Biology I Chapter 35 36 38 Mollusks Annelids

Biology I Chapter 35, 36, & 38 Mollusks, Annelids, Arthropods, & Echinoderms

Review • What is a closed circulatory system? o Blood circulates through the body in a closed circuit of vessels • What is an open circulatory system? o Blood is released directly into spaces in the body tissues. • The advantage of a closed circulatory system over an open circulatory system is that blood moves more efficiently through the tubes of a closed circulatory system.

Phylum Mollusca • Coelomates-have a true hollow, fluid-filled cavity that is completely surrounded by mesoderm

• The evolution of a coelom was significant because it enabled development of more complex organ systems. • All of the animal phyla that evolved after the mollusks have a coelom.

Mollusca • Trochophore-larval stage of development o o o Occur in some mollusks’ life cycles Possess a belt of cilia around their bodies Occur in some annelids’ life cycles.

Body Plan • Head-contains the mouth and a variety of sensory structures • Foot-a large, muscular organ usually used for locomotion

• Visceral Mass-contains the heart and organs of the digestive, excretory, and respiratory tracts.

• Radula-involved in eating. • Mantle-Layer of epidermis that can secrete shells or soft bodies • Found only in Mollusks

Body Plan • Shells of mollusks o o o May consist of one or more pieces. Provide protection. Allow for the attachment of muscles.

Class Gastropoda • “Stomach foot” • Largest and most diverse class of mollusks

• Snails-live on land, in fresh water, and in the ocean

• Slugs-snails without shells

• Nudibranchs-marine gastropods that lack shells • Nudibranch

Class Bivalva • Shell is divided into two halves connected by a hinge • Most are sessile filter-feeders

• Clams-live buried in mud or sand • Giant Clam • Goeducks • Clam Moving

Class Bivalva

• Oysters-become permanently attached to a hard surface early in their development • Not for Eating • Filtration • Pearl

• Scallops-can move through jet propulsion • Swimming • Fleeing • Scallop Escaping

Class Bivalva • Shipworm-does not filter-feed

Class Cephalopoda • • “Head foot” Specialized for free-swimming Predators Nervous system is more advanced than any other group of mollusks. • Closed Circulatory System

Class Cephalopoda • Squid-have tentacles • Giant Squid • Squid Inking

• Octopus-Eight tentacles; crawl along the ocean bottom and lie in wait for prey • Octopus vs. Shark

• Chambered Nautilus-the only cephalopod that has retained its external shell • Nautilus

Phylum Annelida • “Segmented Worms” • Segmentation-Most significant evolutionary advancement of annelids over mollusks • Each segment of an annelid may contain some organ systems that duplicate systems in other segments.

• Setae-external bristles • Parapodia-fleshy protrusions

Class Oligocheta • Earthworm • Coordinated movements of an earthworm’s body segments are possible because of the ventral nerve cord and ganglia that carry impulses to the muscles.

Class Oligocheta • Digestive tube is divided into three regions o o o Crop Gizzard Intestine

• Closed circulatory system with 5 aortic arches • Nephridia-Small tubules that collect wastes from the coelom of annelids and discharge the wastes from the body

Class Oligocheta • Clitellum-thickened section of the body associated with reproduction.

Class Oligocheta • Earthworms are considered to be beneficial to the environment because o o o They help release nutrients into the soil. They aerate the soil as they move through it. They break up the soil in which they live.

Class Polychaeta • “Many bristles” • Have numerous setae that help them to move

Class Hirudinea • • • Leeches No setae or parapodia Use suckers to aid in movement. Are segmented May be parasitic. Leech Cure

Phylum Arthropoda • “Jointed leg” • A similarity between annelids and arthropods is that they both have segmented body patterns.

• Appendages-jointed extensions • The appendages of arthropods o o o May serve as walking legs. May be modified into large pincers. May be modified into antennae.

Arthropoda • Jointed appendages of arthropods may o o o Become specialized for particular functions. Function in locomotion. Function in feeding.

Arthropoda • Exoskeleton-provides protection and support • Chitin-Tough polysaccharide that makes up exoskeleton • Compound Eyes-eyes made of many individual light detectors, each with its own lens. • Open circulatory system • Molting-periodic shedding of the exoskeleton

Class Crustacea • Two pairs of antennae • Five pairs of legs • Isopod-terrestrial crustaceans o o Ex. Pill bugs & bed bugs Bed bugs

• Decapod-” 10 feet”; aquatic crustaceans o Ex. Crayfish, lobsters, crabs, shrimp

• Have three body segments: Head Thorax-Covered by single, tough covering called the carapace o Abdomen o o

Class Chelicerata • Spiders, Scorpions, Mites, Sea Spiders, and Horseshoe Crabs • First pair of appendages are modified into pincers or fangs • Jumping Spider • Brown Recluse

Class Myriapoda • Millipedes have two pairs of legs per segment and feed mainly on decaying plants. • Centipedes have one pair of legs per segment and eat other animals. • Centipede vs. Tarantula

Class Insecta • Live almost everywhere in the world except in salt water • Have the ability to fly. • Tympanum-sound-sensing organ • Insect Candy

Phylum Echinodermata • “Spiny Skin” • Ex. Sea stars, Sea urchins, Sand dollars

• Do not exhibit cephalization • Radially symmetric as adults; bilaterally symmetric as larvae. • Embryological evidence suggests that the echinoderms are closely related to the chordates.

• Pentaradial symmetry • Endoskeleton made of calcium carbonate plates known as ossicles.

Echinoderms • Water vascular system-network of waterfilled canals inside the body • Tube feet-aid in movement, feeding, respiration, and excretion. • Tube Feet • Sea Urchin

Phylum Chordata: • Dorsal nerve cord-develops into the brain and spinal cord in humans • Notochord-develops into vertebrae • Pharyngeal pouches-develops into lungs • Postanal Tail-develops into tail or tailbone

Invertebrate Chordates • Vertebrates, tunicates, and lancelets are all members of the phylum Chordata. • Tunicates and Lancelets retain their notochord throughout their life and do not develop a vertebrae.

• Lancelets filter food from water that enters the mouth.

Invertebrate Chordates • Tunicates-“Sea Squirts”-squirt out a stream of water when touched