Caligus asymmetricus Kabata, 1965

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 : 44-46

Caligus asymmetricus Kabata, 1965

( Fig. 19 )

Material examined. 3♀♀, 2♂♂ from Euthynnus affinis (Cantor, 1849) (TC18121), 21 November 2016, QM Reg. No. W53056 ; I ♀ from Thunnus tonggol (Bleeker, 1851) (TC17991), NHMUK Reg. No. 2017.233; I ♀ from Auxis thazard (Lacepède, 1800) (TC18122), 21 October 2016, NHMUK Reg. No 2017.234.

Site on host. Body surface.

Differential diagnosis. Cephalothorax dorsoventrally flattened with well-developed marginal membranes; frontal plates with lunules. Genital complex about 1.2 times longer than wide, wider posteriorly, with rounded posterolateral corners ( Fig. 19A ); abdomen short, just wider than long; genital complex about 3.8 times longer than abdomen. Antenna with very small, narrow posterior process on proximal segment ( Fig. 19B ). Post-antennal process with small, acutely-pointed tine; associated papillae multi- or bisensillate. Maxilliped of female with slight expansion on myxal margin ( Fig. 19C ). Sternal furca ( Fig. 19D ) small, with slender, pointed tines (often asymmetrical). Distal exopodal segment of leg 1 with 3 short plumose setae on posterior margin; distal spine 1 simple, longer than spines 2 and 3, each armed with accessory process; seta 4 about as long as spine 1 and shorter than segment. Leg 2 with double row of about 7 or 8 strong denticles along outer margin of endopodal segment 2 ( Fig. 19E ); outer spines on exopodal segments 1 and 2 lying obliquely across axis of ramus ( Fig. 19F ); proximal outer spine on segment 3 long and slender, longer than distal outer spine. Leg 3 with 3-segmented exopod ( Fig. 19G ); first exopodal segment bearing curved outer spine, lacking inner seta; second segment with outer spine and inner seta; third segment with 3 small spines, plus 4 plumose setae: endopod 2-segmented, first segment forming long velum, and armed with inner seta; compound distal segment with slightly swollen lateral margin, armed with 6 plumose setae. Leg 4 uniramous, 3-segmented; first and second exopodal segments with I and IV spines, respectively ( Fig. 19H ). Mean body length of female 3.78 mm, range 3.58 to 3.97 mm (based on 3 specimens): male lengths 3.73 and 3.81 mm.

Remarks. Caligus asymmetricus was originally described as a new species by Pillai (1963) but the name he proposed, Caligus thynni , was preoccupied by Caligus thynni Dana, 1852 .

The replacement name, C. asymmetricus , is attributed to Kabata (1965b) and refers to the often asymmetrical form of the sternal furca. Kabata’s (1965b) brief account was based on a single female from Euthynnus alletteratus caught off Queensland and Pillai’s (1963) description was based on a single female from E. affinis taken off Trivandrum in the south of India. Lewis (1967) subsequently provided full descriptions of both sexes based on material collected off Hawaii on E. affinis (as E. yaito ). Cressey & Cressey (1980) and Cressey et al. (1983) recorded C. asymmetricus on ten different scombrid host species across the Indo-West Pacific, including E. affinis , Sarda australis (MacLeay, 1881) , Scomberomorus commerson (Lacepède, 1800) and Auxis sp. all from New South Wales, and Cybiosarda elegans (Whitley, 1935) from western Australia. The single female reported here from Thunnus tonggol caught in Moreton Bay constitutes a new host record.

There is a group of 12 species that share the possession of a 3-segmented leg 4 armed with four spines on the compound distal 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. This group, referred to here as the C. bonito -group, comprises C. asperimanus Pearse, 1951 , C. asymmetricus , C. biseriodentatus , C. bonito , C. cossacki Bassett- Smith, 1898, C. grandiabdominalis Yamaguti, 1954 , C. hoplognathi Yamaguti & Yamasu, 1959 , C. malabaricus , C. mutabilis Wilson, 1905 , C. omissus Cressey & Cressey, 1980 , C. phipsoni Bassett-Smith, 1898 , and C. triabdominalis . Several other members of this group, i.e. C. biseriodentatus , C. bonito , C. mutabilis , and C. omissus primarily use scombrids as hosts, but the small size and slender pointed tines of the sternal furca of C. asymmetricus , in addition to the proportional lengths of the genital complex and abdomen, serve to distinguish this species from these others.

Figures

FIGURE 19. Caligus asymmetricus Kabata, 1965, female.A, habitus, dorsal; B, antenna, post-antennal process and maxillule, drawn in situ; C, maxilliped; D, sternal furca; E, endopod of leg 2, showing denticulate ornamentation on lateral margin of second segment; F, exopod of leg 2; G, rami of leg 3, drawn in situ; H, leg 4. Scale bars: 1.0 mm on A, 200 µm on B, C, G, H, 100 µm onE, F, 50 µm on D.