Chapter 30: Introduction to Animals

Vocabulary practice flashcards covering fundamental animal evolutionary lineages, embryonic tissue layers, body symmetry, sensory systems, feeding strategies, and reproductive modes.

Opisthokonta

The monophyletic eukaryotic lineage that encompasses animals, choanoflagellates, and fungi.

Choanoflagellates

Sessile single-celled or colonial protists that are recognized as the closest living relatives to animals.

Sessile

Describing an organism that lives permanently attached to a surface rather than freely moving.

Sponges-First Hypothesis

The hypothesis proposing that sponges (Porifera) are the sister group to all other animals and were the earliest lineage to branch off.

Ctenophores-First Hypothesis

The phylogenetic hypothesis proposing that comb jellies (Ctenophora) are the sister group to all other animals, supported in part by their unique lack of microRNAs.

Epithelium

A continuous layer of tightly joined cells that covers the exterior and interior surfaces of an animal body.

Developmental Tool-Kit Genes

A conserved set of genes within an animal's genome that establishes basic developmental processes, body plans, and embryonic organization.

Diploblasts

Animals whose embryos develop from two primary germ layers: an outer ectoderm and an inner endoderm.

Triploblasts

Animals whose embryos develop from three distinct germ layers: the ectoderm, mesoderm, and endoderm.

Ectoderm

The outer embryonic germ layer that gives rise to the skin and the nervous system.

Mesoderm

The middle embryonic germ layer that gives rise to muscles, the circulatory system, bones, and most internal organs.

Endoderm

The inner embryonic germ layer that gives rise to the lining of the digestive tract and associated digestive organs.

Epitheliomuscular Cells

Contractile cells in diploblasts (such as cnidarians and ctenophores) derived from endoderm or ectoderm that function similarly to true mesodermal muscle cells via convergent evolution.

Sarcomere

The repeating structural and contractile unit of a myofibril, bounded by Z disks and containing alternating thick and thin filaments.

Sliding-Filament Model

The mechanism of muscle contraction whereby thin actin filaments slide past thick myosin filaments to shorten the sarcomere without altering filament length.

Radial Symmetry

A body plan possessing at least two planes of symmetry across a central axis, typical of cnidarians and ctenophores.

Bilateral Symmetry

A body plan characterized by a single plane of symmetry that divides an organism into mirror-image left and right halves along an anterior-posterior axis.

Cephalization

The evolutionary trend toward concentrating feeding structures, sensory organs, and neural processing units in a distinct head region.

Nerve Net

A diffuse, interconnected network of nerve cells without a centralized brain, characteristic of radially symmetrical cnidarians and ctenophores.

Coelom

An internal, fluid-filled body cavity located between the gut tube and the body wall that provides space for organ movement and nutrient circulation.

Coelomates

Bilaterian animals that possess an enclosed body cavity completely lined with mesodermally derived tissue.

Acoelomates

Bilaterian animals, such as flatworms (Platyhelminthes), that lack an internal body cavity entirely.

Pseudocoelomates

Bilaterian animals, such as nematodes and rotifers, whose internal body cavity is only partially lined with mesodermally derived tissue.

Protostomes

A major bilaterian lineage characterized by spiral, determinate cleavage and embryonic development where the mouth typically forms before the anus from or near the blastopore.

Deuterostomes

A major bilaterian lineage characterized by radial, indeterminate cleavage and embryonic development where the blastopore becomes the anus while the mouth forms secondarily.

Segmentation

The division of the animal body or parts of the body into repeated, serial structural units, as seen in annelids, arthropods, and chordates.

Ommatidia

The independent light-focusing and visual receptor columns that together form the compound eye of arthropods.

Hair Cells

Specialized mechanoreceptor cells possessing stiff stereocilia that open ion channels and cause membrane depolarization when bent by pressure waves or physical force.

Lateral Line System

A mechanoreceptive organ system running along the bodies of fish and aquatic amphibians containing hair cells embedded in cupulae to detect water movement and pressure changes.

Ampullae of Lorenzini

Specialized electroreceptive organs located in the lateral line system of sharks that detect electrical potentials generated by prey.

Infrasound

Acoustic frequencies below $20\,\text{Hz}$ that travel long distances and are utilized by animals like elephants for communication.

Detritivores

Heterotrophic organisms that obtain nutrients primarily by feeding on dead, decomposing organic matter.

Suspension Feeders

Animals that capture food by filtering small organisms or organic debris out of the surrounding water or air using specialized structures.

Deposit Feeders

Animals that feed by swallowing nutrient-rich sediments and digesting the organic matter contained within them.

Fluid Feeders

Animals equipped with specialized mouthparts that enable them to suck or mop up liquid food such as nectar, blood, or plant sap.

Mass Feeders

Animals that seize, bite off, and ingest substantial solid chunks of food into their digestive tracts.

Adaptive Radiation

The rapid evolutionary diversification of a single ancestral lineage into numerous descendant species adapted to different ecological niches and habitats.

Pharyngeal Jaws

A specialized second set of throat jaws behind the oral jaws in fish such as cichlids, modified for biting, crushing, or compacting diverse food types.

Incomplete Digestive Tract

A digestive system containing only a single opening that serves as both the site of food ingestion and waste elimination.

Complete Digestive Tract

A digestive system with two separate openings (a mouth and an anus/cloaca), permitting continuous, unidirectional, and compartmentalized processing of food.

Viviparous

An embryonic development strategy in which embryos are nourished internally by the mother and born as live offspring.

Oviparous

An embryonic development strategy in which fertilized eggs are deposited externally and develop outside the mother nourished entirely by yolk.

Ovoviviparous

An embryonic development strategy in which fertilized eggs are retained within the female and nourished by egg yolk until hatching inside or immediately upon release as live young.