Chaitanya's Random Pages

August 19, 2011

Biological systems in various animal groups

Filed under: nature — ckrao @ 1:41 pm

I was curious to find out something about the inner workings of animals. For example do invertebrates have blood? (Answer: some, such as earthworms) Which animals have a brain? (Answer coming up.) Below is a list of the biological systems of humans. We shall see the extent to which these are present in other animals.

System Organs/Cell types Function
Circulatory heart, blood, blood vessels circulating blood to and from body and lungs
Digestive tongue, salivary glands, esophagus, stomach, liver, gall bladder, pancreas, small intestine, large intestine, appendix, rectum, anus processing food
Endocrine hypothalamus, pituitary gland, pineal gland, thyroid, parathyroids, adrenal glands, Islets of Langerhans (in pancreas) release of hormones to send messages to other parts of body
Integumentary skin, hair, fat, nails protects body from external damage, insulation, detection of pain/pressure/temperature, vitamin D synthesis
Lymphatic (inc. immune) lymph, lymph vessels, lymphoid tissue, lymph nodes, leukocytes, bone marrow, tonsils, adenoids, thymus, spleen removal of interstitial fluid from tissue, transport of white blood cells into bones, absorption of fatty acids from circulatory system
Muscular muscles, tendons, fasciae movement
Nervous brain, spinal cord, peripheral nerves, nerves, includes sensory systems of ear, eye etc. sensing and processing information
Reproductive ovaries, fallopian tubes, uterus, placenta, vulva, vagina, mammary glands, testes, prostate, epididymis, vas deferens, seminal vesicles, prostate, penis reproduction
Respiratory nose, pharynx, larynx, trachea, bronchi, lungs, diaphragm breathing
Skeletal bones, cartilage, ligaments, tendons structural support
Urinary kidneys, ureters, bladder, urethra fluid balance, electrolyte balance, excretion

Next are some notes on the presence of these systems in some of the main animal groups. In the following an “open circulatory system” means there is no difference between blood and tissue fluid, while in a closed circulatory system blood (in vessels) is separate from tissue fluid.



(e.g. fish, amphibians, reptiles, birds, mammals)


(starfish, sea urchins, sea cucumbers etc.)


(snails, slugs, squid, clams, etc.)


 (arachnids, insects, crustaceans, centipedes etc.)

Circulatory closed system, platelets unique to mammals open circulatory system, no heart blood and coelomic fluid circulate in main body cavity, heart present in cephalapods (squids/octopus etc.) open circulatory system, hexapods have tracheae and no gases in their blood
Digestive simple digestive gut most graze on algae, possess stomach and gut spiders etc. have chelicerae at mouth opening
Integumentary most fish/reptiles have scales, birds have feathers, mammals have hair some have a shell jointed limbs
Lymphatic (inc immune) insects have hemolymph
Muscular muscular foot attached to inside of exoskeleton
Nervous brain and spinal cord simple radial nervous system, no brain some have brains, most have two nerve cords; octopus and squids have eyes, snails have antennae paired ganglia in each segment; sensory organs (e.g. compound eyes)
Reproductive larval stage in bony fish, amphibians; most reptiles, birds, amphibians, birds, monotremes lay eggs while marsupials and placental mammals give birth to live young; in birds and playpuses the right ovary never matures; mammary glands unique to mammals gonads may occupy entire cavity terrestrial species have external fertilisation, metamorphosis in some insects, no larval stage in arachnids
Respiratory gills in most fish, otherwise lungs; gas exchange with water/air also occurs through skin in amphibians; syrinx in birds responsible for singing varying methods of gas exchange most have one pair of gills; snails/slugs have lungs varying, e.g. booklungs in spiders, gills in crustaceans, tracheae in insects
Skeletal sharks, rays etc. have cartilaginous skeleton; otherwise bony skeleton contain spines emerging from endoskeleton calcareous endoskeleton exoskeleton made of cuticle
Urinary waste diffuses, no specialised excretory organs nephridia play role of kidneys, they also have role in reproduction malpighian tubules in insects, green glands in crustaceans


(segmented worms)






(corals, sea anemones, jellyfish, hydra etc.)



Circulatory closed circulatory system, some with blood vessels along length circulation of gases and nutrients through pseudocoelom fluid. no specialised organs no organs no organs
Digestive full gut from mouth to anus no stomach specialised system no specialised system no specialised system
Integumentary segments covered by cuticle  no symmetry
Lymphatic (inc immune)
Muscular muscular, movement by peristalsis muscular pharynx hydras have muscle no muscle
Nervous bundle of nerves serve as brain four nerves run its length, dense nerve ring serves as brain first forms in which we see brain-like structure no distinct brain no neurons in adults
Reproductive some reproduce asexually, no larval stage in earthworms ovaries and testes present sexual or asexual reproduction sperm cells released into water
Respiratory variable, via skin or through gills no specialised organs, rely on diffusion no specialised organs
Skeletal mesohyl acts as endoskeleton
Urinary waste excreted through body wall primitive, made of flame cells, excretory ducts and excretory pores. no specialised system no specialised system

Edit: I later found just the thing I was looking for here.


Zoology Review –


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