Lecture 22 Vocabulary (BIOL211)

Vocabulary flashcards covering the phylogenetic context, developmental patterns, and morphological traits used to categorize animal diversity.

Unikonts

A group of organisms whose cells never have more than one flagellum.

Opisthokonts

A group where the single flagellum is always located at the posterior end of the cell; includes animals, choanoflagellates, and fungi.

Choanoflagellates

Unicellular or colonial protists that are the sister-taxon to the animals, characterized by a single flagellum surrounded by a ring of microvilli.

Microvilli

Projections from the cell membrane that form a ring around the flagellum in choanoflagellates and trap food particles.

Suspension feeders

Organisms that beat a flagellum to create currents, trapping particles suspended in water on microvilli to be phagocytosed.

Cell adhesion proteins

Proteins such as cadherins and integrins that allowed multicellularity to evolve by enabling cells to stick together after mitosis.

Cytoplasmic cadherin domain (CCD)

A specific additional domain found in the animal version of cadherin proteins that is absent in choanoflagellates.

Cell junctions

Unique structures in animals, including tight junctions, desmosomes, and gap junctions, that adhere cells together.

Hox genes

A family of genes present in almost all animals that controls the patterning of the embryo along the anterior-posterior axis.

Radial symmetry

A body plan organized around one axis (oral-aboral) where many planes yield mirror-image halves; lacks left-right and dorsal-ventral sides.

Bilateral symmetry

A body plan with only one plane of mirror-image halves, characterized by anterior-posterior, left-right, and dorsal-ventral axes.

Cephalization

The concentration of nerve tissue (a brain) and sensory structures at the anterior end of an organism.

Radial cleavage

A pattern where all embryonic cell divisions are parallel or perpendicular to the animal-vegetal pole; typical of echinoderms.

Spiral cleavage

A pattern where, from the 3rd division on, all divisions are slightly off-parallel or perpendicular from the animal-vegetal pole.

Indeterminate cleavage

A developmental pattern where each cell in the early embryo retains the capacity to develop into a complete organism.

Determinate cleavage

A developmental pattern where each cell in the early embryo is already destined to give rise to a specific partial portion of the organism.

Blastula

A hollow ball of cells formed during the early stages of animal embryonic development.

Blastocoel

The hollow, fluid-filled space inside the blastula.

Gastrulation

The process in which cells from the outside of the blastula move inward, creating embryonic tissue layers.

Ectoderm

The outermost layer of embryonic tissue formed during gastrulation.

Endoderm

The innermost layer of embryonic tissue that surrounds the archenteron.

Archenteron

The primitive gut or space formed within the endoderm during gastrulation.

Blastopore

The opening that connects the archenteron to the outside of the embryo.

Diploblast

An animal that develops from only two embryonic tissue layers: ectoderm and endoderm.

Triploblast

An animal that develops from three embryonic tissue layers: ectoderm, endoderm, and mesoderm.

Mesoderm

The third embryonic tissue layer formed between the ectoderm and endoderm in triploblastic animals.

Protostomes

A group of animals where the blastopore becomes the mouth, and the anus forms later elsewhere.

Deuterostomes

A group of animals where the blastopore becomes the anus, and the mouth forms later elsewhere.

Acoelomate

A triploblast that lacks a fluid-filled cavity between the gut and the ectoderm; the space is filled with mesoderm.

Pseudocoelomate

An animal with a fluid-filled cavity between the gut and ectoderm that is not completely lined by mesodermal tissue.

Coelomate

An animal with a fluid-filled cavity between the gut and ectoderm that is completely lined by mesodermal tissue called peritoneum.

Hydrostatic skeleton

A system where pressurized fluid, rather than bones, serves to antagonize sets of muscles to provide structure and movement.

Direct development

A life cycle where the zygote develops into an embryo, then a juvenile, and finally an adult without a larval stage.

Larva

An immature stage that looks very different from the juvenile or adult and must undergo metamorphosis to transition.

Colonial organisms

Adult organisms composed of many genetically identical individuals that function together, such as bryozoans.

Bilateria

A monophyletic clade of animals characterized by bilateral symmetry and triploblastic development.

Cambrian explosion

A period approximately $535$ million years ago characterized by a huge burst of diversification in bilaterian animals.