Animal Phylogeny and Classification

Flashcards covering the classification and traits of various animal groups, including their phylogenetic relationships and synapomorphies.

Animalia

The biological kingdom that encompasses all animals, characterized by multicellularity, heterotrophic nutrition (obtaining nutrients by consuming other organisms), and typically motile bodies. Examples include humans, insects, jellyfish, and sponges.

Eumetazoa

A major clade within Animalia that includes all animals possessing true tissues, such as nervous and muscle tissues, and usually exhibit body symmetry. This group excludes sponges (Porifera). Examples include jellyfish, worms, insects, and vertebrates.

Deuterostomes

One of the two major lineages of bilaterian animals (animals with bilateral symmetry). Characterized by a pattern of embryonic development where the anus develops from the blastopore before the mouth. This lineage includes echinoderms (e.g., sea stars, sea urchins) and chordates (e.g., fish, birds, mammals).

Protostomes

One of the two major lineages of bilaterian animals. Characterized by a pattern of embryonic development where the mouth typically develops from the blastopore before the anus. This diverse lineage includes arthropods (e.g., insects, spiders), mollusks (e.g., snails, octopuses), and annelids (e.g., earthworms).

Porifera

Known as sponges, this phylum comprises simple, sessile aquatic animals characterized by a porous body structure through which water is filtered to obtain food. They lack true tissues and organs. Examples include various species of sea sponges.

Cnidaria

A phylum of aquatic animals (mostly marine) that exhibit radial symmetry and possess specialized stinging cells called cnidocytes (nematocysts) for defense and prey capture. Examples include jellyfish, corals, sea anemones, and hydras.

Lophotrochozoa

A large clade of protostome animals identified by either the presence of a lophophore (a ciliated feeding structure) or a trochophore larva (a specific type of larval stage). This diverse group includes mollusks (e.g., snails, clams), annelids (e.g., earthworms, leeches), and flatworms.

Mollusca

A diverse phylum of invertebrates, mostly marine, characterized by a soft body usually protected by a shell, a muscular foot for movement, and a mantle. Examples include snails, slugs, clams, oysters, octopuses, and squids.

Ecdysozoa

A major clade of protostome animals distinguished by their growth through ecdysis (molting of an exoskeleton or cuticle). This group includes arthropods (e.g., insects, spiders, crustaceans) and nematodes (e.g., roundworms).

Arthropoda

The largest phylum of animals, characterized by an exoskeleton made of chitin, a segmented body, and jointed appendages. They are incredibly diverse and found in nearly all habitats. Examples include insects (e.g., butterflies, ants), arachnids (e.g., spiders, scorpions), and crustaceans (e.g., crabs, lobsters).

Nematoda

Commonly known as roundworms, this phylum consists of slender, unsegmented worms with a tough outer cuticle. They are incredibly diverse and found in almost every habitat, including parasitic forms affecting plants and animals. Examples include Ascaris (intestinal roundworm) and C. elegans (a model organism).

Myriopoda

A subphylum of arthropods characterized by having many body segments, each typically bearing one or two pairs of legs. Examples include centipedes (one pair of legs per segment) and millipedes (two pairs of legs per segment).

Chelicerata

A subphylum of arthropods distinguished by having chelicerae (pincer-like or fang-like mouthparts) instead of antennae. They typically have a two-part body (cephalothorax and abdomen). Examples include spiders, scorpions, ticks, mites, and horseshoe crabs.

Crustacea

A large class within the phylum Arthropoda, predominantly aquatic, characterized by two pairs of antennae, a hard exoskeleton, and biramous (two-branched) appendages. Examples include crabs, lobsters, shrimp, barnacles, and copepods.

Insecta

The largest class within Arthropoda, distinguished by a body divided into three parts (head, thorax, and abdomen), three pairs of legs, typically one or two pairs of wings, and a pair of antennae. Examples include butterflies, beetles, ants, bees, and flies.

Echinoderms

A phylum of exclusively marine animals, characterized by radial symmetry (typically five-fold) in adulthood, an endoskeleton of calcareous plates, and a unique water vascular system with tube feet used for locomotion, feeding, and gas exchange. Examples include sea stars, sea urchins, sand dollars, and sea cucumbers.

Chordates

A phylum of animals defined by four key unique characteristics present at some stage of their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. This phylum includes urochordates (tunicates), cephalochordates (lancelets), and vertebrates (e.g., fish, amphibians, reptiles, birds, mammals).

Tunicates

Also known as urochordates, these are marine filter-feeding organisms belonging to the phylum Chordata. Adults are sessile and often sac-like, retaining only pharyngeal slits, while larval forms exhibit all four chordate characteristics. Examples include sea squirts and salps.

