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Module 14 in the Syllabus

Animals Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Animals
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Though it may be useful, detailed knowledge of animal taxonomy is not required for the MCAT
Basic Terms

AnimalAnimals are a major group of multicellular organisms whose body plan becomes fixed as they develop, usually early in development, although some undergo a process of metamorphosis later on in their life. Most members of this group are motile.
ExoskeletonAn exoskeleton is an external anatomical feature that supports and protects an animal's body, in contrast to the internal endoskeleton.
EndoskeletonAn endoskeleton is an internal support structure of an animal.
PrimateA primate is any member of the biological order that contains all the species commonly related to the lemurs, monkeys, and apes, with the last category including humans.
DeuterostomeThe two superphyla of animals are distinguished in embryonic development. With deuterostomes, the first opening, the blastopore, becomes the anus, while in protostomes it becomes the mouth.
ChordateChordates, which includes the vertebrates and some closely related invertebrates, are animals which have, at some time in their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail.
ThoraxThe thorax is a division of an animal's body that lies between the head and the abdomen.
MetamorphosisMetamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's form or structure.
GillA gill is a respiration organ that functions for the extraction of oxygen from water and the excretion of carbon dioxide.
ProtostomeIn protostome development, the first opening in development, the blastopore, becomes the animal's mouth, unlike deuterostomes in which the blastopore becomes the animal's anus.
AmphibianAmphibians are a taxon of animals that include all living tetrapods that do not have amniotic eggs, are ectothermic, and generally spend part of their time on land.
ReptileReptiles are tetrapods, amniotes and members of the class Sauropsida. There are approximately 8000 species within this taxon which includes crocodiles, turtles, lizards and snakes.
BirdBirds are bipedal, warm-blooded, egg-laying vertebrate animals characterised by feathers, a beak with no teeth, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton.
MammalMammals are warm-blooded, vertebrate animals characterized by the presence of sweat glands, including those that produce milk and by the presence of hair.
MarsupialMarsupials are mammals in which the female typically has a pouch in which it rears its young through early infancy.
ArthropodArthropods are the largest phylum of animals and include the insects, arachnids, crustaceans, and others.
SegmentationSegmentation in biology refers to the division of some metazoan bodies and plant body plans into a series of semi-repetitive segments.
CrustaceanThe crustaceans are a large group of arthropods, comprising approximately 52,000 described species including various familiar animals, such as lobsters, crabs, shrimp, crayfish and barnacles.
MoultMoulting signifies the manner in which an animal routinely casts off a part of its body, often but not always an outer layer or covering, either at specific times of the year, or at specific points in its life-cycle.
ArachnidArachnids are a class of joint-legged invertebrate animals in the subphylum Chelicerata comprising some 65,000 to 73,000 named species including spiders, scorpions, harvestmen, ticks, and mites.
InsectInsects are a major group of arthropods and the most diverse group of animals on the Earth, with over a million described species-more than all other animal groups combined.
LarvaA larva is a juvenile form of animal with indirect development, in other words, which undergoes metamorphosis.
EggIn most birds and reptiles, an egg is the zygote, resulting from fertilization of the ovum.
CropA crop is a thin-walled expanded portion of the alimentary tract used for the storage of food prior to digestion that is found in many animals, including gastropods, earthworms, leeches, insects, and birds.
GizzardA gizzard is a specialized stomach with a thick, muscular wall used for grinding up food. It is found in birds, reptiles, earthworms, some fish, insects, mollusks, and other creatures.
MonotremeMonotremes are mammals that lay eggs.
TrilobiteTrilobites are extinct arthropods that form the class Trilobita that appeared in the 2nd Epoch of the Cambrian period and flourished throughout the lower Paleozoic era before beginning a drawn-out decline to extinction.
Compound eyeA compound eye is a visual organ found in arthropods such as insects and crustaceans consisting of one to thousands of ommatidia which are tiny independent photoreception units.
PupalIn the life cycle of an insect the pupal stage follows the larval stage and precedes adulthood.
PheromoneA pheromone is a chemical that triggers a natural behavioral response in another member of the same species.
CephalothoraxThe cephalothorax (sometimes called prosoma) is an anatomical term used in arachnids and malacostracan crustaceans for the anterior major body section.
MolluscaThe very large and diverse phylum Mollusca includes a wide variety of animals such as clams and snails, squid and octopus.
NephridiaNephridia are invertebrate organs which function similarly to kidneys in many different invertebrate lines.
AnnelidaAnnelida is a large phylum of animals, comprising the segmented worms, with about 15,000 modern species including the well-known earthworms and leeches.
ChondrichthyesThe Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage rather than bone.
OsteichthyesOsteichthyes is a taxonomic superclass of fish, also called bony fish that includes the ray-finned fish and the lobe finned fish.
SpongeThe sponges are animals of the phylum Porifera, primitive, sessile, mostly marine, water dwelling, filter feeders that pump water through their bodies to filter out particles of food matter.
DorsumThe dorsum is the upper side of animals that typically run, fly or swim in a horizontal position, and the back side of animals like humans that walk upright.

