Thalia sibogae Van Soest, 1973

Karunarathne, Krishan D. & Croos, M. D. S. T. De, 2021, Pelagic tunicates (Appendicularia and Thaliacea) of Sri Lanka: two first records with an annotated checklist, Zootaxa 5067 (3), pp. 352-376 : 358-360

Thalia sibogae Van Soest, 1973

Thalia sibogae Van Soest 1973: 204 , 205, Fig. 8; 1998: 235, Table 14.1. Kim et al. 2011: 147, Fig. 5. Purushothaman et al. 2017. Ishak et al. 2018: 454, 459–465, Figs. 4a–e , 5.

Material examined. One solitary zooid ( MDAFWU 2018 /85), St.133, January 2018 ( Fig. 2D–F ) .

Description. Solitary zooid: Transparent body bulky rounded with a very thick, smooth test, with two long (about one third of body length), tapering processes on the posterior end ( Fig. 2D–F ); length without processes 7 mm. Atrial palps fairly small and bifurcate ( Fig. 2F ); lateral projections very small, simple and not bifurcated ( Fig. 2D, F ); medioventral projections are small and of unequal length, the anterior ones are the smallest ( Fig. 2E ). Six body muscles broad; M I narrowly interrupted dorsally, M II–IV converged mid-dorsally, M V and M VI near but do not touch dorsally; M II–V in complete rings, M VI interrupted ventrally ( Fig. 2D ). Totally (M I–VI) 60 muscle fibers. The nucleus (stomach + intestine) is close to the middle posterior projection ( Fig. 2D–F ).

Aggregate zooid: Not collected.

Global distribution. The Central Indo-Pacific ( Van Soest 1973, 1998; van der Land 2008); Korean waters ( Kim et al. 2011); the east coast of Peninsular Malaysia ( Ishak et al. 2018). Type locality: Pulu Sanguisapio, Tawi-Tawi Island, Sulu archipelago ( Siboga -Expedition St. 93, 05°N, 120°E).

Remarks. Although Van Soest (1973) did not observe lateral projections on the type material of T. sibogae , tiny lateral projections may exist with solitary zooids of T. sibogae according to Kim et al. (2011) and Ishak et al. (2018). Therefore, the Sri Lankan specimen resembles the specimens of Kim et al. (2011) and Ishak et al. (2018). The total number of muscle fibres (M I–VI) in solitary zooids of Thalia democratica ( Forskål, 1775) shows a clinal variation, decreasing from higher to lower latitudes ( Van Soest 1975b); and there is a possibility to be such a variation in T. sibogae , but data is not enough in the literature for comparison.

Local name: Indi Gaduwa (in Sinhalese) [note: usually fishers use this term for tiny salps, while the Pegea -like larger salps are called ‘ Rata-indi Gadu ’ in Sinhalese and ‘ Pereechcham Katti ’ in Tamil].

Local importance: None [but, Pegea -like larger salps regularly clog into fishing nets (authors’ observations)].

Figures

FIGURE 2. Firstly reported pelagic tunicates to Sri Lanka in “Waya-jel-Survey” (A–F): a live colony of Pyrostremma spinosum near to the sea surface (A & B), and an illustration of its blastozooid (C); Thalia sibogae solitary zooid in preserved form (D), ventral view of medioventral projections (E), and an illustration of its posterior part (F). a—anus; ap—atrial palp; dmp— dorsal medioventral projection; e—endostyle; es—excurrent/buccal siphon; g—ganglion; is—incurrent/atrial siphon; lp—lateral projection; n—nucleus; o—ovary; pb—pharyngeal basket; pp—posterior projection; sl—stolon; sm—stomach; t—testis; vmp—ventral medioventral projection. Scales: E = 0.5 mm; C, D, F = 1 mm; A & B = 0.4 m. Images A & B by Franco Banfi from off Mirissa, Sri Lanka

FIGURE 4. Schematic diagrams of Sri Lankan pelagic tunicates, showing the general morphology of their families (A–H): the lateral view of mature individuals of Fritillariidae (A) and Oikopleuridae (B); gonozooid (C) and degenerated oozooid / nurse (D) of Doliolidae; dorsal view of a solitary zooid (E) and aggregate zooid (F) of Salpidae; a blastozooid (G) and sagittal section of a colony (H) of Pyrosomatidae. Adapted from Claus (1883), Esnal (1981), Barnes et al. (1993) and Sri Lankan specimens. Note: The tails of appendicularian diagrams have been rotated through 90º for clarity.