Lancelets

Small, fish-like marine animals belonging to the phylum Chordata (cephalochordates). They are unique in that they retain all four chordate characteristics (notochord, dorsal hollow nerve cord, pharyngeal slits, and post-anal tail) throughout their entire life cycle. An example is Branchiostoma (formerly Amphioxus).

Vertebrates

A subphylum within Chordata, characterized by the presence of a vertebral column (backbone) composed of individual vertebrae, which replaces the notochord in adults and protects the dorsal hollow nerve cord. This group includes a vast diversity of animals. Examples include fish, amphibians, reptiles, birds, and mammals.

Agnatha

An ancient class of jawless fish that represent some of the earliest vertebrates. They lack paired fins and possess a cartilaginous skeleton. Modern examples include lampreys and hagfish.

Chondrichthyes

A class of jawed fish, often called cartilaginous fish, because their skeletons are primarily composed of cartilage rather than bone. They typically have placoid scales and lack a swim bladder. Examples include sharks, rays, skates, and chimaeras.

Actinopterygii

The class of ray-finned bony fish, comprising the vast majority of all fish species. They are characterized by fins supported by bony rays, a swim bladder, and an operculum covering the gills. Examples include tuna, salmon, trout, goldfish, and most common freshwater and marine fish.

Sarcopterygii

The class of lobe-finned bony fish, characterized by fleshy, muscular fins supported by a single bone and internal skeletal elements, which are homologous to the limbs of tetrapods. This group includes the ancestors of all terrestrial vertebrates. Examples include coelacanths and lungfish.

Tetrapods

A superclass of vertebrates that are characterized by typically having four limbs, an adaptation for life on land. This group evolved from lobe-finned fish and includes amphibians, reptiles, birds, and mammals.

Amphibians

A class of tetrapods that typically have a dual life cycle, beginning as aquatic larvae with gills and undergoing metamorphosis into terrestrial or semi-aquatic adults with lungs and moist, permeable skin for gas exchange. They usually require water for reproduction. Examples include frogs, toads, salamanders, and newts.

Amniotes

A group of tetrapods characterized by the production of an amniotic egg, which contains specialized membranes (amnion, chorion, yolk sac, allantois) that protect and nourish the embryo, enabling reproduction on land without dependence on water. This group includes reptiles, birds, and mammals.

Reptiles

A class of amniotes characterized by dry, scaly skin, lung respiration, and typically laying shelled eggs on land. They are primarily ectothermic, meaning they rely on external heat sources to regulate their body temperature. Examples include snakes, lizards, turtles, tortoises, and crocodilians.

Lepidosaurs

A diverse subgroup of reptiles that includes the scaly reptiles. Key characteristics often include overlapping scales and the ability to shed their skin. This group encompasses lizards and snakes (Squamata) and the tuataras.

Chelonia

An order of reptiles distinguished by a unique bony shell that encloses their body, providing protection. This order includes both aquatic and terrestrial species adapted to various environments. Examples include turtles (aquatic and semi-aquatic) and tortoises (terrestrial).

Archosaurs

A major group of diapsid reptiles that includes crocodiles, alligators, birds, and their extinct relatives such as dinosaurs and pterosaurs. They are characterized by antorbital and mandibular fenestrae (skull openings). Examples include modern crocodiles, alligators, caimans, and ostriches.

Birds

A class of endothermic (warm-blooded) vertebrates characterized by feathers, beaks without teeth, laying hard-shelled eggs, a high metabolic rate, and a strong yet lightweight skeleton, typically adapted for flight. Examples include eagles, penguins, hummingbirds, and chickens.

Mammals

A class of endothermic (warm-blooded) vertebrates distinguished by the presence of mammary glands (producing milk to nourish young), hair or fur, and a neocortex region in the brain. Most mammals give birth to live young. Examples include humans, dogs, whales, bats, and mice.

Monotremes

A basal order of mammals unique for their egg-laying reproduction, although they still possess mammary glands to feed their young with milk (which is secreted through pores, not nipples). Examples include the platypus and echidnas.

Marsupials

A group of mammals characterized by giving birth to relatively underdeveloped young that typically complete their embryonic development inside a maternal pouch (marsupium), where they suckle milk. Examples include kangaroos, koalas, opossums, and wallabies.

Eutherians

Also known as placental mammals, this group includes the vast majority of living mammals. They are characterized by having a complex placenta that allows for a prolonged gestation period, leading to the birth of relatively well-developed young. Examples include humans, dogs, cats, whales, elephants, and rodents.