Classification of Non-Chordates

Topics: Cnidaria, Arthropod, Annelid Pages: 6 (1386 words) Published: August 18, 2013
ION OF
CLASSIFICATION OF NON-CHORDATES UPTO CLASSES
WITH SALIENT FEATURES
Vanramliana
Pachhunga University College
Aizawl, Mizoram

1. Phylum Porifera: From the Latin porus for pore and Ferre to bear, hence an animal with with pores. ~5000 species. Characteristic features:-
a) Multicellular; no true tissue; asymmetric; sessile
b) spongin- protein fibers for structure; spicules for skeleton c) filter feeders using collar cells (choanocytes) & amoebocytes d) Water enters pores and exits osculum
e) asexual reproduction - fragmentation
f) sexual reproduction - hermaphroditic
g) External fertilization – shed gametes in water
Classification
Phylum Porifera can be divided into four classes:
a) Class Calcarea: They are characterized by the presence of spicules made of calcium carbonate. e.g. Sycon, Leucosolenia. b) Class Hexactinellida: They are characterized by the presence of spicules six-rayed spicules are made silica. Eg. Euplectella . c) Class Demospongiae: They are characterized by the presence of siliceous spicules , in some species by spongin fibres, and others have a mixture of spongin and spicules. Eg: Hippospongia communis and Spongia officinalis, d) Class Sclerospongiae: They are characterized by the presence of spicules constructed from calcium carbonate, silica and spongin. e.g. Sclerospongia sp.

2. PHYLUM COELENTERATA(Cnidaria):~ 9000 species
Characteristics features:
a) Radial symmetry; true tissues; sessile and/or motile
b) Cnidocytes - stinging barbs to capture prey
c) Tentacles to bring prey into gastrovascular cavity
d) Nervous system in the form of a nerve net
e) Two body forms
–Polyp – sessile with mouth dorsal
–Medusa – motile with mouth ventral
f) Asexual reproduction - budding
g) Sexual reproduction - external fertilization
Classification
a) Class Hydrozoa: They may be solitary or colonial form. Cnidocytes present in the epidermis; they possess many polyps. eg. Hydra, Obelia. b) Class Scyphozoa : They are solitary cnidarians. Medusa prominent in the life history; polyp are small; cnidocytes present in the gastrodermis as well as epidermis; Eg. Aurelia. c) Class Cubozoa : They are also solitary cnidarians. Medusa prominent in the life history; polyp are small; Eg Chironex, carybdea d) Class Anthozoa Colonial or solitary polyps; medusa absent; cnidocytes present in the gastrodermis; Eg. Metridium, Sea anemones

3. Phylum Platyhelminthes ~25,000 known species.
Characteristic features
a) Bilateral symmetry
b) Nervous system: ganglia and nerve chords
c) Excretory system: flame cells
d) Digestive system: two-way digestive tract with common mouth/anus; gastrovascular cavity e) Respiratory system: diffusion through epidermis
f) Circulatory system: none (diffusion)
g) Reproductive system:
I. Sexual – internal fertilization; hermaphroditic; lay eggs II. Asexual – fragmentation
Classification
A. Class Turbellaria: Usually free-living forms with soft flattened bodies. Eg: Dugesia, Planocera. B. Class Trematoda :Body Leaflike or cylindrical in shape; endoparasites OR ectoparasites complex life cycle with more than one host. Eg: Fasciola, Schistosoma. C. Class Monogenea :B ody usually leaflike to cylindrical in shape, all parasitic, mostly on skin or gills of fish. Eg: Dactylogyrus, Polystoma, D. Class Cestoda: (Tape worms)Body plan tapelike; Head or scolex with suckers or hooks; body usually divided into segments of proglottids; parasitic in digestive tract of all classes of vertebrates. Eg: Diphyllobothrium, Taenia.

4. Phylum Nematoda – The Roundworms, ~12,000 species
Characteristic features
a) The body of a roundworm is long, smooth and unsegmented. b) Roundworms have a complete digestive system with mouth and anus. c) Bilateral symmetry.
d) Excretory system of either one or more gland cells, a canal system...
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