Define the terms and give one example of each
(a) Bilateral symmetry
(b) Coelom
(c) Triploblastic
Define the terms and give one example of each
(a) Bilateral symmetry
(b) Coelom
(c) Triploblastic
(a) Bilateral symmetry: When the body is divided into identical left and right halves in only one plane, it is called bilateral symmetry.
It is also known as plane symmetry. In bilateral symmetry, the body can be divided into two identical halves in only one plane.
E.g., Chordata, Annelida, Arthropoda, Platyzoa, Nematoda, and most Mollusca have bilateral symmetry.
(b) Coelom:
A coelom is a hollow, fluid-filled cavity found in many living things, where it acts as a protective cushion for their internal organs.
It is the body cavity which is filled with fluid and is lined by mesoderm. Animals possessing coelom are called coelomates,
E.g., annelids, molluscs, arthropods, and echinoderms.
- Acoelomate:
The coelom is absent. The blastocoel is completely occupied by mesoderm.
- Pseudocoelomate
The true coelom is not present. The blastocoel is partly filled by mesodermal cells.
- Eucoelomate
Animals that have a true coelom. The coelom is lined by mesoderm on both sides, towards the body wall and towards the gut.
(c) Triploblastic:
Animals having three germinal layers (ectoderm, mesoderm, and endoderm) are called triploblastic.
E.g.: Nematoda.
(a) Bilateral symmetry: When the body is divided into identical left and right halves in only one plane, it is called bilateral symmetry.
It is also known as plane symmetry. In bilateral symmetry, the body can be divided into two identical halves in only one plane.
E.g., Chordata, Annelida, Arthropoda, Platyzoa, Nematoda, and most Mollusca have bilateral symmetry.
(b) Coelom:
A coelom is a hollow, fluid-filled cavity found in many living things, where it acts as a protective cushion for their internal organs.
It is the body cavity which is filled with fluid and is lined by mesoderm. Animals possessing coelom are called coelomates,
E.g., annelids, molluscs, arthropods, and echinoderms.
- Acoelomate:
The coelom is absent. The blastocoel is completely occupied by mesoderm.
- Pseudocoelomate
The true coelom is not present. The blastocoel is partly filled by mesodermal cells.
- Eucoelomate
Animals that have a true coelom. The coelom is lined by mesoderm on both sides, towards the body wall and towards the gut.
(c) Triploblastic:
Animals having three germinal layers (ectoderm, mesoderm, and endoderm) are called triploblastic.
E.g.: Nematoda.
