Anuretes amplus, Boxshall, 2018

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 : 14-19

Anuretes amplus sp. nov.

( Figs. 3 , 4 )

Type material. Holotype ♀, 7 paratype ♀♀ from Diagramma pictum (Thunberg, 1792) (TC17266), 19 January 2016, QM Reg. Nos Holotype ♀ W53042, 3 paratype ♀♀ W53043; 4 paratype ♀♀ NHMUK Reg. Nos 2017.176– 179.

Type Host. Diagramma pictum (Thunberg, 1792) .

Site on host. Gills.

Etymology. The species name is derived from the Latin amplus , meaning large, ample, and alludes to the broad genital complex of the female.

Description. Adult female ( Fig. 3A ) mean body length including caudal rami 1.01 mm, range from 0.97 to 1.04 mm (based on 7 specimens). Cephalothorax subcircular with small posterior sinuses; cephalothorax comprising about 56 % of total body length. Free margin of thoracic portion of dorsal cephalothoracic shield extending posteriorly about level with rear margins of lateral portions. Frontal plates without lunules. Free fourth pedigerous somite visible in dorsal view ( Fig. 3A ). Genital complex distinctly wider than cephalothorax, about 1.7 times wider than long, with strongly convex lateral margins ( Fig. 3A ). Abdomen reduced and incorporated into genital complex. Caudal rami directed posterolaterally on margin of abdomen, about 1.4 times longer than wide: each ramus ( Fig. 4A ) armed with long setae at inner and outer distal angles, 1 shorter plumose seta on lateral margin, and 3 long plumose setae on distal margin.

Antennule ( Fig. 3B ) 2-segmented; large proximal segment with 25 hirsute setae arrayed along anteroventral surface and 2 setae located dorsally; distal segment bearing 12 elements (10 setae plus 2 aesthetascs) around apex, plus isolated seta on posterior margin. Antenna ( Fig. 3C ) comprising proximal segment bearing acutely-pointed, posteriorly-directed spinous process equipped with long medial flange extending onto inner margin of segment; middle segment subrectangular, tapering slightly distally, unarmed; terminal segment forming recurved claw bearing blunt element proximally and slender seta near anterior margin. Post-antennal process ( Fig. 3C ) weakly curved; ornamented with 2 unisensillate papillae on basal part and single similar unisensillate papilla on adjacent ventral cephalothoracic surface.

Mandible of typical caligid, stylet-like structure, with 12 marginal teeth ( Fig. 3D ). Maxillule ( Fig. 3C ) comprising anterior papilla bearing 3 unequal, naked setae and simple, tapering posterior process. Pair of rounded post-oral processes present ( Fig. 3C ). Maxilla 2-segmented, comprising elongate syncoxa and basis: syncoxa unarmed; basis ( Fig. 3E ) bearing spiniform flabellum on anterior margin and terminating in 2 claw-like elements (calamus and canna). Calamus much longer than canna, both ornamented with strips of finely serrated membrane. Maxillary whip with broad base and tapering distal whip ( Fig. 3E ). Maxilliped subchelate ( Fig. 3F ); robust proximal segment with ridge-like swelling on myxal surface; distal subchela short and strongly curved; with slender seta present proximally, surface of apical claw ornamented with striations.

Sternal furca with widely separated and slightly divergent tines, each ornamented with marginal flanges ( Fig. 3G )

First swimming legs biramous ( Fig. 4B ); joined by intercoxal sclerite; sympod with inner and outer plumose setae derived from basis, ornamented with surface spinules: endopod represented by minute flaccid vestige. Exopod 2-segmented; directed laterally and forming main axis of leg; first segment armed with small outer (anterior) spine and ornamented with interrupted row of spinules along posterior margin; second segment armed with 3 very short plumose setae along posterior margin and 4 distal elements along distal margin as follows: spine 1 (anterior-most) longest with minute serrations along both margins; spine 2 markedly longer than spine 3, each with accessory process and with bilateral strips of finely serrated membrane; seta 4 offset, originating on anterior surface of segment, about as long as spine 2 and shorter than segment.

Second leg ( Fig. 4C ) biramous, with flattened protopodal segments and 3-segmented rami. Coxae of leg pair joined by intercoxal sclerite bearing extensive flap of marginal membrane posteriorly. Coxa with plumose seta and surface sensilla. Basis armed with outer naked seta; ornamented with surface sensilla, marginal membrane posteriorly, and flap of membrane anteriorly, reflexed back over dorsal surface of segment. Exopodal segments 1 and 2 each with bilaterally serrate outer spine, plus inner plumose seta; spines aligned close to longitudinal axis of ramus; flap of membrane originating on first segment reflexed back over dorsal surface of ramus; segment 3 with naked proximal spine and curved bilaterally-serrate distal spine; apical spine with marginal membrane laterally and pinnules medially, plus 5 inner plumose setae. Endopodal segments 1 and 2 armed with 1 and 2 inner plumose setae respectively, outer margins smooth; segment 3 with 6 plumose setae.

Third leg pair ( Fig. 4D ) forming flattened plate closing posterior part of cephalothoracic sucker. Protopodal part flattened, joined by plate-like intercoxal sclerite forming apron, ornamented with marginal membrane posteriorly and along lateral margin anterior to exopod: bearing inner plumose seta at junction with intercoxal plate and outer plumose seta located dorsally near base of exopod; sensillae located adjacent to inner coxal seta and adjacent to origin of endopod; rami originating close together. Exopod 2-segmented; first segment armed with acutely-pointed claw directed over ventral surface of ramus, lacking inner seta; compound distal segment armed with 4 outer spines and 5 plumose setae. Endopod 2-segmented; first segment with slightly expanded lateral margin (forming small velum) ornamented with spinules and lacking inner plumose seta; compound distal segment with 5 plumose setae.

