Lernanthropus seriolii Shishido, 1898

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 : 73-74

Lernanthropus seriolii Shishido, 1898

( Figs. 38 , 39A )

Syn: Lernanthropus seriolae: Yamaguti, 1963

Lernanthropus paenulatus C.B. Wilson, 1922 new synonym

Lernanthropus paenulatus: Rohde et al., 1995 ; Hutson et al., 2007

Material examined: 7♀♀, 1♂ on Seriola hippos Günther, 1876 , Coffs Harbour , New South Wales; December 1980 – January 1981; collected by K. Rohde. 10♀♀, 1♂ on S. hippos, Coffs Harbour , New South Wales; December 1980 – January 1981; collected by K. Rohde; NHMUK Reg. No. 1984.97–98 . 17♀♀ on Seriola lalandi Valenciennes, 1833 , Coffs Harbour , New South Wales; December 1980 – January 1981; collected by K. Rohde. 3♂♂ on S. lalandi, Coffs Harbour , New South Wales; December 1980 – January 1981; collected by K. Rohde; NHMUK Reg. No. 1984.99–100 .

Comparative material examined: Holotype ♀ ( USNM 54058 ) and paratype ♀♀ ( USNM 54057 ) of Lernanthropus paenulatus C.B. Wilson, 1922 stored in the United States National Museum of Natural History , Washington D.C., USA.

Differential diagnosis: Cephalothorax longer than wide with weakly convex lateral margins and straight frontal margin: trunk elongate, about 5 times longer than cephalothorax; anterior part (second and third pedigerous somites) just wider than cephalothorax and bearing third legs posteriorly; posterior part (fourth pedigerous somite) covered by large dorsal trunk plate; plate becoming wider posteriorly and with evenly convex free posterior margin ( Fig. 38 A–C). Urosome comprising fifth pedigerous somite, genital complex and abdomen, all fused ( Fig. 39A ). Genital complex with conspicuous gonopores located dorsolaterally and with paired copulatory pores located posterolaterally on ventral surface. Genital complex ornamented with 2 pairs of sensillae on dorsal surface between gonopore openings. Paired caudal rami slightly curved; about 3.4 times longer than maximum width, tapering from broad base towards apex; not extending beyond posterior margin of dorsal trunk plate; each ramus armed with 2 plumose setae proximally on dorsal surface, 1 small lateral seta located about at 58% of ramus length, and 2 small apical setae ( Fig. 39A ). Leg 3 bilobate, located ventrally inner lobe forming fleshy lamella, shoehorn-shaped with distal part curved towards head; outer lobe much smaller than inner, but clearly visible in lateral view ( Fig. 38A ). Leg 4 bilobate; inner lobe longer than outer; tips of both lobes protruding beyond posterior margin of dorsal trunk plate. Leg 5 represented by large lamellate lobe ( Fig. 39A ) about 4.7 times longer than maximum width, tapering towards tip extending beyond tips of caudal rami: armed with single protopodal seta located in proximal quarter on dorsal surface. Body length of ♀ ranging from 7.85 to 9.00 mm, with a mean of 8.48 mm (based on 10 specimens); mean body length of ♂ 2.43 mm (based on 4 specimens).

Distribution: Lernanthropus seriolii was originally described by Shishido (1898) based on material collected from the gills of Seriola lalandi caught off Japan. Izawa (2014) redescribed this species (as L. seriolae ) after examination of material from the same host caught in Japanese waters. The change in spelling to seriolae is an unjustified emendation, first used by Yamaguti (1963); the original spelling was subsequently used by Izawa (2018) and is maintained here.

Lernanthropus seriolii is very similar in gross morphology to L. paenulatus Wilson, 1922 which was described from material collected from the gills of the same host ( S. lalandi ) caught off the Atlantic coast of the USA at Woods Hole, Massachusetts and at Beaufort, North Carolina ( Wilson, 1922). According to Izawa (2014), L. seriolii can be distinguished from L. paenulatus most readily by the form of the female leg 5. In L. seriolii the fifth legs form elongate lamellae, which extend well beyond the tips of the caudal rami, whereas in L. paenulatus the fifth legs were described by Wilson (1922: 52) as “a pair of short fifth leg rudiments just in front of genital segment”. Re-examina- tion of the type material of L. paenulatus stored in the USNM revealed that Wilson’s description was erroneous: L. paenulatus possesses elongate lamellate fifth legs, as described for L. seriolii . In the absence of other substantive differences, we propose to treat L. paenulatus as a junior subjective synonym of L. seriolii .

Previous records of L. paenulatus from Australia should be attributed to L. seriolii: Hutson et al. (2007a) reexamined material from S. lalandi caught in New Zealand waters, originally reported as Lernanthropus sp. by Smith et al. (2004) and one of us (GAB) identified it as L. paenulatus . Rohde et al. (1995) had first reported L. paenulatus from Australia, on S. lalandi caught at Coffs Harbour (NSW). Re-examination here of Rohde’s material stored in Natural History Museum, London confirms that the Australian material from Coffs Harbour is L. seriolii . The material reported by Hutson et al. (2007a) as L. paenulatus from the same host taken at Sir John Woods Banks (NSW) and off Killarney (Victoria) and material reported by Hutson et al. (2007b) from Seriola hippos is also now reassigned to L. seriolii , as is the record of L. paenulatus from a Seriola sp. caught in China ( Song & Chen, 1976).

Remarks: This is a distinctive species with a long slender body in the female. A characteristic feature of this species is the small triangular outer (exopodal) lobe located proximally at the base of leg 3.

Lernanthropus micropterygis is similar to L. seriolii , both species have a similar elongate body form in the female and both have long, lamellate fifth legs and caudal rami. However, L. micropterygis differs from L. seriolii in the relative lengths of these structures: the fifth legs are longer than the caudal rami in L. seriolii but shorter than the caudal rami in L. micropterygis . In addition, the dorsal trunk plate is much shorter in L. micropterygis so that almost the whole of the elongate fourth legs are visible in dorsal view whereas in L. seriolii only the distal 40% is visible. Lernanthropus micropterygis has a more restricted distribution than L. seriolii , as it is known only from the Mediterranean Sea ( Richiardi, 1884; Goggio, 1906), Red Sea ( Wilson, 1924) and South Africa ( Kensley & Grindley, 1973, as L. ecclesi ).

Figures

FIGURE 38. Lernanthropus seriolii Shishido, 1898, adult ♀. A, habitus, lateral; B, habitus, lateroventral; C, habitus, dorsolat- eral. Scale bar 5 mm.

FIGURE 39. Lernanthropus seriolii Shishido, 1898, adult ♀. A, urosome, dorsal view showing paired fifth legs, genital open- ings and caudal rami. Mitrapus oblongus (Pillai, 1964) ♂, B, habitus, dorsal. Scale bars A, 0.5 mm, B, 200 μm.