Mollusks, Arthropods, Echinoderms Mollusks, Arthropods, Echinoderms
Feb 09, 2016
Mollusks, Arthropods, EchinodermsMollusks, 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
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!
Crayfish Anatomy
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
Insect Anatomy
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
Complete Metamorphosis
Gradual Metamorphosis
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