Fourth leg ( Fig. 4E ) 3-segmented, comprising slender protopodal segment and 2-segmented exopod: protopodal segment with plumose seta distally; first exopodal segment armed with slender bilaterally-serrate outer spine; second segment with 3 distal margin spines, each ornamented with bilateral strips of serrated membrane. Fifth legs well defined comprising anterior protopodal seta located on surface of genital complex and process representing exopod ( Fig. 4F ) armed with 3 plumose setae and ornamented with conspicuous sensilla.

Remarks. The new species combines possession of a maxillary whip with a I; III spine formula for the 2- segmented exopod of leg 4. Seven other species exhibit this same combination: A. anomalus Pillai, 1967 , A. grandis Ho & Lin, 2000 , A. hoi Prabha & Pillai, 1986 , A. justinei Venmathi Maran, Ohtsuka & Boxshall, 2008 , A. occultus Ho & Lin, 2000 , A. rotundigenitalis Hameed, 1976 , and A. similis Ho & Lin, 2000 . Three of these species possess a very large genital complex: in A. grandis the female genital complex is usually longer than wide and about two-thirds as long as the cephalothorax, in A. rotundigenitalis it is about as long as wide and about as long as the cephalothorax, and in A. occultus it is longer than wide and longer than the cephalothorax. The proportions of these three species are markedly different from those of the new species, with its enlarged genital complex that is distinctly wider than long and shorter than the cephalothorax. Anuretes hoi differs from the new species in possessing a large pointed myxal process on the maxilliped ( Prabha & Pillai, 1986) and in the setation of both rami of leg 3 (exopod I-0; III,4 and endopod 0-0; 6 compared to I-0; IV,5 and 0-0; 5 in the new species). Both A. justinei and A. similis are similar to the new species in having a transverse fold in the myxal area of the female maxilliped. The tines of the sternal furca are strongly divergent in A. justinei , the posterior process of the maxillule is broadbased triangular in shape, and the endopod of leg 3 has setation of 0-0; 6 ( Venmathi Maran et al., 2008). In contrast, the new species has straight to weakly divergent tines on the sternal furca, the posterior process of the maxillule is long and narrow at the base, and the endopod of leg 3 has setation of 0-0; 5. The new species differs from A. similis in the setation of both rami of leg 3: the exopod has I-0; IV,5 and the endopod 0-0; 5 in the new species compared to I-0; III,5 and 0-0; 6, respectively, in A. similis ( Prabha & Pillai, 1986) .

Using the key to species of Anuretes provided by Ho & Lin (2000), the new species keys out as A. anomalus which, as Lepeophtheirus anomalus , has already been reported from Queensland, on the same host (as Spilotichthys pictus ) caught at Heron Island (Ho & Dojiri, 1977). However, there are numerous differences between the Moreton Bay females and A. anomalus . The most obvious is the disproportionate width of the genital complex of the new species. It is markedly wider than the cephalothorax in the holotype and all 7 female paratypes whereas in A. anomalus it is narrower than the cephalothorax. In addition, there are differences in leg setation: A. anomalus has 6 setae on the distal endopodal segment of leg 3 whereas the new species has only 5 setae ( Fig. 4D ), and the first exopodal segment of leg 3 has an inner seta in A. anomalus (Ho & Dojiri, 1977) but none in the new species. Finally, the presence of the long medial flange on the proximal segment of the antenna is a unique feature of the new species. These differences are sufficient to justify the establishment of a new species.

Comparison with A. brevis Pearse, 1951 is problematic since this species is known only from a single male. The body lengths of known species ( Table 2) provide relevant data. Anuretes brevis has a male body length of 1.55 mm ( Pearse, 1951): the female of the new species has a mean body length of only 1.01 mm and it is the second smallest member of the genus discovered to date. In caligid species, the female is typically larger than the conspecific male, although exceptions are known (e.g. Caligus curtus Müller, 1785 and C. dicentrarchi Cabral & Raibaut, 1987) where the male is larger than the female. A sexual size disparity of such a magnitude (female of 1.01 mm versus male of 1.55 mm) is unknown and in all Anuretes species where both sexes are known, the female is larger than the male ( Table 2). In addition, there are apparent differences between the new species and A. brevis in some of appendages that do not usually show sexual dimorphism, for example, the exopod of leg 4 of A. brevis carries 4 long spines, whereas in the new species the 3 more proximal spines are markedly shorter than the distal spine. Leg 3 also appears very different in the illustration of Pearse (1951: Fig. 67g ) but the leg may have been damaged or misinterpreted since it does not resemble leg 3 in any of its congeners.

Figures

FIGURE 3. Anuretes amplus sp. nov., paratype female. A. habitus, dorsal; B, antennule, ventral; C, antenna, post-antennal process, maxillule and post-oral process, drawn in situ; D, mandible; E, left maxilla and maxillary whip, drawn in situ; F, maxilliped;G, sternal furca. Scale bars:0.5 mm on A, 50 µm on B–C, E–G, 25 µm on D.

FIGURE 67. Lepeophtheirus acutus Heegaard, 1943, female. A, habitus, dorsal; B, maxillule; C, distal margin spines on exopod of leg 1; D, first and second endopodal segment of leg 2; E, leg 4. Scale bars: 1.0 mm on A, 100 µm on B, D, 200 µm on E, 50 µm on C.

FIGURE4. Anuretes amplus sp. nov., paratype female. A.caudal ramus, ventral; B,leg 1; C, leg 2,D, leg 3; E, leg 4;F, leg 5. Scale bars 25 µm on A, 50 µm on D–F.