The Evolution of Invertebrate Diversity

Flashcards covering the characteristics, classification, evolutionary history, and body plans of the Kingdom Animalia and invertebrate diversity.

Invertebrates

Animals without a backbone, making up more than $95\%$ of animal species.

Vertebrates

Animals with a backbone, making up less than $5\%$ of animal species.

Metazoa

The formal name for the Animal Kingdom, comprising all multicellular eukaryotic organisms with wall-less, non-photosynthetic cells.

Holozoic feeders

Organisms (heterotrophs) that take in solid organic material by ingestion and digest it within the body.

Collagen

Extracellular structural proteins that hold animal cells together.

Blastula

A hollow ball of cells formed when a zygote undergoes mitosis.

Gastrula

The developmental stage formed when a blastula folds inward and cells rearrange to create tissue layers.

Larva

An immature individual that looks different from the adult animal and undergoes metamorphosis to become a reproductively mature adult.

Homeotic genes (Hox genes)

Clusters of master control genes that regulate the transformation of a zygote into an adult animal and account for genetic innovation in body structures.

Ediacaran biota

Impressions of soft-bodied animals dating from $560\,\text{mya}$, ranging in size from $1\,\text{cm}$ to $1\,\text{m}$.

Cambrian Explosion

A period between $535$ and $525\,\text{mya}$ characterized by a rapid increase in animal diversity and the appearance of hard body parts.

Burgess Shale

A site in British Columbia containing sedimentary rock where most Cambrian fossils, including many bilateral organisms and arthropods, are found.

Body plan (Bauplan)

A set of morphological and developmental characteristics used by biologists to categorize animals, including symmetry, tissue organization, and body cavities.

Radial Symmetry

A body plan where parts radiate out from a central axis, with no distinct left or right sides.

Bilateral Symmetry

A body plan with mirror image right and left sides, featuring a head (anterior), tail (posterior), back (dorsal), and bottom (ventral).

Cephalization

The evolutionary trend toward the concentration of sensory equipment and a nervous system at the anterior (head) end of the body.

Diploblastic

An animal that possesses only two embryonic tissue layers: the ectoderm and the endoderm.

Triploblastic

An animal possessing three embryonic tissue layers: the endoderm (digestive lining), mesoderm (muscles/organs), and ectoderm (skin/nervous system).

Protostomes

A category of animals characterized by 'mouth first' development, where the blastopore becomes the mouth.

Deuterostomes

A category of animals characterized by 'anus first' development, where the blastopore becomes the anus and the mouth forms second.

Coelom

A fluid-filled space between the digestive tract and the outer body wall that cushions organs and allows them to move independently.

Hydrostatic skeleton

A structure found in soft-bodied animals where fluid in the body cavity provides support and allows for movement.

Eucoelomate

An organism with a 'true' coelom that is completely lined by tissues derived from the mesoderm.

Pseudocoelom

A body cavity that is not completely lined by tissues derived from the mesoderm.

Acoelomate

An organism that lacks a body cavity entirely after gastrulation.

Schizocoely

The process of coelom formation in protostomes where solid masses of mesoderm split to form the cavity.

Enterocoely

The process of coelom formation in deuterostomes where the mesoderm grows from the endoderm as folds of the archenteron.

Spiral and determinate cleavage

The early embryonic cell division pattern typical of protostomes where the fate of each cell is pre-planned early on.

Radial and indeterminate cleavage

The early embryonic cell division pattern typical of deuterostomes where cells maintain the potential to develop into any part of the embryo.

Metamerism

The serialized repetition of segments as seen in the Phylum Annelida.

Tagmatisation

The specialized grouping of body segments into functional units, as seen in the Phylum Arthropoda.