Anuretes amymichaelae, 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 : 19-24

Anuretes amymichaelae sp. nov.

( Figs. 5–7 )

Type material. Holotype ♂, 2 paratype ♀♀, 4 paratype ♂♂, I immature ♀ from Diagramma pictum (TC17266) 19 January 2016, QM Reg. Nos Holotype ♀ W53044, 1 paratype ♀, 2 paratype ♂♂ W53045; 2 paratype ♀♀, 1 paratype ♂, NHMUK Reg. Nos 2017.180–182.

Type Host. Diagramma pictum (Thunberg, 1792) .

Site on host. Unknown (in body soak).

Etymology. The species is named after my daughter Amy Michaela Boxshall who has helped to database and curate numerous collections of parasitic copepods over the years.

Description. Female ( Fig. 5A ) body length 0.92 and 0.93 mm. Cephalothorax subcircular (length 0.81 x width 0.69 mm), with small posterior sinuses; cephalothorax comprising about 86 % of total body length. Frontal plates without lunules. Free margin of thoracic portion of dorsal cephalothoracic shield extending posteriorly beyond rear margins of lateral portions and almost completely concealing free fourth pedigerous somite ( Fig. 5A ). Genital complex sub-rectangular, about 1.5 times wider than long ( Fig. 5B ) incorporating abdomen although vestiges of sutures defining limits of abdomen visible in ventral view ( Fig. 6A ). Genital complex with copulatory pores and genital apertures located dorsally. Fifth legs positioned on posterior margin and directed medially, overlaping dorsal surface of abdomen. Caudal rami about as long as wide (22 µm x 23 µm). Each ramus armed with 6 subequal plumose setae ( Fig. 5B ).

Antennule ( Fig. 5C ) 2-segmented; large proximal segment with 25 plumose 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. 5D ) comprising proximal segment bearing tapering, posteriorly-directed spinous process; middle segment subrectangular, unarmed; terminal segment forming recurved claw with weak swelling proximally, bearing small blunt element, and slender distal seta near anterior margin. Post-antennal process weakly curved; ornamented with 2 unisensillate papillae on basal part and single similar unisensillate papilla on adjacent ventral cephalothoracic surface.

Mandible of typical stylet-like structure, with 12 marginal teeth ( Fig. 5E ). Maxillule ( Fig. 5D ) comprising anterior papilla bearing 3 unequal, naked setae and simple posterior process. Pair of pointed post-oral processes present ( Fig. 5D ). Maxilla 2-segmented, comprising elongate syncoxa and basis: syncoxa unarmed; basis ( Fig. 5F ) bearing semicircular membranous flabellum on anterior margin, terminating in 2 claw-like elements (calamus and canna); calamus about 3 times longer than canna. Maxillary whip short, tapering process ( Fig. 5F ). Maxilliped subchelate ( Fig. 5G ); robust proximal segment with smooth myxal margin; distal subchela short with slender seta on concave margin.

Sternal furca ( Fig. 6B ) with widely separated, short, more-or-less parallel tines. Pair of hook-like processes present on ventral cephalothoracic surface posterior to intercoxal sclerite of leg 1 ( Fig. 6B ).

First swimming legs joined by slender intercoxal sclerite ( Fig. 6C ); sympod with inner and outer plumose setae derived from basis; endopod vestigial. Exopod 2-segmented; directed laterally and forming main axis of leg; first segment armed with small outer (anterior) spine and ornamented with row of setules along middle section of posterior margin; second segment armed with 3 plumose setae along posterior margin and 4 distal elements along distal margin as follows: spine 1 (anterior-most) longest, ornamented with row of fine spinules along concave margin, longer than spine 2; spine 2 markedly longer than spine 3, each with accessory process; seta 4 plumose, almost as long as spine 2, shorter than segment.

Second leg ( Fig. 6D ) biramous, with flattened protopodal segments and 3-segmented rami. Coxae of leg pair joined by intercoxal sclerite bearing expanded marginal membrane posteriorly; each 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 segment 1 with slightly curved outer spine aligned almost with longitudinal axis of ramus, plus inner plumose seta, carrying flap of membrane anteriorly, reflexed back over dorsal surface of ramus; segment 2 with outer spine directed distally plus inner plumose seta; segment 3 with small naked proximal spine and broader 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; segment 3 with 6 plumose setae; free outer margins of all endopodal segments ornamented with fine setules.

