Question

What characteristics link phyla mollusca, annelida in the trochozoa clade?

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Answer 1

Phylum Mollusca is a diverse group of marine species. They comprise of species ranging from small grazing forms to the giant squid and octopus which are predatory in nature. They are triploblastic, billaterally symmetrical and unsegmented animals. Their body is covered by a skin fold mantle which secretes the shell. They have a feeding organ called radula. Circulatory system is mainly of open type. Fertilization is external, development is direct or through free larvalforms like trochophore. They consists of 7 different classes. Phylum Annelida are too bilateral in nature, schizocoelic in nature.Their blood vascular system is usually closed type. Development is usually direct. If there is indirect development, it includes trochophore larvae as in Nereis. The trochozoa clade includes all the protostomes which is characterised by the development of mouth first in the young embryo. Both of the phylum Mollusca and Annelida share these characteristics. They also share similar developmental patterns in their early embryonic stages. The trochophore larvae, which is found in both the phylum is essentially used for swimming and gathering food and at the top is a cluster of flagella. So, they are placed in the clade together based on a combination of morphological and RNA characteristics.