Caligus laminatus (Rangnekar, 1955)

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 : 77-79

Caligus laminatus (Rangnekar, 1955)

( Fig. 33 )

Syn: Pseudocaligus laminatus Rangnekar, 1955

Material examined. 1♀ from Lagocephalus lunaris (Bloch & Schneider, 1801) (TC 17944) 0 6 July 2016, QM Reg. No. W53077.

Site on host. Unknown (in body wash).

Differential diagnosis. Cephalothorax trapezoidal in outline ( Fig. 33A ), dorsoventrally flattened with welldeveloped marginal membranes; frontal plates with small lunules. Genital complex rectangular, about 1.5 times longer than wide and about 7.2 times longer than abdomen; abdomen reduced, 1-segmented, wider than long and bearing caudal rami on oblique posterolateral margins. Antenna with broadly rounded posterior margin on proximal segment ornamented with flange ( Fig. 33B ), without defined process; second segment with striated outer margin; subchela strongly recurved. Post-antennal process with short tine ornamented with surface striations; associated papillae bi- or trisensillate; additional swelling present medial to post-antennal process, ornamented with membranous flange. Posterior process of maxillule simple, ornamented with surface striations ( Fig. 33B ). Maxilla with short basis ( Fig. 33C ) bearing inconspicuous membranous flabellum; canna short, not reaching tip of segment; calamus, stout, tapering and bilaterally serrate. Maxilliped of female ( Fig. 33D ) with 3 rounded ridges basally on proximal segment, surface around ridges wrinkled; myxal area lacking ornamentation; subchela with claw bearing large, blunt-tipped, accessory element, ornamented with short surface setules. Sternal furca with more or less parallel, blunt-tipped tines ( Fig. 33E ). Distal exopodal segment of leg 1 with 3 plumose setae on posterior margin; distal margin spine 1 larger than other spines ( Fig. 33F ); spines 1, 2 and 3 each with accessory process and with marginal fringe; seta 4 absent. Leg 2 with marginal membrane on outer edge of endopodal segment 1 ( Fig. 33G ); segments 2 and 3 with short marginal setules; outer margin spines on exopodal segments 1 and 2 aligned closer to longitudinal axis of ramus. Leg 3 apron with medial and lateral patches of spinules; exopod 2-segmented ( Fig. 33H ); first segment with slightly curved outer spine and with inner plumose seta; compound distal segment with 4 outer spines and 5 plumose setae; first endopodal segment forming small velum, bearing inner seta; compound distal segment with 6 setae. Leg 4 vestigial, represented by small lobe with 2 setae ( Fig. 33I ). Body length of female 2.92 mm.

Remarks. On the basis of both morphological (Dojiri & Ho, 2013; Özak et al., 2013) and molecular evidence (Freeman et al., 2013), the genus Pseudocaligus is no longer considered valid; it is treated as a junior subjective synonym of Caligus . Pseudocaligus laminatus was formally transferred to Caligus by Özak et al. (2013).

The type host of C. laminatus is Lagocephalus lunaris ( Rangnekar, 1955a) . A single female was subsequently recorded from Liza macrolepis (Smith, 1846) caught off Taiwan ( Lin & Ho, 2003), although Ho & Lin (2004) expressed some reservations about the conspecificity of their specimen with Rangnekar’s species. The Moreton Bay female was also from L. lunaris and its features conform closely to the redescription given by Ho & Lin (2004). In particular, it possesses two very unusual shared character states, the absence of seta 4 from the distal exopodal segment of leg 1, and the presence of a large, hirsute, accessory process on the subchela of the maxilliped. I consider that these shared features, plus others such as the tridentate process at the posterolateral corner of the proximal segment of the antennule, serve to validate Ho & Lin’s identification. Ho & Lin (2004) noted the presence of the usual 6 setae on the compound distal exopodal segment of leg 3. This was a difference between their Taiwanese specimen and the Indian type material described by Rangnekar (1955a), which was reported as having only 4 setae. The Australian specimen from L. lunaris agrees with Ho & Lin’s (2004) account, and might indicate that this apparent difference is an inaccuracy in Rangnekar’s original description.

There is, however, one minor difference between the previously described material of C. laminatus from India and Taiwan, and the Moreton Bay female. Leg 4 was described by Rangnekar (1955a) as bearing 3 apical setae whereas Ho & Lin (2004) showed only a single vestigial seta on the stub of this leg. The Moreton Bay specimen possessed 2 setae on the leg on one side, but the other side was damaged. This character relates to a vestigial limb which is hard to observe; there may be variability but its significance cannot be assessed yet since only single females were found by Ho & Lin (2004) and in the present study. Ho & Lin (2004) stated that the male was unknown, but Rangnekar (1955a) described the male and noted that the maxilliped of the male was similar to that of the female in possessing the large accessory element on the subchela.

The discovery of C. laminatus in Australian waters significantly extends its known geographical range, as it had previously been reported only from India and Taiwan. The typical host of this rare copepod is the tetraodontid L. lunaris: Rangnekar (1955a) reported “some 20 females and 8 males” from an unspecified number of hosts collected over a period of two months. The Australian record is from the same host, and it seems possible that the single female found on a Liza macrolepis landed at the fish market in Dong-shi, Taiwan (Ho & Lin, 2004) might be a contaminant, resulting from transfer after the death of the commercially-caught host.

Figures

FIGURE33.Caligus laminatus (Rangnekar, 1955), female.A, habitus, dorsal;B,antenna, post-antennalprocess and maxillule drawn in situ; C, brachium of maxilla; D, maxilliped; E, sternal furca; F, distal armature on exopod of leg 1; G, endopod of leg 2; H, exopod of leg 3; I, reduced leg 4. Scale bars: 1.0 mm on A, 100 µm on B, D, G, H, 50 µm on C, E, F, I.