Hyrtios collectrix (Schulze, 1879a) forms thick irregular masses with a conulose surface, often overgrown with algae and other encrusting organisms. It is greyish black in colour, and its distinguishing feature is that the skeleton consists largely of sand and other debris. It is a southern species predominantly occurring in the Mediterranean, but known from the Atlantic coasts of Portugal and Spain.
Colour: Upper surface black becoming lighter coloured, greyish along the sides; interiorly yellowish white.
Shape, size, surface and consistency: Irregular thick masses, 2-4 cm thick, and 20 cm in lateral expansion. Surface conulose, conules about 1 mm high, 2-3 mm apart, spaced regularly. Oscules small, about 1 mm in diameter, not obvious. Surface irregularly but strongly encrusted by algae and other sponges. Consistency firm, barely compressible, due to the great amounts of sand. The sponge can be easily broken.
Skeleton: The ectosome is a distinct thick black epidermis of 400-500 µm in thickness, charged with sand and other foreign material. It can be easily peeled off. The choanosomal skeleton is a system of spongin fibres completely filled with foreign objects like sand grains, broken spicules, etc. The spongin is visible only here and there; it is ditinctly stratified. Primary fibres are 250-500 µm in diameter, and they end in the conules. Secondary fibres connecting the primary fibres at right angles are likewise completely filled with foreign material, but are slightly thinner than the primary fibres.
Aquiferous system: The interior canals are relatively weakly developed and have a small diameter. The choanocyte chambers are rounded, 35-40 µm in diameter.
Ecology: On rocks between 0 (caves) and 150 m; mostly in deeper water.
Distribution: West coast of Portugal, Galicia; Mediterranean; Madeira.
Etymology: The name refers to the sand collected by this sponge.
Type specimen information: No type material in the Natural History Museum, London.
This species is distinctive and cannot be easily mistaken for another sponge. Hyrtios dendyi (Ferrer-Hernandez) is an ill-known sympatric species of the same genus, but its fibres are reported to be much thicker and the surface is smooth and free from encrusting organisms.
Superficially, species of the genus Dysidea may be mistaken for Hyrtios because they share the sand-filled skeletal fibres, but Dysidea are soft sponges with osculiferous lobes; their choanocyte chambers are elongate and much larger than those of Hyrtios.
Pleraplysilla minchini (Topsent) likewise has sand-filled fibres, but these are dendritic (have no or very few interconnecting fibres), and these are thinly encrusting sponges.
Source: Vacelet, 1959.