Organisms of this phylum leave behind casings.
Porifera
Cnidaria
Nematoda
Platyhelminthes
Annelida
Echinodermata
Mollusca
Arthropoda
Answers
Answer:
The following phyla of multicellular animals (called metazoans) are usually included in general biology courses. Remember that the botanical counterpart of a phylum is called a division. Unicellular animals (called protozoans) are usually placed in the kingdom Protista along with the divisions of unicellular and multicellular algae. True multicellular animals are typically without cellulose cell walls and photosynthetic pigments, and they form diploid embryos developing from a blastula stage. The blastula is a hollow, fluid-filled sphere bounded by a single layer of cells surrounding a central cavity or blastocoel. The blastula develops from a spherical cluster of cells called a morula. In addition, animals are capable of locomotion or body movement by means of contractile muscle tissue. In a cross sectional view, animal embryos are composed of an outer layer called ectoderm, a middle layer or mesoderm, and an internal layer or endoderm that surrounds the digestive cavity. Multicellular animals are heterotrophic by ingestion of food into a body cavity (coelom) that is completely lined by the mesoderm. Primitive phyla without a true coelom include the Porifera and Coelenterata (Cnidaria).
Animal phyla are classified according to certain criteria, including the type of coelom, symmetry, body plan, and presence of segmentation. Sponges (Porifera) have a primitive cellular level of organization and lack tissues and symmetry. They depend on a flow of water through the body to acquire food. Cnidaria and comb jellies (Ctenophora) have radial symmetry and a saclike body composed of two tissue layers derived from the germ layers ectoderm and endoderm. Cnidaria typically develop a polyp body plan (e.g. Hydra) or a medusa body plan (e.g. jellyfish), or they alternate between these two forms (e.g. Obelia). In species with both polyp and medusa, the polyp is the asexual form while the medusa contains the sex organs.
Flatworms (Platyhelminthes) and ribbon worms (Nemertea) have tissues and organs derived from a third germ layer called the mesoderm. They have the organ level of organization and are bilaterally symmetrical. Planaria are free-living predators, but flukes and tapeworms are adapted to a parasitic mode of life.
Answer:
Organisms of this phylum leave behind casings.
Porifera
Cnidaria
Nematoda
Platyhelminthes
Annelida
Echinodermata
Mollusca
Arthropoda
Explanation:
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