Mollusks, Arthropods, Echinoderms Mollusks, Arthropods, Echinoderms
Mollusks • Soft-bodied invertebrates • Have bilateral symmetry • Usually have one or two shells with organs in a fluid filled cavity • Most live in water • Many different species
Mollusks’ Body Plan • Mantle • Thin layer of tissue that covers the body organs • Mantle cavity (between soft body and mantle) • Contains the gills that are used to breathe by exchanging oxygen and carbon dioxide in the water • Open Circulatory System • Most mollusk have this • Moves blood through vessels and into open spaces around body organs
Mollusks’ Body Plan • Have a well developed head with a mouth and some sensory organs • Underside is a muscular foot • Moves by making rhythmic contractions
Classification of Mollusks • Classified into three common groups based on shell presence, type and foot type • Gastropods • Bivalves • Cephalopods
Gastropods • Largest group of mollusks • Usually have a single shell • Use a radula (a tongue-like organ with rows of teeth) to get food • Have foot glands that secrete a layer of mucus for sliding • Includes snails, conchs, and garden slugs
Obtaining Food • Some gastropods are herbivores. These include animals that eat only plants. • Other gastropods are carnivores. These include animals that eat only other animals.
Bivalves • Have a hinged, two-part shell • To open or close their shell they either contract or relax their muscles • Includes clams, oysters, scallops, & mussels • Well adapted for water • Clams can burrow in sand • Mussels attach themselves to a solid surface • Scallops escape predators by rapidly opening and closing their shell
Cephalopods • Most specialized and complex mollusks. • Include squid, octopuses, and chambered nautiluses. • Have a well developed head and many tentacles for capturing prey. • Closed circulatory system • Moves blood through the body in a series of closed vessels like humans. • Use jet propulsion to move at speeds of 6 m/s.
Origin of Mollusks • Mollusk fossils date to more than 500 million years ago • Some species of mollusk, like the chambered nautilus, have changed very little from their ancestors • Today’s mollusks are descendants of ancient mollusks
Value of Mollusks • Provide food for people and other animals • Many people make their living raising or collecting mollusks to sell • Shells can be used for jewelry and decoration • Pearls are produced by several species of mollusks most are made by pearl oysters
Negative Effects of Mollusks • Land slugs and snails can damage plants • Certain species of snails are hosts for parasites that can infect humans • Bacteria and viruses can become trapped in these animals because they are filter feeders…thus eating them could result in sickness or even death!
Arthropods • Characteristics • Largest group of animals (over 1 million species) • Have jointed appendages which include legs, antennae, claws and pincers (Chelipeds) • Have bilateral symmetry, segmented bodies, exoskeletons, a body cavity, a digestive system with two openings and a nervous system • Most have separate sexes and reproduce sexually
Origin of Arthropods • Some fossils are more than 500 million years old • Scientist hypothesized that arthropods probably evolved from an ancestor of segmented worms because they have body segments • The hard exoskeleton and walking legs allowed arthropods to be among the first animals to live successfully on land
Value of Arthropods • A source of food • Agriculture would be impossible without bees and other insects to pollinate crops • Useful chemicals are obtain from some arthropods • Important part of ecological community
Arthropods • Body Segments • Bodies of these animals are divided into segments similar to segmented worms • Some have many segments, others have segments that are fused together to form body regions • Exoskeleton • A hard outer covering that supports and protects the internal body and provides places for muscle to attach. • Doesn’t grow as the animals does, it is shed and replaced during a process called molting
Crustaceans • Have jointed appendages which include legs, one or two pairs of antennae, claws and pincers (Chelipeds) which are used for crushing food. • Most live in water, but some live in moist environments on land—such as pill bug. • Have five pair of legs, first pair of legs are claws for catching and holding food.
Crustaceans • Swimmerets are appendages on the abdomen which help in movement and are used in reproduction; also force water over the gills used in O2 and CO2 exchange • If a crustacean loses an appendage it can regenerate it!
Arachnids • Have two body sections, four pairs of legs, and no antennae. • Scorpions • Have sharp, poison filled stinger at the end of abdomen. • Have a well-developed appendages which they can grab their prey. • Spiders • Can’t chew their food, release enzymes into prey to digest it—then suck the predigest liquid into its mouth. • Have book lungs where O2 and CO2 are exchanged.
