Suberites lutkenii var. lanata

Suberites lutkenii var. lanata

(Fig. 2a–i 1)

Material analyzed. Barents Sea, PINRO trawl survey 2006, st. T5 (70.2N, 33.399E), depth 263 m, temperature 4 °C, salinity 34.79 psu (1 specimen; KFU-LH-2/001). Barents Sea, PINRO trawl survey 2003, st. 107 (69.0015N, 43.0134E), depth 62 m, temperature 2.37 °C, salinity 34.08 psu (2 specimens; KFU-LH-2/002).

Description. The larger specimen remarkably resembles the sole of the foot (Fig. 2a), 14 cm length × 6 cm wide × 1.5 cm thick. The upper surface has flattened, irregularly shaped scales or projections, above contiguous and below separated by grooves covered with a coarse sieve (Fig. 2 f–g). Surface looks and feels like fur. Hence the name (lānāta means woolly in Latin). The underside is relatively smooth and even (sponge appears to have rested on this side, when in situ). The single apical, relatively wide (~ 2 cm) osculum is surrounded by a short fringe and partitioned by a few septa (Fig. 2c). Osculum occupies the position, corresponding to the toe of foot. The opposite end of the sponge is fixed on bivalve shell. Texture is soft and elastic. Color dark-brown.

The other two specimens are more irregular, slightly lobose in shape, about 5 cm in length. Color pale-yellow. Grow freely. Gemmules were found in the basal parts lying on the substrate (Fig. 2e).

Spicules. Megascleres (choanosomal vs. ectosomal) are of two categories: choanosomal subtylostyles and ectosomal tylostyles. Choanosomal subtylostyles with only barely visible basal swelling, straight or slightly curved, rather slender, cylindrical, ranging in shape from short- to long-pointed: 220–389.9±59–519 × 3–6±1–8.4 (n = 100) µm. Small tylostyles, slightly fusiform, short-pointed: 183–253±29–350 × 3.4–4.7±0.5–5.8 (n = 50) µm.

Microscleres are minutely spined centrotylote microrhabds of three kinds. These spicules, except microtrongyles, often seem to be completely smooth, even under high magnification (× 400). Microstrongyles, 10–21.9±4.5–36 (n = 80) µm; microxeas, 19.85–34.6±6.9–47.7 (n = 150) µm; microstyles, 20.9–28.3±4.6–40.3 (n = 50) µm.

Overall, no variation occurred in spicule complement between Suberites lutkenii s. str. and S. l. var. lanata.

Skeleton. Choanosomal skeleton is a sparse reticulation of spicule tracts and single spicules with some tendency to radial arrangement. Tylostyles and subtylostyles are arranged in thick tracts ending as bouquets at the ectosome where they support surface ridges. A thin membrane forming a coarse sieve area in between the ridges is additionally reinforced with microrhabds.

Remarks. As compared to Suberites lutkenii s. str., S. lutkenii var. lanata showed phenotypic differences with respect to external morphology and skeletal architecture. In S. l. var. lanata the skeleton has a tendency to radial arrangement, as clearly seen from relatively thick (> 100 µm) sections, while in S. lutkenii skeleton is almost chalichondroid. Additionally, conulose surface together with a septate osculum sets S. l. var. lanata apart from its congeners.