(Fig. 5a–d)
Raspalia syringella: Schmidt 1868, p. 10, pl. II, fig. 9; Topsent 1938, p. 13.
Suberites spec.: Vosmaer 1885, p. 21, pl. I, fig. 9a,b; pl. IV, fig. 33.
Suberites glabra: Hansen 1885, p. 11, pl. II, fig.9.
Suberites carnosus var. ramosus: Topsent 1900, p. 237, pl. VII, figs. 1, 2; Lundbeck 1909, pp. 453–454; Breitfuss 1911, p. 218; Breitfuss 1912, p. 74; Topsent 1913, p. 26; Topsent 1928, p. 155; Koltun 1964, p. 150; Rezvoi 1928, p. 82.
Suberites carnosus: Hentschel 1929, p. 926.
Pseudosuberites carnosus: Koltun 1966, p. 99, fig. 72, pl. XXXIII, figs. 3–4.
Suberites syringella: Pulitzer-Finali 1978, pp. 24–25, figs. 2–3; Pulitzer-Finali 1983, p. 483; Voultsiadou-Koukoura and Van Soest 1993, pp. 182–183; Bertolino et al. 2015, pp. 1372–1373, figs. 2B,C & 3A–C.
Material analyzed. Barents Sea, PINRO trawl survey, F. Nansen, 2005, st. 4 (78.0132N, 9.9735E), depth 163 m, temperature 3.93 °C, salinity 35.053 psu (9 specimens; KFU-LH-2/014); st. 16 (76.6442N, 13.5676E), depth 423 m, temperature 3.33 °C, salinity 35.08 psu (8 specimens; KFU-LH-2/015); st. 21 (75.9898N, 14.3593E), depth 373 m, temperature 3.29 °C, salinity 35.057 psu (4 fragments; KFU-LH-2/016). Muklevich, 2003, st. 5 (69.8658N, 31.1627E), depth 93.4 m, temperature 3.35 °C (1 specimen); st. 7, (69.9163N, 31.3416E), 1 specimen, KFU-LH-2/017.
Description. The numerous fragments of this species are all of an elongated, cylindrical shape, with anastomosing side branches and rather broad basal attachment which, when intact, closely embrace small pebbles and stones (Fig. 5c). Conical oscula are scattered along the sides of branches. Surface smooth. The consistency is rather soft and delicate. Color pale yellow (in alcohol).
Spicules. Tylo- and subtylostyles straight or slightly curved near the basal end of spicule, fusiform, rather short-pointed (Fig. 5a–b). Megascleres (choanosomal vs. ectosomal) not clearly distinguishable into two distinct size categories, vary in dimensions significantly: 118–350±165–694× 4.1–8.8±0.97–10.6 (n = 260) µm. Yet size ranges of megascleres were statistically different (p value <0.001), when spicules were prepared from the different tissue sections, with ectosomal scleres on average 30% shorter as compared to choanosomal.
Skeleton. Choanosomal skeleton is ill-developed and shows loose longitudinal spicule tracts and confused mass of single spicules. There are usual bouquets of smaller tylostyles in the ectosome (Fig. 5d).
Remarks. Suberites syringella is quite common in the Mediterranean Sea, sub-arctic (Nordic Seas) and adjacent Arctic (namely, the Barents Sea). However, there is much confusion surrounding this species in the Arctic/Subarctic region. Originally described by Schmidt as Raspalia syringella (1868) from Mediterranean Sea, it was subsequently re-described under different synonyms by Hansen (as Suberites glabra, 1885), Vosmaer (S. spec. 1885, p. 21) and Topsent (Suberites carnosus var. ramosus, 1900; 1913) from the Arctic/Subarctic. Later Topsent (1938) allocated Suberites carnosus var. ramosus as a junior synonym of S. c. var. syringella (Schmidt 1868).
Additionally Topsent (1938) recognized that the two taxa nowadays accepted as valid, viz. Suberites carnosus and S. syringella (= S. c. var. ramosus Topsent), are very close. Lundbeck (1909) supposed that “ S. carnosus seems to occur in the arctic seas only in the form ramosus ”. This notion was supported by other Arctic spongiologists (Breitfuss 1911; Rezvoi 1928; Hentschel 1929; Koltun 1964, 1966).
In the Subarctic region Suberites syringella was reported from the Nordic Seas, including Greenland (Lundbeck 1909; Burton 1934; Koltun 1964a) and Iceland (Lundbeck 1909; Burton 1959) Seas. S. syringella is also well known from the Barents Sea, where its distribution is apparently related to the inflow of warm Atlantic water: most records are from south-western Barents Sea (Vosmaer 1885; Breitfuss 1911; Topsent 1913; Rezvoi 1928; Hentschel 1929). Our own records include numerous specimens from the shelf and upper slope region west off Svalbard and from the Murman Coast. Additionally, S. syringella has been reported from the north off Franz Josef Land (Koltun 1964a). The latter is the northernmost record of species in the Arctic (Fig. 6).
The species has also been extensively recorded in the Mediterranean segment of the Lusitania Province: most records, including type specimen, are from the Mediterranean Sea (Pulitzer-Finali 1978, 1983; Voultsiadou-Koukoura & Van Soest 1993; Bertolino et al. 2015; Santín et al. 2018; Longo et al. 2018).
Thus there is a huge gap in geographic distribution of Suberites syringella, extending along the Atlantic segment of the Lusitania Province, from the Gibraltar Strait to the North Sea. This area is a direct and continuous connection between Nordic and Mediterranean Seas and it has been subject to extensive collecting and research. Thus, the distribution gap cannot be explained by suggesting the lack of data. Perhaps, future research will show that we are dealing with two separate, closely allied species, Mediterannean vs. Arctic.