Levels of organization :
- Cellular level
- Tissue level
- Organ level
- Organ system level
Circulatory System :
Open type: Blood pumped out through heart. Cells and tissues are directly bathed in it.
Closed type: Blood is circulated through vessels.
Symmetry :
- Asymmetrical: Cannot be divided into equal halves through median plane. e.g., Sponges.
- Radial symmetry: Any plane passing through central axis can divide organism into equal halves. e.g., Hydra.
- Bilateral symmetry: Only one plane can divide the organism into equal halves. e.g., Annelids and Arthropods.
CLASSIFICATION ON BASIS OF GERMINAL LAYERS :
- Diploblastic: Cells arranged in two embryonic layers i.e. external ectoderm and internal endoderm. (Mesoglea may be present in between ectoderm and endoderm) e.g., Coelenterates. (Cnidarians)
- Triploblastic: Three layers present in developing embryo i.e., ectoderm, endoderm and mesoderm. e.g., Chordates.
- Coelom (Body cavity which is lined by mesoderm)
- Coelomates: Have coelom e.g., Annelids, Chordates etc.
- Pseudocoelomates: No true coelom as mesoderm is present in scattered pouches between ectoderm and endoderm. e.g., Aschelminthes.
- Acoelomates: Body cavity is absent. E.g. Platyhelminthes.
- Metamerism: If body is externally and internally divided into segments with serial repetition of at least some organs then phenomenon is called metamerism. e.g., Earthworm.
- Notochord: Rod-like structure of mesodermal origin, formed during embryonic development on the dorsal side. e.g., Chordates.
PHYLUM PORIFERA :
- Also called sponges.
- Are usually marine and asymmetrical.
- Have cellular level of organization.
- Food gathering, respiratory exchange and removal of wastes occur through water canal system.
- Digestion intracellular.
- Ostia (minute pores on body), spongocoel (body cavity) and osculum help in water transport. They are lined by choanocytes (collar cells).
- Body wall has spicules and spongin fibers.
- Animals are hermaphrodite.
- Fertilization internal.
- Development is indirect, with larval stage which metamorphoses to adult. e.g., Sycon, Euspongia.
PHYLUM COELENTERATA :
- Also called Cnidarians.
- Are usually marine and radially symmetrical.
- Sessile or free-swimming.
- Have tissue level of organization
- Diploblastic.
- Presence of cnidoblast, for anchorage, defense and capture of prey.
- Central body cavity called gastro-vascular cavity or coelenterone.
- Digestion extracellular and intracellular.
- Blind sac type body plan, with one opening called hypostome.
- Body wall composed of calcium carbonate.
- Exhibit two body forms: polyp and medusa e.g., Hydra, Aurelia.
- Alternation of generation between body forms called Metagenesis occurs in Obelia where Medusa sexually reproduced and polyp asexually reproduced. •e.g., Physalia, Adamsia.
PHYLUM CTENOPHORA :
- Also called as sea walnuts or comb jellies.
- Are exclusively marine, radially symmetrical.
- Have tissue level organisation, are diploblastic.
- Digestion both extra and intracellular.
- Body has eight external rows of ciliated comb plates for locomotion.
- Show Bioluminescence (living organism emit light).
- Sexes are not separate i.e. hermaphrodite.
- Reproduce only by sexual methods.
- External fertilization.
- Indirect development
e.g., Ctenoplana. Pleurobranchia
