BIO 112 Phylum Annelida

What is the Phylum Annelida referred to as?

Segmented Worms

Are flatworms and roundworms segmented?

No, they are non-segmented.

What organisms does this phylum include?

The earthworm, leeches, and many freshwater marine species.

Are Annelids bilaterally symmetrical?

Yes

What is metamerism?

The division of the body into similar segments that are arranged linearly along the anterior-posterior axis.

Annelids exhibit cephalization? What is it?

That is the nervous system concentrated in a ganglionic mass (brain) at the anterior (head).

Are the Excretory and Circulatory systems well developed?

Yes.

Do Annelids have a complete digestive system?

Yes, they do. As well, their digestive tract is straight and tubular and, in contrast with roundworms, they have their own musculature.

What is a musculature?

It enables it to function independently of the muscular activity of the body wall.

Do Annelids have a fluid-filled body like roundworms?

Yes, and this separates their digestive tract from their body.

Do Annelids have a true coelom?

Yes, it is formed by splitting the middle embryonic germ layer, the mesoderm, during development.

What forms the two or three embryonic tissue layers?

Gastrulation cells.

What are the embryonic tissue layers?

Ectoderm, Endoderm, and maybe Mesoderm.

What are the two embryonic tissue layers in a Diploblastic organism?

Ectoderm and Endoderm.

What are the three embryonic tissue layers in a Triploblastic organism?

Ectoderm, Mesoderm, and Endoderm.

What are the three basic body plans?

Acoelomate, Pseudocoelomate, and Coelomate.

What is required in order to be a coelomate?

The coelomic space must be surrounded on all sides by mesoderm.

Roundworms are pseudocoelomates. What is required in order to be a pseudocoelomate?

They also have a body cavity but this space is lined by mesoderm tissue on the body wall but there is no mesoderm tissue associated with the intestine side of the body cavity.

Flatworms are acoelomates. What is required in order to be a acoelomate?

They lack a body cavity altogether.

What is a body cavity?

It is a fluid or air space that holds the organs and protects them from internal injury. In soft body coelomates, the coelom is filled with a non-compressible fluid it acts as a hydrostatic skeleton against which muscles can work.

Coelomates are developed into two modes. What are they?

Protostomes and Deuterostomes

What is a Protostome?

A multicellular organism whose mouth develops from a primary embryonic opening.

What is a Deuterostome?

In an earthworm what are two different muscle layers?

The Circular muscle layer, and the longitudinal muscle layer.

What is made up of chloragogen tissue?

The outermost layer of cells surrounding the intestine, which serves as the same function as the vertebrate liver.

What is a typhlosole?

Prominent in-folding of the intestine.

What is the peritoneum?

The innermost layer of the body wall in the adult earthworm consists of a single layer of flattened cells.

Where do the peritoneum and chloragogen cells derived from?

The embryonic mesoderm layer.

What are mesenteries?

The organs in a coelomate animal are not floating freely within the cavity, but are supported by folds of peritoneal tissue called mesenteries.