1Ch. 35 – Mollusks & Annelids Mollusks and annelids are grouped together because they were the 1st organisms to develop a true coelom.This suggests that these two groups of animals may have evolved from a common ancestor.The coelom provides space for a circulatory system to function without interference from other organs. They can contract muscles without hindering the movement of food through the gut.Both have the same 1st stage in larva development which is called a trochophore.
2Phylum: MolluscaSnails, clams, octopuses, oysters, squidsVideoMollusk is Latin for “soft”Most have a shell to protect them and are soft inside the shell.Develop from a trochophore larva which is a free-swimmer. Cilia helps them swim.
3Mollusk Characteristics Most are filter feeders (100,000 + species).True coelom3 main body parts: muscular foot, head, & visceral mass.Circulation, respiration, digestion, excretion, reproduction, nerve impulses.
4Body Arrangement 1. Muscular foot – used for locomotion. 2. Head – has a cerebral ganglia & mouth.3. Visceral Mass – contains many organs.4. Mantle – protects the visceral mass. It secretes a shell in most mollusks.Shell is made of calcium carbonate.How does the mollusk breathe with a shell?Gills are used for respiration.
54 Classes of Mollusks 1. Class: Gastropoda – snails & slugs Largest class of mollusksGastropoda means “stomach foot”Slugs have no shellSnails have a single shellThe body mass can turn 180 degrees this is called torsion
6Snails Gills for respiration Survive in moist environments Open Circulatory SystemHemocoel – open body cavity for blood circulation.Radula – a saw-like tongue made of chitin.Use foot to move with wavelike contractions.
123. Class: Cephalopoda – squids & octopus Cephalopod means “head foot”They have tentacles and a sharp radula to kill prey.Closed Circulatory System – blood circulates in vessels.
13Squids Largest invertebrate Giant squid are up to 3 meters long. Squid have the ability to squirt ink.They have the ability to change colors.VideoSquids have separate sexesSquid & octopus use jet propulsion to move.
144. Class: Bivalvia – clams & oysters Bivalvia means “two halves”They are sessile & filter food from the water.They have a muscular footThey don’t have a distinct head
15If a piece of sand grain gets into its shell the mantle coats the sand grain with secretion to form a pearl.ClamsFilter feedersHave incurrent siphon for water to enter and an excurrent siphon for water to exit.Have separate sexes like most mollusks.
17Annelida Phylum: Annelida – earthworms & leeches Characteristics VideoCharacteristicsBody is divided into segments metamerismTrue coelomWell developed organ systemMost have setae external bristlesSome have parapodia fleshy appendages
181. Class: Polychaeta – marine annelids Have setae & parapodia 3 Classes1. Class: Polychaeta – marine annelidsHave setae & parapodiaHave antannae (the only class)Some are free-swimmers
192. Class: Hirudinea – leeches No setae Live in calm bodies of freshwaterSucker at each endSmallest class of annelidsVideo
203. Class: Oligochaeta – earthworm Have setae – used to anchor their segments to soil as they burrow through the soil.Contract and expand in order to moveVideo
21Main Systems of an Earthworm Digestive systemWorms feed on organic matter in the soil.Worms loosen & aerate soil.Travels in the following pathway: prostomium (lip) mouth pharynx esophagus crop gizzard intestineCrop stores food, gizzard grinds food
22Circulatory systemClosed system – have blood vesselsAortic arches – serve as a heart5 pairHave a dorsal & ventral blood vessel
23Respiratory & Excretory systems No lungs or gill directly through the skinWhen it rains why do worms migrate to the surface?Nephridia is the excretory organ that eliminates waste.
24Reproductive systemHermaphroditesHowever, they can’t fertilize their own eggs.They attach at the clitellum & secrete a mucus layer in which the egg & sperm are placed in.
25Sperm is injected from the seminal receptacle. Eggs are released from the oviducts.