Sycon humboldti Risso (1826) is an oval tube-shaped calcareous sponge resembling other Sycon species from the area, but differing in the very prominent apical fringe of long spicules. Also other details of spiculation make it a distinct species. It is predominantly Mediterranean but has been recorded a few times from Galicia.
Colour: Greyish or brownish white.
Shape, size, surface and consistency: Tubes with apical fringe as characteristic for the genus. The size has not been recorded but may be presumable 1-2 cm high. Shape distinctly oval with a short stalk, and very prominent fringes of long spicules around the apical vent. Surface minutely papillate, slightly hispid. Consistency rather firm.
Spicules: (Sycon humboldti spics) Calcareous. Triactines, occurring in distinct shapes and sizes. The distal cones have triactines thickened, paired rays 30-60 x 10-15 µm, basal ray 150-250 x 20-30 µm; the triactines lining the choanosomal tubes are sagittal, with paired rays 80 x 8 µm and basal rays 120 x 12 µm; the choanosomal triactines in between the tubes are sagittal, paired rays 80-120 x 8 µm and basal rays 120 x 8-12 µm; atrial triactines are more regular, with paired rays 50-120 x 8 µm and basal rays 50-200 x 8 µm.
Atrial tetractines are similar to the triactines, with in addition apical rays of 100-120 x 8 µm.
Oxeas of the distal cones 200-400 x 5-20 µm; oxeas of the apical fringe 50-2000 x 20-40 µm.
Skeleton: Distal cones provided with oxeas and thickened triactines. Tubar skeleton consists of triactines. Atrial skeleton of triactines and tetractines.
Ecology: In small intertidal caves.
Distribution: Galicia; Mediterranean.
Etymology: Named after Alexander von Humboldt (1769-1859), the great German explorer and naturalist.
Type specimen information: No data.
This species resembles S. elegans in much of its spicular characters, but differs from it in the much greater length of the oxeas of the apical fringe. It is not entirely certain that the two are distinct species.
Source: Burton, 1963.