Phylum and different phylas in the classification of animals
Kingdom Animalia is further divided into various phyla. Every phylum has life forms that have regular attributes. In the characterization of creature’s graph, they move from the least difficult to the most unpredictable.
The different phyla in the classification of animals are as follows:
Phylum Porifera (sponges):
· It is usually marine and asymmetrical cellular level of organisation.
· Water canal system helps in food gathering, respiratory exchange and removal of wastes.
· 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 skeleton called spicules and spongin fibres.
· Animals are hermaphrodite (sexes not separate).
· Reproduce asexually by fragmentation and sexually by formation of gametes. Fertilisation is internal and development is indirect.
· E.g., Sycon, Euspongia (bath sponge), Spongilla (fresh water sponge).
Phylum Ctenophora (sea walnuts or combjellies)
· Exclusively marine, radially symmetrical.
· Diploblastic with tissue level organisation.
· 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 and only sexual reproduction occurs.
· External fertilisation.
· E.g. Pleurobrachia, Ctenoplana.
Phylum Platyhelminthes (Flatworms)
· Have dorsoventrally flattened body.
· Endoparasites in animals (found in animals including humans).
· Bilaterally symmetrical, triploblastic, acoelomate with organ level organisation.
· Absorb nutrients through body surface.
· Parasite forms have hooks and suckers.
· Flame cells help in osmoregulation and excretion.
· Fertilisation internal. Many larval stages are present.
· Planaria has high regeneration capacity.
· E.g., Taenia, Fasciola.
Phylum Aschelminthes (Round worms)
· May be free living, parasitic, aquatic or terrestrial.
· Bilaterally symmetrical, triploblastic, pseudocoelomate with organ system level of organisation
· Alimentary canal is complete with muscular pharynx and wastes removed through excretory pore.
· Sexes separate (dioecious).
· Females longer than males.
· Fertilisation internal. Development direct (young one resemble the adult) or indirect.
· E.g., Ascaris, Wuchereria.
Phylum Annelida (Latin: annulus = little ring).
· Aquatic or terrestrial, free-living or parasitic.
· Bilaterally symmetrical, triploblastic & coelomate with organ-system level of organisation.
· Metamerically segmented body (Have longitudinal and circular muscles for locomotion).
· Nereis (dioecious and aquatic annelid) has lateral appendages called parapodia for swimming.
· Have nephridia for osmoregulation and excretion.
· Closed circulatory system.
· Neural system consists of paired ganglia connected by lateral nerves to a double ventral nerve cord. E.g., Earthworm (Pheretima) and Leech (Hirudinaria) which are hermaphrodites (i.e., monoecious).
· Largest phylum mostly oviparous. Coelomates.
· Bilaterally symmetrical, triploblastic, coelomate with organ system level of organisation.
· Body divisible into head, thorax, abdomen and is shielded by a chitinous exoskeleton.
· Jointed appendages are present (arthos – joint, poda – appendages).
· Respiration is by gills, book gills, lungs or tracheal system.
· Circulation is of open type.
· Excretion is through malpighian tubules.
· Antennae, eyes act as sensory organs and statocysts acts as organs of balance present.
· Fertilisation is internal. Development is indirect or direct.
· E.g., apis, bombyx, anopheles, locusta, limulus, anopheles etc.
· Second largest phylum
· Terrestrial or aquatic
· Bilaterally symmetrical, triploblastic, coelomate with Organ system level of organisation
· Body divisible into head, muscular foot and visceral hump and is covered by calcareous shell. It is unsegmented over visceral hump.
· Mantle is a soft and spongy layer of skin; Mantle cavity: Space between visceral hump and mantle.
· Respiration and excretion by feather like gills in mantle cavity.
· Head has sensory tentacles.
· Radula-file like rasping organ for feeding.
· Oviparous, dioecious, have indirect development.
· E.g., Pila, Pinctada, Octopus.
· All marine Spiny bodied organisms.
· Have an endoskeleton of calcareous ossicles.
· Exclusively marine, radially symmetrical in adult but bilaterally symmetrical in larval stage.
· Organ system level of organisation.
· Digestive system complete. Mouth ventral, anus on dorsal side.
· Food gathering, respiration, locomotion carried out by water vascular system.
· Excretory system is absent.
· Fertilisation external. Development indirect (free swimming larva)
· E.g., Asterias, Cucumaria, Antedon
· Small worm-like organisms.
· Was earlier placed as sub-phylum of Phylum Chordata.
· Bilaterally symmetrical, triploblastic and coelomate.
· Cylindrical body, has proboscis, collar and trunk.
· Respiration by gills, excretion by proboscis gland.
· Sexes separate, external fertilisation, indirect development.
· E.g., Balanoglossus.
· Characterised by presence of
o A Notochord
o A dorsal hollow nerve cord
o Paired pharyngeal gill slits
o Post anal tail
o Closed circulatory system
· Bilaterally symmetrical, triploblastic, coelomate with organ system level of organisation
· Divided in to 3 sub phyla:
Urochordata and Cephalochordata are referred to as Protochordates