Annelidia and Molluska Rushdee H. Chris V. 7th AP Biology

Segmented worms. A major protostome, coelomate phylum with about 9000 species worldwide. Most species are marine or terrestrial. They have closed circulatory system, a large ventral nerve cord, and excretion by nephridia. They have a trochophore larvae during development, the life cycle is non-emergent.

The digestive system of annelids consists of an unsegmented gut that runs through the middle of the body from the mouth to the anus. The gut is separated from the body wall by the body cavity, called the coelom They have a separate pharynx and stomach as opposed to a central gastral cavity. Annelids are the most primitive organisms to show some specialization along their digestive tract. The basic units of the annelid excretory system are either protonephridia or metanephridia protonephridia - which have tubules (solenocytes) that end blindly within cells, contain flagella and are joined to a common duct that drains to the outside Metanephridia - which are funnel-shaped structures containing cilia, that open to the outside.

Characteristics of the circulatory system vary within the phylum. The blood usually contains hemoglobin, a red oxygen- carrying pigment; some annelids have a green oxygen- carrying pigment, and others have unpigmented blood. Circulatory system is usually closed Blood flows toward the head through a contractile vessel above the gut and returns to the terminal region through vessels below the gut

They can take up soil from below six inches that are rich in nutrients and bring up four to eight pounds each year to the topsoil. They add calcium carbonate to the soil, which brings its pH to one that is more neutral and around 7 Reproduction is sexual or asexual. Reproduction is by fragmentation, budding, or fission. Among sexually reproducing annelids hermaphrodites are common Fertilized eggs of marine annelids develop into free-swimming larvae. Eggs of terrestrial forms are enclosed in cocoons

Second largest phylum with over 150,000 diverse species Mainly all mollusks live in underwater envitonment They have mainly open circulatory system (in some rare cases closed), very sensitive nerve clusters one head/mouth area, and most molluska can excrete a calcium carbonate chemical to form a protective shell. Almost all larvae start life off as veliger larvae, “free swimming”

Almost all mollusks have a complicate digestion system due to the there method of obtaining food. They have a unique structure for a mouth known as a radula. This structure has unique teeth formations which serve for various purposes such as tearing, scraping, stabbing, cutting. Radula is present in all mollusk except for bivalves and aplacophora types of mollusks. Digested food eventually becomes all filtered though the kidneys and later excreted from the mantle which empties out into the shell (if there is one present) Important ecological role played by mollusks, they keep algae under control, play role as predators to maintain environment, feed many other organisms, and return nutrients to the environment.

Almost all mollusks have an open circulatory system except for cephalopods. Have heart, vessals, and regular respiratory pigments A majority of mollusks are able fertilize themselves in desperate times, but if they can help it they will breed sexually as much as they can instead of breeding by themselves. Once eggs hatch veliger larvae are released, “free swimming larvae.” Some unique snails give live birth

Most mollusks are able to produce there own shell by secreting calcium carbonate from there mantle. Some exotic snails are known to be poisonous Oysters are able to produce valuable pearls when debris is sucked inside the clam and it is unable to get it out. It forms this pearl by “onioning” it around in layers, over lng periods of time it is able to form a rounded pearl which can be varied in colors. Most valuable being a black pearl