leg 2 with setae on distal segments of both rami plumose (not modified as in female). Leg 4 with smooth unornamented outer margin on first exopodal segment; 3 distal margin spines on second exopodal segment similar in length ( Fig. 20J ). Body length of male 3.03 mm.

Remarks. Caligus biseriodentatus was first described from immature specimens of both sexes obtained from Scomberomorus commerson (as Cybium commersoni ) in Chinese waters ( Shen, 1957). It is a member of the C. bonito -group of species characterized by the shared possession of a 3-segmented leg 4 armed with four spines on the compound second exopodal segment, in combination with the presence of the three plumose setae on the posterior margin of the distal exopodal segment of leg 1, and the possession of an ornamentation of large denticles along the outer margin of the second endopodal segment of leg 2. Within this group, C. biseriodentatus can be readily distinguished by the small size of the three plumose setae on the posterior margin of the distal exopodal segment of leg 1: in the female these setae are only about as long as spine 2 and have modified ornamentation ( Fig. 20E ). The male maxilliped of C. biseriodentatus has a conspicuous trifid myxal process.

In their large survey of parasitic copepods of scombrid fishes, Cressey & Cressey (1980) redescribed C. biseriodentatus and reported it from four species of Scomberomorus Lacepède, 1800 as well as from Auxis thazard . Subsequently Cressey et al. (1983) added another three species of Scomberomorus to the list of known hosts. However, they considered that Scomberomorus species served as hosts only for immature stages. The life cycle of C. biseriodentatus is unusual: Cressey & Cressey (1980) noted that adults appear to be found on a different host from the immature stages and they recognized the species originally described as C. auxisi by Pillai (1963) as the adult of C. biseriodentatus . The only host known to harbour an adult was Auxis thazard but Cressey & Cressey (1980) speculated that the adult may prefer a non-scombrid host. The discovery here of two more adult females on A. thazard from Moreton Bay indicates that this scombrid may well be the preferred host of the adult.

This species is widely distributed from the Malagasy Republic, Zanzibar and Somalia in the western Indian Ocean, via the Arabian Sea, India and Sri Lanka, across to the Philippines, Thailand and China in the western Pacific, and as far south as Papua New Guinea and Australia (Cressey & Cressey, 1980). It was first reported from Australian waters (Queensland) by Heegaard (1962), as C. obovatus and C. proboscidatus , both from Scomberomorus queenslandicus and S. commerson . Subsequent records include material from S. queenslandicus caught off West Australia (Cressey & Cressey, 1980). This is the first report of C. biseriodentatus from Moreton Bay.

Figures

FIGURE 20. Caligus biseriodentatus Shen, 1957, female. A, habitus, dorsal; B, sternal furca; C, distal exopodal segment of leg 1; D, endopod of leg 2; E, modified plumose seta from third segment of exopod of leg 2; F, exopod of leg 4. Male, G, habitus, dorsal; H, maxilliped; I, distal exopodal segment of leg 1; J, exopod of leg 4. Scale bars: 1.0 mm on A, G, 200 µm on H, 100 µm on C, D, J, 50 µm on B, E, F, I.