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Learning Outcome G4

Phylum Mollusca, Echinodermata &

Arthropoda

Learning Outcome G4

Analyse the increasing complexity of the Phylum

Mollusca, the Phylum Echinodermata, and the Phylum Arthropoda

Students who have fully met this learning outcome will be able to: Examine members of the Phylum Mollusca and describe

their unifying characteristics

Describe how molluscs carry out their life functions

Examine members of the Phylum Echinodermata and describe their unifying characteristics

Describe how echinoderms carry out their life functions

Examine members of the Phylum Arthropoda and describe their unifying characteristics

Describe how arthropods carry out their life functions

Compare how molluscs, echinoderms, and arthropods have evolved to adapt to different niches

Kingdom Animalia

Phylum Mollusca Class Polyplacophora

Class Cephalopoda

Class Gastropoda

Class Bivalvia

An important food source to both humans and other animals

Great variety between species There are 7 classes of molluscs; we are going

to examine the 4 major classes. All molluscs are protostomes, which means

that during embryological development the first opening to develop is the anus.

Have a free-swimming ciliated larva, which uses a band of muscle to bring food towards the mouth

Largest invertebrate phylum

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Great variation within this phylum, although they have inherited a common body plan form their ancestors. 1. Foot

Muscular and function in locomotion In cephalopods the head has become a modified head and

tentacles

2. Mantle

A folded tissue that folds down around some or all of the body

3. Shell

Made up of calcium carbonate Can be internal or external

4. Gills ◦ Specialized respiratory structure that arises from

outgrowths of the mantle wall

5. Visceral mass ◦ Internal organs consisting of the gut, kidney, heart

and reproductive organs.

6. Radula ◦ a unique rasping “tongue-like” organ with hard

teeth that are used to scrape up food

Generally free-living and inhabit all known aquatic and terrestrial ecosystems.

They are a food source for fish, starfish, birds, humans and a variety of other mammals.

Molluscs live as predators, herbivores, detritus feeders, parasites and form other symbiotic relationships with other organisms.

Bivalves, such as mussels perform an important ecological role of recycling huge amounts of sediment back into the environment.

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Also their empty shells often provide homes for other invertebrates.

Molluscs play a critical role in the food chain

Drastically impacted by oil spills and pollution because most molluscs are filter feeders and these pollutants smother the gills or enter the digestive tract causing inflammation and a variety of digestive problems.

Oil can also fill the mantle causing tumors and irritating muscle.

Marine animals that eat algae or small animals growing on rocks near the shore or in the deep ocean

Most of their bottom surface is taken up by a large muscular foot.

The upper surface consists of 8 overlapping shell valves, which provide protection.

Make up the biggest group of molluscs

Generally have large coiled shell, and this group includes snails and whelks.

Their foot has a hard plate which fills the opening of the shell when the foot is withdrawn and protects the soft body.

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Includes clams, mussels, oysters and scallops

Important food supply for humans

The body of bivalves is held between two protective valves connected by a ligament that holds them apart along one edge.

Two strong muscles pull the valves together.

Bivalves do not move due to their large, heavy shells.

Complex system for filter feeding; that involves the use of gills

These gills are large and covered with cilia; the water circulates between the valves and carries many small particles of food into the mollusc.

This water passes across the gills, and the food particles are filtered out and embedded in the mucus.

Strings of mucus and food are then moved toward the mouth by the cilia.

Digestion occurs in the stomach and undigested material exits via the anus

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Most complex mollusks and includes squids, nautiluses, and octopods.

Only the nautiluses have a complex external shell Octopods have 8 equal appendages all equipped

with suckers and tentacles. Squids have 10 appendages, two of which the

tentacles are longer and have tentacles on expanded tips.

The tentacles trap and grasp prey, which are drawn towards the mouth.

Great predators due to efficient respiratory and circulatory systems

Have a muscular mantle which is well designed for water flow.

