Question

Which one of the following phyla is correctly matched with its two general characteristics?
A.Echinoderms - pentamerous radial symmetry and mostly internal fertilisation
B.Mollusca - normally oviparous and development through a trochophore or veliger larva
C.Arthropoda - body divided into head, thorax and abdomen and respiration by mouth
D.Chordata - notochord persists throughout and separate anal and urinary openings to the outside

Answer 1

Hint: Phylum Mollusca is the second-largest phylum of the animal kingdom followed by Arthropoda. There are about 85,000 species of molluscs which are recognized. There are fossil species also which are estimated to be between 60,000 and 100,000.

Complete answer:
Members of phylum Mollusca are normally oviparous (egg-laying) and their development may be either direct or indirect. In the case of indirect development, there is a trochophore or veliger larva stage before changing into an adult. The Echinoderms are unique as they show bilateral symmetry in larval stages while the adults have pentamerous radial symmetry. They show external fertilisation. In the members of phylum arthropods, the body is divided into three parts: head, thorax and abdomen. The organ for respiration consists of book lungs, book gills, and tracheae. The notochord is found to be present in the chordates in any of the stages in their lifespan. The openings of Urinary and anal may be the same or separate.

Phylum Mollusca can be segregated into seven different classes based on their characters: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda. The differentiation in the classes is based on the presence of and different types of shells they have.

Hence, the correct answer is option (B)

Note: The animals which have coeloms are called coelomates, the animals without coeloms are called acoelomates. There are two types of coelom: schizocoelom: which develops from splitting of the mesoderm and are found in members of phylum annelida, the arthropoda and mollusca; haemocoelom: which is the true coelom reduced and has a cavity which is filled with blood, is found in members of phylum arthropoda to mollusca.