Thysanote rastrelligeri Rangnekar, 1962

Helna, Ameri Kottarathil, Aneesh, Panakkool Thamban, Ismail, Norshida & Maran, Balu Alagar Venmathi, 2025, Complementary description and further record of Thysanote rastrelligeri Rangnekar, 1962 (Copepoda: Siphonostomatoida: Lernaeopodidae) from a new host, Zootaxa 5642 (1), pp. 16-28 : 18-25

publication ID	https://doi.org/10.11646/zootaxa.5642.1.2
publication LSID	lsid:zoobank.org:pub:A7ACF523-0962-4EFE-A09F-2B07A257596D
DOI	https://doi.org/10.5281/zenodo.15563480
persistent identifier	https://treatment.plazi.org/id/03877832-2571-FFBB-6EBE-C5C4FF56870F
treatment provided by	Plazi
scientific name	Thysanote rastrelligeri Rangnekar, 1962
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Treatment

Thysanote rastrelligeri Rangnekar, 1962 View in CoL

( Figures 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Material examined. 9♀♀

Nontype material. All from Megalaspis cordyla collected from the fish market and caught from the Arabian Sea , off Neendakara coast, southwest coast of India, coll. PT Aneesh and AK Helna on 17 December 2018. 1 ♀ (13 mm) (Reg. No. ZSI/WGRC/IR/INV/ 28933 ) ; 1 ♀ (12 mm) (Reg. No. ZSI/WGRC/IR/INV/28934 ) ; 1 ♀ (11.5 mm) (Reg. No. ZSI/WGRC/IR/INV/ 28935 ) .

Redescription of post-metamorphic female ( Figures 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 ): Body elongate ( Figs 1 B – E View FIGURE 1 , 2 A – B View FIGURE 2 ) consisting of cephalothorax and genital trunk. Cephalothorax elongate, cylindrical, in line with genital trunk, constituting 60% of body and 2 times longer than “maxillary arms” (maxillae). Each maxilla carrying two pairs of filament-like processes, one long basal, and short medial. Cephalothorax narrower than genital trunk. Genital trunk, cylindrical, 1. 3 times longer than “maxillary arms”, constituting 40% of body; broadest towards distal side; posterior margin strongly convex towards caudal end. Trunk with four processes, two dorso-laterals and two ventro-laterals.Abdomen imperceptible. Caudal ramus ( Fig. 2E View FIGURE 2 ) consisting of single, moderately elongate, unarmed, conical process. Genital orifices (egg-sac outlets) slit-like, on top of paired, regular hemispheric elevations( Fig. 2E View FIGURE 2 ). Small, paired, copulatory pores present between genital orifices. Egg strings ( Figs. 1 View FIGURE 1 , 2A View FIGURE 2 ) multiseriate.

Antennule ( Fig. 3A View FIGURE 3 ) uniramous, short three-segmented; proximal and middle segments unarmed, distal segment with three short apical spiniform setae. Antenna ( Fig. 3B View FIGURE 3 ) biramous, robust, exopod much broader than endopod, two-segmented, unarmed; endopod, two-segmented, terminal segmented with two-minute apical spiniform setae. Mandible ( Figs 3D View FIGURE 3 , 5A – B View FIGURE 5 ) two-segmented typical lernaeopodid type, heavily sclerotized, basal segment strong and globular; terminal segment denticulate edge with 12 teeth. Maxillule ( Figs 3C View FIGURE 3 , 5D – F View FIGURE 5 , 6C – F View FIGURE 6 ) biramous, small delicate. Exopod tiny, ventrally oriented, consisting of short conical outgrowth. Endopod with two apical setiferous processes. Maxilla ( Figs 2C – D View FIGURE 2 , 4A – C, E – F View FIGURE 4 ) large cylindrical, elongate, transformed into powerful “arms”, distally joined to opposite appendage by bulla; constricted subterminally into terminal peribullar collar; bulla conspicuous, mushroom-shaped ( Figs 2C–D View FIGURE 2 , 4A, E–F View FIGURE 4 ). Maxilla with two pairs of filament-like maxillary processes, ( Figs 1 View FIGURE 1 , 2A–C View FIGURE 2 , 4A View FIGURE 4 ); first pair long basal and located postero-ventrally near basal part of appendage; second pair, short located at middle part of appendage. Maxillary gland orifices located on hemispherical processes, medially at base of appendage ( Figs 2C View FIGURE 2 , 4A–C View FIGURE 4 ). Maxilliped ( Figs. 3E View FIGURE 3 , 5C View FIGURE 5 , 6D View FIGURE 6 ), uniramous, subchelate, located subterminally on cephalothorax. Segmentation obscured by thick layer of wrinkled cuticle. Subchela with one shaft and claw. Shaft with small seta at base of claw, claw without secondary teeth; subchela covered on ventral side by pillow-like cuticular fold.

Size. Ovigerous female: 10.4–11.0 mm (n=9).

Colour. Live specimens white.

Host. Scomber microlepidotus Rüppell, 1836 (= Rastrelliger kanagurta (Cuvier, 1816)) (type host; Rangnekar 1962); Megalaspis cordyla (Linnaeus, 1758) (present study).

Site of attachment. branchial cavity of the Indian Mackerel, Rastrelliger kanagurta ; body surface over the base of the dorsal fin of Megalaspis cordyla (present study).

Distribution. Mumbai Coast, India ( Rangnekar, 1962); Kerala coast (present study) (see Fig. 7 View FIGURE 7 ).

Remarks. Thysanote rastrelligeri is one of eight species of Thysanote known from India ( Rangnekar 1962; Pillai 1985; Helna et al. 2024) and is highly distinct within the genus. It can be distinguished from its congeners by the following combination of morphological characteristics: (1) presence of two pairs of maxillary processes; (2) cephalothorax longer than the trunk; (3) presence of four simple posterior trunk processes, two dorso-laterals and two ventro-laterals; (4) uropods approximately 0.5 times the length of the posterior processes.

Rangnekar (1962) originally described T. rastrelligeri based on specimens recovered from the branchial cavity of the Indian mackerel, Rastrelliger kanagurta . The description was accompanied by six figures of the adult female (see Figs. 4A–F View FIGURE 4 in Rangnekar 1962). While the original description provided some species-specific details, it requires revision to meet modern taxonomic standards. Unfortunately, Rangnekar (1962) did not specify the deposition of the type specimen, and our inquiries at various repositories in India have failed to locate any material that could be identified as the type specimen of T. rastrelligeri .

The newly collected specimens of T. rastrelligeri described here were recovered from a different host species, Megalaspis cordyla , and from a new site of attachment—the body surface—collected from a fish market along the Kerala coast, India. Since these specimens were found on a non-type host and at a novel attachment site, they do not meet the criteria for neotype designation to conserve the species name. However, the present specimens exhibit key diagnostic characteristics consistent with T. rastrelligeri , confirming their identification.

A comprehensive summary of the updated global distribution and host records of Thysanote is provided in Table 1 View TABLE 1 .