General Biology/Classification of Living Things/Eukaryotes/Animals/Phyla
The blood pools in small chambers or sinuses , where it is collected and carried back to the gills. If you watch carefully, you may see them extrude their radula to scrape algae or small critters from the glass. They typically are very abundant. For example, conotoxins or modifications of them may be used to induce paralysis in muscles in specific health applications, similar to the use of botulinum toxin.
Remember that water is relatively incompressible.
BIL - Lecture 15
Within the body of the mollusc, the internal organs are embedded in a solid mass of tissue called the visceral mass.
The earthworm and leech are oligochaetes, while the featherduster worm is a tube-dwelling filter-feeding polychaete. Oligochaetes, which include earthworms and leeches, have a specialized band of segments known as a clitellum, which secretes a cocoon and protects gametes during reproduction.
Although these animals lack a calcareous shell, they get some protection from calcareous spicules embedded in a cuticle that covers their epidermis. Link to Learning This combination video and animation provides a close-up look at annelid anatomy.
As a result, the anus of the adult animal is located over the head.
Molluscs and Annelids
Find its anterior, posterior, ventral and dorsal sides. In the polychaetes, the setae are borne on paired appendages called parapodia. The medusa "jellyfish" is a floating form, and looks like an upside-down version of the polyp. Observe the live earthworms. They can withdraw into their shell, leaving only a single opening to defend, an opening capped by a shelly plate called an operculum.
At night, we commonly see many snails with no shells, the slugs. Class Polychaeta - tubeworms, paddleworms Nereis , sea mice; 5, sp. Their long hairs are actually thick long setae [the worm's hair, that is, not the lab instructor's] Look on the underside of the worm and you will see the clearly segmented body. They are the only molluscs with entirely closed circulatory systems. Darwin was the first person to realize the tremendous importance of earthworms in aerating and churning the soil, and breaking down dead vegetation.
One Illinois stream contained 10, leeches per square meter! Earthworms and polychaetes evolved from a common ancestor, a primitive burrowing marine worm. Cephalopods are marine predators, feeding on fish, crustaceans, and other molluscs. Observe the live leeches. They are parasites of humans and our crops. Typically, each segment has paired epidermal "bristles" setae or chaetae.
Chordates have a segmented body plan, at least in development.