Caligus parvilatus Kim, 1998

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 : 103-107

Caligus parvilatus Kim, 1998

( Figs. 45–47 )

Syn: Caligus latus Kim, 1995

Non Caligus latus Byrnes, 1987

Material examined. 8♀♀, 3♂♂ from Abudefduf bengalensis (Bloch, 1787) (TC16957-61) 11 January 2016, QM Reg. No. W53092; 1 chalimus (TC17966), 4♀♀, 2♂♂ (TC 17806) 2 July 2016, NMHUK 2017.301–306; 1 immature ♀ from Abudefduf whitleyi Allen & Robertson, 1974 (TC16966) 11 January 2016;1♀ from Kyphosus bigibbus Lacepède, 1801 (TC17864) 4 July 2016, 1♀ (TC17792) 1 July 2016, NMHUK 2017.307–308.

Site on host. Body surface.

Description. Adult female ( Fig. 45A ) mean body length including caudal rami 2.18 mm (range 1.95 to 2.43 mm), (based on 11 specimens). Cephalothorax slightly longer than wide with shallow posterior sinuses; comprising about 60% of total body length. Free margin of thoracic portion of dorsal cephalothoracic shield extending posteriorly beyond rear margins of lateral portions. Lunules present ventrally on frontal plates. Genital complex subrectangular, 1.3 times wider than long; with rounded corners ( Fig. 45B ); fifth legs located close to posterolateral corners ( Fig. 45C ). Copulatory pores located near midline, oviduct openings marked by 2 swellings, 1 with finely ridged surface. Genital complex more than 4 times longer than abdomen. Abdomen 1-segmented; about 1.2 times wider than long in ventral view ( Fig. 45B ); carrying paired caudal rami distally; anal slit terminal. Caudal rami with parallel sides, longer than wide, measured at midpoints of margins. Each ramus armed with short hirsute seta at inner distal angle, slightly longer hirsute seta at outer distal angle, minute hirsute seta located just ventral to outer distal seta, and 3 long plumose setae on distal margin.

Antennule ( Fig. 45D ) 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. 45E ) comprising proximal segment bearing spatulate posteriorly-directed spinous process; middle segment subrectangular, tapering distally, unarmed; terminal segment forming short, recurved claw bearing short spinous swelling proximally, and minute setal vestige near anterior margin. Post-antennal process ( Fig. 45F ) well-developed, curved; ornamented with 2 bisensillate papillae on basal part and single bisensillate papilla on adjacent ventral cephalothoracic surface.

Mandible of typical stylet-like structure, with 12 marginal teeth ( Fig. 45G ). Maxillule ( Fig. 46A ) comprising anterior papilla bearing 3 unequal, naked setae and blunt posterior, tine-like process. Maxilla 2-segmented ( Fig. 46B ), comprising elongate syncoxa and basis: syncoxa unarmed; basis bearing membranous subapical flabellum on anterior margin, and terminating in 2 subequal claw-like elements (calamus and canna). Calamus slightly longer than canna, ornamented with strips of serrated membrane arranged obliquely around surface; canna ornamented with strips of serrated membrane. Maxilliped subchelate ( Fig. 46C ); slender proximal segment unarmed and without process on myxal surface; distal subchela with apical claw separated from proximal segmental part by incomplete suture; slender seta present on concave margin.

Sternal furca ( Fig. 46D ) with slightly divergent tines, expanding distally and with bluntly truncated tip.

First swimming leg pair ( Fig. 46E ) with joined by slender intercoxal sclerite; sympod with inner and outer plumose setae derived from basis; endopod represented by unarmed process on posterior margin of basis. Exopod 2-segmented; directed laterally and forming main axis of leg; first segment robust, about 2.8 times longer than wide and armed with small outer (anterior) spine and ornamented with row of setules along middle section of posterior margin; second segment armed with 3 long plumose setae along posterior margin and 4 distal elements along oblique distal margin. Distal elements as follows: spine 1 (anterior-most) simple, longer than spine 2; spine 2 markedly longer than spine 3, each with accessory process; seta 4 about 25% longer than spine 1, and shorter than segment.

Second leg ( Fig. 46F ) biramous, with flattened protopodal segments and 3-segmented rami. Coxae of leg pair joined by intercoxal sclerite bearing 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 large unilaterally-dentate, reflexed outer spines extending obliquely across ventral surface of ramus ( Fig. 46G ), plus inner plumose seta; first segment also with flap of membrane anteriorly, reflexed back over dorsal surface of segment: segment 3 with 2 outer spines (proximal spine minute; distal spine unilaterally pinnate), apical spine with marginal membrane laterally and pinnules medially, and 5 inner plumose setae. Endopodal segments 1 and 2 armed with 1 and 2 inner plumose setae respectively; segment 3 with 6 plumose setae; outer margins of second and third endopodal segments ornamented with fine setules.

Third leg pair ( Fig. 47A ) forming flattened plate closing posterior part of cephalothoracic sucker as typical for genus. 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 dorsal to base of exopod; long sensillae located adjacent to inner coxal seta and adjacent to origin of endopod. Exopod 3-segmented; first segment armed with weakly curved outer spine directed over ventral surface of ramus, spine and outer distal margin of segment ornamented with strips of membrane, lacking inner seta; second segment with slender outer spine and inner plumose seta; third with 7 setal elements (3 outer spiniform elements and 4 inner plumose setae); outer margin of segment 2 ornamented with row of slender setules. Endopod 2-segmented; first segment expanded laterally to form flap-like velum closing off space between rami; velum ornamented with row of fine setules along free margin; segment bearing inner plumose seta; second segment with 6 setal elements increasing in length from outermost to innermost.

