Biodiversity

CNIDARIANS (eg Hydra species) are radially symmetrical.
According to this plan, its tentacles are arranged all around the top of the body
This allows the hydra to obtain food and ward off danger coning from any direction.
Nerve cells are located over the entire body surface making it sensitive all around .
This is useful to the hydra which is sedentary, not being about to move in search of food or quickly way from danger

PLATYHELMINTHES (g Taenia species, like tapeworms) are Bilaterally Symmetrical and have a flattened body form.
Because of the flattened form, the tapeworm is able to obtain food from the intestine of the host by simple diffusion.
The flat surface also exposed a large surface area for absorption of food

ANNELIDA (eg Lumbricus species, like the Earthworm) are Bilaterally Symmetrical showing Cephalisation. As a result,
the front end of the earthworm is more sensitive to the environment.
This is important for an organism such as the earthworm, which moves in a forward direction .
This allows danger to be detected before entering a new environment.


How the Body Plans Relate To the Modes of Living

The HYDRA is diploblastic consisting of an Ectoderm and an Endoderm, with non-living Mesoglea in between.
The Endoderm lines a cavity called a coelenteron which as a blind-ending gut.
Food can diffuse easily into all cells so a blood system is not necessary

The TAPEWORM is triploblastic consisting of ectoderm, mesoderm and endoderm.
There is a body cavity within the organisms

The EARTHWORM is triploblastic consisting of ectoderm, mesoderm and endoderm.
There is a body cavity in the mesoderm called a COELOM containing the coelom fluid , which acts as a hydrostatic skeleton .
The coelomic fluid also keeps s the skin moist for gas exchange


The HYDRA has a single digestive opening, which serves as a mouth and an anus
The opening can only be on one end since the other end is attached
The position of the...