Tetilla sibirica Fristedt 1887

Tetilla sibirica Fristedt, 1887

Figure 6; Table 6

Synonymy:

Tethya sibirica Fristedt, 1887: 436 –437 pl. 28, fig. 17.

Tetilla sibirica: Koltun 1966: 61 –62, fig. 32–33. Morozov et al. 2019: 21 –22, fig. 12. Dinn & Leys 2018: 86.

Material examined. CMNI 2018-0165, specimen in 95% ethanol, collected by Philippe Archambault by ROV

hydraulic manipulator; 25 October 2015, 65 m depth, (63° 38.5745’N, 68° 36.5265’W). CMNI 2018-0183, specimen in 95% ethanol, collected by Curtis Dinn by Agassiz trawl; July 15, 2017, 141 m depth, (63° 38.390’N, 68° 37.642’W). All operations performed from the CCGS Amundsen near Hill Island in Frobisher Bay.

Description. Two specimens of different sizes were collected in the inner bay near Hill Island. CMNI 2018- 0 165 (Fig. 6B) is a large spherical sponge about 20 cm in diameter in situ (Fig. 6A), and the root is nearly 13 cm long after collection, and CMNI 2018-0183(Fig. 6D) is less spherical and more club shaped, about 2 cm in width, 3.5 cm in height with a root length of 2.5 cm. The surface of both specimens is hispid due to protruding spicules. The sponges are firm and incompressible, are covered in sediment in situ, and appear light brown or grey immediately after collection. (Fig. 6B, D). The spicules from CMNI 2018-0183 consist of large oxeas 2811 (1784– 4080) x 37 (28–54) µm; short oxeas 1026 (754–1290) x 40 (26–52) µm; anatriaenes 3030 (1992–4378) x 21 (9–35) µm; protriaenes, sometimes with one whip-like clad 2219 (1150–3452) x 21 (6–29) µm, clads are 57 (29–83) µm, whip-like clads, when present are 91 (64–113) µm; and sigmaspires 17 (11–20) µm in length (Fig. 6 E–K).

Genetic data. 28S rDNA sequences suggest this specimen groups with Cinachyra and Antarctotetilla specimens based on the D3–D5 domain sequence (GenBank accession MH394249). This species and the sympatric C. polyura appear to be closely related based 28S sequences.

Taxonomic Remarks. The original description by Fristedt (1887) is of a firm sponge that is ovoid or subspherical with numerous roots. Koltun (1966) gives the same description. Fristedt (1887) does not specify a range of spicule lengths, and does not provide widths, yet the lengths reported largely agree with the measurements given by Koltun (1966) (Table 6). Fristedt does not distinguish between protriaenes with or without whip-like clads. In CMNI 2018-0165, protriaenes with clads of similar lengths were rare, therefore both regular protrienes and those with whip-like clads are treated as similar spicules here. Fristedt (1887) described the sigmaspires as smooth sigmas (“sigmoid bihamate spicules”) in comparison to the “knotty” sigmaspires found in Craniella polyura (T. polyura in Fristedt, 1887 and Koltun, 1966). Koltun (1966) shows sigmaspires which appear smooth in his illustration, but they differ from the sigmaspires of C. polyura, as they do not possess a centrotylote swelling. The sigmaspires from the Frobisher Bay specimens are entirely spined with fine teeth, an aspect that is not always apparent from light micrographs. Micrographs of C. polyura (described as T. polyura, Van Soest 2016) show the centrotylote swelling clearly, which the sigmaspires in these specimens lack. Since the spicules match the descriptions by Fristedt and Koltun, and lack sigmaspires with central swellings, this sponge is considered to be T. sibirica.

1 Koltun, 1966 describes regular protriaenes without a whip like clad to be 2000–3700 in length x 6–12 in width with clads of 70–150 µm. The protriene types in CMNI 2018-0183 were treated as one, as the shaft length did not appear different between the two types.

Discussion. This is the first record of T. sibirica in the Northern Labrador marine ecoregion. The World Porifera Database suggests that the species has a circumpolar high Arctic distribution and is also found in the Barents Sea and coastal Northern Russia in the Laptev Sea. Koltun (1966) suggests that the species even occurs off the Pacific coast of the Kuril Islands. The sponge is also suggested to occur in James Bay and SE Hudson Bay (Stewart & Lockhart 2005), but source material is not listed or available for taxonomic assessment and so those identifications cannot be presently confirmed. This is a shallow water species. The specimens in this study were found at 65 m and 141 m, whereas Koltun (1966) found it at depths of 7–54 m in the Arctic and 127–414 m in the Pacific Ocean. In Frobisher Bay, this sponge is quite common on sandy substrates at the site near Hill Island. In ROV video transects the sponge is seen growing amongst solitary tunicates near the gardens formed by Iophon koltuni, and in areas with few other sponges growing nearby. Both the large and small specimens have small tube worms attached to the base and embedded in the distal portions of the sponge. It is common to see echinoderms on the surface of the sponge. Brittle stars are often attached to the surface, and large crinoids are often perched near the osculum (Fig. 6 A, C).