8/11/2019 Of One Sub Division

1/2

of one sub division.

Sub division 1. Enterocoelous coelomata : Coelom is enterocoel which originatesas pouches of embryonic gut (archenteron)

(i) Character of Non Chordata (Invertebrates) : The animals which lack anotochord are called invertebrates. e.g. Amoeba, sponges, Hydra, worms, insects, etc.,

Invertebrates are characterised by the following salient features

(1) The vertebral column is absent.

(2) the nerve cord is solid in nature.(3) The nerve cord is present on the ventral side and never on the dorsal side.

(4) When alimentary canal is present, it lies dorsal to the nerve cord.(5) Invertebrates may be acoelomate or pseudocoelomate or true coelomate.

(6) They have either asymmetry or radial symmetry or bilateral symmetry.(7) The circulatory system is open type or closed type.

(8) They exhibit all possible type of reproduction.The invertebrates are grouped into about 30 phyla. These phyla are of two types,

namely major phyla and minor phyla.

(a) Major Phyla : (1) Protozoa (2) Porifera (3) Coelenterata (4) Platyhelminthes (5)Aschelminthes (6) Annelida (7) Arthropoda (8) Mollusca, and (9) Echinodermata.(b)Minor Phyla :(1) Mesozoa (2) Nemertinea (3) Endoprocta (4) Acanthocephala (5)

Rotifera (6) Gastrotricha (7) Kinorhyncha (8) Nematomorpha (9) Ectoprocta (10)Brachiopods (11) Phoronida (12) Chaetognatha (13) Priapulida (14) Sipunculida (15)Echiuroidea (16) Pogonophora etc.

1.3 Phylum Protozoa.

(i) Introduction : All unicellular (or acellular)

eukaryotic animals : Most primitive (Gr. Porots = first +

zoon = animal) organisms considered animals because of

heterotrophic nutrition and motility. Although the wholebody is a single minute cell. About 50,000 species (30,000

present and 20,000 extinct) are so far known.

(ii) Brief History : Protozoans were first studied by

Leeuwenhoek (1677). The name Protozoa was coined

by Goldfuss (1817). The branch of their study is called

Protozoology.

(iii) Salient Features

(1) Protozoans are the simple and primitive

organisms

(2) They are free living or parasitic

(3) All the free living forms are aquatic

(4) They are asymmetrical or radially symmetrical or

bilaterally symmetrical

(5) They are unicellular (acellular)

(6) They have protoplasmic grade of organization.

(7) Locomotion is effected by flagella, cilia or

pseudopodia.

(8) Nutrition is holophytic, holozoic, saprozoic or

parasitic.(9) Digestion is intracellular

Volvox

Giardi

Ceratium

Chlamydomona

8/11/2019 Of One Sub Division

2/2

(10) Excretion & Respiration occurs by diffusion(11) In fresh water protozoans osmoregulation is carried out by the contractile

vacuoles.(12) Encystment is a common phenomenon

(13) Reproduction occurs by asexual and sexual methods.