Intermediate Terms

Horseshoe crabThe horseshoe crab is a chelicerate arthropod, so it is more closely related to spiders, ticks, and scorpions than to true crabs.
Ventral nerve cordThe ventral nerve cords make up the nervous system of some phyla of the invertebrates particularly within the nematodes, annelids and the arthropods.
BivalviaMollusks belonging to the class Bivalvia typically have two-part shells, with both valves being symmetrical along the hinge line.
GastropodThe gastropods, more commonly known as snails and slugs, are the largest and most successful class of mollusks, with 60,000-75,000 known living species.
CephalopodThe mollusc class Cephalopoda, which includes octopuses, squids, and the nautilus, is characterized by bilateral body symmetry, a prominent head, and a modification of the mollusk foot into the form of arms or tentacles.
AgnathaAgnatha is a paraphyletic superclass of jawless fish in the phylum Chordata, subphylum Vertebrata which includes the lampreys and the hagfish.
EutheriaEutheria is a taxon containing the placental mammals, such as humans.
ChoanoflagellateThe choanoflagellates are a group of flagellate protozoa considered to be the closest living relatives of the animals.
CtenophoreThe phylum Ctenophora, commonly known as Comb Jellies, is classically grouped with Cnidaria in the Coelenterata infrakingdom.
CnidariaCnidaria is a phylum containing some 11,000 species of apparently simple animals found exclusively in aquatic environments including anemones, corals, jellyfish, and box jellies.
EchinodermEchinoderms are a phylum of marine animals found at all ocean depths which includes starfish, sea urchins, and sea cucumbers. This is the second largest grouping of deuterostomes, after the chordates
NematodaMembers of the large phylum Nematoda are unsegmented, bilaterally symmetric and triploblastic protostomes with a complete digestive system but no circulatory or respiratory systems, so they use diffusion to breathe.
ChelicerataThe Subphylum Chelicerata constitutes one of the major subdivisions of the Phylum Arthropoda. It includes the arachnids and horseshoe crabs.
MandibleThe mandible is either of a pair of arthropod mouthparts used for biting, cutting and holding food.
OmmatidiaThe compound eye of insects is composed of units called ommatidia.
TagmaA tagma is a specialized grouping of arthropodan segments with a common function, such as the head, the thorax, and the abdomen.

