Alebion maculatus Wilson, 1932

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 : 11-14

Alebion maculatus Wilson, 1932

( Fig. 2 )

Material examined. 1♂ from Carcharhinus cf. limbatus (Müller & Henle, 1839) (TC17372), 21 January 2016, QM Reg. No. W53041.

Site on host. Body surface.

Differential diagnosis. Cephalothorax dorsoventrally flattened with well-developed marginal membranes; frontal plates well developed, lacking lunules. Fourth pedigerous somite with bilobed dorsal plate in female; with small dorsal expansions in male ( Fig. 2A ). Female genital complex with lateral swellings and elongate fifth legs extending beyond tip of abdomen. Male genital complex about 1.5 times longer than wide; lateral margins linear, tapering slightly posteriorly ( Fig. 2A ). Abdomen 2-segmented in both sexes. Caudal rami incompletely fused to anal somite. Male antenna with blunt spinous process on proximal segment; subchela with accessory claw ( Fig. 2B ). Post-antennal process without tine, sclerite forming corrugated adhesion pad; associated papillae unisensillate ( Fig. 2B ). Posterior process of maxillule broad and flat, forming adhesion pad ornamented with fine surface striations ( Fig. 2B ). Post-oral process present; elongate with corrugated surface. Maxilliped with smooth myxal margin in female; with prominent myxal process in male. Sternal furca lacking. Leg 1 with 2-segmented endopod armed with 0-0; 3 setae: distal exopodal segment with 3 plumose setae on posterior margin: distal margin ( Fig. 2C ) armed as follows: spine 1 simple, spine 2 modified plate-like, spine 3 short and stout, with accessory process, seta 4 naked, longer than spine 3. Leg 2 sexually dimorphic: with modified plate-like spines on second and third exopodal segments of female; spines forming highly ornamented rods in male ( Fig. 2D ), spine on second segment about as thick as, and extending nearly to tip of, spine on third segment. Leg 3 with 3-segmented rami: spine on first exopodal segment linear and directed away from ramus ( Fig. 2E ); spine on second segment and 2 proximal spines on third segment modified, plate-like: endopod ( Fig. 2F ) with unarmed first segment expanded to form velum; second segment elongate, with outer velum-like expansion and 2 inner plumose setae; small third segment with 4 plumose setae. Leg 4 reduced to single segment bearing 4 short setal elements. Fifth leg of male located near mid-length of genital complex, comprising isolated outer seta plus exopodal lobe bearing 3 setae ( Fig. 2G ). Body length of adult male 4.50 mm.

Remarks. Cressey (1972) revised the genus Alebion , recognizing eight species as valid and providing a key to the adults of both sexes. Following Cressey’s key, the single male from Moreton Bay is identified as A. maculatus , based on the size and form of the modified spines on the second exopodal segment of leg 2 ( Fig. 2D ).

Alebion maculatus was first figured by Bassett-Smith (1898a) who reported two mature females (under the name Alebion carchariae Krøyer, 1863 ) taken from an unidentified “small shark” caught off Aden. Wilson (1932) pointed to significant differences in the shape of the genital complex and abdomen between Bassett-Smith’s description and the original description of A. carchariae by Krøyer (1863) and proposed A. maculatus as a new species to accommodate Bassett-Smith’s specimens. This species has previously been recorded from Aden, India (Gnanamuthu, 1951; Rangnekar, 1959), Sri Lanka (Kirtisinghe, 1956) and Madagascar (Cressey, 1967). This is the first report of A. maculatus from Australian waters, and this represents a significant range extension.

The only identified host species known for A. maculatus is Carcharhinus limbatus caught at Nosy Bé, Madagascar (Cressey, 1967, 1972); most other reports have named hosts only as “carcharhinid shark” (e.g. Gnanamuthu, 1951 - as Alebion alatus Gnanamuthu, 1951 , and Kirtisinghe, 1956 - as Alebion megacephalus Kirtisinghe, 1956 ), or “unidentified shark” (e.g. Rangnekar 1959 - as Alebion spinosus Rangnekar, 1959 ).

Figures

FIGURE 2. Alebion maculatus Wilson, 1932, male. A, habitus, dorsal; B, antenna, post-antennal process, maxillule and postoral process, drawn in situ; C, setal elements on distal margin of exopod of leg 1, showing modified spatulate spine 2; D, outer margin of exopod of leg 2 showing sexually dimorphic modified spines on segments 2 and 3; E, exopod of leg 3, showing modifiedspatulate outer spines onsegments 2 and 3; F, endopod of leg3; G,leg 5, ventral.Scale bars:1.0 mm on A, 200 µm on B,E, F, 100 µm on D, 50 µm on C, G.