Type of body cavity (coelom) in earthworm is
A. Acoelomic
B. Schizocoel
C. Haemocoel
D. Enterocoelic
VerifiedHint: In most species, the coelom is the largest body cavity which is located within the body to surround the digestive tract and other organs and contain them.
Complete answer:
There is a large cavity of earthworms called the coelom, which extends across the whole length of the body. The cavity is formed by the division of the embryonic mesoderm.
Based on types of animals based on coelom, there are three types of body plans:
Acoelomates (animals with no coelom)
Pseudocoelomates (animals with false coelom)
Eucoelomates (animals with true coelom)
Acoelomic species do not have a body cavity at all and the lungs are in close contact with the epithelium.
In Pseudocoelomate species, the body cavity is not lined by mesoderm, instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. The internal organs lie freely within pseudocoelom.
Eucoelomates are true coelomates in which the coelom is lined by mesoderm both inside the body wall and around the gut. The coelom is lined by the mesodermal epithelium called peritoneum.
Haemocoel is a body cavity that usually absorbs blood and acts as part of the circulatory system. Enterocoel is the cavity that emerges from the pockets of the endoderm.
Based on the mode of formation, the coelom is divided into two groups, as Schizocoelom and Enterocoelom. respectively.
a) Schizocoelomates (True coelomates): At the time of gastrulation, the body cavity originates by splitting of mesodermal tissue. It is present in the protostomes. This method of coelom formation is called schizocoelous, and occurs in animals like annelids, arthropods and mollusks.
b) Enterocoelomates: At the time of gastrulation, the body cavity is formed from the fusion of the internal outgrowths of the archenteron, which expands and its mesoderm lines the gut on the inner side and body wall on the outer side. It is present in the deuterostomes. It is found in Chordates and Echinodermata.
Protostomes are the organisms undergoing protostomy during embryonic formation, i.e. the blastopore grows into the mouth and the opposite end develops into the anus. The term protostome has a Greek root, where proto means first and stoma means mouth. The word protostome means first-mouth. Examples of protostomes include earthworms, leeches, etc.
In protostomes, Schizocoelom is present. The body cavity originates from the mesoderm splitting. One portion binds to the endoderm and the other circles the endoderm. The chamber between them expands into the coelom. The blastopore shapes your mouth. Annelida (Earthworm), Arthropoda, and Mollusca are examples of schizocoelous animals. The coelom is filled with blood in Arthropoda and Mollusca and is known as Haemocoel.
Hence, the correct answer is option (B).
Note: The cavity has Coelomic fluid which the worms secrete. The substance is milky white in colour and is dense and gelatinous. In fact, it is secreted in times of tension to avoid drying up under dry conditions and to defend itself against predators.