The squid’s body is stream-lined and maintains its shape, with the aid of a pen.

An octopod has no shell and the body is incredibly flexible.

A pen is the internal remnants of a shell. Both the squid and octopus use water jets that are

powered by contractions of the mantle for fast swimming.

Nautiloids swim with the aid of their numerous arms Both squids and octopods have digestion occur in

their stomach, which is aided by enzymes secreted by the digestive glands.

Nutrients are absorbed in the stomach and some additional absorption occurs in the starting of the small, coiled intestine.

Undigested material is excreted into the mantle cavity

The circulatory system of a cephalopod is closed and capable of maintaining a high flow rate and blood pressure.

The large, extensively folded gills have a separate “gill heart” to pump blood back to the “systemic heart” which pumps it out of the body.

The cephalopods nervous system is also highly developed with a large brain that contains several ganglia.

In the octopus the brain has 10 lobes, and the animals are good learners.

Octopods have been trained to solve simple problems and have the ability to remember

Squids and octopods have image forming eyes, which are very close to the eyes of vertebrates but have a different embryonic origin (convergent evolution).

Complex eyes are crucial to the survival of these predatory animals which depend of vision to find their prey.

Cephalopods are dieoccius and fertilization is internal. In squid the fertilized eggs are deposited in a

gelatinous capsule and both the male and female die after mating.

In octopods, the fertilized eggs are attached to the roof of the cave or crevice in which the female live and she guards and cleans them for several months until they hatch.

During this time the female eats little or nothing

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Kingdom Animalia

Phylum Echinodermata Class Asteroidea

Class Ophiroidea

Class Echinoidea

Class Holothuroidea

Class Crinoidea

Generally large and live on the bottom of large bodies of water

Usually marine

Have spiny skin, which is a key characteristic of this group

Have radial symmetry and many have 5 similar body segments around a central core.

The larval sate is bilaterally symmetrical

The development of echinoderm eggs is similar to the development of chordate eggs.

Deutrostomes Have a endoskeleton that is made up of

calcified plates covered by an epidermis These plates may be a single plate Example – starfish have a single flexible plate

or a fused solid shell has in sea urchins. Has a complicated water vascular system. The coelom is separated into two parts: ◦ the perivisceral coelom which plays a role in

circulation and excretion ◦ The hydrocoel which function in locomotion and

feeding

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Bottom dwellers of all ocean

May live in large numbers Recycle nutrients in ecosystems by feeding on

dead and decaying materials

Starfish are important marine carnivores that control the population of other animals

However large population ofechinoderms can be troublesome, they can wipe out whole populations of molluscs.

They can also cause severe damage to coral reefs

Sea urchins are essential to the control and distribution of algae

Non parasitic but are home to many parasites.

1800 species Have tube feet which help in movement and

feeding. Tube feet are part of the water vascular system At the end of each arm, starfish have a

microscopic eyes that can only see light and dark. The mouth is located on the underside of the

stomach Able to regenerate Feed on mussels and other molluscs. Wide diversity in body plan and feeding Pentaradial symmetry Bodies made of calcium carbonate which form

ossicles.

Closely related to sea stars

5 long slender whip-like arms

Arms can be up to 60 cm

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Spiny globular animals

Move via tube feet

Vary in color

Food source for sea otters and seals

Sea urchin eggs are a human delicacy

Elongated both with leathery skin

Sends hormones through the water to attract a mate

Body contains collagen, so the body can looses and tighten at will which allows this organism to move through small spaces.

Can expose it’s intestines to predators when feeling threatened, this is known as eviceration.

Form large herds and can form symbiotic relationships

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Live in shallow and deep water

Mouth is on the surface surrounded by feeding arms

Generally attached to substrate but can be unattached.

