Caligus platytarsis Bassett-Smith, 1898

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 : 109-111

Caligus platytarsis Bassett-Smith, 1898

( Fig. 49 )

Syn: Caligus bombayensis Rangnekar, 1955

Material examined. 9♀♀, 4♂♂ from Mugil cephalus Linnaeus, 1758 (TC17257) 18 January 2016, QM Reg. No. 9♀♀, 1♂ W53094; 4♀♀ (TC17714) 29 June 2016, NHMUK Reg. Nos 2017.309–311.

Site on host. Gill arches.

Differential diagnosis. Cephalothorax dorsoventrally flattened with well-developed marginal membranes along lateral zones of dorsal cephalothoracic shield; frontal plates with lunules. Female genital complex about 1.2 times longer than wide, becoming wider posteriorly, with slightly convex lateral margins and nearly transverse posterior margin; fifth legs forming conspicuous process on posterolateral corner of genital complex ( Fig. 49A ): abdomen elongate, about 2.9 times longer than wide and just longer than genital complex. Antenna without posterior process on proximal segment ( Fig. 49B ). Post-antennal process vestigial; associated papillae unisensillate. Posterior process of maxillule with broad tine ( Fig. 49B ). Maxilliped of female with smooth myxal margin. Sternal furca with extremely broad (about as wide as long), spatulate tines ( Fig. 49C ). Distal exopodal segment of leg 1 with 3 plumose setae on posterior margin; distal margin spine 1 distinctly shorter than spine 2 ( Fig. 49D ); spines 2 and 3 lacking accessory process but with minutely pointed apex; seta 4 longer than spine 3, naked. Leg 2 with patches of fine setules extending onto surface of endopodal segments 2 and 3; outer spine on exopodal segment 1 passing obliquely across surface of ramus; spine on segment 2 aligned closer to long axis of ramus. Leg 3 lacking distinctive ornamentation on apron; exopod 3-segmented ( Fig. 49E ); first segment with straight outer spine not reaching articulation with second segment, lacking inner seta; second segment with outer spine and inner plumose seta; third with 3 outer spines and 4 plumose setae: endopod 2-segmented ( Fig. 49E ); first segment forming well developed velum, armed with inner plumose seta; compound distal segment with lateral margin expanded proximal to partial suture marking plane of fusion, armed with 6 plumose setae. Leg 4 uniramous ( Fig. 49F ), 4-segmented; exopodal segments with I, I, III spines; all spines sub-equal in length, proximal 4 spines hirsute, apical spine with smooth membrane bilaterally; each spine with elongate pecten associated with base. Mean body length of female 5.09 mm, range 4.88 to 5.31 mm (based on 7 specimens): mean body length of male 3.15 mm, range 3.11 to 3.19 mm (based on 3 specimens).

Remarks. Originally described from Mugil sp. caught at Muscat, Oman (Bassett-Smith, 1898b), C. platytarsis has been reported infrequently but is known to occur widely across the Indo-Pacific, from the Arabian Gulf and India ( Rangnekar, 1955b; Pillai, 1967b, 1985), and to Australia (Kabata, 1965b). Pillai (1967b) considered C. bombayensis Rangnekar, 1955 , described from specimens collected from M. cephalus caught off Bombay, to be a junior subjective synonym of C. platytarsis and confirmed this after examining Bassett-Smith’s types ( Pillai, 1971). The first report of C. platytarsis from Australia (as C. bombayensis ) was from Mugil cephalus caught off Heron Island (Kabata, 1965b).

The distinctive features of C. platytarsis are the body proportions, with its long abdomen, the prominent fifth legs on the posterolateral corners of the genital complex, the highly flattened, spatulate tines of the sternal furca, and the form of the spines on leg 4. Caligus platytarsis belongs in the newly identified C. diaphanus -group and it shares with another member of the group, C. tanago , the unusual form of the spines on the exopod of leg 4. However, these species differ in the form of the sternal furca, since C. platytarsis has extremely flattened spatulate tines that are wider than long, compared to longer than wide in C. tanago . The post-antennal process lacks a tine in C. platytarsis but has a small tapering tine in C. tanago .

The reported body lengths for females vary: Kabata (1965b) gave a length for the female of 4.75 mm, and commented that it was larger than the Indian material from Bombay studied by Rangnekar (1955b) which had a length of 3.74 mm. In contrast, Pillai (1985) gave a length of 6.00 mm for the female. The Australian females from Moreton Bay have a mean body length of 5.09 mm (range 4.88 to 5.31 mm).

Figures

FIGURE 49. Caligus platytarsis Bassett-Smith, 1898, female. A, habitus, dorsal view with inset showing detail of leg 5; B, antenna, post-antennal process and maxillule drawn in situ; C, sternal furca; D, distal armature on exopod of leg 1; E, rami of leg 3; F, exopod of leg 4. Scale bars:A, 1.0 mm on A, 200 µm on B, F, 100 µm on C, E, 50 µm on D.