The body cavity found in echinoderms and chordates is

The correct option is enterocoelom.

To understand why this is the correct answer, let us break down the classification of body cavities (coeloms) in multicellular animals:

1. What is a coelom?
A coelom is a fluid-filled body cavity located between the outer body wall and the digestive tract. It is lined by mesoderm. Based on how the coelom develops during embryonic growth, true coeloms are classified into two main types: schizocoelom and enterocoelom.

2. Schizocoelom vs. Enterocoelom:
- Schizocoelom: This type of body cavity develops by the splitting of the mesodermal band or mass during embryonic development. It is typically found in protostomes such as annelids, arthropods, and mollusks.
- Enterocoelom: This type of cavity forms from the fusion of pouches that bud off from the embryonic gut (archenteron). The mesoderm pinches off from the wall of the digestive tube to form the coelom. This mode of development is characteristic of deuterostomes.

3. Evolutionary grouping of Echinoderms and Chordates:
Both echinoderms (e.g., starfish, sea urchins) and chordates (e.g., vertebrates, tunicates) belong to the group Deuterostomia. A key developmental feature shared by all deuterostomes is enterocoelous development, where the body cavity arises from the archenteric pouches. Therefore, the body cavity found in echinoderms and chordates is an enterocoelom.

4. Analysis of other options:
- haemocoel: A blood-filled cavity found in arthropods and mollusks.
- pseudocoelom: A "false" cavity not completely lined by mesoderm, typical of roundworms (nematodes).
- schizocoelom: A true coelom formed by the splitting of mesodermal tissue, found in annelids, arthropods, and mollusks.