animal bio2

Animal

Animals are multicellular heterotrophs. Their cells are embedded in an extracellular matrix, they generally have motile stages, and they develop specialized tissues and body plans.

Animal species diversity

Less than one million animal species were described in the lecture; estimates suggested roughly 3–30 million species on Earth.

When did animals evolve?

Animals evolved about 600 million years ago.

Heterotroph

An organism that obtains organic nutrients by consuming other organisms or their products; animal feeding modes include carnivory, herbivory, omnivory, and parasitism.

Animal reproduction

Most animals reproduce sexually; gametes are produced by meiosis, and the animal life cycle is predominantly diploid.

Diploid

Having two chromosome sets (2n).

Haploid

Having one chromosome set (n).

Haplodiploidy

A reproductive system in ants, wasps, and bees in which females are diploid (2n) and males are haploid (n), developing from unfertilized eggs.

Parthenogenesis

Development of offspring from an unfertilized egg or other gamete; the word means “virgin birth.”

Parthenogenesis in ants, wasps, and bees

Unfertilized eggs develop into haploid males; fertilized eggs develop into diploid females.

Parthenogenesis in turkeys

The lecture example uses the ZW sex-determination system: females are ZW and males are ZZ; a parthenogenetic turkey develops as a male and carries maternal chromosomes.

ZW sex-determination system

Females are heterogametic (ZW) and males are homogametic (ZZ), as in birds discussed in the lecture.

Heterogametic sex

The sex with two different sex chromosomes; in the lecture's bird example, the female is ZW.

Homogametic sex

The sex with two matching sex chromosomes; in the lecture's bird example, the male is ZZ.

Asexual reproduction in animals

A minority of animals reproduce asexually through budding, fragmentation, or parthenogenesis.

Budding

Asexual reproduction in which a new individual grows from the parent; the offspring are genetic clones (2n). Examples shown include sea anemones and corals.

Fragmentation

Asexual reproduction in which a body fragment develops into a new individual; the lecture example is sea stars.

Parthenogenetic vertebrates

The lecture lists a few vertebrates, including some fish, bonnethead sharks, turkeys, rattlesnakes, and lizards.

Animal locomotion

Animals are generally motile during at least one life stage, even if the adult is sessile.

Sessile

Fixed in place; unable to move from place to place as an adult.

Sessile adults with motile stages

Lecture examples include sponges, corals, barnacles, oysters, and sea squirts.

Extracellular matrix (ECM)

Material outside cells that supports and connects them; animal cells are embedded in an ECM that includes collagen.

Evidence that fungi and animals share a common ancestor

The lecture cites collagen in fungal fimbriae and opisthokont cells with a single posterior flagellum as evidence of a shared ancestry.

Opisthokont

A member of the eukaryotic group that includes animals and fungi; its flagellated cells characteristically have a single posterior flagellum.

Animal development

Animal development uses embryonic germ layers and regulatory genes to build a fixed body plan and specialized tissues.

Hox gene (homeobox gene)

A regulatory “master control” gene that turns large numbers of other genes on or off during embryogenesis and helps establish body organization.

Hox genes in basal animal groups

The lecture notes that Porifera and Ctenophora lack Hox genes and are considered basal taxa in the illustrated tree.

Hox gene replacement example

If a mouse Hox 13 gene were replaced with Hox 1, the lecture's hypothetical answer is that development might produce two heads and no tail because body-region identities could change.

Metamorphosis

A developmental change in body form between life stages.

Incomplete metamorphosis

Development through egg, nymph, and adult stages; the nymph resembles a smaller version of the adult and there is no pupal stage.

Complete metamorphosis

Development through egg, larva, pupa, and adult stages; the larva differs greatly from the adult.

Animal body plan

The morphology of an animal, determined by developmental cues.

Four traits used to classify animal body plans

Symmetry; tissue layers and organization during embryogenesis; body cavity; and mode of development, including the fate of the blastopore.

Morphology

An organism's form or shape.

Asymmetry

A body plan with no plane that divides the animal into matching halves.

Radial symmetry

A body plan in which multiple planes through the central axis can divide the animal into similar halves.

Bilateral symmetry

A body plan with one plane that divides the animal into right and left mirror-image halves.

Animal germ layers

The embryonic tissue layers that form during development: ectoderm, mesoderm, and endoderm.

Diploblastic animal

An animal with two germ layers, ectoderm and endoderm; cnidarians and ctenophores are shown as diploblastic.

Triploblastic animal

An animal whose embryo develops three germ layers: ectoderm, mesoderm, and endoderm.

Ectoderm

The outer germ layer of an embryo; it covers the embryo's surface.

Mesoderm

The middle germ layer, located between the ectoderm and endoderm.

Endoderm

The innermost germ layer of an embryo.

Ectoderm derivatives

Includes epidermis and its derivatives (sweat glands and hair follicles), nervous and sensory systems, pituitary gland, adrenal medulla, jaws and teeth, and germ cells.

Mesoderm derivatives

Includes skeletal and muscular systems, circulatory and lymphatic systems, excretory and reproductive systems except germ cells, dermis of skin, and adrenal cortex.

Endoderm derivatives

Includes epithelial lining of the digestive tract and associated organs such as liver and pancreas; linings of respiratory, excretory, and reproductive tracts and ducts; and thymus, thyroid, and parathyroid glands.

Zygote

The fertilized egg cell that begins embryonic development.

