Sagum vespertilio Kabata, 1979

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 : 91-95

Sagum vespertilio Kabata, 1979

( Figs. 49–50 )

Material examined: Holotype ♀ and paratype ♀ from Lethrinus laticaudis Alleyne & MacLeay, 1877 (as Lethrinus fletus ), Moreton Bay , Queensland; 08 April 1964; collected by P.C. Young; NHMUK Reg. No. 1977.122–123. 2♀♀ from L. laticaudis, Sunshine Coast, Queensland; date of collection unknown; collected by D.P. Barton; QM Reg. No. W29506.

1♀ from Lutjanus sebae (Cuvier, 1816) ( SSRE2015006 ), Joseph Bonaparte Gulf , Northern Territory, 03 August 2015; collected by D.P. Barton ; MAGNT Reg. No. Cr 019252 . 2♀♀ from L. sebae ( SSRE2015008 ), Joseph Bonaparte Gulf , Northern Territory, 03 August 2015; collected by D.P. Barton ; MAGNT Reg. No. CR019253 . 1♂ from L. sebae ( SSRE2015012 ), Joseph Bonaparte Gulf , Northern Territory, 03 August 2015; collected by D.P. Barton ; MAGNT Reg. No. Cr 019254 . 1♀ from L. sebae ( SSRE2016010 ), Arafura Sea East , Northern Territory, 03 February 2016; collected by D.P. Barton. 1♀ from L. sebae ( SSRE2016013 ), Arafura Sea East , Northern Territory, 03 February 2016; collected by D.P. Barton. 1♀ from L. sebae ( SSRE2016031 ), Arafura Sea West , Northern Territory, 30 March 2016; collected by D.P. Barton ; NHMUK 2019.1037 – 1039 .

1♀ from Lutjanus malabaricus (Bloch & Schneider, 1801) ( SSSTS2015016 ), Joseph Bonaparte Gulf , Northern Territory, 03 August 2015; collected by D.P. Barton ; 1♀ from L. malabaricus ( SSSTS2015024 ), Joseph Bonaparte Gulf , Northern Territory, 03 August 2015; collected by D.P. Barton ; 1♀ from L. malabaricus ( SSSTS2015039 ), Arafura Sea East , Northern Territory, 14 August 2015; collected by D.P. Barton. 1♀ from L. malabaricus ( SSSTS2015044 ), Arafura Sea East , Northern Territory, 14 August 2015; collected by D.P. Barton. MAGNT Reg. No. Cr 019255 . 1♀ from L. malabaricus ( SSSTS2015058 ), Arafura Sea East , Northern Territory, 14 August 2015; collected by D.P. Barton. 1♀ from L. malabaricus ( SSSTS2015063 ), Gulf of Carpentaria , Northern Territory, 21 August 2015; collected by D.P. Barton. 1♀ from L. malabaricus ( SSSTS2015075 ), Gulf of Carpentaria , Northern Territory, 21 August 2015; collected by D.P. Barton. 2♀♀ from L. malabaricus ( SSSTS2015104 ), Timor Reef Fishery Zone , Northern Territory, 16 September 2015; collected by D.P. Barton. 1♀ from L. malabaricus ( SSSTS2015110 ), Timor Reef Fishery Zone , Northern Territory, 16 September 2015; collected by D.P. Barton. 1♀ from L. malabaricus ( SSSTS2016003 ), Arafura Sea West , Northern Territory, 22 April 2016; collected by D.P. Barton. 1♀ from L. malabaricus ( SSSTS2016009 ), Arafura Sea West , Northern Territory, 22 April 2016; collected by D.P. Barton ; NHMUK Reg. No. 2018.1040–1047 .

1♀ from Lutjanus erythropterus Bloch, 1790 , outer Darwin Harbour , Northern Territory, August 2012; collected by B K Diggles.

