Lernanthropus gnathanodontus, Boxshall & Bernot & Barton & Diggles & Q-Y & Atkinson-Coyle & Hutson, 2020

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 : 48-52

publication ID	https://doi.org/ 10.11646/zootaxa.4736.1.1
publication LSID	lsid:zoobank.org:pub:970D7D36-6D8C-4463-B9EA-D3B8E191BE72
DOI	https://doi.org/10.5281/zenodo.3671097
persistent identifier	https://treatment.plazi.org/id/554BDB52-734E-FFFC-5FC9-FD572805F800
treatment provided by	Plazi
scientific name	Lernanthropus gnathanodontus
status	sp. nov.

Treatment

Lernanthropus gnathanodontus sp. nov.

( Figs. 21–23 View FIGURE 21 View FIGURE 22 View FIGURE 23 , Fig. 24 View FIGURE 24 A–F)

Type material: Holotype ♀, 6 paratype ♀♀, 1 allotype ♂ from Gnathanodon speciosus (Forsskål, 1775) ( TC17577 ), Moreton Bay, Queensland, 25 January 2016; collected by G.A. Boxshall, QM Reg Nos. W29489 (Holotype ♀), W29490 (allotype ♂), W29491 (paratype ♀♀). 3 paratype ♀♀ from G. speciosus ( TC17074 ), Moreton Bay, Queensland, 13 January 2016; collected by G.A. Boxshall. 1 paratype ♀ from G. speciosus ( TC17075 ), Moreton Bay , Queensland, 13 January 2016; collected by G.A. Boxshall. 2 paratype ♂♂ G. speciosus ( TC17116 ), Moreton Bay , Queensland, 13 January 2016; collected by G.A. Boxshall. 2 paratype ♂♂ G. speciosus ( TC17950 ), Moreton Bay , Queensland, 06 July 2016; collected by G.A. Boxshall, NHMUK Reg. No. 2018.254–262.

Etymology: The name of the new species refers to the generic name of its only known host.

Description: Female body comprising cephalothorax, trunk and small urosome concealed beneath dorsal trunk plate ( Fig. 21 View FIGURE 21 A–C): body length ranging from 3.98 to 4.45 mm, with a mean of 4.27 mm (based on 9 specimens). Cephalothorax slightly wider than long (length measured along dorsal midline); lateral margins slightly convex in dorsal view and produced ventrally and anteriorly into conspicuous “horns” either side of frontal margin. Trunk with narrow anterior part (second and third pedigerous somites) gradually becoming wider towards base of third legs; posterior part covered by dorsal trunk plate covering entire abdomen, with only tips of leg 4 lamellae visible in dorsal view: dorsal trunk plate with narrow anterior base, expanding posteriorly and with shallow median indentation in posterior margin ( Fig. 21C View FIGURE 21 ). Urosome comprising fifth pedigerous somite, genital complex and abdomen, all fused ( Fig. 22A View FIGURE 22 ). Genital complex widest anteriorly at level of conspicuous paired, dorsolateral genital openings and narrower posteriorly, bearing paired copulatory pores on ventral surface (arrowed in Fig. 22A View FIGURE 22 ). Abdomen slightly wider than long, with median anal slit; ornamented with paired sensillae dorsally. Caudal rami located on ventral surface: each ramus about 4.0 times longer than wide; armed with 2 plumose setae dorsally near base, 1 short lateral seta located at about 80% of ramus length, and 2 short apical setae ( Fig. 22A View FIGURE 22 ).

