Caligus aesopus Wilson, 1921

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 : 37

Caligus aesopus Wilson, 1921

( Fig. 15 )

Material examined. 2♀♀, 1♂ from Seriola hippos Günther, 1876 (TC18352) 28 March 2017, 1♀, 1♂ QM Reg.No. W53053; 1♀ NHMUK Reg. No. 2017.212.

Site on host. Unknown.

Differential diagnosis. Cephalothorax dorsoventrally flattened with well-developed marginal membranes along lateral zones; frontal plates with lunules; thoracic zone very small, extending posteriorly about level with posterior ends of lateral zones ( Fig. 15A ). Genital complex about 1.5 to 1.6 times longer than wide; abdomen indistinctly 2-segmented, with constriction at about posterior third; genital complex about 2 times longer than abdomen ( Fig. 15A ). Antenna with rounded posterior process on proximal segment ( Fig. 15B ). Post-antennal process bifid, main tine straight; associated papillae multisensillate. Posterior process of maxillule bifid; main (inner) tine much larger than outer. Maxilliped of female with rounded process proximally ( Fig. 15C ). Sternal furca with broad gape; tines incurved with rounded tips. Sympod of leg 1 ornamented with spinules and bearing rounded process anteriorly on ventral surface (arrowed in Fig. 15D ); vestigial endopod elongate with 2 setal vestiges apically: distal exopodal segment with 3 plumose setae on posterior margin; distal spine 1 longer than other spines; spines 2 and 3 with accessory processes; seta 4 longer than spine 1 and about as long as segment. Leg 2 with marginal setules on endopodal segments 2 and 3; outer spine on exopodal segment 1 lying obliquely across segment 2, spine on segment 2 aligned close to longitudinal axis of ramus. Leg 3 ( Fig. 15E ) apron with raised rib, with bluntly rounded tip, plus circular array of large denticles on ventral surface and corrugated adhesion pad near outer margin on dorsal surface; exopod indistinctly 3-segmented, first segment with large recurved outer spine, lacking inner seta; second and third segments incompletely separated, outer margins hirsute, with multiple rows of long setules: endopod 2-segmented, first endopodal segment forming velum and bearing inner seta; distal segment with partial suture, armed with total of 6 plumose setae. Leg 4 uniramous, 4-segmented; exopodal segments ( Fig. 15F ) with I; I; III spines; innermost spine distinctly longer than middle spine. Body lengths of adult females 4.54 and 4.79 mm; length of adult male 3.46 mm.

Remarks. Caligus aesopus was first described from off the Juan Fernandez Islands in the East Pacific and the host was given as probably Seriola peruana Steindachner, 1881 ( Wilson, 1921) . Hewitt (1963) subsequently reported C. aesopus from Seriola lalandi Valenciennes, 1833 (as Seriola grandis Castelnau ) caught off New Zealand. However, C. aesopus has been confused with a very similar species, C. spinosus Yamaguti (1939) , which was originally described by Yamaguti (1939) based on material from Seriola quinqueradiata Temminck & Schlegel, 1845 caught off Japan. Unfortunately, Yamaguti did not compare his new species with C. aesopus . Caligus spinosus was recognised as a junior subjective synonym of C. aesopus by Fernandez & Villalba (1986) and this synonymy was followed by Lin & Ho (2007). However, Choe & Kim (2010) recently found two Caligus species on species of Seriola Cuvier, 1816 in Korean waters. They provided full descriptions of both sexes of both species, and they reinstated C. spinosus as a valid species, distinct from C. aesopus . Caligus aesopus can be distinguished by the presence of a constriction subdividing the female abdomen into a wider anterior part (two thirds) and a narrower posterior part (one third), by the large size and lower number (less than 15) denticles present in a rosette on the apron of leg 3, and by the apical spine on the distal exopodal segment of leg 4 being distinctly longer than the adjacent middle spine. Choe & Kim (2010) listed a few other minor character differences for the females, such as the presence of an anterior process on the surface of the sympod of leg1 ( Fig. 15D ), and documented a difference in the form of the myxal processes on the male maxilliped.

Caligus aesopus was found on S. lalandi in Korean waters (Choe & Kim, 2010) and it can be found on the same host from South Africa (Kensley & Grindley, 1973) to New Zealand (Hewitt, 1963). In addition, it occurs on S. dumerili (Risso, 1810) in Taiwan ( Lin & Ho, 2007) and on “probably S. peruana ” in the eastern Pacific ( Wilson, 1921). Choe & Kim (2010) concluded that the material from Sphyraena obtusata caught off India and described by Pillai (1963) could be attributed to C. aesopus , but possible confusion with C. abigailae sp. nov. described above from this host should also be considered. Choe & Kim (2010) demonstrated that the material redescribed and illustrated by Shiino (1960) as “ C. spinosus ” should be attributed to C. aesopus . The host in Moreton Bay, S. hippos , is a new host record for C. aesopus .

Caligus spinosus has previously been reported from Australian waters (e.g. Rohde, 1978, Byrnes, 1986, Hutson et al., 2007a, b) but there is uncertainty over these identifications since during at least some of the period covered by these reports, the two species were considered to be synonyms.

Figures

FIGURE15.Caligus aesopusWilson,1921, female.A, habitus, dorsal; B, antennaand post-antennal process, drawn insitu; C, maxilliped;D, sympod of leg 1, showing anteriorprocess on ventral surface; E, leg 3; F, exopodof leg 4. Scalebars:1.0 mm on A, 100 µm on B, D, 200 µm on C, E, F.