Unit 11 Mollusks and Echinoderms Guided Notes Molluks General Characteristics of Mollusks are a very diverse group of animals that. They contain members that are. However, all have. These body parts are the. The for those molluscs that have one. Phylum Mollusca is made up of over 112,000 species of soft-bodied animals. These animals generally exhibit as well as the three main body parts (visceral mass, foot and mantle) introduced above. Mollusks. Many mollusks have. Nitrogenous waste is excreted through. Mollusks have an with a dorsal heart and vessels. The hemocoel aids fluid return to the heart. A (a flexible tongue like strip of tissue covered with tough abrasive teeth that point backward). The radula is used to graze, drill, or function as a poisonous dart. The nervous system has a with the development of the (nearly indistinguishable from
annelids). The trochophore larvae becomes the veliger larvae for swimming. Mollusks are true with a reduced main body cavity called the hemocoel. They are also Protostomes so the mouth develops first in the embryo. There are four main classes of Mollusks that we will study in this unit. They are Amphineura (polyplacophora), Bivalvia, Gastropoda, and Cephalopoda. The Chitons The Chitons belong to Class. Chitons are with a shell that is made up of. They have a muscular foot for locomotion (crawling). Chitons have a reduced head. There are about 650 species of these organisms. They can be found clinging to rocks in the intertidal zone and use a tooth-like radula to scrape food off of rocks. Chitons are herbivores. Breathing is facilitated by.... Gastropods Class has adapted their foot so it is located on their ventral surface or belly. This is the largest molluscan class and includes. They are characterized by a with the characteristic cone shape or no shell. Gastropods. The muscular foot extends along the ventral surface of the
organism. Gastropods undergo a process called during larval development. In torsion the visceral mass twists 180 degrees in relation to the head. This results in the mantle cavity, gills and anus being brought to the front of the animal. This allows the gastropod to retract its head into its mantle cavity when threatened. The head of gastropods contains. A scraping is used to pick up food. Slugs do not have a shell. They. They usually become active during the cool moist part of the day. Gastropods are the only molluscan class to become terrestrial. Gastropods have an with a circulatory fluid called hemolymph. Nudibranchs (Sea Slugs) are marine gastropods that lack shells. Nudibranch means naked gill and refers to the fact that gas exchange happens across the entire surface of these animals. The images below show how these animals maximize their surface area and their vivid colours. Bivalves The name. The mantle of a bivalve is responsible for excreting the shell to surround and protect the body. Strong muscles hold the shell closed in all members to the class. The muscular foot varies from bivalve to bivalve. It is most prominent in the clam which uses its large muscular foot to dig through the sand. Scallops can move by jet propulsion and swim through the water escaping predators such as sea stars. An oyster's shell will grow directly on a rock to provide
a permanent home. but here is a scallop swimming. Bivalves are animals and live in the intertidal zone. They exhibit a large visceral hump and a muscular foot with a reduced head covered with a thin mantle.. Bivalves are and take water containing food into the mantle cavity via the incurrent siphon and pass it over the mouth. Excess water is forced out through the excurrent siphon. The. They have no radula. The general anatomy of a clam is shown above as an example of a bivalve. Respiration is performed by the. This food then passes the, where it follows an. Food is digested in the stomach and then passes to the for absorption. The intestine is a long coiled organ ending in an where the waste is expelled. Also found in the visceral mass is the heart. The to supply it with oxygen and remove nutrients and wastes.the diagram below shows the circulatory system of a clam. Recall,
with a dorsal heart and vessels. Geoducks burrow in the sand or amongst rocks or attach to substrate by secreting byssal threads. They many leap with a foot. They have separate sexes and external fertilization...mmmm oysters!... Clam Anatomy Review Exercises
Cephalopods The name are given this term because the. All members of this class are. Of the invertebrates, it can be argued that the. This is because of their. Their ability to learn and muscular control are so advanced that they can be trained to open jars to obtain food. They have quite an that is distinctly different from that of a human. The cephalopods are also fast swimmers and