Antennule ( Fig. 22B View FIGURE 22 ) indistinctly 6-segmented with irregular cuticular thickening; setation comprising total of 8 setae on proximal part and 11 + 2 aesthetascs on compound apical segment; proximal 3 setae on anterior margin plumose, all other setae naked. Parabasal flagellum broader proximally with narrow distal part curved ( Fig. 22B View FIGURE 22 ), located near of base of antennule. Antenna ( Fig. 22C View FIGURE 22 ) robust, comprising long corpus bearing papilliform element on medial surface, and distal subchela showing traces of suture line; subchela armed with small process in zone of arthrodial membrane in articulation between corpus and subchela, minute distal seta on concave margin (arrowhead on Fig. 22C View FIGURE 22 ) and blunt proximal process; terminal claw with striated cuticle. Rounded post-antennal process present on ventral cephalothoracic surface immediately posterior to base of antenna (arrowed in Fig. 22D View FIGURE 22 ). Mandible stylet-like, armed with 8 marginal teeth distally ( Fig. 22E View FIGURE 22 ). Maxillule ( Fig. 22F View FIGURE 22 ) bilobate, smaller lobe tipped with 1 spiniform element; larger lobe tipped with 3 unequal spiniform elements. Maxilla ( Fig. 22G View FIGURE 22 ) 2-segmented: comprising proximal syncoxa (lacertus) and distal basis (brachium); basis ornamented with patch of spinules distally and bearing bifid element plus long process originating adjacent to terminal claw; claw ornamented with sharp denticles along both edges. Maxilliped ( Fig. 22H View FIGURE 22 ) 2-segmented comprising massive corpus with papilliform element on medial surface opposing tip of claw, and distal subchela; corpus ornamented with minutes spinules on medial surface; subchela comprising compound endopodal segment and strongly curved terminal claw; armed with minute seta on inner concave margin and distal knob-like process; surface of claw striated.

Leg 1 with protopodal part fused to somite; intercoxal sclerite absent ( Fig. 23A View FIGURE 23 ): leg biramous with outer basal seta plus short, stout inner spine on incorporated protopod; exopod 1-segmented, armed with 5 terminal spines with smooth margins, surface of segment ornamented with rows of spinules distally; endopod 1-segmented, armed with terminal seta about twice as long as segment, and ornamented with patches of spinules. Leg 2 ( Fig. 23B View FIGURE 23 ) mounted on inflated subspherical prominence derived from incorporated protopod and armed with outer seta on papilla: both rami 1-segmented and ornamented with scattered spinules; exopod armed with 4 small distal spines; endopod armed with apical seta about twice as long as segment. Leg 3 lamellate and trilobate ( Fig. 23C View FIGURE 23 ); 3 digitform lobes connected by membranous web; outer and middle lobes located closer to each other, separated from inner lobe by wider gap; outer lobe ornamented with minute serrated scales on tip ( Fig. 23D View FIGURE 23 ), ornamentation lacking on middle and inner lobes; members of leg pair separate along ventral mid-line. Leg 4 ( Fig. 23E View FIGURE 23 ) biramous with both rami forming elongate processes about equal in length; dorsal seta present basally (arrowed in Fig. 23E View FIGURE 23 ). Leg 5 well developed; forming cylindrical lobe about 6.6 times longer than wide, reaching beyond tips of caudal rami ( Fig. 22A View FIGURE 22 ); armed with outer basal seta proximally on dorsal surface.

Male. Body smaller than female, mean body length 2.00 mm (based on 2 specimens). Cephalothorax comprising about 47% of total body length; slender, broadest at middle, with angular lateral margins; frontal area of cephalothorax carrying antennule and antennae, defined by slight indentation ( Fig. 23F View FIGURE 23 ). Trunk slender, comprising second to fourth pedigerous somites fused to urosome. Urosome comprising fifth pedigerous somite, genital somite and 1-segmented abdomen, all fused. Genital somite with convex lateral margins, wider than abdomen. Caudal rami as in female.

