Question

Body cavity is the cavity present between body wall and gut wall. In some animals the body cavity is not lined by mesoderm. Such animals are called ______.

Options

• Acoelomates

• Pseudocoelomates

• Coelomates

• Haemocoelomates

Answer 1

Body cavity is the cavity present between body wall and gut wall. In some animals the body cavity is not lined by mesoderm. Such animals are called pseudocoelomates.

Explanation:

(i) Acoelomate: The animals in which the body cavity is absent are called acoelomates, e.g.: Porifers, Coelenterates, Ctenophores and Platyhelminthes.

(ii) Pseudocoelomate: In some animals, the body cavity is not lined by mesoderm, instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. Here body cavity is directly connected to the archenteron. Such a body cavity is called pseudocoelom and the animals possessing them are called pseudocoelomates. E.g.: Aschelminthes (Ascaris). Pseudocoelom is derived from blastocoel.

(iii) Coelomate: The body cavity, which is lined by mesoderm (on both sides) is called coelom. Animals possessing coelom are called coelomates, or coelom is a cavity between the alimentary canal and body wall enclosed by mesoderm on both sides. E.g.: Annelids, Arthropods, Molluscs, Echinoderms, Hemichordates and Chordates.

Depending upon its origin, true coelom or eucoelom is of two types:

(a) Schizocoelous: The coelom is formed by the splitting of mesoderm. E.g.: Annelida, Arthropoda and Mollusca.

(b) Enterocoelom: The coelom develops as an outgrowth of the enteron or embryonic gut. E.g.: Deuterostomia (Echinodermata and Chordata). Echinodermata is an enterocoelomate invertebrate.