. To generate this propulsion they take water in slowly and expel it so quickly that they are propelled forward. Other features of cephalopods include a and a which is a toothed tongue. Many of the animals that an octopus typically feeds on have either a shell or an exoskeleton so the chitinous beak is necessary for feeding. For predator diversion the cephalopods posses an. Cephalopods contain which enable them to change color. The octapus puts this skill to good use as and the cuttlefish uses colour change to attract a mate and warn off the competition all at the same time. Here is a part of a TED video with a great octapus camouflage video.... Cephalopods have. Their circulatory system is a, so the circulatory fluid is contained within the vessels. Jet propulsion can be used to escape predators by forcing water out a siphon.. Sexual reproduction results in internal fertilization followed by egg laying. Echinoderms General Characteristics of Echinoderms. This means that the first embryonic opening becomes the anus and the second becomes the mouth. Because of this trait, it is thought that echinoderms are more advanced than some of the other animals. However,. For example, their
would usually be considered more primitive than bilateral symmetry, so it is difficult to see their relation to the vertebrates. Also, echinoderms have, and have a for controlling motor and sensory functions. However, when in larval form, an echinoderm is a free swimming bilaterally symmetrical organism. It is this larval form that scientists believe evolved into some of the prochordates that are mentioned later in this course. Echinoderms are fairly diverse in appearance within the phylum. Typified by the they vary in outer appearance but have similar internal structures. They are and can be found from the intertidal zone to deep ocean waters. The digestive system is relatively short, and digestive glands are located within the arms of the starfish, or on the outer body wall of the other members. Digestion, however, is a bit different from other animals, in that, much of it takes place outside the body of the starfish. The echinoderm will put its stomach outside of its body and begin to digest its prey before it takes it in to finish the process. They can be. Sex organs are also located in the arms of the starfish, and echinoderms are capable of both. External reproduction. The regeneration properties of starfish allow them to regrow lost limbs as well as the limb to regrow a body., are found throughout the body wall providing the echinoderm with oxygen. The method of locomotion in the starfish is truly unique. The is a network of tubes ending in. An organ called an will pump water into the tubes increasing the pressure in the tube foot causing it to expand and create suction on a nearby surface. As the pressure on the tube foot decreases, the tube contracts without decreasing the suction, and the starfish is pulled in that direction. Class Asteroidea Sea Stars have with several arms (5 or multiple of 5) radiating from a central body. The. The anus is at the center of the disc together with the water intake ( ). The upper surface is often very colorful with. Sea stars have a
to allow movement. Sea stars have. They have a. Reproduction is with most species having separate sexes. Free swimming larva called bipinnaria are produced. Sea stars are and feed on and externally digested their food. The picture below shows a sea star feeding on a bivalve. Notice all the tube feet at work. They also have two stomachs. Food moves first into the. Sea stars also exhibit the ability to regenerate body parts...flip themselves over..even with an arm missing.
Sea Star Review Exercises
Class Crinoidea (feather stars) Feather stars have. The body of a typical feather star is cup-shaped with. Some have five arms while others may have as many as 200. The arms, called pinnules, are coated with a sticky substance that helps them catch food. Cirri attached to the underside of the body. The mouth and their anus are situated on the upper side of the feather star. Below is a video of a feather star swimming.... Class Ophiuroidea (brittle stars). They have with a central disc and five highly flexible arms that protrude. Unlike sea stars, there is no replication of internal organs in each arm just one set in the central disk. Brittle stars have a much smaller central disc and no anus. Wastes are eliminated through the mouth which is situated on the underside in the center. On the underside of the body disk there is an opening at the base each arm on both sides. These ten openings are breathing and reproductive outlets. They take in water to gain oxygen and shed eggs or sperm into the sea. Class Echinoidea (sea urchins)... Sea urchins have a body and an external. The mouth consists of a complex arrangement of muscles and plates surrounding the circular opening. Sea urchins have a centrally located jaw (called Aristotle's lantern) with
horny teeth. The anus is located on the upper surface. Some sea urchins have a spherical, bulb-like cloaca to store fecal material. The cloaca protrudes from the anal opening and can be withdrawn into the shell. Sea urchins have movable spines of various sizes and forms that are attached to the body.. They also have. Some of these pedicellaria are poisonous.... Class Holothuroidea (sea cucumbers) unlike most other Echinoderms that display radial symmetry. Sea cumcubers have a distinct dorsal and ventral side or back and bottom. They are cucumber shaped with an elongated, muscular, and flexible body. The mouth is at one end and the anus is at the other. Around the mouth there are - used in food collecting. These tentacles are modified tube feet. Here is a sea cucumber feeding.