2. Welcome to BiologyDiscussion!
In other forms it may attain a high degree of complexity, but its general evolution can nevertheless be reduced to simple process of growth on the part of primitive Olynthus resulting in folding of the walls and accompanied by a restriction of the collared (choanocyte) cells to certain regions.
Our mission is to provide an online platform to help students to discuss anything and everything about Zoology. II. They may show asconoid, syconoid, or leuconoid structure.
They may cause the death of some sessile animals by growing over them and cutting off their food and oxygen supply. ii.
The blastula is called an amphiblastula after the formation of flagella. Body perforated by a number of pores. xiii. In hatching, the archeocytes streamout of the micropyle, then these multinucleate archeocytes divide to form uninucleate archeocytes and small cells called histoblasts. Examples: This embryo attaches itself to some solid object by its blastoporal end and it begins to grow. Diagnostic Features of Phylum Porifera 3. The development of a multicellular body from a fertilised egg by cleavage; and in this feature the sponges become more complex than a colonial protozoan and resemble with the Metazoa.
1.17A), Hyalonema (Fig. Demospongiae (Gr., dermos = frame; spongos = sponge): 1. Asexual reproduction occurs throughout the Porifera.
1.17B), Pheronema (Fig. 3.
The upper wall bearing a row of small, oval flagellated chambers is called spongophare. If the sponge is macerated and squeezed through fine silk cloth, its cells and clusters of cells will pass through, these can regenerate new sponges. Many freshwater and marine sponges disintegrate in adverse circumstances. No sponging. Sponges exhibit resemblances with colonial Protozoa in having the following features: 1.
CLASSIFICATION OF PORIFERA Subkingdom PARAZOA. Monaxon megascleres in the form of tylostyles. Name the types of nitrogenous bases present in the RNA. They are always irregular in structure but the flow of the current of the water is fairly rapid and efficient.
At first these radial canals are free projections and the outside water surrounds their whole length, for there are no definite incurrent channels. The sponges do not possess an anterior end or head like those of Metazoa. The outer or dermal epithelium here termed epidermis consists of a single layer of flat cells. In calcareous sponges, the leuconoid structure may be attained by way of asconoid and syconoid stages.
But in Demospongiae it is derived from a stage termed a rhagon which in turn arises by direct rearrangement of the inner cell mass. Amphidiscs are straight rods with thorny sides and a ring of hooks at each end. Reproduction occurs both asexually by buds and gemmules, and sexually.
5. The organisation of sponges has been grouped into three main types, viz., ascon type, sycon type and leuconoid type due to simplicity in some forms and complexity in others. There is complete absence of digestive cavity in sponges, unlike those of Metazoa. The incurrent canals lead into the small rounded flagellated chambers by opening still termed prosopyles.
The morphology and physiology of sponges were first adequately understood by who created in 1836 the name Porifera for the group by which it is now generally known, iuxle (1875) and Sollas (1884) proposed the complete separation of sponges from other Metazoa on the grounds of many peculiarities. 4. The body shape is highly variable. Systematic Resume. 3.
They are not attached by root tufts but commonly attached to a hard object. Sycon (Scypha) (Fig. The wall thickens and gets folded to form canals, perforations form ostia and osculum.