ASIM'S WEBWORLD View: Main School Main AP Biology Chapter Guides RELATED LINKS Chapter Outline		AP BIOLOGY: Chapter Forty Review Answers 1. The prominent feature of lophophorate animals is the lophophore, a circular or U-shaped ridge around the mouth, with one or two rows of ciliated hollow tentacles. This functions in food collection and as a gas exchange organ. The coelomic cavity is within the lophophore and tentacles. 2. The protostomic and deuterostomic features are radial cleavage like deuterostomes, in two phyla, the blastopore becomes a mouth (protostomic) and, in the third, it becomes the anus (deuterostomic). The three phyla in this group are brachiopods (shelled, clamlike organisms), bryozoans (mosslike organisms), and phoronids (tube worms). 3. The basic body plan of a mollusc is a visceral mass with a soft epithelium and a muscular foot, and in the mass is contained digestive, excretory, and reproductive organs; this animal may have a differentiated head at the anterior end. The mantle is outside the visceral mass. This allows the gills to develop from its tissues, and the mantle may secrete the protective shell. In the mantle cavity of aquatic molluscs the water passes through, bringing in oxygen and food and carrying out wastes and gametes. This has developed into the jet propulsion system of squid and octopus. 4. A radula is a (usually) barbed rasping strip that allows molluscs to scrape nutrients off of hard substrates such as rocks (or aquarium walls). In some molluscs, the radula has been secondarily lost (bivalves), and in others it has been modified into a sharp puncturing organ, through which toxic materials or enzymes can be delivered to immobilize or kill prey (cone shells). 5. The circulatory system of most molluscs is an open system with a three-chambered heart. Cephalopod circulation differs from others because it has a closed system of vessels to carry the blood to and from the heart. The coelom represents the area around the heart. 6. The mollusc excretory system is composed of two tubular structures called nephridia; the opening is a funnel-like nephrostome that is lined with cilia that collect fluid from the coelom; and a coiled tubule leads to the bladder which is connected to an excretory pore. This type of excretory system allows for concentration of an excretory product. 7. The reproductive individuals in the molluscs are generally male and female individuals. Trochophores are distinct mollusc larvae with a row of cilia around the middle of the body. A veliger is a second larval stage of marine snails and bivalves with a distinct foot, shell, and mantle. 8. The four characteristics of the bivalves are (1) two hinged shells, (2) a wedge-shaped foot, (3) lack of radula, and (4) tentacles. The adductor muscles open and close the shells. The mantle secretes the shell and forms the ingoing and outgoing siphons. Bivalves feed as the cilia on the gills bring in water, and food particles become entangled in the mucus secreted by glands; then the palps direct the mass into the mouth. Bivalves disperse as larvae because adults are relatively fixed and immobile. 9. The annelid nervous system has diverse sensory organs that are concentrated on the anterior end, cerebral ganglion, and a primitive brain that is found in the anterior segment with separate interconnected ganglia in each segment. Annelid and nematode locomotion are similar because muscles move against a hydrostatic skeleton. Annelid locomotion is more advanced because each segment can move independently. Annelid setae are bristles of chitin that serve as anchors in certain crawling movements and may aid in swimming. 10. Annelids are similar developmentally to molluscs because both possess free-swimming trochophore larvae. It is likely that molluscs and annelids are derived from a common unsegmented ancestor. The relationship between segmentation in annelids and arthropods and that in vertebrates is that annelids and arthropods may share a same segmented ancestor whereas vertebrate segmentation evolved independently. 11. The circulatory system of annelids is a closed system with five hearts. They exchange gases with the environment directly through the skin-they lack gills or lungs. 12. Parapodia are feathery outgrowths of the body wall next to the setae in polychaete annelids that function in increased surface area for respiration. Some parapodia may also assist in movement. 13. Earthworms obtain nutrients by sucking soil into their mouth via contraction of the pharynx; then muscles in the gizzard grind up the organic material and the food moves through a long, straight digestive tract, with undigested material deposited as castings. Earthworm sensory structures sense light, touch, and moisture. Earthworms do not have parapodia. Earthworm reproduction is hermaphroditic. They orient head to tail when mating, held together by a mucous band produced by the clitellum. Each exchanges sperm with the other. After separation the clitellum secretes a cocoon, and as it passes the female openings, it receives the eggs. It then picks up the other worm's sperm from the sperm receptacles. Young worms eventually hatch from the cocoon. 14. Leeches and earthworms both possess a clitellum (during breeding season) and are both hermaphroditic with cross-fertilization. Leeches differ in that they have a reduced coelom, they are not divided into individual segments, they have suckers at one or both ends of the body, they generally have no setae, and many are external parasites. The adaptations that allow leeches to suck blood are a mouth with chitinous teeth that rasp through skin, an anticoagulant that prevents the wound from clotting, and powerful sucking muscles that suck up the blood. The anticoagulant as well as leaches are still used in medicine today in reduction of superficial hematomas.