Cleavage

A series of mitotic cell divisions of the zygote without overall growth of the embryo.

Blastomere

An individual cell formed by cleavage of a fertilized ovum.

Morula

The solid ball of cells formed at about the eight-cell stage of cleavage; the name means mulberry.

Blastula

The hollow ball of cells that forms after cleavage; it contains a fluid-filled blastocoel.

Blastocoel

The fluid-filled cavity inside a blastula; “coel” means hollow.

Gastrulation

The process in which the blastula folds inward and reorganizes to form a gastrula and establish germ layers.

Gastrula

The embryo stage formed during gastrulation, with germ layers and an embryonic gut beginning to form.

Archenteron

The primitive gut cavity that forms during gastrulation; “archenteron” means little gut.

Blastopore

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

Order of early embryonic development

Zygote → cleavage → morula → blastula → gastrulation → gastrula; neurulation and organogenesis follow.

Neurulation

The embryonic process that forms the nervous system, including the neural tube.

Organogenesis

The process by which embryonic organs develop from germ layers.

Determinate cleavage

A cleavage pattern in which each blastomere's developmental fate is tightly specified early.

Indeterminate cleavage

A cleavage pattern in which early blastomeres retain stem-cell-like flexibility and are not yet committed to specific cell types.

Body cavity (coelom)

A fluid- or air-filled space within the body; a true coelom is derived from mesoderm.

Functions of a coelom

Cushions organs, can act as a hydrostatic skeleton, and provides room for organs to expand and grow independently of the body wall.

Acoelomate

An animal without a body cavity between the digestive tract and body wall.

Pseudocoelomate

An animal with a body cavity that is not completely lined by mesoderm.

Eucoelomate

An animal with a true coelom completely lined by mesoderm.

Acoelomate example

Flatworms (Platyhelminthes).

Pseudocoelomate examples

Nematodes and rotifers.

Eucoelomate groups

Annelids and most of the other groups shown in the lecture's body-cavity comparison.

Protostome

A bilaterian lineage in which the blastopore is associated with formation of the mouth first.

Deuterostome

A bilaterian lineage in which the blastopore is associated with formation of the anus first.

Protostome and deuterostome development

The lecture compares cleavage pattern (spiral, radial, or neither), cleavage plane (diagonal or perpendicular), coelom formation, and blastopore fate.

Schizocoely

Coelom formation in which a solid mass of mesoderm splits apart, creating the coelom.

Enterocoely

Coelom formation in which mesodermal pouches pinch off from endodermal tissue; the cavity inside the pouches becomes the coelom.

Typical cleavage pattern shown for protostomes

Spiral cleavage, with diagonal cleavage planes.

Typical cleavage pattern shown for deuterostomes

Radial cleavage, with cleavage planes perpendicular to the embryo's surface.

Parazoa

Animals without true tissues or organs; the lecture places sponges and placozoans in or near this group.

Eumetazoa

Animals with true tissues.

Animal clades in the lecture's five-group overview

Placozoa; Parazoa/Porifera; Cnidaria; Ctenophora; and Bilateria.

Placozoa

A group of tiny, simple animals described in the lecture as resembling multicellular amoebae; they lack true tissues.

Porifera

The phylum of sponges; sponges lack true tissues and are placed among basal animals in the lecture's tree.

Cnidaria

An animal group that includes jellyfish and their relatives; cnidarians are diploblastic in the lecture's body-plan diagram.

Ctenophora

The phylum of comb jellies; ctenophores are diploblastic in the lecture's body-plan diagram.

Bilateria

The clade that includes most animal phyla; bilaterians have bilateral symmetry and are triploblastic.

Body-cavity classification shown on the animal tree

Platyhelminthes are acoelomates; nematodes and Rotifera are pseudocoelomates; most other triploblastic groups are eucoelomates.

Ecdysozoa

A protostome group that includes arthropods and nematodes in the lecture's preferred animal tree.

Lophotrochozoa

A protostome group that includes flatworms, rotifers, ectoprocts, brachiopods, annelids, and mollusks in the lecture's preferred tree.

Protostome examples shown in the lecture tree

Arthropoda, Nematoda, Platyhelminthes, Rotifera, Ectoprocta, Brachiopoda, Annelida, and Mollusca.

Deuterostome examples shown in the lecture tree

Echinodermata, Hemichordata, and Chordata.

Acoela

A lineage shown among the animal groups in the lecture's preferred tree.

Segmentation

The division of an animal body into repeated sections; it can enable specialization of body regions and better control of movement.

External appendages

Structures that can enhance locomotion and serve in sensing, reproduction, prey capture, or feeding.

Feeding strategies shown in the lecture

Filter feeding, predation, herbivory, parasitism, and detritivory.

Detritus

Nonliving organic material, such as feces or parts of dead organisms.

Detritivore

An organism that feeds on detritus.

Animal life cycle and lifestyle

Additional traits used to describe animals alongside body plan include life cycle and lifestyle.

Phylogeny

The evolutionary relationships among organisms.

Preferred animal phylogenetic tree

One of several hypothetical trees, based on morphology, fossil records, and molecular data.

Modern animal systematics

Zoologists recognize about three dozen animal phyla; current phylogenetic hypotheses combine morphological, fossil, and molecular data, and relationships among animal groups remain under discussion.

Points of agreement in animal phylogeny

All animals share a common ancestor; sponges are basal animals; Eumetazoa is the clade of animals with true tissues; and most animal phyla belong to Bilateria.