Advanced Terminology

EumetazoaEumetazoa is the clade of animals characterized by true tissues organized into germ layers, and an embryo that goes through a gastrula stage. This includes all animals except sponges.
HemolymphHemolymph is the scientific name for insect blood.
FlatwormThe flatworms, phylum Platyhelminthes, comprise a phylum of relatively simple soft-bodied invertebrate animals. They are the largest phylum of acoelomates.
MalacologyMalacology is the branch of invertebrate zoology which deals with the study of mollusks, the second-largest phylum of animals in terms of described species
RadulaThe radula is the toothed chitinous ribbon in the mouth of most mollusks, used for cutting and chewing food before it enters the esophagus.
Deposit feederDeposit feeders are organisms that feed on the particles of matter in the soil, usually the top sediment where it is filled with organic matter.
RadiataThe Radiata are the radially symmetric animals of the Eumetazoa subregnum.
UrochordataUrochordata, sometimes known as tunicata and commonly called urochordates, tunicates, or sea squirts, is a subphylum of Chordata. They are saclike filter feeders with incurrent and excurrent siphons.
LanceletThe lancelets, subphylum Cephalochordata, are a group of primitive chordates which are an important object of study in zoology as they provide indications about the origins of the vertebrates.
MyriapodaMyriapoda is a subphylum of arthropods containing millipedes, centipedes and others.
HexapodaThe subphylum Hexapoda constitutes the largest grouping of arthropods and includes the insects as well as three much smaller groups of wingless arthropods.
TrematodaThe Trematoda is a class within the phylum Platyhelminthes that contains two groups of parasitic worms, commonly referred to as flukes.
CestodaCestoda is the class of parasitic flatworms, called cestodes or tapeworms, that live in the digestive tract of vertebrates as adults and often in the bodies of various animals as juveniles.
Flame cellA flame cell is a specialized excretory cell found in the Platyhelminthes. the simplest animals to have a dedicated excretory system.
TrochophoreA trochophore is a type of larva with several bands of cilia representing a life stage among entoprocts, mollusks, annelids, echiurans, and sipunculans.
AmnioteThe amniotes are a group of tetrapod vertebrates that includes reptiles, birds and mammals, whose embryos are protected and aided by several extensive membranes, whether laid as eggs or carried by the female.
TrichoplaxTrichoplax adhaerens is a simple balloon-like marine animal with a body cavity filled with pressurized fluid. It is given its own phylum, called Placozoa, sometimes referred to commonly as the tablet animals.
AnthozoaAnthozoa is a class within the phylum Cnidaria that contains the sea anemones and corals. Unlike other cnidarians, the members of this group do not have a medusa stage in their development.
OrthonectidaOrthonectida is a small phylum of poorly-known parasites of marine invertebrates that are among the simplest of multi-cellular organisms. Members of this phylum are known as orthonectids.
RhombozoaRhombozoa, or Dicyemida, is a phylum of tiny parasites that live in the renal appendages of cephalopods.
AcoelomorphaThe Acoelomorpha are a phylum of animals formerly considered to be in Platyhelmintha, but recently classified as a separate phylum, basal among the Bilateria. They are very small flatworms that do not have a gut.
ChaetognathaChaetognatha is a phylum of predatory marine worms that are a major component of plankton worldwide. The common term for the phylum is Arrow Worms.
KinorhynchaKinorhyncha is a phylum of small marine pseudocoelomate invertebrates that are widespread in mud or sand at all depths as part of the meiobenthos. They are also called mud dragons.
LoriciferaLoricifera is a small phylum of marine sediment-dwelling animals characterised by a protective outer case called a lorica.
PriapulidaPriapulida are a phylum of marine worms with an extensible spiny proboscis.
NematomorphaNematomorpha (commonly known as Horsehair worms or Gordian worms) are a phylum of parasitic animals which are morphologically and ecologically similar to nematode worms.
Velvet wormThe velvet worms are segmented, caterpillar-like, terrestrial animals somewhat resembling both arthropods and annelid worms. They are generally regarded either as a class of arthropods or as a separate phylum.
TardigradeTardigrades (commonly known as water bears) comprise the phylum Tardigrada. They are small, segmented animals, similar and probably related to the arthropods.
AcarinaAcarina are a taxon of arachnids that contains mites and ticks.
RotiferThe rotifers make up a phylum of microscopic and near-microscopic pseudocoelomate animals which get their name from ciliated tufts around the mouth that in motion resemble a wheel.
AcanthocephalaThe Acanthocephala is a phylum of parasitic worms, characterised by the presence of an evertable proboscis, armed with spines, which it uses to pierce and hold the gut wall of its host.
SipunculaThe Sipuncula, or peanut worms, are a phylum containing 144-320 species (estimates vary) of bilaterally symmetrical, unsegmented marine worms.
NemerteaNemertea is a phylum of invertebrate animals also known as ribbon worms or proboscis worms.
PhoronidPhoronids, commonly known as horseshoe worms, are a relatively small animal phylum.

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