Lernanthropus mollis Kabata, 1979

(Figs. 27–29)

Material examined: Holotype ♀ from Sillago analis (Whitley, 1943) Moreton Bay, Queensland; 08 May 1963; collected by P.C. Young; NHMUK Reg. No. 1977.119 . Paratype ♀ from S. analis, Moreton Bay, Queensland; 08 May 1963; collected by P.C. Young; NHMUK Reg. No. 1977.120 .

49♀♀, 1♂ from Sillago bassensis Cuvier, 1829 Coffs Harbour, New South Wales; 15 May 1982; collected by K. Rohde. 44♀♀, 2♂♂ from S. bassensis, Coffs Harbour, New South Wales; 15 May 1982; collected by K. Rohde; NHMUK Reg. No. 1984.101–102 . 66♀♀ from S. bassensis, Coffs Harbour, New South Wales; February 1982; collected by K. Rohde; NHMUK Reg. No. 1984.105 . 4♀♀ from Whiting, Red Rock, February 1980; collected by K. Rohde; NHMUK Reg. No. 1984.104 . 1♂ from Whiting, Arrawarra Beach, 21 February 1980; collected by K. Rohde; NHMUK Reg. No. 1984.103 .

3♀♀ from Sillago ciliata Cuvier, 1829 (TC17210), Moreton Bay, Queensland; 18 January 2016; collected by G.A. Boxshall; QM Reg. No. W29493 . 1♀ from S. ciliata (TC17590), Moreton Bay, Queensland; 26 June 2016; collected by G.A. Boxshall; NHMUK Reg. No. 2018.265 .

Differential diagnosis: Cephalothorax longer than wide with almost linear lateral margins extended anteroventrally. Trunk about 2.6 times longer than cephalothorax; anterior part (second and third pedigerous somites) as wide as cephalothorax, separated by slight narrowing from posterior part (fourth pedigerous somite) covered by short dorsal trunk plate (Fig. 27 A–C). Dorsal trunk plate ovoid, wider than long, with convex lateral margins and linear free posterior margin. Urosome comprising fifth pedigerous somite, genital complex and abdomen, all fused; tip of abdomen visible extending beyond margin of dorsal trunk plate in dorsal view. Genital complex with conspicuous paired gonopores located dorsolaterally (Fig. 28A): surface ornamented with 2 pairs of sensillae located between gonopores; paired copulatory pores located posterolaterally on ventral surface. Paired caudal rami elongate; each ramus about 3.3 times longer than wide; armed with 2 plumose setae on dorsal surface proximally, 1 tiny lateral seta located at about 45% of ramus length and 2 small apical setae. Rami extending well beyond posterior margin of dorsal trunk plate.

Antennule indistinctly segmented: proximal part with total of 7 setae; apical segment with 11 setae plus 2 aesthetascs (Fig. 28B). Parabasal flagellum with swollen base and long distal part, curved at tip; almost as long as entire antennule (Fig. 28C). Antenna, mandible, and maxillule typical for genus. Maxilla (Fig. 28D) with short apical claw. Maxilliped with long and strongly curved subchela (Fig. 28E); ornamented with papilla on corpus opposing tip of subchela, plus minute seta present on concave surface of subchela. Leg 1 biramous with 1-segmented rami: members of leg pair connected by intercoxal sclerite: basis with outer seta and stout inner spine with point on apex; exopod armed with 5 spines; endopod with long apical seta. Leg 2 exopod with 4 spines; endopod with no apical seta but ornamented with spinules. Leg 3 located on ventral surface of third pedigerous somite, forming fleshy lamella, directed laterally and splayed out ventrally: third legs separate along midline. Leg 4 bilobate; inner and outer lobes elongate, almost equal in length, protruding well beyond free posterior margin of dorsal trunk plate. Leg 5 absent. Body length of ♀ ranging from 1.95 to 2.42 mm, with a mean of 2.19 mm (based on 10 specimens).

Description of male. Body smaller than female, mean body length 1.01 mm (based on 4 specimens). Cephalothorax large (Fig. 29A), comprising about 47% of total body length, broadest anterior to middle, with convex lateral margins; frontal area of cephalothorax carrying antennule and antennae produced, defined by slight indentation (Fig. 29A). Trunk slender comprising second to fourth pedigerous somites, and fused to urosome. Urosome comprising fifth pedigerous somite, genital complex and abdomen, all fused. Anterior part of genital complex tapering posteriorly with linear lateral margins contiguous with genital opercula. Abdomen narrow, with strongly convex lateral margins (Fig. 29B). Caudal rami as in female, except dorsal setae apparently naked rather than plumose.

