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

Review What is a closed circulatory system? Blood circulates through the body in a closed circuit of vessels What is an open circulatory system? 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 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 May consist of one or more pieces. Provide protection. Allow for the attachment of muscles.

“Stomach foot” Largest and most diverse class of mollusks 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

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

Shipworm-does not filter-feed 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

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

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.

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

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

Class Oligocheta Earthworms are considered to be beneficial to the environment because 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.

“Many bristles” Have numerous setae that help them to move 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 May serve as walking legs. May be modified into large pincers. May be modified into antennae.

Arthropoda Jointed appendages of arthropods may 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 Ex. Pill bugs & bed bugs Bed bugs

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

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

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

“Spiny Skin” Ex. Sea stars, Sea urchins, Sand dollars 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 water-filled 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