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Comprehensive Description

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General Description

Description: An erect, fan-shaped sponge consisting of a short stem from which branches arise that divide dichotomously three or four times in a single plane, with the last branches being long and parallel. Live specimens are approximately 8 cm high and 16 cm wide. The fixation base is slightly enlarged and attached to a small rocky fragment. The primary stem is contorted, smooth and 1 mm in diameter. The secondary branches are flattened and bear short lateral processes that are regularly arranged perpendicularly on both sides of the branch with a regular spacing of 0.5 mm. The tertiary branches are similar to the secondary ones, but up to 45 mm long and 0.4-0.5 mm in diameter, covered by lateral processes that are regularly arranged on both sides, facing each othe and 250-300 um apart. Most of the lateral processes are only 100-125 um long, most probably because they are broken, with a few of them extending in a filament 2.5-3.7 mm long lying parallel to the branch. A flattened enlargement is present at each point where the branches divide dichotomously, containing numerous oocytes or embryos. There is no visible aquiferous system or aperture. The living tissue was poorly represented in the preserved specimens except at the branching points. The tissue consistency is rather rigid, but highly fragile, and pure white in colour.

Skeleton: The stem and branches have an axis of large fusiform styles mixed with a few substrongyles (especially near the base), covered on the lateral side of the flattened branches by a dense cover of microstrongyles, less developed on the enlarged side of the branches. The lateral processes have an axis of small styles, inserted on the main axis by an enlarged base and arising through the lateral cover of microstrongyles. Enlargement occurs at the division points, with both sides having a cover of fusiform styles and substrongyles parallel to the surface and pressed against each other. There is a dense feltwork of microstrongyles, and a palisade of slender styles of the same type as those of the axis of the lateral processes on the edge. The base of the stem has a cover of numerous microtylostyles of a particular type, themselves covered by an external layer of short fusiform styles and substrongyles. The anisochelae are dispersed on the branches, with no visible special arrangement except anisochelae 1, which are grouped in rosettes.

Embryos are numerous in every enlargement at the branching points, each in a cavity surrounded by microstrongyles, 180-300 um in diameter. The embryos show various stages of development, most containing spicules as usual in embryos of Asbestopluma. The earliest stages are spherical, without spicules and made of blastomeres 20-22 um in diameter filled with large vitelline inclusions and with a large nucleolated nucleus. In more advanced stages the blastomeres are more elongated and radially arranged near the border. The later stages are made of poorly distinct cells, including a few layers of small cells near the surface, with a central fascicle of styles varying from 1-4 um in thickness, to which are added in more advanced stages numerous rosettes of anisochelae 2.

Spicules: The styles of the axis of the stem and branches are strongly fusiform (e.g. for a spicule 925 um long, the diameter is 11 um at the head and 40 um in the middle), straight or feebly curved, with a sharp point. Size 200-1025 x 20-45 um.

The substrongyles of the axis are more numerous and smaller near the base, curved near the middle, sometimes double bent or even a little flexuous, with two ends nearly equal. Size 8-500 x 15-30 um.

The styles of the lateral processes and of the palisade of the enlargements are slightly fusiform, straight and with a short, sharp point. Size 180-350 x 7-9 um.

The microstrongyles are very numerous and slightly curved. Some are more sharply bent near the centre, most of the spicules are covered in minute spines 0.04 um high. Size 25-60 x 5-7 um.

The microtylostyles are present only at the base where they are numerous and very peculiar in shape, resembling 'spear-like' spicules with a round head, short neck and an enlarged cylindrical body with a long point. The whole spicule is covered by minute spines 0.1 um high that are more numerous on the enlarged 'body'. Size 25-45 x 4-7 um.

The anisochelae are grouped in rosettes with lateral alae that are attached to the shaft along most of their length. The frontal ala of the foot is either simple or bifid. Size 72-90 um, shaft diameter 5-5.5 um.

The anisochelae 2 are very numerous and dispersed along the branches, grouped in rosettes in the more advanced embryos. The free part of the shaft is very short and curved. The head has very large lateral alae. The foot has two vestigial lateral alae, and a long frontal ala bearing two lateral expansions which are strongly curved towards the shaft. Size 10-15 um.

(Vacelet, 2006)


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