Differential diagnosis: Cephalothorax extremely broad (more than twice as wide as long); anterolateral margins of dorsal cephalothoracic shield expanded laterally into large triangular processes ( Fig. 49 A–C); ventral surface with paired ventrally-directed ridge-like lobes located lateral to base of antennae and postantennal processes. Ceph- alothorax separated from trunk by short neck bearing paired cylindrical processes laterally. Trunk wide; anterior part (second and third pedigerous somites) forming rounded anterior shoulders and lateral margins extended posteriorly overlapping broad dorsal trunk plate on both sides ( Fig. 49 A–C); dorsal trunk plate covering fourth pedigerous somite and extending posteriorly to overlap all except flagellate tips of fourth legs; posterior margin of dorsal trunk plate with weak median indentation. Lateral surface of head and dorsal surface of trunk ornamented with numerous small tubercles. Urosome comprising fifth pedigerous somite, genital complex and abdomen, all fused; entirely concealed beneath dorsal trunk plate. Egg sacs loosely coiled beneath dorsal trunk plate and concealed laterally by exopods of third legs. Caudal rami broad proximally, with long distal part tapering to acute tip; armed with 2 dorsal, 1 lateral and 2 apical setae. Leg 1 biramous, lacking intercoxal sclerite; with 1-segmented rami; partly concealed by ventral lobe adjacent to protopod. Leg 2 biramous with 1-segmented rami. Leg 3 with foliaceous rami: exopod flattened and orientated in horizontal plane; endopod orientated vertically and forming looped fold, open posteriorly. Leg 4 biramous; both rami forming foliaceous lobes with broad basal part tapering to distal flagellate part; outer and inner lobes similar in length. Leg 5 as short lobe with single seta. Body length of ♀ ranging from 4.44 to 6.22 mm, with a mean of 5.05 mm (based on 10 specimens from L. malabaricus ).

Description of male. Body smaller than female, comprising cephalothorax covered with dorsal shield and irregularly tapering trunk, terminating in narrow, angular posterior margin ( Fig. 50A ). Cephalothorax comprising about 52% of total body length: about as long as wide with rounded corners and slightly concave posterior margin: dorsal shield with narrow antennal part anteriorly and broader posterior part. Trunk about 1.3 times longer than maximum width (at anterior end); lateral margins sinuous; posterior margin with indentations at base of leg 3. Genitoabdomen bearing paired caudal rami, concealed beneath trunk in dorsal view. Caudal rami with broad base and narrow distal part ( Fig. 50B ); about 4.1 times longer than wide; armed with 2 dorsal setae proximally plus 2 apical setae; lateral seta absent.

Antennule indistinctly 6-segmented ( Fig. 50C ), armed with 5 setae on proximal segments plus 11 and 2 aesthetascs on compound apical segment; scar on proximal segment probably indicating lost seta in observed specimen. Parabasal flagellum absent. Antenna ( Fig. 50D ) comprising robust proximal segment, armed with papilliform process on myxal margin, and distal subchela: small process present in articulation at base of subchela; terminal claw tapering gradually, lacking armature. Mandible short, stylet-like; armed with 8 marginal teeth near apex ( Fig. 50E ). Maxillule with small inner lobe bearing single apical seta; longer outer lobe with 1 apical seta plus 2 setae on mid posterior margin ( Fig. 50F ). Maxilla with claw fused to basis; spinular ornamentation extending over claw and onto distal part of basis ( Fig. 50G ). Maxilliped with papilliform process surrounded by minute spinules on myxal surface; subchela with small proximal process on concave margin; apical claw unornamented ( Fig. 50H ).

Leg 1 biramous, with robust intercoxal sclerite joining members of leg pair ( Fig. 50I ); protopod with slender outer seta and stout inner spine: exopodal segment short, broader at tip, armed with 5 stout spines distally; endopod 1-segmented, armed with apical spine about as long as segment. Leg 2 ( Fig. 50J ) with outer seta on basis; exopod 1- segmented with partial transverse suture proximally; armed with 3 stout spines distally: endopod armed with single apical seta, shorter than segment. Leg 3 biramous ( Fig. 50A ) with each ramus forming elongate cylindrical lobe; anterior (exopodal) lobe apparently with swollen apex; armed with outer protopodal seta situated on small papilla located dorsally at base. Leg 4 biramous ( Fig. 50A ) with each ramus forming elongate cylindrical lobe; outer lobe slightly longer than inner; armed with outer protopodal seta situated on small papilla located dorsally at base. Leg 5 absent. Leg 6 represented by paired genital apertures, unarmed. Body length of single ♂ 1.81 mm.