Arachnids • Mites & Ticks • Most are parasites • Ticks have specialized mouthparts to remove blood from the host. • Ticks often carry disease such as Lyme Disease.
Centipedes & Millipedes • Have long bodies and many segments, exoskeleton, jointed legs, antennae and simple eyes. • Found in damp environments • Reproduce sexually • Make nests for eggs and stay with them until they hatch. • Centipedes are predators • Millipedes feed on decaying plant matter.
Insects • Have three body regions • Head • Has a pair of antennae, eyes and a mouth • Thorax • Three pairs of legs and one or two pairs of wings if present are attached here • Abdomen • Where reproductive structures are found
Insects • Have an open circulatory system that carries digestive food to cells and removes wastes • Insect blood doesn’t carry O2 instead air enters and exits through openings called spiracles found on the abdomen and thorax • Are the only invertebrate animals that can fly
Insects & Food • Feed on a number of things have different mouth parts to obtain food • Grasshoppers and ants have large mandibles for chewing • Butterflies and honey bees have siphons for lapping up nectar • Aphids and mosquitoes have mouth parts that are adapted for piercing into plants or other organisms
Metamorphosis • A series of changes that an insect goes through • Two types • Complete • Includes stages of egg, larva, pupa, and adult • Ex. Butterflies, bees, flies • Incomplete • Includes stages of egg, nymph, adult • The nymph form molts several times before becoming an adult • Ex. Grasshoppers, crickets
Insects success • Insects are extremely successful based these reasons • Tough flexible, waterproof exoskeleton • Ability to fly • Rapid reproduction cycles • Small sizes • Some insects have other adaptations that allow them to be successful • Camouflage/mimicry.
Controlling Insects • Not all arthropods are of value some are pests that carry disease or can damage crops
Controlling Insects • Common ways to control insects • Insecticides, but these also kill non-harmful insects • Biological controls • Types of bacteria, fungi, and viruses can be used to control insects • Natural predators being released to kill the harmful insect • Some how interfere with reproduction of the particular insect
Echinoderms • Characteristics • Have an endoskeleton covered by a thin, bumpy or spiny epidermis • Radial symmetrical—allowing them to sense food, predators and other things in the environment from all directions • Have mouth, stomach, intestines • Feed on a variety of plants and animals • Have no head or brain, but have a nerve ring that surrounds the mouth • Also have cells that respond to light and touch
Water-Vascular System • A characteristic unique to echinoderms • Allows them to move, exchange CO2 and O2, capture food, and release wastes • It is a network of water-filled canals with thousands of tube feet connected to it. • Tube feet—hollow, thin walled tubes that ends in a suction cup. • As pressure in the tube feet changes the animal is able to move along by pushing out and pulling in its tube feet
Characteristics of Echinoderms • Echinoderms, such as this sea star, have a water vascular system that helps them move and catch food.
Types of Echinoderms • Sea Stars • Echinoderms with at least 5 arms arranged around a central point • Uses tube feet to open shells of prey, once open pushes its stomach into shell and uses an enzyme to digest it • Reproduce sexually • Can repair themselves by regeneration
Types of Echinoderms • Brittle Stars • Have fragile, slender, branched arms that break off easily • This adaptation allows them to survive • They can regenerate broken off body parts • Use flexible arms for movement and tube feet to get food into their mouths
Types of Echinoderms • Sea Urchins & Sand Dollars • Disk or globe-shaped animals covered in spines • Spines help in movement and in burrowing • Also can protect them from predators • Sea Urchins have five tooth like structures around their mouth
Types of Echinoderms • Sea Cucumber • Soft bodied echinoderms • Have a leathery covering • Have tentacles around their mouth and rows of tube feet on their upper and lower surfaces • When threatened, they may expel their internal organs which will then be regenerated in a few weeks.
Value of Echinoderms • Feed on dead organisms in the marine environment • Help recycle material • Used for food • Possible sources of medicine • Sea stars can help control the population of other organisms
Origin of Echinoderms • Date back more than 400 million years ago • Earliest echinoderms had bilateral symmetry as adults • Scientists hypothesize that echinoderms more closely resemble animals with backbones than any other group of invertebrates • Have similar embryos that develop similar to vertebrates • Complex body systems