Animals are multicellular organisms with eukaryotic cellular organization. A representative animal cell has a cell membrane, cell nucleus and mitochondria, but no cell wall or chloroplasts. A neuron illustrates how this common plan can acquire a specialized shape and signaling function. See OpenStax Biology 2e, 4.3: animal cell organization.
Chelicerate arthropods, typically with four adult walking-leg pairs and lacking antennae.
A parasitic roundworm with intestinal adults and larvae in skeletal muscle.
The human whipworm, with its thin anterior end embedded in colonic mucosa.
The specialized external covering of parasitic flatworms.
The tapeworm group, lacking an alimentary canal and including species with tissue larvae and intestinal adults.
The developing attachment region of certain larval tapeworms, capable of giving rise to the scolex of an adult in a suitable definitive host.
A larval bladder with multiple protoscolices, distinct from a single-scolex cysticercus and the brood capsule architecture of a typical hydatid cyst.
Historical designation for the cerebral coenurus larva associated chiefly with Taenia multiceps; it denotes a larval form rather than an independent adult species.
The living inner parasite layer of an echinococcal hydatid cyst, distinguished from its laminated layer and the surrounding host tissue.
The classical cystic-hydatid organism; historical usage often covers a complex of organisms distinguished more finely in current classification.
The beef tapeworm.
The pork tapeworm. Human intestinal adults and tissue cysticerci follow different routes of infection.
Historical assemblage used for groups including some worms and echinoderms; its boundaries varied and it is not a modern natural clade.
Historical worm assemblage whose composition varied between classification schemes.
A member of the molluscan group with a shell comprising two articulated valves. Marine bivalves provide abundant fossils for studying extinction selectivity, geographic distributions and changes in species assemblages.
A genus of snapping shrimp. Comparisons of related Alpheus lineages separated by the Isthmus of Panama have been used to study geographical isolation and allopatric speciation; inferred separation times vary among pairs.
A small bivalved crustacean. Sexually dimorphic fossil carapaces can provide indirect evidence about reproductive investment.
A member of the animal lineage characterized ancestrally by bilateral organization, including chordates and many other groups. bilaterian affinity does not imply vertebrate affinity.
An Ediacaran animal interpreted as a mollusc-like bilaterian. It informs the timing of animal differentiation without being a proposed vertebrate ancestor.
Active sensing in which an animal uses emitted sounds and their returning echoes to obtain information about its surroundings.
A member of the animal group including vertebrates, tunicates and cephalochordates, with a notochord as part of the characteristic developmental body plan.
A cephalochordate lineage used in comparative analysis of chordate genomes. Modern amphioxus is a living relative, not the actual ancestor of vertebrates.
A member of the lancelet lineage. Its anatomy is informative for comparisons, but a living lancelet is not an unchanged ancestor of vertebrates.
A member of the chordate lineage that molecular evidence places closer to vertebrates than are living cephalochordates.[ref]
A larvacean tunicate with dispersed Hox genes whose expression still shows aspects of anteroposterior ordering. The derived dispersed state is a counterexample to obligatory linkage for all spatial Hox regulation.
A tunicate genus used in comparative chordate developmental biology. Experiments on one lineage do not establish all vertebrate neural-crest properties throughout the genus.
A nematode species used to investigate early cell lineages and germline regulation, including inherited PIE-1 activity.
A group of New World primates used in comparative studies of embryonic development; conclusions from a particular species or experiment should not be assigned to all primates.
A member of the chordate lineage that includes jawless and jawed vertebrates. Features of the head, neural crest and internal skeleton vary across its descendant groups.
A Cambrian fossil animal with evidence of segmented musculature, sensory anatomy and serial branchial structures.
A Chengjiang fossil animal described with Haikouichthys in studies of early vertebrate organization.
A traditional assemblage of armoured jawless fossil vertebrates. It is not a complete clade, and many members are stem relatives of gnathostomes, rather than early cyclostomes.
A member of the jawed-vertebrate lineage. Crown usage includes the ancestor of living cartilaginous and bony vertebrates and all its descendants; a total-group usage additionally includes jawless stem relatives. The usage must be stated when discussing early fossils.
A member of an extinct armoured jawless lineage with differentiated pectoral fins and usually recovered close to jawed vertebrates.
A member of an extinct armoured jawless lineage commonly placed on the gnathostome stem outside osteostracans and jawed vertebrates.
A Silurian jawless vertebrate preserving continuous paired ventrolateral fins, interpreted as a precursor to more localized paired appendages.
An Early Devonian stem jawed vertebrate combining an extensively ossified dermal roof with informative braincase anatomy.
An armoured jawed fish in a traditional Palaeozoic assemblage. Whether the assemblage is monophyletic or a succession of branches affects ancestral state reconstruction.
An Early Devonian Siberian jawed vertebrate whose braincase–shoulder relationship supplies evidence for a posterior pharyngeal component of the pectoral girdle.
An Early Devonian Mongolian jawed vertebrate whose braincase contains a trabecular internal tissue interpreted as endochondral bone. Implications for ancestral bone depend on both tissue identity and phylogenetic placement.
A Silurian armoured jawed vertebrate with large marginal jaw bones previously associated with bony vertebrates.
A member of a traditionally recognized assemblage of Palaeozoic spiny jawed fishes. Many analyses resolve these taxa as a succession on the Chondrichthyes stem rather than a separate complete clade.
The cartilaginous-fish clade, including sharks, ray fish and chimaeras. Extant lack of extensive bone does not demonstrate that their ancestors never possessed it.
The little skate, used experimentally to compare branchial and appendage patterning.
An Early Silurian jawed vertebrate known from mineralized tooth whorls, illustrating the information carried by isolated hard parts.
The bony-vertebrate lineage including ray-finned vertebrates and Sarcopterygii; descendants remain members even after extensive modification of their ancestral skeleton.
A ray-finned vertebrate whose skin expression of enamel-matrix genes contributes to comparisons of enamel and ganoine evolution.
A fossil bony vertebrate whose dermal odontodes preserve enamel despite teeth without an enamel coating, important for separating tissue origin from oral deployment.
In crown-based usage, the clade comprising the most recent common ancestor of living coelacanths, lungfish and tetrapods, and all its descendants. Lobed, internally supported paired appendages provide a traditional diagnostic character; inherited organization can persist despite conversion of fins into limbs.
A finned Devonian relative of digit-bearing vertebrates. Its pectoral skeleton combines retained fin rays with jointed internal structures relevant to limb evolution.
A member of the coelacanth lineage of sarcopterygians. Living representatives are specialized descendants, not unchanged ancestral fish.
A member of the lineage uniting living hagfish and lampreys. Jawlessness alone cannot assign an extinct vertebrate to this lineage.
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Formal name: "animalia".