Pyrostremma spinosum ( Herdman, 1888 )

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

Pyrostremma spinosum ( Herdman, 1888)

Pyrosoma spinosum Herdman 1888: 29 , Pl. 2 Figs. 9–15. Smith et al. 1901: 100, Fig. 20. Neumann 1913: 380, Pl. 42 Figs. 1–3 , Text-figs. 12, 13. Metcalf & Hopkins 1919: 219, Pls. 19–21. Sewell 1953: 60, Figs. 18–20. Tokioka 1960: 399. Godeaux 1972: 270, 271; 1979: 118; 1987: 201, Table 2 .

Pyrosoma (Pyrostremma) spinosum: Baker 1971: 109 , Pls. 1–4.

Pyrostremma spinosum: Van Soest 1974b: 25 , Figs. 1A–B , 2A , 3 –5; 1981: 607–609, Figs. 2 , 3 ; 1998: 236, Table 14.1. Godeaux 1998: 278, Fig. 17.4. Gershwin et al. 2014: 10. Purushothaman et al. 2017.

Material examined. A piece of ascidiozooid colony ( MDAFWU 2017 /470), St.133, March 2017., a piece of ascidiozooid colony ( MDAFWU 2017 /471), St.62, April 2017 ( Fig. 2A–C ) .

Description. Free-swimming tubular colony with a soft, semitransparent, reddish test; size up to 6.5 m long and about 0.4 m in diameter; broadening from the narrow closed (anterior) end to the wide-open (posterior) end, which provides a single whip-like process ( Fig. 2A, B ). The sexual individuals (blastozooids / ascidiozooids) are longer than high, with angular endostyle; arranged in thousands in neat oblique rows with their incurrent siphons to the outside of the tube, and excurrent siphons to the inside. Excurrent siphons with silt-like opening and short appendix ( Fig. 2C ).

Global distribution. The Atlantic Ocean, Indian Ocean and the western Pacific ( Van Soest 1998); the Mediterranean Sea ( Costello et al. 2001); New Zealand waters ( Gordon 2009). Type locality: Atlantic Ocean.

Remarks. In most of the cases, the P. spinosum colonies are found as fragments ( Sewell 1953; Van Soest 1981). Some specimens collected from the tropical waters (Central Arabian Sea) were reported to be 80 cm in length and 16 cm in width, while the lengthiest individual was approximately 2 m ( Gauns et al. 2015). But P. spinosum reported from temperate waters ( New Zealand) was size over 20 m long and 1.2 m in diameter ( Baker 1971). Of the only two species in the genus, Pyrostremma agassizi ( Ritter & Byxbee, 1905) forms smaller colonies with length and width up to only about 0.5 m and 5 cm respectively ( Van Soest 1981).

Local names: Saari Gaduwa (in Sinhalese); Welladei Soriyan (in Tamil).

Local importance: Ecologically important, because P. spinosum is predated by Leatherback turtles (authors’ observations).

Figures

FIGURE 1. Sampling localities of pelagic tunicates within the three regions of Sri Lankan Exclusive Economic Zone (EEZ) denoted by BBR (Bay of Bengal Region), LSR (Laccadive Sea Region) and IOR (Indian Ocean Region). Source of the map: Maritime Boundaries Geodatabase, Flanders Marine Institute (https://www.marineregions.org/). Remarks of each sampling station (St.) indicated by open circles are in Table 1

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 3. Re-reported salp, Pegea confoederata, to Sri Lanka in “Waya-jel-Survey” in preserved form (A–D): a colony of zooids (A); embryo (B); aggregate zooid (C); solitary zooid (D). E—endostyle; G—gill; N—nucleus; S—stolon. Scales: B = 5 mm; C & D = 8 mm; A = 20 mm.