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