Phylum Mollusca- characteristics, classification, examples

Phylum Mollusca

Mollusca (Mollusks) Definition Molluscs (also know as mollusks) are soft-bodied, bilaterally symmetrical, segmented, coelomate animals; usually shelled having a mantle, ventral foot, anterior head, and a dorsal visceral mass. Phylum Mollusca (Mollusks) Characteristics They are essentially aquatic mostly marine, few freshwater and some terrestrial form. They may be found as hidden parasites in the interior of other animals. They vary in size from giant squids and clams to little snails, a millimeter long. They have at least two characters radula … Read more

Protozoa- Definition, characteristics, classification, examples

General Characters of Phylum Protozoa

Protozoa Definition Protozoa may be defined as  “microscopic acellular animalcules existing singly or in colonies, without tissue and organs, having one or more nuclei”. Some of the characteristics are: There are about 50,000 known species of Phylum Protozoa. Protozoans exhibit mainly two forms of life; free-living (aquatic, freshwater, seawater) and parasitic (ectoparasites or endoparasites). They are also commensal in habitat. They are small, usually microscopic, not visualize without a microscope. They are the simplest and primitive of all animals. They … Read more

Phylum Nematoda- characteristics, classification, examples

Phylum Nematoda

Nematoda Definition Nematodes (Gr., nema thread+ eidos, form) are commonly referred to as non-segmented roundworm, threadworm or pinworm, as distinct from flatworm and higher segmented annelids. Image Source: Wikipedia Phylum Nematoda Characteristics They are widely distributed, aquatic or terrestrial, parasitic or free-living. Their body is elongated, cylindrical, unsegmented, worm-like, bilaterally symmetrical and tapering at both ends. They are triploblastic animals with perivisceral cavity more extensive than that of platyhelminths. The body is of organ -system grade organization. The body is … Read more

Phylum Ctenophora- characteristics, classification, examples

Phylum Ctenophora

Ctenophora Definition Ctenophores are free-swimming, transparent, jelly-like, soft-bodied, marine animals having biradial symmetry, comb-like ciliary plates for locomotion, the lasso cells but nematocytes are wanting. They are also known as sea walnuts or comb jellies. Phylum Ctenophora Characteristics They are free-swimming, marine, solitary, pelagic animals. No polymorphism and no attached stages were found. The body is transparent, gelatinous, pear-shaped, cylindrical, or flat or ribbon-shaped. They have a biradially symmetrical body along an oral-aboral axis. They have an external surface with … Read more

Phylum Aschelminthes- characteristics, classification, examples

Phylum Aschelminthes

What are Aschelminthes? Aschelminthes are pseudocoelomate, bilaterally symmetrical, triploblastic, unsegmented, vermiform, organ- system grade of construction with complete digestive tubes. Phylum Aschelminthes characteristics They are mostly aquatic, free-living or parasitic. They are bilaterally symmetrical, unsegmented worms. The body is slender, vermiform and usually worm-like or flattened. They are usually small, even microscopic, while some reach a meter or more in length. They are triploblastic and pseudocoelomate with organ system grade of body organization. Body wall with a syncytial or cellular … Read more

Phylum Porifera- Characteristics, classification, examples

Phylum Porifera

Porifera Definition The Porifera may be defined as an asymmetrical or radially symmetrical multicellular organism with a cellular grade of an organization without well- definite tissues and organs; exclusively aquatic; mostly marine, sedentary, solitary or conical animals with body perforated by pores, canals, and cambers through which water flows; with one or more internal cavities lined with choanocytes; and with a characteristic skeleton made of calcareous spicules, siliceous spicules or horny fibers of spongin. Phylum Porifera Characteristics Porifera are all … Read more

Phylum Arthropoda- Characteristics, classification, examples

Phylum Arthropoda

Arthropoda (Arthropods) Definition Arthropods are bilaterally symmetrical, triploblastic, metamerically segmented animals with coelom which is reduced and modified. Their body is covered externally in a chitinous exoskeleton which molts periodically and their appendages are joined. Phylum Arthropoda Characteristics They are bilaterally symmetrical, triploblastic, metamerically segmented animals. Body organization is of an organ-system level. The body is covered with a thick chitinous cuticle forming an exoskeleton. Body segments usually bear lateral and jointed appendages with varied functions as jaws, gills, legs, … Read more

Phylum Platyhelminthes- characteristics, classification, examples

Phylum Platyhelminthes (flatworms)

Platyhelminthes (flatworms) definition Platyhelminthes are triploblastic, bilaterally symmetrical, dorsoventrally flattened, acoelomate flatworms with organ grade of construction without a definite anus, circulatory, skeletal or respiratory system but with Protonephridial excretory system and mesenchyme filling the space between the various organ of the body. Figure: Phylum Platyhelminthes. Source: WebMD and Wikipedia. Phylum Platyhelminthes (flatworms) characteristics They are free-living, commensal or parasitic. They are bilaterally symmetrical and dorsoventrally flattened, triploblastic worm. Bilaterally symmetrical with the definite polarity of head and tail ends. … Read more

Phylum Echinodermata- Characteristics, classification, examples

Phylum Echinodermata

Echinodermata (Echinoderms) Definition Echinoderms are enterocoelous coelomates with pentamerous radial symmetry, without distinct head or brain having a calcareous endoskeleton of separate plates or pieces and a peculiar water vascular system of coelomic origin with podia or tube-feet projecting out of the body. Phylum Echinodermata Characteristics They are exclusively marine and are among the most common and widely distributed marine animals. They occur in all seas from the intertidal zones to great depths. They have an organ grade system of … Read more

Phylum Coelenterata (Cnidaria)- Characteristics, classification, examples

Phylum Coelenterata

Coelenterata (Cnidaria) Definition The Coelenterata may be defined as diploblastic metazoa with tissue grade of construction having nematocyst and a single gastrovascular cavity or the coelenteron. Phylum Coelenterata (Cnidaria) Characteristics They are aquatic, mostly marine except few freshwater forms like the hydra. They are multicellular with tissue grade of organization. They are solitary or conical. Sedentary or free-swimming. Individuals are radially or biradially symmetrical about a longitudinal oral-aboral axis. Body organization of cell-tissue grade. Cells mostly scattered and specialized for … Read more