Question

Which one of the following is not a characteristic of phylum Annelida?
A. Pseudocoelom
B. Ventral nerve cord
C. Closed circulatory system
D. Segmentation

Answer 1

The word ‘Annelida’ comes from Latin language, meaning ‘tiny rings’. It is one of the phyla in kingdom Animalia, which includes worms having a segmented body.

Step by step answer: Annelida is one of the phyla in the animal kingdom. The animals belonging to the phylum are characterized by a segmented body. This segmentation is also called metamerism. The body is internally and externally segmented into a number of parts called a segment or metamere. These segments help the worm for locomotion as they have got muscles called setae which help them get attached to the support and stay in a place and even to move from one place to another through anchoring of these setae. The ventral nerve cord forms the central nervous system of vertebrate animals. It is homologous to the spinal cord present invertebrates. These animals have a closed type of circulation, where blood flows through a system consisting of various blood vessels and is never exposed to the body cavity of the exterior. The coelom is a cavity or space present between the body wall and the digestive organ system. Pseudocoelomates are the animals who have false body cavities, it is called so as it is not derived from mesoderm and thus is not a true cavity. But the animals belonging to phylum Annelida that have true or well-developed coelom are called coelomates. Thus being ‘pseudocoelomate’ is the only character not possessed by animals of the phylum Annelida.
Hence, the correct answer is option A, i.e., Pseudocoelomate.
Additional information: animals belonging to this phylum breathe through the skin as they lack lungs. Organisms like Leech, Earthworm, Clitellata belong to this phylum.

Note: The phylum Annelida is the first phylum which includes animals having true coelom. If we look chronologically, all phylum which comes before phylum Annelida has pseudocoelom. And all the phyla which come after Annelida, chronologically have animals having true coelom and are called coelomates.