Lernanthropus brevicornutus Kabata, 1979

Boxshall, Geoff A., Bernot, James P., Barton, Diane P., Diggles, Ben K., Q-Y, Russell, Atkinson-Coyle, Toby & Hutson, Kate S., 2020, Parasitic copepods of the family Lernanthropidae Kabata, 1979 (Copepoda: Siphonostomatoida) from Australian fishes, with descriptions of seven new species, Zootaxa 4736 (1), pp. 1-103 : 29-30

Lernanthropus brevicornutus Kabata, 1979

( Figs. 10B, D–H, Fig. 11)

Material examined: Holotype 1♀ from Arrhamphus sclerolepis Günther, 1846 , Moreton Bay , Queensland, 01 October 1963; collected by P.C. Young; NHMUK Reg. No. 1977.114.

Paratype 4♀♀, 1♂ from A. sclerolepis, Moreton Bay , Queensland, 01 October 1963; collected by P.C. Young; NHMUK Reg. No. 1977.115–118 . 3♀♀, 1♂ from Arrhamphus sclerolepis ( TC17221 ), Moreton Bay , Queensland; 18 January 2016; collected by G.A. Boxshall ; 3♀♀ and 1♂ QM Reg. No. W29483 .

1♀ from Hyporhamphus regularis (Günther, 1866) ( TC17638 ), Moreton Bay , Queensland, 27 June 2016; collected by G.A. Boxshall; NHMUK Reg. No. 2018.251 .

Differential diagnosis: Cephalothorax longer than wide, with linear lateral margins narrowing anteriorly, and bearing small posterolateral processes ( Fig. 10B, 11 A–C). Trunk about 3 times longer than cephalothorax with more-or-less parallel lateral margins; anterior part (second and third pedigerous somites) slightly wider than cephalothorax, bearing third legs ventrally; posterior part of trunk (fourth pedigerous somite) covered by long, cloak-like dorsal trunk plate, with convex lateral margins and weak median indentation on posterior margin ( Fig. 10B, 11 A–C). Urosome comprising fused genital complex and abdomen bearing paired caudal rami ( Fig. 10D). Caudal rami short and broad, with bluntly pointed apex; all 5 caudal setae located in distal half of ramus. Parabasal flagellum long and slightly curved, reaching to middle of subapical segment of antennule. Leg 3 forming shoehorn-shaped lamella, projecting ventrolaterally ( Fig. 11B); third legs separate along midline and slightly diverging from opposite member of leg pair. Leg 4 biramous ( Fig. 10E); rami forming subequal elongate lobes, completely concealed beneath dorsal trunk plate in dorsal view ( Fig. 11A); both lobes with complex apical ornamentation ( Fig. 10F,G). Leg 5 absent. Body length of ♀ ranging from 3.98 to 4.21 mm, with a mean of 4.12 mm (based on 3 specimens).

Male with cephalothorax about as long as wide; comprising 37% of total body length ( Fig. 10H). Leg 3 uniramous. Leg 4 forming elongate lobe with bifid tip ( Fig. 10H). Body length of single ♂ 1.49 mm.

Distribution: Originally described from Moreton Bay by Kabata (1979a), this species was based on material of both sexes collected from Arrhamphus sclerolepis (the type host) and from Hyporhamphus quoyi (Valenciennes, 1847) (as Hemirhamphus quoyi ). This is only the second report of this copepod and Hyporhamphus regularis is a new host record.

Remarks: Cressey & Collette (1970) recognized only two species of Lernanthropus on belonid hosts, L. belones and L. tylosuri , both of which are globally distributed on needlefish hosts ( Belonidae ). They noted variation in size of the posterolateral processes on the margins of the cephalothorax but treated the state of development of the processes almost as a continuous variable, although they identified all specimens bearing processes as L. tylosuri . When establishing L. brevicornutus, Kabata (1979a) highlighted the close similarity between it and both L. belones and L. tylosuri , but he chose to recognize three species which he distinguished primarily on the basis of the presence and size of the paired posterolateral processes on the cephalothorax: these are absent in L. belones ( Fig. 10A), short in L. brevicornutus ( Fig. 10B) and long in L. tylosuri ( Fig. 10C). The validity of these three very similar species should be tested using molecular data. The female photographed in Figure 11 A–C has a distorted dorsal trunk plate (a post-fixation artefact) but a slight median indentation in the posterior margin of the plate is visible and was present in the holotype ( Kabata, 1979a: Fig. 3). In both L. belones and L. tylosuri the posterior margin of the dorsal trunk plate is evenly convex. This is an additional feature which might help to distinguish L. brevicornutus .