Fourth leg ( Fig. 47B ) 2-segmented, comprising slender protopodal segment and 1-segmented exopod: protopodal segment armed with plumose seta distally; exopodal segment armed with slender outer spine with pecten at base, and 1 long naked apical spine plus shorter naked subapical spine, each with pecten at base.

Fifth legs located posterolaterally on genital complex ( Fig. 45B,C ); each fifth leg comprising anterior spinous process bearing short plumose seta (representing outer protopodal seta) and long exopodal process with bifid tip armed with 2 plumose setae.

Mean body length of male including caudal rami 1.71 mm (range 1.61 to 1.75 mm) (based on 5 specimens).

Remarks. Caligus parvilatus was originally described by Kim (1995) under the name C. latus , which was preoccupied by Caligus latus Byrnes, 1987 . Kim (1998) proposed C. parvilatus as a replacement name. The adult female body form of C. parvilatus resembles C. tylosuri ( Rangnekar, 1956) and C. cordiventris Shiino, 1952 , particularly in the shared possession of a short broad genital complex which bears a distinctive fifth leg in the form of two rigid marginal processes, the anterior bearing the outer protopodal seta and the posterior representing the exopod and bearing plumose setae at its tip. It seems likely that the inadequately described C. eventilis Leigh- Sharpe, 1934 is also closely related to these three species.

Rangnekar (1956) originally placed C. tylosuri in Tuxophorus Wilson, 1908 but Pillai (1961) re-assigned it to Caligus . Comparison with Lin & Ho’s (2007) redescription of female C. tylosuri reveals many differences from C. parvilatus : the post-antennal process is bifid in the former but simple in C. parvilatus ; the tines of the sternal furca are strongly divergent in C. tylosuri but weakly divergent with expanded truncate tips in C. parvilatus ; the outer margin spines on the first and second exopodal segments of leg 2 are ornamented with finely serrate marginal membrane and are aligned close to the longitudinal axis of the ramus in C. tylosuri whereas in C. parvilatus they both lie obliquely across the surface of the ramus and are strongly serrated; leg 4 is slender in both species but carries 3 unequal apical spines in C. tylosuri , the longest of which is as long as the entire exopod, whereas in C. parvilatus there are only 2 relatively shorter, apical spines.

Shiino (1952) established C. cordiventris on the basis of five females collected from Prionurus scalprum (as Xesurus scalprum ) in Japanese waters. Subsequently he described the male from the same host ( Shiino, 1955a). This appears to be a rare species as it has not been reported since 1955, although it has been listed in syntheses such as the compendium of Yamaguti (1963). Caligus cordiventris is very similar to C. parvilatus : both species have serrated outer spines on the first and second exopodal segments of leg 2 and both have only 2 well developed spines on the distal margin of leg 4. These two species are best distinguished by the form of the exopod of leg 4: the spine marking the edge of the proximal exopodal segment is located about a third of the distance along the ramus in C. cordiventris and it extends less than half the distance to the apex of the limb, whereas in C. parvilatus the homologus outer margin spine is located about mid-margin along the unsegmented exopod, and it reaches nearly three quarters of the way to the tip. In addition, the sternal furca has slender tines with rounded tips in C. cordiventris whereas in C. parvilatus it has spatulate tines with broad, truncated tips.

Leigh-Sharpe (1934) described C. eventilis from a “black pomacentrid fish” caught north of Damar Island in the Banda Sea (= Siboga Station 144, Anchorage. Salomakië Island). The description lacks detail but the structure and armature of leg 4 and the possession of a broad genital complex with prominent anterior and posterior processes representing the fifth legs, suggest a close relationship with C. tylosuri , C. cordiventris and C. parvilatus . The shape of the short abdomen, with its unusually broad base, serves to separate C. eventilis from these other three species.

Caligus parvilatus was originally established on the basis of females found on the body surface of Ditrema temmincki Bleeker, 1853 (Embiotocidae) caught in the Korea Strait (Kim, 1995). Subsequently Kim (1998) reported both sexes of C. parvilatus from a parrotfish Calotomus japonicus (Scaridae) collected in Korean waters. In Moreton Bay, it was found on three different hosts, two species of the pomacentrid Abudefduf , A. bengalensis and A. whitleyi , and Kyphosus bigibbus (Kyphosidae) .

Figures

FIGURE 45. Caligus parvilatus Kim, 1998, female. A, habitus, dorsal; B, fourth pedigerous somite, genital complex and abdomen, ventral; C, right corner of genital complex showing fifth leg, ventral; D, antennule; E, antenna, ventral; F, postantennal process, ventral; G, mandible. Scale bars:0.5 mm on A, B, 200 µm onC, 100 µm D–G.

FIGURE46. Caligus parvilatus Kim, 1998, female.A, maxillule; B, maxilla; C, maxilliped; D, sternal furca; E, leg 1, ventral; F, leg 2, ventral; G,detail of outer spines on exopod of leg 2. Scale bars: 100 µm on A–E, 200 µm on F.

FIGURE 47.Caligus parvilatus Kim, 1998, female.A, leg 3, ventral; B,leg 4. Scale bars: 200 µm on A, 100 µm on B.