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The phyla of Invertebrates were commonly called lower and higher invertebrates.

The phyla of Invertebrates were commonly called lower and higher invertebrates. In body organization the lower invertebrates are basic and usually smaller in size. The lower invertebrates include various phyla such as Porifera, Coelenterata(Cnidaria), Nematoda and Platyhelminthes.

Species of this phylum are widely referred to as sponges and about 5000 species are known. Porifera Characteristics

Phylum Porifera Examples: Euplectella, Sycon, Spongilla. [Image will be uploaded soon]

These species are commonly called as flatworms because of their dorso-ventrally flattened body. These are mostly endoparasites found in animals, including humans. About 6500 species are known. Platyhelminthes Characteristics

Phylum Platyhelminthes Examples: Taenia (Tapeworm), Fasciola (Liver fluke). [Image will be uploaded soon]

Both forms show Metagenesis (alternation of generation). Polyps generate medusae asexually and medusae generate the polyps sexually (example: Obelia) For Examples: Physalia (Portuguese man-of-war), Adamsia (Sea anemone), Pennatula (Sea-pen), Gorgonia (Sea-fan) and Meandrina (Brain coral). [Image will be uploaded soon]

Ctenophores, usually called as sea walnuts or comb jellies. They are exclusively marine possessing radial symmetry. They are diploblastic organisms with tissue level of organisation. Phylum Ctenophora Characteristics

Phylum Ctenophora Examples: Pleurobrachia and Ctenoplana. Classification of Phylum Ctenophora Ctenophora classification is based on presence of tentacles on the body and they are classified into two classes, they are: Tentaculata and Nuda. Class 1 Tentaculata They exhibit tentacles and small stomodaeum. Ctenophora examples with names: Hormiphora (The Sea Walnut), Ctenoplana, Cestum (The Venus’ Girdle), Pleurobrachia (The Sea gooseberry). Class 2 Nuda Species under this class don’t have tentacles. They exhibit spacious mouth and stomodaeum. Example: Beroe. [Image will be uploaded soon]

The body of the aschelminthes is circular in cross-section, therefore, they are named as roundworms. They may be free living, terrestrial, aquatic and about 10000 species are well known. Phylum Aschelminthes Characteristics

Phylum Aschelminthes Examples: Ascaris (Roundworm), Ancylostoma (Hookworm), Wuchereria (Filaria worm). [Image will be uploaded soon]

Q1. What are some Lower Invertebrates? Ans. Lower invertebrates include species which belong to phylum Porifera, Cnidaria, Ctenophora, Platyhelminthes, Aschelminthes. Q2. What are Lower Animals? Ans. Lower animals include fishes and invertebrates and they are the dominant species on the planet, both in numbers and diversity. Q3. What is the difference between Cnidaria and Ctenophora? Ans. Cnidarians and Ctenophores are diploblastic animals. Cnidarians show radial symmetry while ctenophores show biradial symmetry. They both have tentacles, covering their mouth. Its body symmetry is the key difference between cnidarians and ctenophores.

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