7.16 Animal Diversity Lecture

A comprehensive set of Q&A flashcards to review terminology, structures, and evolutionary concepts introduced in the first two ‘Introduction to Animals’ lectures.

What are the four universally accepted characteristics of animals?

Multicellular eukaryotes, heterotrophic nutrition, lack of cell walls, and (at some life stage) active movement.

Which animal phylum is asymmetrical and lacks true tissues?

Porifera (sponges).

What term describes animals that rely on outside food sources for energy?

Heterotrophic.

Name the only major animal group that is diploblastic and radially symmetrical.

Cnidaria (e.g., jellyfish, hydra, sea anemones).

Which two embryonic germ layers are present in diploblastic animals?

Ectoderm and endoderm.

Define ‘triploblastic’.

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

What type of symmetry allows an organism to be divided into identical halves along ONLY one plane?

Bilateral symmetry.

What is cephalization and with which type of symmetry is it usually associated?

Concentration of nervous tissue and sense organs at the anterior end; typically associated with bilateral symmetry.

Which two phyla are classic examples of pseudocoelomates?

Nematoda (roundworms) and Rotifera (rotifers).

Give an example of acoelomate triploblastic animals.

Platyhelminthes (flatworms).

What is a ‘true coelom’?

A body cavity completely lined by mesoderm-derived tissue.

In protostomes, the blastopore becomes the _.

Mouth.

In deuterostomes, the blastopore develops into the _.

Anus.

What type of early embryonic cleavage do protostomes exhibit?

Spiral, determinate cleavage.

Describe early embryonic cleavage in deuterostomes.

Radial, indeterminate cleavage.

How does the coelom form in protostomes?

Schizocoely – solid masses of mesoderm split to form body cavities.

How does the coelom form in deuterostomes?

Enterocoely – mesoderm buds from the archenteron to form body cavities.

List the four key developmental distinctions that separate protostomes from deuterostomes.

1) Fate of blastopore (mouth vs anus), 2) Pattern of cleavage (spiral vs radial), 3) Determinate vs indeterminate fate, 4) Type of coelom formation (schizocoely vs enterocoely).

Which two major phyla belong to the deuterostomes?

Echinodermata and Chordata.

What are Hox genes?

Highly conserved ‘toolkit’ genes that control body plan and segment identity in animals.

Why are Hox genes described as ‘conserved’?

Homologous sequences are present across nearly all animal phyla and perform similar body-patterning roles.

What geological period saw a rapid diversification of animal body plans?

The Cambrian Period (Cambrian explosion).

Where was critical fossil evidence of Cambrian animals discovered?

The Burgess Shale site (Canadian Rockies).

What feeding category includes animals that consume both plant and animal matter?

Omnivores.

Name three forms of asexual reproduction found in animals.

Budding (e.g., Hydra), fragmentation & regeneration (e.g., planarians, sea stars), parthenogenesis (e.g., some rotifers and insects).

What is parthenogenesis?

Development of an embryo from an unfertilized egg.

Define ‘larval stage’.

An immature life stage that often differs in form and habitat from the adult and may possess its own mode of locomotion.

What is a hydrostatic skeleton and which body feature is crucial for it?

A support structure where fluid-filled body cavities provide rigidity; the body cavity (coelom or pseudocoelom) is essential.

Which enzyme-mediated process allows arthropods and nematodes to shed their external covering?

Ecdysis.

Which clade includes molting animals such as arthropods and nematodes?

Ecdysozoa.

What term describes animals that produce live young that hatch from eggs retained inside the mother?

Ovoviviparous.

During gastrulation, the primitive gut is called the _.

Archenteron.

What cavity forms inside the blastula?

Blastocoel.

Which early embryonic stage resembles a solid ball of 16–32 cells?

Morula.

Why do ruminant mammals possess a multi-chambered stomach?

To house symbiotic microorganisms that digest cellulose from plant material.

Give one adaptive advantage of internal fertilization over external fertilization.

Greater likelihood of successful fertilization and often better protection of gametes/embryos.

Which simple animal feeds by drawing water through flagellated collar cells (choanocytes)?

Sponges (Porifera).

What is the major evolutionary significance of the rise in atmospheric oxygen before the Cambrian explosion?

Higher oxygen levels supported increased metabolic activity, larger body sizes, and the diversification of complex animals.