Antennule indistinctly segmented (Fig. 29C) with irregular cuticular thickenings, setal formula: 1, 3, 2, 1, 1, 11 + 2 ae. Parabasal flagellum linear (Fig. 29D), tapering, more than half length of antennule. Antenna (Fig. 29E) comprising massive corpus and distal subchela; corpus with smooth medial surface; subchela armed with rounded process distally; well developed process present in articulation between corpus and subchela. Postantennal process (Fig. 29F) rounded, about 25 um in diameter. Mandible (Fig. 29G) and maxillule (Fig. 29H) similar to those of female. Maxilla with conspicuous blunt-tipped process and additional spinular ornamentation distally on basis (Fig. 29I). Maxilliped corpus with small conical process on myxal surface and ornamented with patches of minute spinules (Fig. 29J); subchela with rounded process at mid-length.

Leg 1 with protopod distinct from somite; members of leg pair joined by intercoxal sclerite (Fig. 28F). Each leg biramous with outer seta and short, hirsute inner spine on basis; basis ornamented with patches of spinules: exopod 1-segmented, armed with 5 robust terminal spines and ornamented with spinules distally; endopod 1-segmented, armed with terminal seta about 1.4 times longer than segment. Leg 2 (Fig. 28G) biramous, no trace of intercoxal sclerite observed; protopod armed with outer plumose seta: exopod armed with small distal spine and ornamented with spinules over distal surface; endopod 1-segmented, armed with terminal seta just longer than segment. Leg 3 (Fig. 28A) biramous, comprising long cylindrical exopodal process protruding ventrolaterally from trunk with small ventrally-directed endopodal process (Fig. 28I) near base of exopod; endopod ornamented with surface spinules and conspicuous papillae as present on exopodal lobe (Fig. 28H); outer protopodal seta present dorsally at base of limb (arrowed in Fig. 29A): surfaces of both rami ornamented with papillae; tips of rami with irregular spinule rows (Fig. 28G, H). Leg 4 (Fig. 29A) biramous, comprising 2 long cylindrical processes, armed with outer protopodal seta on common base; leg 4 longer than exopod of leg 3; surfaces of both rami ornamented with conspicuous papillae as present on leg 3. Leg 5 absent.

Distribution: Lernanthropus mollis was originally described from only two females, both collected in Moreton Bay, Queensland. The type host was Sillago analis (Whitley, 1943) and the paratype female was found on S. ciliata Cuvier, 1829 (Kabata, 1979a) . In his large scale survey of the ectoparasites of sillaginid fishes in the Indo-West Pacific, Hayward (1997) expanded the known distribution of L. mollis to include localities in Western Australia, the Northern Territory, and New South Wales, and added five new host species, Sillago burrus Richardson, 1842, S. flindersi McKay, 1985, S. maculata (Quoy & Gaimard, 1824), S. schomburgkii Peters, 1864, and S. sihama . In addition, Hayward (1997) reported the presence of L. mollis in the Gulf of Thailand on S. aeolus Jordan & Evermann, 1902. This remains the only record of L. mollis outside of Australian waters. Sillago bassensis is a new host record.

Remarks: The only other Lernanthropus species reported from a sillaginid host is L. sillaginis Pillai, 1963 which was described from females collected from the gills of Sillago sihama caught off Trivandrum, India (Pillai, 1963). The male of L. sillaginis was described subsequently by Song & Chen (1976) based on Chinese material from the same host. There is also material of L. sillaginis in the NHM, London collections, from S. sihama caught off the Iraq coast in the Arabian Gulf (NHMUK 2013.52–53). Lernanthropus sillaginis was reported from Sillago maculata caught off Thailand (Sirikanchana, 1982) and by Hayward (1997) from S. aeolus, S. arabica McKay & McCarthy, 1989, S. attenuata McKay, 1985, S. chondropus Bleeker, 1849, S. parvisquamis Gill, 1861 and S. sihama over a range extrending from the Arabian Gulf in the west through to China in the east and Bali (Indonesia) in the south. Subsequently, Raja et al. (2018) reported it from S. vincenti McKay, 1980 in Indian waters. The only record from a non-sillaginid host is that of Ho & Kim (2004), who found L. sillaginis on Priacanthus tayenus Richardson, 1846 caught off Thailand.

The females of these two species are readily distinguishable: L. sillaginis has a large trunk with a broad dorsal trunk plate that flares out posteriorly so that it is twice as wide as the cephalothorax, whereas the trunk of L. mollis is slender and the small dorsal trunk plate is only about 1.2 times wider than the cephalothorax. In addition, the bilobed, foliaceous third legs are separated in the midline in L. sillaginis, but are unilobate and fused in the midline in L. mollis . The male of L. mollis is described here for the first time. It is very similar to the male of L. sillaginis, but can be distinguished by its better defined abdomen, slightly longer caudal rami, and longer exopodal lobe of leg 3 (relative to leg 4).