13. This forms a blastula which has a blastocoel cavity internally. Sponges are at the cellular grade of construction but the Metazoa are at the tissue and organ grade of construction. Our mission is to provide an online platform to help students to discuss anything and everything about Zoology. Microscleres are typically chelas, sigmas and toxas. The interior of the sponge becomes permeated by many incurrent and ex-current canals join to form larger ex-current canals and spaces which lead to the oscula. Thus, a gemmule is formed after which the surrounding amoebocytes, scleroblasts and trophocytes depart. Spongocoel is lined by flattened endoderm cells. The boring sponges also destroy rocks by penetrating into them and breaking them into pieces. 8. For a long time sponges were not regarded to be animals, exactly because of their non- animal-like appearance; they are sessile and do not possess the ability to catch the food or getting rid of their wastes and exhibit more or less no response to stimuli. Role and Significance of Canal System in Sponges, Canal Systems Encountered in Different Sponges, Leucosolenia: Habitat, Structure and Reproduction. Skeleton composed of network of spongin fibres only. Spongin present or absent. The syconoid sponges retain the radial vase form of the asconoids and the spongocoel opens to the exterior by the single terminal osculum. 2. According to Haeckel few sponge inhabitant of deep sea have a pseudo skeleton composed entirely of foreign bodies without any elements secreted by the sponge itself. ii. The incurrent and ex-current canals may be complex and branched. Sponges are beneficial to mankind and other animals in the following way: Sponges are rarely taken as food by other animals because of their bad taste, odour and sharp spicules. However, classification of Porifera followed here is based on Storer and Usinger (1971) which appears to be a modified form of Hyman’s classification. Adult sponges are usually sessile; the motile phase is the larva produced through sexual reproduction. 3. The nature of sponges was debated until well into the nineteenth century, although evidence of their animal nature was given in 1765 by who saw the water currents and movements of the oscula. Presence of collar cells and amoeboid cells like those of colonial flagellates. What are the modifications that are observed in birds that help them fly? Welcome to NotesOnZoology.com! Size can vary from a few cm to several metres. But the biologists after Aristotle believed them as plants for centuries on account of their sessile habit and insensitive nature. Since these incurrent canals represent the original outer surface of the asconoid sponge, they are necessarily lined by epidermis. 1. Oscarella; Plankina. vi. Acanthochaetetes, Astrosclera, Stromatospongia. The disintegrating sponge will usually collapse leaving small rounded balls, called reduction bodies. The interior of the syconoid sponge is hollow and forms a large spongocoel which is lined by the flat epithelium derived from epidermis. Ex. They may show asconoid, syconoid, or leuconoid structure.

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