Chapter 33 – Introduction to Animal Diversity Vocabulary

Vocabulary flashcards covering key terms from Chapter 33: an overview of animal characteristics, classification, embryology, and evolutionary history.

Animal

A eukaryotic, multicellular, heterotrophic organism that ingests food then absorbs nutrients, is motile at some life stage, and reproduces sexually with sperm and egg.

Heterotrophic (by ingestion then absorption)

Nutritional mode where an organism eats food particles and then absorbs the digested nutrients; characteristic of animals.

Hox genes

Homeotic genes that regulate an animal’s body plan during development; their evolution helped drive the Cambrian explosion.

Muscle tissue

Specialized contractile tissue present in animals, enabling movement.

Nervous tissue

Tissue composed of neurons and supporting cells that receive and transmit signals in animals.

Cell junctions

Protein complexes that connect animal cells to each other and to the extracellular matrix.

Extracellular matrix

Network of protein fibers and carbohydrates outside animal cells that provides structural support.

Cambrian Explosion

Evolutionary event 533–525 mya marked by a rapid increase in the number and diversity of animal phyla.

Invertebrate

Animal lacking vertebrae; includes the earliest known animals (~590 mya).

Vertebrate

Animal possessing a backbone; first appeared as fish about 520 mya.

Internal fertilization

Reproductive adaptation in which sperm fertilizes the egg inside the female body, facilitating life on land.

Lungs

Respiratory organs that allow vertebrates to breathe air on land.

Amniote egg

Shelled, water-retaining egg that permits embryonic development on land.

Choanoflagellate

Protist with a collar of microvilli around a single flagellum; the closest living relative of animals.

Choanocyte

Flagellated feeding cell in sponges that closely resembles a choanoflagellate.

Sessile lifestyle

Mode of life in which an adult organism is attached to a substrate and does not move, as in sponges and choanoflagellates.

Monophyletic group

A clade that includes a common ancestor and all of its descendants; animals form one.

Parazoa

Subkingdom containing animals without true tissues, represented by the sponges (Phylum Porifera).

Eumetazoa

Clade of animals that possess true tissues.

Asymmetry

Body plan lacking any plane that produces mirror-image halves.

Radial symmetry

Body plan with two or more planes of symmetry, typical of cnidarians.

Bilateral symmetry

Body plan with a single plane producing left and right halves; exhibited by over 99 % of animals.

Cephalization

Concentration of sensory organs and nerve cells at the anterior end (head) of a bilaterian animal.

Diploblastic

Having two embryonic germ layers—ectoderm and endoderm.

Triploblastic

Having three embryonic germ layers—ectoderm, mesoderm, and endoderm.

Ectoderm

Outer germ layer that forms skin and nervous system.

Endoderm

Inner germ layer that forms the lining of the digestive tract.

Mesoderm

Middle germ layer that forms muscles, bones, and most internal organs.

Protostome

Developmental mode in which the blastopore becomes the mouth and cleavage is determinate.

Deuterostome

Developmental mode in which the blastopore becomes the anus and cleavage is indeterminate.

Determinate cleavage

Early embryonic cleavage in which the fate of each cell is fixed; characteristic of protostomes.

Indeterminate cleavage

Cleavage in which early cells retain the capacity to develop into a complete embryo; characteristic of deuterostomes.

Acoelomate

Triploblastic animal lacking a fluid-filled body cavity.

Pseudocoelom

Body cavity that is not completely lined by mesoderm.

Coelom

Fluid-filled body cavity completely lined by mesoderm.

Hydrostatic skeleton

Support system in which a fluid-filled cavity provides rigidity against which muscles contract, as in earthworms.

Segmentation

Division of an animal body into repetitive segments, allowing specialization; found in annelids, arthropods, and vertebrates.

Cleavage (embryology)

Series of rapid mitotic cell divisions after fertilization that produce a multicellular embryo without overall growth.

Blastula

Hollow ball of cells formed after cleavage.

Gastrula

Embryonic stage produced by inward folding of the blastula, establishing germ layers.

Archenteron

Primitive digestive tract formed during gastrulation.

Blastopore

Opening of the archenteron to the exterior of the gastrula.

Ecdysozoa

Protostome clade whose members secrete an external cuticle (exoskeleton) and grow by molting (ecdysis).

Exoskeleton

Nonliving external skeleton secreted by ecdysozoans such as arthropods and nematodes.

Ecdysis

Molting process in which an ecdysozoan sheds its old exoskeleton to permit growth.

Lophotrochozoa

Protostome clade containing animals with either a lophophore feeding structure or a trochophore larva.

Lophophore

Horseshoe-shaped crown of tentacles used for suspension feeding in some lophotrochozoans.

Trochophore

Free-swimming larval stage with a band of cilia around the middle, characteristic of mollusks and annelids.

Ribosomal RNA (rRNA)

Universal molecular component used to compare species and infer evolutionary relationships.

Molecular phylogeny

Evolutionary tree constructed by comparing DNA, RNA, or protein sequences among organisms.