Body Structure The nematode body is cylindrical, elongated and smooth with no limbs protruding, such as is seen in the common garden worm though generally on a smaller scale. The body is contained within a tough elastic cuticle which in many species forms elaborate structures useful for identification.

Correlated with their lack of cilia, nematodes do not have protonephridia; their excretory system consists of one or more large gland cells opening by an excretory pore, or a canal system without gland cells, or both cells and canals together.

The word “worm” is not very scientific. This informal term describes animals (usually invertebrates) that have long bodies with no arms or legs. Worms with round, non-segmented bodies are known as nematodes or roundworms (Figure below). They are classified in the phylum Nematoda, which has over 28,000 known species.

Additionally, do sponges have segmentation? No. Sponges display a lower grade of body-plan organization than all other animal phyla (true metazoans). All animals that have segmented bodies (annelids, arthropods) also have internal body cavities (coelom) that are lined by mesodermal tissue.

Sponges do not have a coelom. The body cavity of sponges is large, it is open to the outside world, and it enables the sponge to consume food (Dawkins 2004). Sponges do not have any internal organs or a nervous system.

Taxonomic level: phylum Porifera; grade of construction: cellular, with no distinct tissues or organs; symmetry: variable; type of gut: none; type of body cavity other than gut: none; segmentation: none; circulatory system: none; nervous system: none; excretion: diffusion from cell surface.

the segmentation of a sponge is present, but rather than saying it has a segmented body it is a body with many pores, they are part of microscopic animals.

The sponges draw water carrying food particles into the spongocoel using the beating of flagella in the choanocytes. The food particles are caught by the collar of the choanocyte and brought into the cell by phagocytosis. Nematocysts are “stinging cells” designed to paralyze prey.

Earthworms are classified in the phylum Annelida or Annelids. Annelida in Latin means, “little rings.” The body of the earthworm is segmented which looks like many little rings joined or fused together. The earthworm is made of about 100-150 segments. Each segment or section has muscles and bristles called setae.

The eyes of these worms are also quite different. Roundworms are considered a less evolved form of worm. However, they have a more complicated visual system than many segmented worms. Most species of segmented worms have eyespots.

Segmented worms are the most complex animals of these three invertebrates. They are placed in Annelida. Segmented worms have a true coelom, a circulatory system and a digestive system.An earthworm is a segmented worm.

Segmented worms have a well-developed body cavity filled with fluid, which serves as a hydroskeleton, a supportive structure that helps move the worm’s muscles. Segmented worms also tend to have organ systems that are more developed than the roundworms or flatworms.