Sycandra utriculus (Schmidt, 1869)

Synonyms and citations: Sycandra utriculus (Haeckel 1872; Fristedt 1887; Burton 1963; Rapp 2015). Grantia utriculus (Breitfuss 1898; Lundbeck 1909).

Previous records: West Greenland (Schmidt 1869; Haeckel 1872), East Greenland and Jan Mayen (Lundbeck 1909), southern Barents Sea (Breitfuss 1898, 1911), Svalbard and Novaya Zemlya archipelagos (Fristedt 1887).

Material examined: Spitsbergen, Kongsfjorden, Kapp Mitra, st. 9 (79.1N, 11.13E), 5 m, 2 Sep. 1996, leg. A. Voronkov, diving collection (frame + pump), 2 specimens, ZISP 13317; Kapp Guissez, st. 47 (79.03N, 11.62E), 5 m, 28 Aug. 1998, leg. A. Voronkov, diving collection (frame + pump), 2 specimens, ZISP 13318; st. 6 (79.03N, 11.37E), 5 m, 30 Aug. 1996, leg. A. Voronkov, diving collection (frame + pump), 3 specimens, ZISP 13319 .

Description: Morphology and anatomy. Sponge tubular, compressed laterally, about 2 cm height, narrows towards the base which closely embraces the substrate (Fig 5A–A 2). Colour dark brown in alcohol. Surface velvety. Texture soft and delicate. Single osculum (either naked or fringed) at the summit. Aquiferous system syconoid. Choanocyte chambers fused in their entire length.

Skeleton. In the atrial cavity there is an additional tissue network, sometimes quite extensive, supported by bundles of small diactines.

Atrial skeleton comprises sagittal tetractines with their basal actines lying tangentially and the apical actine projecting into the atrium.

Subatrial skeleton composed of sagittal triactines arranged in several rows with paired actines supporting the atrial skeleton, and unpaired one pointing towards the cortex.

Tubar skeleton composed of subregular triactines, with the unpaired actine, which is frequently longer than the paired ones, pointing towards the outer surface.

Distal cones decorated with trichoxeas and sickle-shaped diactines protruding through the external surface. In the examined specimens diactines were found exclusively in the distal cones.

Spicules. Atrial diactines with one tip fusiform and the other lanceolated. Small spines present near the lanceolated tip (Figs 5B–B 2). Size: 137–235.8–356 × 3.7–6–8.9 µm (n = 20).

Distal cone diactines, with one fusiform tip, the other curved, sickle-shaped (Figs 5C–C 3). These spicules are often bent and relatively short. Size: 83–231–564 × 6.8–10.8–15 (n = 50) µm.

Trichoxeas with unequal tips—one slightly fusiform, the other sharply pointed.

Subatrial triactines sagittal, with a wide angle between the paired actines and straight unpaired actine (Figs 5D–D 1). Size: paired—48.3–80–105.8 × 5.9–7.4–9.7 µm (n = 50); unpaired—75.7–128.4–164.4 × 5.3–7.9–10.5 µm (n = 50).

Tubar triactines subregular, “ Y-shaped ” (Figs 5E–E 1). Size: paired—69.6–99–142.4 × 6–7.9–10.3 µm (n = 50); unpaired—61.5–127.4–208 × 6.7–8.6–11 µm (n = 50).

Atrial tetractines parasagittal, subregular, with straight, cylindrical basal actines, paired actines forming a “ U ”. The apical actine is often much thicker and longer than the basal ones (Figs 5F–F 1). Size: paired—89–119–163.7 × 3.8–7.2–9 µm (n = 20); unpaired—159–193.5–224 × 7–8.1–9 µm (n = 20); apical—128–238–335 × 8.7–11.3–14 µm (n = 20).

Remarks: The species was found during expeditions of the Norwegian Polar Institute (1996, 1998) to Kongsfjorden, Spitsbergen, and was originally assigned to S. utriculus by V.M. Koltun. As mentioned earlier, the description of S. utriculus given by Rapp (2015) can be considered as a description of S. utriculus sensu stricto. Our specimens from Spitsbergen definitely bear many similarities with S. utriculus sensu Rapp (2015), but they differ slightly in the complement of spicules.

In Sycandra utriculus sensu Rapp (2015) there are two types of diactines, whose size ranges do not overlap: long and relatively thin diactines (~330–572 × 7.3 µm) and small (~50–100 × 12 µm), stout, sickle-shaped diactines found in the distal end of the chambers. In the specimens from Spitsbergen there is only one type of diactine, gradually varying from very stout and characteristically curved and sickle-shaped, to relatively long and thin, rarely almost straight. However, all intermediate shapes between these two extremes can be found (Figs 5C–C 3). The size variation of diactines in our specimens (~83–564 × 10.8 µm) also fall within Rapp’s measurements. Thus, afore mentioned differences can be assigned to the regional trait variation.