Chapter 23 Invertebrate Diversity Section 1 –Diverse animals share several key characteristics Section 2 –Sponges are relatively simple animals with porous bodies Section 3 –Cnidarians are radial animals with stinging cells Section 4 –Flatworms are the simplest bilateral animals Section 5 –Roundworms and rotifers have complete digestive tracts Section 6 –Annelida are segmented worms Section 7 –Mollusks show diverse variations on a common body form Section 8 – Echinoderms have spiny skin and a water vascular system Section 9 –Animal diversity “exploded” during the Cambrian period

The Body of a Mollusk Although squids, clams, and snails look different from each other, these animals all have certain features in common that classify them as mollusks ( phylum Mollusca ). Although squids, clams, and snails look different from each other, these animals all have certain features in common that classify them as mollusks ( phylum Mollusca ). Definition: member of a group of invertebrates characterized by a muscular foot and a mantle Definition: member of a group of invertebrates characterized by a muscular foot and a mantle All mollusks have a muscular mass of tissue called a foot and a multifunctional structure called a mantle. All mollusks have a muscular mass of tissue called a foot and a multifunctional structure called a mantle. The mollusk foot functions in locomotion, but its structure is very different from a human foot. The mollusk foot functions in locomotion, but its structure is very different from a human foot. The mantle produces the shell in mollusks such as clams and snails. The mantle produces the shell in mollusks such as clams and snails. Definition: body surface outgrowth that drapes over a mollusk Definition: body surface outgrowth that drapes over a mollusk

The mantle also functions in respiration, waste disposal, and sensory reception. The mantle also functions in respiration, waste disposal, and sensory reception. The mantle is related to another distinctive feature called the mantle cavity – this is where the gill is located. The mantle is related to another distinctive feature called the mantle cavity – this is where the gill is located. The gills extracts oxygen dissolved in the water and sometimes disposes of wastes. The gills extracts oxygen dissolved in the water and sometimes disposes of wastes.

Another body feature found in many mollusks is a unique rasping organ called a radula. Another body feature found in many mollusks is a unique rasping organ called a radula. Definition: scraping organ characteristic of mollusks Definition: scraping organ characteristic of mollusks An aquatic snail’s radula extends from the mouth and slides back and forth like a garden rake, scraping and scooping algae off rocks. An aquatic snail’s radula extends from the mouth and slides back and forth like a garden rake, scraping and scooping algae off rocks. Other mollusks use their radulas to drill through shells to prey on other mollusks. Other mollusks use their radulas to drill through shells to prey on other mollusks. All mollusks have a coelom – a snail’s coelom consists of three cavities : All mollusks have a coelom – a snail’s coelom consists of three cavities : one around the heart one around the heart one around the reproductive organs one around the reproductive organs one that forms part of the kidney one that forms part of the kidney

Most mollusks have an open circulatory system that includes a heart that pumps blood into vessels. Most mollusks have an open circulatory system that includes a heart that pumps blood into vessels. Definition: blood transport system in which blood is pumped into chambers where it comes in direct contact with tissues and organs Definition: blood transport system in which blood is pumped into chambers where it comes in direct contact with tissues and organs The Diversity of Mollusks The phylum Mollusca is very diverse, with about 150,000 known species. The phylum Mollusca is very diverse, with about 150,000 known species. Gastropods make up the largest group of mollusks. Gastropods make up the largest group of mollusks. Definition: member of a group of mollusks that includes snails and slugs Definition: member of a group of mollusks that includes snails and slugs CLASS: Gastropoda CLASS: Gastropoda Most organisms in this class have a single shell that is often spiral-shaped. Most organisms in this class have a single shell that is often spiral-shaped. Gastropods live in freshwater, saltwater, and terrestrial environments. Gastropods live in freshwater, saltwater, and terrestrial environments.

Most gastropods are marine – land snails and slugs are the only mollusks that live on land. Most gastropods are marine – land snails and slugs are the only mollusks that live on land. Bivalves include clams, oysters, mussels, and scallops. Bivalves include clams, oysters, mussels, and scallops. Definition: member of a group of mollusks with hinged shells, such as clams, mussels, scallops, and oysters Definition: member of a group of mollusks with hinged shells, such as clams, mussels, scallops, and oysters CLASS: Bivalvia CLASS: Bivalvia Bivalves have hinged shells divided into two halves. Bivalves have hinged shells divided into two halves. Most bivalves live in marine or freshwater environments – they use their muscular feet for digging and anchoring in the mud or sand. Most bivalves live in marine or freshwater environments – they use their muscular feet for digging and anchoring in the mud or sand. Bivalves feed by pumping water over their gills and trapping food particles that are suspended in water. Bivalves feed by pumping water over their gills and trapping food particles that are suspended in water. Cephalopods such as squids and octopuses are faster and more agile than gastropods and bivalves. Cephalopods such as squids and octopuses are faster and more agile than gastropods and bivalves. Definition: member of a group of mollusks that includes squids and octopuses Definition: member of a group of mollusks that includes squids and octopuses

CLASS: Cephalopoda CLASS: Cephalopoda The cephalopods called chambered nautiluses have external shells, but in most cephalopods the shell is small and internal (squids) or missing altogether (octopuses). The cephalopods called chambered nautiluses have external shells, but in most cephalopods the shell is small and internal (squids) or missing altogether (octopuses). Cephalopods are marine predators, using beak-like jaws and a radula to crush or rip prey apart. Cephalopods are marine predators, using beak-like jaws and a radula to crush or rip prey apart. Their mouth is at the center of their foot, which is surrounded by 8-10 inch long tentacle-like arms that catch and hold prey. Their mouth is at the center of their foot, which is surrounded by 8-10 inch long tentacle-like arms that catch and hold prey.