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

The Radula

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

Pearls

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 Adapted to live in almost every environment and range in size from dust mite to Japanese spider crabs

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 While the animal are molting they are very vulnerable to predators because they have a soft out covering until the new exoskeleton hardens. Before the exoskeleton hardens the animal makes itself larger by taking in air or water so that there is room to grow into the exoskeleton

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!

Crayfish Anatomy

Arachnids Scorpions Spiders 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. Centipedes have one pair of legs per segment Millipedes have two pair of legs per segment

Insects Have three body regions Head Thorax Abdomen 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 Centipedes and praying mantises eat other animals, some moths eat wool clothing

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 Insects have other adaptations that allow them to be successful

Controlling Insects Not all arthropods are of value some are pests that carry disease or can damage crops Another negative for using insecticides is that some toxins stay in the environment and can accumulate in other organisms that eat those insects which in turn can be eaten by larger organisms causing illness or death

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 While the predator is eating the broken off arm the remaining part of the animal can escape

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