Kingdom Animalia

Phylum Arthropoda Divided into 4 subphyla

1. Trilobitomophas

Trilobites are currently extinct but are extremely important part of the fossil record

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2. Myriapods

Include centipedes and millipedes

Many legs and strongly segmented

3. Chelicerata – includes spiders

4. Crustacea – crustaceans such as crayfish

5. Uniramia – insects

Most numerous and diverse group of animals

Live in all habitats including arctic ice, deserts, the deep ocean, the mountains, prairie lands and the skies.

Their ability to live in such a diverse range of habitat and to adapt to changing environments, ensures that this phylum will be around for a long time.

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Live closely with humans in symbiotic relationships Example – tiny mites living in hair follicles

May eat and destroy plant/crops

Primary pollinator of plants

Utilize many food sources, as well as are the source of food for many different animals

Many parasitic forms control the number of other arthropods.

Evolved from a segmented ancestor, who either lost their segments or the segments have become fused together.

Have a well developed head with jointed appendages that may be used for locomotion or adapted for prey manipulation.

Posterior to the head is a thorax, which may bear walking appendages.

The head and thorax are fused together to form a cephalothorax.

Skeletons may be either inside or outside the body

An exoskeleton is present in crustaceans such as crabs, lobsters, spiders and insects

The exoskeleton is composed of chitin, which is a non-living material that may be thick and heavy.

An exoskeleton is a strong protective covering on the exterior of the body

The exoskeleton protects the arthropod but is very heavy

Arthropods shed their exoskeleton as they grow become it does not grow with them.

This process is known as molting.

In molting the inner layer of the cuticle dissolves and is recycled to make a new larger cuticle beneath the old one.

This new cuticle is initially flexible and has many folds

The animals take in water or air causing the exoskeleton to swell up.

This pressure created by the swelling splits the remaining old cuticle and expands the new cuticle.

Once it has stretched, the new cuticle begins to harden.

An arthropod is very vulnerable during molting, as it lacks the protection of its cuticle and may not have enough ridigity in its body to escape predators.

Due to having an exoskeleton arthropods are not quick movers.

Once the cuticle hardens the excess water or air that has caused the body to swell is expelled.

Endoskeletons are present in chordates such as fish, frogs, reptiles and mammals.

The skeletons of some kinds of fish are composed of flexible cartilage while other fish and most chordates have exoskeletons composed mainly of living bone.

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Many terrestrial arthropods have specialized excretory organs called malphigian tubules.

This organ lies in blood-filled spaces and secretes fluid into the hind gut where reabsorption of fluids and dissolved materials occurs.

The nervous system of primitive arthropods resemble that of annelids.

More complex forms especially those with complex social behaviors show an increase in brain size and complexity and an increase in sensory abilities.

The eyes of arthropods may be simple and consist of only a few photoreceptors or they may have thousands of receptors and be capable of forming a crude image.

Have attenae Have primitive ears composed of a flexible membrane

stretched across an opening in the cuticle.

The circulatory system of arthropods is open, with blood bathing tissues in spaces called sinuses.

This system of open spaces replaces the coelom as the major body cavity.

This is known as a homocoel. The coelom exists but is reduced A heart and arteries deliver blood to the body and sinuses. The blood may be oxygenated by gills in aquatic forms or by

book lungs in terrestrial forms. The blood serves a secondary role in delivering oxygen to the

cells and removing carbon dioxide. This groups has a tracheal system, consisting of open tubes

connecting to the outside by spiracles, which are openings in the cuticle.

The branched and cuticle-lined tracheal system reaches through the body and connects directly to the atmosphere.

Most arthropods have internal fertilization and separate sexes.

The eggs of many species hatch directly into a form which resembles the adult with no larval stage.

In other the first free living stage after the egg is similar to the adult but different in some way.

A series of molts is required before the adult form is attained.

Many arthropods have a larval stage the resembles the adult only superficially or not at all this is known as metamorphosis.

Pheromones are hormones that attract the opposite sex

Parthenogenesis is a type of asexual reproduction where unfertilized eggs develop into offspring.

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