Learning Outcome G4 Phylum Mollusca, Arthropoda and Echinodermata

Learning Outcome G4

Phylum Mollusca, Echinodermata & ArthropodaLearning Outcome G4Analyse the increasing complexity of the Phylum Mollusca, the Phylum Echinodermata, and the Phylum ArthropodaStudents 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 functionsExamine members of the Phylum Echinodermata and describe their unifying characteristics Describe how echinoderms carry out their life functionsExamine members of the Phylum Arthropoda and describe their unifying characteristicsDescribe how arthropods carry out their life functionsCompare how molluscs, echinoderms, and arthropods have evolved to adapt to different niches

Student Achievement IndicatorsPhylum Mollusca

Kingdom AnimaliaPhylum MolluscaClass PolyplacophoraClass CephalopodaClass GastropodaClass Bivalvia

ClassificationAn important food source to both humans and other animalsGreat variety between speciesThere 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 mouthLargest invertebrate phylum

CharacteristicsGreat variation within this phylum, although they have inherited a common body plan form their ancestors.1. FootMuscular and function in locomotionIn cephalopods the head has become a modified head and tentacles

2. MantleA folded tissue that folds down around some or all of the body

3. ShellMade up of calcium carbonateCan be internal or external

Body Plan4. GillsSpecialized respiratory structure that arises from outgrowths of the mantle wall

5. Visceral massInternal organs consisting of the gut, kidney, heart and reproductive organs.

6. Radulaa unique rasping tongue-like organ with hard teeth that are used to scrape up food

Body Plan

Radula

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.

Ecological RolesAlso their empty shells often provide homes for other invertebrates.Molluscs play a critical role in the food chainDrastically 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.

Ecological RolesMarine animals that eat algae or small animals growing on rocks near the shore or in the deep oceanMost of their bottom surface is taken up by a large muscular foot.The upper surface consists of 8 overlapping shell valves, which provide protection.

Class Polyplacophora (the chitons)

Make up the biggest group of molluscsGenerally 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.

Class Gastropoda (the Gastropods)

Includes clams, mussels, oysters and scallopsImportant food supply for humansThe 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

Class Bivalvia (the bivalves)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

Class Bivalvia (the bivalves)

Most complex mollusks and includes squids, nautiluses, and octopods.Only the nautiluses have a complex external shellOctopods 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 systemsHave a muscular mantle which is well designed for water flow.

Class Cephalopoda (the cephalopods)The squids 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 armsBoth 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.

Class CephalopodaUndigested material is excreted into the mantle cavityThe 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

Class CephalopodaSquids 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

Class Cephalopoda

Phylum Echinodermata

Kingdom AnimaliaPhylum EchinodermataClass AsteroideaClass OphiroideaClass EchinoideaClass HolothuroideaClass Crinoidea

ClassificationGenerally large and live on the bottom of large bodies of waterUsually marineHave 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 symmetricalThe development of echinoderm eggs is similar to the development of chordate eggs.

CharacteristicsDeutrostomesHave a endoskeleton that is made up of calcified plates covered by an epidermisThese plates may be a single plateExample 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

CharacteristicsBottom dwellers of all oceanMay live in large numbersRecycle nutrients in ecosystems by feeding on dead and decaying materialsStarfish are important marine carnivores that control the population of other animalsHowever large population ofechinoderms can be troublesome, they can wipe out whole populations of molluscs.They can also cause severe damage to coral reefsSea urchins are essential to the control and distribution of algaeNon parasitic but are home to many parasites.

Ecological Roles1800 speciesHave tube feet which help in movement and feeding.Tube feet are part of the water vascular systemAt 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 stomachAble to regenerateFeed on mussels and other molluscs.Wide diversity in body plan and feedingPentaradial symmetryBodies made of calcium carbonate which form ossicles.

Class Asteroidea (sea stars)

Closely related to sea stars5 long slender whip-like armsArms can be up to 60 cm

Class Ophiuroidea (brittle stars)

Spiny globular animalsMove via tube feetVary in colorFood source for sea otters and sealsSea urchin eggs are a human delicacy

Class Echinoidea (sea urchins)

Elongated both with leathery skinSends hormones through the water to attract a mateBody contains collagen, so the body can looses and tighten at will which allows this organism to move through small spaces.Can expose its intestines to predators when feeling threatened, this is known as eviceration.Form large herds and can form symbiotic relationships

Class Holothuroidea (sea cucumbers)

Live in shallow and deep waterMouth is on the surface surrounded by feeding armsGenerally attached to substrate but can be unattached.

Class Crinoidea (sea lilies or feather stars)

Phylum Arthropoda

Kingdom AnimaliaPhylum ArthropodaDivided into 4 subphyla

1. TrilobitomophasTrilobites are currently extinct but are extremely important part of the fossil record

Classification

2. MyriapodsInclude centipedes and millipedesMany legs and strongly segmented

Classification

3. Chelicerata includes spiders

Classification

4. Crustacea crustaceans such as crayfishClassification

5. Uniramia insectsClassification

Most numerous and diverse group of animalsLive 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.

CharacteristicsLive closely with humans in symbiotic relationshipsExample tiny mites living in hair follicles

May eat and destroy plant/cropsPrimary pollinator of plantsUtilize many food sources, as well as are the source of food for many different animalsMany parasitic forms control the number of other arthropods.

Ecological RolesEvolved 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.

Adaptations for SuccessSkeletons may be either inside or outside the bodyAn exoskeleton is present in crustaceans such as crabs, lobsters, spiders and insectsThe 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 bodyThe exoskeleton protects the arthropod but is very heavyArthropods 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. Endoskeleton & ExoskeletonThis new cuticle is initially flexible and has many foldsThe 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.Endoskeleton & ExoskeletonDue 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. Endoskeleton & Exoskeleton

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 attenaeHave primitive ears composed of a flexible membrane stretched across an opening in the cuticle.

Other Arthropod FeaturesThe 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 reducedA 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.

Other Arthropod FeaturesMost 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 sexParthenogenesis is a type of asexual reproduction where unfertilized eggs develop into offspring. Other Arthropod Features