Third leg pair ( Fig. 6E ) forming flattened plate closing posterior part of cephalothoracic sucker. Protopodal part flattened, limb pair joined by broad, 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 dorsal to base of exopod; sensillae located adjacent to inner coxal seta and adjacent to origin of endopod; rami originating close together, no velum present. Exopod 2-segmented ( Fig. 6F ); first segment armed with short claw directed over ventral surface of ramus; compound distal segment armed with 3 outer spines and 5 plumose setae along margins. Endopod 2-segmented; first segment unarmed; compound distal segment with 6 plumose setae.

Fourth leg ( Fig. 5B ) comprising protopodal segment with plumose seta distally, plus 2-segmented exopod: first exopodal segment armed with long outer distal spine; distal segment with 3 long distal margin spines ornamented with finely serrated or smooth membrane.

Fifth legs forming setose lobe originating posterolaterally on genital complex ( Fig. 5B ) and extending medially over surface of abdomen beneath: each fifth leg comprising lateral seta located near corner of genital complex and process representing exopod armed with 3 reduced setae.

Male ( Fig. 7A ) mean body length 0.74 mm, range 0.72 to 0.77 mm (based on 5 specimens). Cephalothorax subcircular as in female (length 0.63 mm x width 0.56 mm). Paired areas of striated cuticle located either side of middle on ventral surface of frontal plates ( Fig. 7B ) forming weakly defined adhesion pads. Genital complex about 2.4 times wider than long, as measured along mid-line ( Fig. 7C ); with smoothly convex lateral margins and fifth and sixth legs together forming posterior margin of genital complex ( Fig. 7C, D ). Abdomen incorporated into genital complex but with traces of sutures ventrally helping to define original boundaries ( Fig. 7D ); carrying paired caudal rami distally. Caudal rami about as long as wide, armed with 6 plumose setae around distal margin.

Antennule, mandible and maxilla as in female. Antenna modified ( Fig. 7E ); first segment elongate; second segment reflexed with large digitiform process arising ventromedially, opposing tip of subchela; distal segment forming short powerful subchela, with accessory claw. Post-antennal process ( Fig. 7F ) more highly curved than in female; associated papillae unisensillate. Maxillule with minute tooth on surface of posterior process ( Fig. 7G ). Post-oral processes ( Fig. 7G ) longer in male than in female. Maxilliped ( Fig. 7H ) with smooth myxal margin; distal subchela as in female. Sternal furca with short, widely-separated but strongly incurved tines ( Fig. 7I ).

Leg 4 ( Fig. 7J ) more slender than in female. Legs 5 and 6 ( Fig. 7D ) together with caudal rami forming evenly convex, setose, posterior margin of body; consisting of paired fifth legs, each with 4 plumose setae, paired sixth legs, each with 2 plumose setae, and paired caudal rami, each with 6 plumose setae.

Remarks. This unusual copepod keys out to the Pseudanuretes / Anuretes couplet in the most recent key to genera of Caligidae (Dojiri & Ho, 2013) . The genus Pseudanuretes was maintained as valid by Dojiri & Ho (2013) and was defined by the presence of an accessory claw on the female antenna, combined with the absence of the post-antennal process, the posterior process of the maxillule, and the sternal furca. The new species from Moreton Bay lacks an accessory claw on the antenna but possesses a post-antennal process, a posterior process on the maxillule, and a sternal furca. On this basis it is placed in Anuretes .

The new species has a total of 4 spines on the exopod of leg 4, a character state shared with 12 other species: A. amplus sp. nov., A. anomalus , A. branchialis , A. grandis , A. hoi , A. justinei , A. occultus , A. perplexus Bassett- Smith, 1898, A. plectorhynchi , A. quadrilaterus Shiino, 1954 , A. rotundigenitalis and A. similis . Three of these species, A. branchialis , A. perplexus , and A. quadrilaterus , differ from the new species in lacking a maxillary whip. Of the remaining species only two, A. rotundigenitalis and A. similis , exhibit a total of 8 setal elements on the distal exopodal segment of leg 3, as found in the new species ( Fig. 6E, F ). The other species either have 9 ( A. anomalus , A. grandis and A. justinei ) or 7 ( A. hoi and A. occultus ) setal elements on this segment (Ho & Lin, 2000; Venmathi Maran et al., 2008).

