Invertebrates

Anatomy and Physiology in Invertebrates

Support and Movement

Almost all animals have muscle-like tissue for movement

Three types of skeletons: Hydrostatic skeleton Exoskeleton Endoskeleton

Hydrostatic Skeleton

Muscles supported by a water-filled body cavity No hard structures for muscles to pull

against Push against the water in the body

cavity Cnidarians, flatworms, nematodes,

mollusks, annelids

Exoskeleton External skeleton, muscles attached inside Arthropods have exoskeletons made of

chitin Exoskeletons are thin and flexible at

joints, allowing for flexion and extension Very adaptable, very strong Drawbacks are that the animal must shed

it and grow a new one as it gets larger, and it is heavy

Endoskeleton

Present in sponges and echinoderms (also in vertebrates)

Internal skeleton

Feeding and Digestion

Intracellular digestion vs extracellular digestion

Sponges filter food particles from the water and digestion is intracellular with nutrients being distributed among cells

Feeding and Digestion

Cnidarians and flatworms have a gastrovascular cavity Digestive sac with a single opening –

food enters, wastes leave Food particles broken down into

smaller pieces, then are taken up by cells lining the cavity and digestion is intracellular

Feeding and Digestion Extracellular digestion takes place in

annelids, mollusks, arthropods, invertebrate chordates

Tube within a tube digestive system – food enters through mouth and leaves through anus, digestive tract forms a separate tube within the body

Food is digested extracellulary in digestive tract and nutrients are absorbed

Internal Transport Constant supply of oxygen and

nutrients necessary for survival Carbon dioxide and posionous

wastes need to be eliminated Invertebrates like sponges,

cnidarians, flatworms, and nematodes do not have circulatory systems – all done by diffusion

Internal Transport

More complex invertebrates (and vertebrates) have circulatory systems, which include one or more pumps and tubes that move things around within the body

Open and closed circulatory systems

Open Circulatory System Blood from heart is not entirely

contained within blood vessels Heart pumps blood through a series of

vessels, and it is released directly onto body tissues

Flows through tissues and is collected in sinuses, eventually flowing back to heart

Seen in some types of mollusks (clams, oysters), arthropods, echinoderms

Closed Circulatory System Blood contained within a system of

closed vessels that pass through various parts of the body and return to the heart

Blood does not come in direct contact with tissues – more rapid and efficient

Seen in some mollusks (squids, octopuses), and annelids

Respiration (gas exchange) Small soft-bodied invertebrates

exchange oxygen and carbon dioxide by diffusion through body surfaces

Two respiratory problems: Respiratory system must have large surface

area to allow for enough gas exchange to support organism’s demands

Surface of organs must be kept wet because diffusion can only take place across moist membranes

Respiration (gas exchange)

Animals that live in water do not have these problems (sponges, cnidarians, flatworms, nematodes, echinoderms)

Mollusks and crustaceans have gills, which are rich in blood vessels and provide a large surface area for gas exchange

Respiration (gas exchange)

Terrestrial invertebrates have special organs for breathing air

Spiders have book lungs – sheet-like layers of thin tissue that contain blood vessels

Insects have trachea – tubes that bring air to each body cell

Excretion (waste elimination)

Related to maintaining proper water balance

Ammonia is a highly toxic, water soluble byproduct of the breakdown of amino acids – carried in blood and body fluids

Eliminating ammonia means eliminating water

Excretion (waste elimination) Marine invertebrates (like sponges,

cnidarians) have thin bodies and get rid of ammonia by diffusion through body surfaces or gill surfaces

Freshwater flatworms have flame cells, which remove water and water soluble wastes

Flame cells form a network that empties water and wastes through opening in the skin

Can also diffuse waste

Excretion (waste elimination)

Annelids, mollusks, invertebrate chordates have nephridia – structures that remove wastes from body fluids and return water and solutes to the body

Waste products eliminated as urine

Excretion (waste elimination)

Land invertebrates convert ammonia into urea (less toxic) which is concentrated into urine and expelled

Insects and some spiders convert ammonia into uric acid, which is removed by Malpighian tubules – uric acid excreted with solid waste, conserving water

Response All animals have some sort of nervous

system, with individual nerve cells functioning the same

Primitive invertebrates have a nerve net spreading through their body

Some cnidarians (jellyfish) show centralization where nerve cells are more concentrated, forming nerve cords or rings around the mouth

Response

Cephalization comes with concentrations of nerve and sensory cells in the head

Primitive flatworms have ganglia (clumps of nerve cells) while insects and some mollusks have actual brains

Brains lead to nerve cords

Response

Along with nervous development comes increased sensory development

Flatworms have eye spots Insects have well developed,

compound eyes

Reproduction

All invertebrates are capable of sexual reproduction, though some also reproduce asexually

Sexual reproduction creates and helps maintain genetic variation