Thenea levis

Thenea levis von Lendenfeld, 1907

(Figures 18 C–D, 19, 20)

Synonymy.

Thenea levis von Lendenfeld, 1907: von Lendenfeld 1907, p. 215; Steenstrup & Tendal 1982, p. 259; Klitgaard 1995, p. 1; Cárdenas et al. 2011, Table S1.

Material. ZMBN 85230, 85249, West of Marstein, western Norway, 60°8'18''N, 4°50'47''E, 300 m, Agassiz trawl; NTNU-VM 55838, 55839, 55842, Haltenbanken, western Norway, 64°14'56''N, 9°0'3.7''E; ZMBN 85250, Røst reef, northern Norway, 67°30.41'N, 9°25.60'E, 312 m, large boxcore; ZMBN 85229, Sotbakken, northern Norway, 70°45.32'N, 18°40.11'E, 286 m, large boxcore; University of Tromsø, Marbank, field# M07GOS0081-7, off Tromsø, 71°08'N, 18°39.33'E, 190 m, beamtrawl.

Comparative material.

Thenea levis, ZMAPOR 21501, SW of Rockall Bank, 55°31'7.9"N, 15°48'27.54"W, 844- 857 m.

Description. Outer morphology. Massive elongated sponge. ZMBN 85230 is straight (8 cm long, 2 cm high) (Fig. 19 A) while ZMBN 85249 (6.5 cm long, 2.5 cm high) is slightly bent. Both have a minutely hispid surface.

ZMBN 85251 (3 cm long, 2 cm high) is very hispid with very long hair-like oxeas. Specimens are not compressible. Color alive and in ethanol is brown. Choanosome is whitish to brownish (alive and in ethanol). Pore and oscule areas (both with sieves) are along the longitudinal sides, opposite to each other. They are more or less long and high. A thick overhang protects the pore area (Fig. 19 B). Small roots extend from the base of the sponge.

Skeleton (Fig. 19 C–D). Like T. abyssorum except for the presence of many protriaenes (below the ectosome) and abundance of plesiasters, especially near the poral area (Fig. 19 C).

Spicules (ZMBN 85230) (Figs. 18 C–D, 19D–F). (a) oxeas, stout, straight or slightly bent, length: 3375- 5311.5 - 7750 µm (N=13); width: 35- 70 -95 µm (N=17). (b) dichotriaenes (Fig. 19 D), straight rhabdome, length: 4500- 5187 -6500 µm (N=4); width: 33- 58.6 -85 µm; protoclad length: 130- 196.3 -260 µm; deuteroclad length: 230- 574.8 - 950 µm. (c) anatriaenes (Fig. 19 E), straight rhabdome (which can become flexible at its end), many irregular swellings were observed on some rhabdomes, length up to 1,35 cm; rhabdome width: 5- 14.4 -20 µm; clad length: 15- 111.9 -160 µm (N=14). A more or less developped swelling can be found above the cladome. (d) protriaenes (Fig. 19 F), common, straight, rhabdome length: from 3825 µm to>5700 µm; rhabdome width: 40- 54.1 -75 µm (N=18); clad length: 400- 609.6 -1200 µm (N=14). (e) spirasters (Fig. 18 D), spined, length: 17,5- 21,4 -29,1 µm. (f) plesiasters (Fig. 18 C), very abundant, 3-6 actines, faintly spined (not visible with an optical microscope), actine length: 30- 83,7 -145 µm; actine width: 4,2- 10,8 -24,3 µm.

Distribution (Fig. 20). South-East Greenland, Denmark Strait and Iceland (Steenstrup and Tendal, 1982); Norway and western Barents Sea (Tendal et al. 2001; this study); north of Wyville Thomson Ridge (von Lendenfeld, 1907); Rockall Bank (this study).

Depth. 190–1480 m (this study; Steenstrup & Tendal 1982).

Discussion. This is the first record of T. levis from Rockall Bank. These findings extend its geographical range to the south (Fig. 20). It is sympatric with T. muricata in the Greenland / Iceland /southern Norway area, and sympatric with T. valdiviae in northern Norway. The spicules measured in our specimen (ZMBN 85230) fit the general redescription given by Steenstrup and Tendal (1982) except for the presence of mesoprotriaenes and prodiaenes that we did not find. The plesiasters of T. levis are on average as large as in T. abyssorum but there is a wider range of sizes and they are not strongly spined. The spirasters of T. levis are smaller that in T. abyssorum and in the same size range as in T. muricata and T. valdiviae. SEM pictures (Fig. 18) suggest that T. levis plesiasters are more delicately spined than T. muricata and T. valdiviae plesiasters: the spines are not only smaller but their density is higher, more uniform (same goes for the spirasters). However, to generalize this observation, one would need to look at many more specimens with the SEM. The distinctive elongated shape with longitudinal opposite poral and oscular areas may be used to identify T. levis in the field.