Antennule indistinctly 6-segmented ( Fig. 23G View FIGURE 23 ) with irregular cuticular thickenings, setal formula: 1, 3, 2, 1, 1, 11 + 2 ae. Parabasal flagellum absent. Antenna ( Fig. 23H View FIGURE 23 ) comprising massive corpus and distal subchela; corpus armed with papilliform process and small spinous process medially; subchela armed with 2 blunt elements; small process present in articulation between corpus and subchela. Postantennal process small, hemispherical ( Fig. 24I View FIGURE 24 ). Mandible ( Fig. 23J View FIGURE 23 ) and maxillule similar to those of female. Maxilla as for female but with additional spinular ornamentation distally on basis ( Fig. 24A View FIGURE 24 ). Maxilliped similar to female but with slightly different myxal ornamentation ( Fig. 24B View FIGURE 24 ); corpus with papilliform element and adjacent spinous elements at mid-level, plus small bifid element distally; subchela as in female.

Leg 1 with protopod distinct from somite; members of leg pair joined by intercoxal sclerite ( Fig. 24C View FIGURE 24 ). Each leg biramous with outer seta and short, stout 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 very long terminal seta about 2.5 times longer than segment, and ornamented with spinules. Leg 2 ( Fig. 24D View FIGURE 24 ) mounted on inflated prominence derived from partly incorporated protopod armed with outer seta: trace of intercoxal sclerite retained: exopod showing traces of subdivision with distal part set at angle to proximal part, exopod ( Fig. 24E View FIGURE 24 ) armed with 3 small distal spines and larger curved element; endopod well defined basally, armed with long terminal seta about 2.0 times longer than segment, and ornamented with patches of spinules. Leg 3 ( Fig. 23F View FIGURE 23 ) biramous; comprising long cylindrical exopodal process protruding ventrolaterally from trunk with small ventrally-directed endopodal process near base of exopod; endopod ornamented with surface spinules and conspicuous papillae ( Fig. 24F View FIGURE 24 ) as present on exopodal lobe; outer protopodal seta present dorsally at base of limb. Leg 4 biramous, comprising 2 long cylindrical processes, with outer protopodal seta on common base ( Fig. 23F View FIGURE 23 ); leg 4 longer than exopod of leg 3; surfaces of both rami ornamented with conspicuous papillae, as present on leg 3. Leg 5 reduced to small conical process ( Fig. 23K View FIGURE 23 ) with minute vestige of seta at apex.

Remarks. The species of Lernanthropus recorded on hosts belonging to the family Carangidae are listed in Table 2 View TABLE 2 and their characteristics are discussed above in the remarks section supporting the establishment of L. alepicolus sp. nov. Comparison of L. gnathanodontus sp. nov. with congeneric species known from carangids is relatively easy since the new species can be distinguished by the trilobate form of leg 3; no other species of Lernanthropus shares this form of third leg. The new species also has prominent anterolateral processes on the cephalothorax which represent frontal projections of the ventrally folded lateral margins of the dorsal cephalic shield. Prominent frontal projections are most notably present in L. corniger , but smaller paired processes are also present in L. alatus , L. indicus and L. koenigii , and detailed comparisons are necessary between the new species and these four species known to utilize carangid hosts.

In L. corniger the frontal projections are enormous, almost half the length of the dorsal cephalic shield, whereas in the new species they are only about 20% of shield length. The dorsal trunk plate of L. corniger is subcircular and about as wide as long whereas that of L. gnathanodontus sp. nov. is distinctly longer than wide and has a narrow anterior base, expanding posteriorly towards a broader posterior margin which is slightly concave.

Lernanthropus gnathanodontus sp. nov. has elongate fifth legs (6.6 times longer than wide) which extend beyond the tips of the caudal rami. This serves to distinguish it from L. alatus and L. alepicolus sp. nov., both of which have short fifth legs. Both L. indicus and L. koenigii have elongate fifth legs as in the new species, but the dorsal trunk plate of L. indicus and L. koenigii is broadest anteriorly and tapers towards the rear margin which is relatively narrow, whereas in the new species the plate has a narrow anterior base and becomes broader posteriorly. The third legs of L. indicus and L. koenigii are biramous, comprising two flattened lobes (fused in L. koenigii , according to Pillai (1985)) and are readily distinguishable from those of the new species which comprise 3 digitiform lobes connected by cuticular membrane. These differences from similar congeneric species fully justify the establishment of the new species.