Instead, Devonian Period reefs were dominated by a group of calcareous sponges known as stromatoporoids. The pore cells or porocytes occur among the pinacocytes at frequent intervals. The overwhelming majority of the roughly 9000 known species live exclusively in marine environments, with between 100 and 200 … Tuzet (1963) expressed the view that though sponges possess many primitive features (such as cellular grade of body organization, gas exchange, and response to external stimuli represent the unicellular protozoan-like animals), yet there is no doubt that they are in direct line of metazoan evolution. In tropical coral reefs, they dwell mainly in shaded and/or cryptic habitats and prefer calmer waters. 2. They have all in common certain structural features. Most sponges belong to which Class? What can you infer about the changes in water depth or benthic habitat from a rock outcropping that contains a limestone formation with abundant fossil calcareous sponges and calcareous algae that is conformably overlain by a formation containing siliceous sponges and cephalopod fossils? SPONGE SPECIES All of the following sponges are found within the coral cap region of the sanctuary (0-130 ft, 0-40m deep). Sponges may be of varied colours and their shape depends upon the sites of their stay. Habitat: S. quadrangulatum seems to prefer shallow waters, where it can be found attached … Certain sponges, e.g., Tethya can contract its entire body, while in most cases the contractility is restricted around the osculum. Amoebocytes with slender and branching pseudopods. Up to 18th century sponges were not considered as animals. The outer layer of cells is primarily responsible for protection and inner layer of cells carries on the nutritive functions. What is the one unique feature of the freshwater sponges? In a few coastal locations, however, such as Antarctica, the northeastern Pacific, New Zealand, and some caves in the Mediterranean, species are found at depths accessible by scuba divers. 7. TOS4. 11.17). Due to farming practices and the nature of the land, these vineyards produce tiny yields, resulting in fruit of profound depth and sense of place. Absence of definite germ layers which are the most diagnostic feature of metazoans. Within the aggregate, all the cells lose their identity and become homogeneous. What are the other general characteristics of this class? 4. ... new RNA evidence suggest that Calcareous sponges are closer related to ther metazoans than to siliceous sponges. The development of sponges like Oscarella shows similar processes as in metazoa. 9 Traditionally, spicules made of silicate (or calcium carbonate in the case of calcareous sponges) and proteins have been the most fundamental synapomorphy; size, type, shape, … Origin of Sponges: There is a great controversy regarding the origin of Porifera. The evolutionary origin of sponges poses some interesting problems for their peculiar features. 4. The sponges exhibit close protozoan affinities but the attempts to include sponges under the Phylum Protozoa failed because of the development of germ layers in developing sponges. In freshwater sponges specialised bodies, called gemmules, are formed for the same purpose. Which of these is considered to be the simplest? . Most sponges live in a salt water environment, attached to objects on the sea floor. Mesophyl: Jelly filled layer to hold two layers together, Explain the function of the following archaeocytes; totipotent, scleroblast, spongioblast, collencytes and lophocytes, Totipotent: undifferentiated cells, become other cells, Explain the difference between the skeletal systems found in the Class Calcarea, Class Demospongiae and Class Hexactinellida, Calcarea: Spicules (Monaxon, Triradiate, T-shaped), Describe the ingestion and digestion of food in a typical sponge, Intracellular digestion Largely controlled by water current. Scientists have identified around 400 species of calcareous sponges. Many annelids and crustaceans live as symbionts with sponges. In m any species both . Habitat. This website includes study notes, research papers, essays, articles and other allied information submitted by visitors like YOU. The low level of cellular differentiation and presence of canal system, cellular totipotency and absence of tissues, basement membrane, body polarity, reproductive organs and functionally independent cells indicate a primitive stage of metazoan organization. The Devonian Marine Habitat ... made up of the familiar corals we see today. The body surface is perforated by pores acting for ingress of water. In tropical coral reefs, they dwell mainly in shaded and/or cryptic habitats and prefer calmer waters. Description. The amoebocytes are most important cellular entities in the life of sponges. With lobose pseudopods and many food reserves. How do the characteristics of this class differ from the other classes? Fossil sponges were discovered from beds of Europe, Asia and North America, which are more than 600 million years old. Most are filter-feeders/suspension feeders, Most are marine, No true tissue or organs, Adults are sessile, Filled with holes. Stromatoporoids filled the same ecological niche as the stony corals of today, and thus, played the same role in reef construction. Less than 200 sponge species inhabit freshwater habitats. Calcareous sponges. Taxonomic Retrospect of Sponges 2. R. E. Grant (1825) studied the morphology and physiology of sponges in greater details and named the group Porifera. 2. The protozoan affinity is attested by the following evidences: (3) Mode of secretion of skeleton within single cell; (5) Existence of totipotency of cell-types; and. What structures prevent the collapse of the canals found in sponges?