Distribution: This distinctive species was originally described from Lethrinus laticaudis (as L. fletus (Whitley)) caught in Moreton Bay ( Kabata, 1979a). It was subsequently reported from L. nebulosus (Forsskål, 1775) landed in Taiwan by Ho et al. (2008) and from L. rubrioperculatus Sato, 1978 caught off New Caledonia ( Justine et al., 2010b). The Australian records presented here from Lutjanus sebae , L. malabaricus and L. erythropterus represent new host records. This species is now known from four species of Lethrinus and three species of Lutjanus . Ho et al. (2008) treated Sagum tuberculatum Pillai, 1985 described from Indian waters, as a junior synonym of S. vespertilio . The host of S. tuberculatum was given as Lutianus sp. by Pillai (1985) and its true identity cannot now be established. Pilla et al. (2012) reported S. vespertilio (as S. tuberculatum ) from Lutjanus fulviflamma (Forsskål, 1775) caught off the coast of India at Visakhapatnam.

Remarks: The original description of this species by Kabata (1979a) focused on the female habitus only and provided little detail of limb structure but Ho et al. (2008) were able to redescribe the female in detail based on new material from Taiwan. The male is described here for the first time, but only a single specimen was collected and, unfortunately, the urosome was damaged.

The description here of two previously unknown males of Sagum species allows us to attempt to formulate a set of diagnostic features for the males in this genus even though it appears that Sagum males vary markedly. We exclude the specimen described as the male of S. enneacentri Pillai, 1985 because, on the basis of the leaf-like third legs, we consider that it is probably an immature female (a possibility already noted by Pillai (1985)). The male of the New Zealand species, S. foliaceus , described by Hewitt (1968) is essentially similar to the males of many Lernanthropus species, having a trunk that is longer than the cephalothorax, biramous legs 3 and 4, but with the endopod of leg 3 reduced to a knob-like lobe, and with the genital complex and anal somite projecting posteriorly from the rear margin of the trunk. The males of a cluster of other species including S. folium , S. gurukun , S. lativentris , S. vespertilio and S. pillaisebastiani (described by Pillai (1985) as the male of S. epinepheli ) all share a relatively large cephalothorax, a broad trunk incorporating the genital complex, and biramous legs 3 and 4 where both rami are cylindrical and elongate. All of these species utilize hosts belonging to the closely related fish families Lutjanidae , Lethrinidae and Caesionidae .

The male of Norion tayenus Ho & Kim, 2004 , which occurs on the priacanthid host, Priacanthus tayenus ( Ho & Kim, 2004) , shares numerous character states with this cluster of Sagum species, indicating possible close affinity. Interestingly, these characteristics appear to be shared by Lernanthropus holmbergii von Nordmann, 1864 which was described on the basis of the male only, collected from an unknown fish caught off Hawaii (von Nordmann, 1864). This species could belong either to Sagum or to Norion , but at present should be considered as a species inquirendum since too few details are available to assess its identity.

Figures

FIGURE 49. Sagum vespertilio Kabata, 1979, adult ♀. A, habitus, lateral; B, habitus, dorsal; C, habitus, ventral. Scale bar 2 mm.

FIGURE 50. Sagum vespertilio Kabata, 1979, adult ♂. A, habitus, dorsal; B, caudal ramus, ventral; C, antennule; D, antenna; E, mandible; F, maxillule; G, basis of maxilla; H, maxilliped; I, leg 1 and part of intercoxal sclerite; J, leg 2. Scale bars A, 0.5 mm, B,C,H,I, 100 μm, D, 200 μm, E–G, J, 50 μm.