Pseudocorticium jarrei Boury-Esnault, Muricy, Gallissian & Vacelet, 1995

Morphology: The sponge is thickly encrusting to lobate (Fig.3, 4). Lobes can reach 12 cm in length and 2 cm in diameter, and hang down from the walls and the ceiling of the cave. The surface of the base is 3-10 cm wide and 0.5-3 cm thick. Colour in vivo is cream (colours 3A4, 4A3 and 5A2 in Meuthen Handbook of Colour (Kornerup and Wanscher 1978)); in alcohol it varies from yellowish white to brownish grey (colours 1A2, 2A2, 4B4, 7B2 and 7C2). Pigment is present only in the choanosome. Consistency is firm and cartilaginous.
The surface is smooth and slippery but corrugated, folded with irregular depressions 0.1-1 cm long by 1-2 mm deep (Fig.4). Abundant inhalant ostia 10-20 µm in diameter are located at the free surface or inside the depressions. Surficial 2- to 5-mm-diameter exhalant canals lead to 0.5- to 1-cm-diameter oscula. Oscula are located at the extremity or on the sides of the lobes, 0.5 cm high above the surface, and are surrounded by a slightly transparent oscular rim. Within the lobes there is usually a central exhalant canal 1-3 mm in diameter.

General organisation: The ectosome is 50 to 350 µm thick (Fig. 5), and externally limited by exopinacocytes. It is composed of a dense, homogeneous collagenous matrix, with spherulous cells, abundant collencytes, and scarce bacteria.
Within the choanosome, the choanocyte chambers are ovoid to irregular, diplodal (Fig. 6), and 25-42-60 µm in diameter. An estimated volume of up to 90,000 µm3 has been calculated, with about 300 choanocytes per chamber. The inhalant canals ramify into prosodi 3-12 µm in diameter and 10-45 µm long. Water enters the choanocyte chambers through one to three prosodi, each terminating in 3- to 12-µm-diameter prosopyles, and leaves the chambers through an 11- to 25-µm-wide apopyle (Fig.7), surrounded by apopylar cells and leading to an aphodus 20 to 40 µm long. In light microscopy, the choanosomal mesohyl has a granular appearance due to the presence of abundant bacteria; it also contains collencytes, archaeocytes and cells with inclusions. Choanocyte chambers and canals are surrounded by a clear, 1- to 6-µm-thick, relatively bacteria-free layer. A dense 20-nm-thick layer of fibrils forms a basement-membrane-like layer lining both choanoderm and pinacoderm. Among different individuals, the proportion in volume of mesohyl to choanocytes chambers in the choanosome varies between 2.2 and 2.8: 1. Spicule and fibre skeleton are absent.