The new species can be distinguished from A. rotundigenitalis by the size of the female genital complex: in the latter species it is almost as long as the cephalothorax and is about as long as wide, whereas in the new species it is wider than long and comprises only 15% of the length of the cephalothorax. The armature of the exopod of leg 3 also differs: all 8 setal elements on the compound distal segment are of similar length in A. rotundigenitalis (cf. Hameed, 1976) whereas in the new species they are clearly differentiated into 3 short outer spines and 5 longer inner setae. In addition, the outer spine on exopodal segment 1 is tiny in the new species but extends almost to the distal tip of the ramus in A. rotundigenitalis .

The new species is most similar to A. similis , the original description of which is published in Prabha & Pillai (1986) under the misapplied name of A. plectorhynchi (see Ho & Lin, 2000). These two species can be distinguished by: the maxillary whip is apparently bifid in A. similis but simple in the new species, the 3 outer spines on the compound distal exopodal segment of leg 3 differ in length (1 short, 1 medium and 1 long) in A. similis , but all are more or less equal in length in the new species, and the outer spine on the first exopodal segment of leg 3 is tiny in the new species but extends almost to the distal tip of the ramus in A. similis . These differences are sufficient to justify the establishment of a new species.

Comparisons have been restricted to limb structure despite an obvious difference between these two species in the size and shape of the genital complex (which is unusual in the new species in its small size, in the dorsal location of the genital apertures, and in the inward-facing orientation of the fifth legs), because of uncertainty over the state of maturity of the female specimen. The figured female is the best developed female collected and was found in amplexus with the figured male, which displays the typical secondary sexual characteristics of caligid males and is clearly adult. However, as caligids exhibit pre-copulatory mate guarding (Boxshall, 1 990b) it is possible that this female is either adult and has yet to undergo a post-mating enlargement of the genital complex which is known to occur (e.g. Boxshall, 1974), or is the final moult stage prior to the adult. In either case the shape of the genital complex might be unreliable as a species discriminant.

The male exhibits sexual dimorphism in the configuration of the genital complex, and in the antenna, the postantennal process, maxillule, post-oral process, maxilliped, and sternal furca, as well as in legs 5 and 6. The paired areas of striated cuticle either side of mid-line on the ventral surface of the frontal plates ( Fig. 7B ) are interpreted here as weakly defined adhesion pads. They appear to be involved in mating behaviour as they were held in contact with the dorsal surface of the female cephalothoracic shield in the pair observed in amplexus.

Figures

FIGURE 5. Anuretes amymichaelae sp. nov., paratype female. A. habitus, dorsal; B, fourth pedigerous somite, genital complex and abdomen, dorsal view, with inset showing position of caudal rami on distal margin of abdomen; C, antennule; D, antenna, post-antennal process, maxillule and post-oral process, drawn in situ; E, mandible; F, right maxilla and maxillary whip, drawn in situ; G, maxilliped.Scale bars:0.5 mm on A, 100 µm on B, D, F, G, 50 µm on C, 20 µm on E.

FIGURE 6. Anuretes amymichaelae sp. nov., paratype female. A, genital complex and abdomen, ventral; B, sternal furca, drawn in situ relative to interpodal bar of leg 1; C, leg 1; D, leg 2; E, leg 3; F, detail of exopod of leg 3. All scale bars 100 µm.

FIGURE7. Anuretesamymichaelae sp. nov., holotypemale.A.habitus,dorsal; B,corrugated adhesionpads on ventral surface of cephalothorax, either side of midline near frontal plates; ventral; C, genital complex and abdomen, dorsal view; D, genital complex and abdomen, ventral view showing fifthand six legs; E, antenna; F, post-antennal process; G, maxillule and post-oral process, drawn in situ; H, maxilliped; I, sternal furca; J, leg 4. Scale bars: 0.5 mm on A, 100 µm on C, D, J, 50 µm on B, E, G, 20 µm F, I.