INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM PROMETAZOA (PROMETAZOA)

PHYLUM SPONGES (PORIFERA)

CLASS GLASS SPONGES (HYALOSPONGIA)

Exclusively marine, predominantly deep-Water species of considerable size (up to 1 m), possessing a siliceous Skeleton, solitary or occasionally colonial. Their body Organization follows the sycon type. It is most frequently goblet-shaped, tubular, or sac-like, and fragile. All Cells are fused into a continuous syncytium (a multinucleated Structure lacking distinct Cell boundaries), which forms the outer membrane, the walls of the flagellated chambers, and a dynamic network of strands and membranes interconnecting all PARTS OF THE body (Fig. 66). Numerous cavities, or lacunae, through which water circulates, are located between these strands and membranes. The flagellated canals are lined with a continuous choanosyncytium. From this lining, individual collar complexes emerge, consisting of a flagellum and a surrounding ring of microvilli. Amoebocytes lack amoeboid activity and contain no digestive vacuoles, which are found exclusively in the Cytoplasm of the choanosyncytium. Pinacocytes, myocytes, and any contractile elements are completely absent.

The skeleton is composed of hexactine (triaxial) spicules and their derivatives. In addition to large spicules (macroscleres), there are smaller microscleres that appear as six-rayed stars or amphidiscs of various shapes (Fig. 66, c). In most modern species, the spicules are fused together to form a continuous supporting skeleton.

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Fig. 66. Diagram of the body wall structure of a Glass sponge:

a - section through the body wall (after Dogel); b - wall of the flagellated chamber (after Malakhov):

1 - dermal layer; 2, 3 - spicules; 4 - syncytial membranes; 5 - flagellated chambers; 6 - collar complex

Well-known species include Venus' flower basket (Euplectella aspergillum) and hyalonema (Hyalonema elegans, Fig. 67).

Fig. 67. Glass Sponges:

a - Hyalostylus dives; b - Hyalonema elegans (after Dogel); c - Euplectella aspergillum (after Polyansky)