Simulation · Biology · Class 11

Build a body plan, layer by layer

From the lesson Coelom, segmentation and notochord in Animal Kingdom. Change the values and watch what happens.

The idea behind it

NCERT §4.1.4–§4.1.6, Figure 4.4

Classification leans heavily on the body cavity: is there a space between the gut and the body wall, and what lines it?
A coelom is a body cavity lined by mesoderm. Coelomates: annelids, molluscs, arthropods, echinoderms, hemichordates and chordates.
In a pseudocoelom the cavity is not lined by mesoderm; the mesoderm lies as scattered pouches between ectoderm and endoderm. Aschelminthes are pseudocoelomates.
Acoelomates have no body cavity at all; Platyhelminthes are the example.
Metameric segmentation (metamerism): the body is divided externally and internally into segments, with at least some organs repeated in series, as in the earthworm.
The notochord is a rod-like structure of mesodermal origin formed on the dorsal side of the embryo. Animals that form it are chordates; those that do not (Porifera to Echinodermata) are non-chordates.
Figure 4.4 sorts the phyla step by step: cellular level (Porifera) versus tissue or higher; radial versus bilateral symmetry; then no coelom, pseudocoelom or true coelom; then segmented or not; then notochord or not.

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