7.17 Invertebrates Lecture

Question-and-answer style flashcards covering key terms, structures, life cycles, and developmental concepts for sponges (Porifera), cnidarians, and basic animal phylogeny discussed in the lecture.

Roughly what percentage of all animal species are invertebrates?

About 95 % of animal species are invertebrates.

Which phylum of animals completely lacks true tissues?

Phylum Porifera (sponges).

What kind of symmetry do sponges (Porifera) exhibit?

They are asymmetrical (no symmetry).

What symmetry characterises the phylum Cnidaria?

Radial symmetry.

How many germ layers do cnidarians possess, and what adjective describes them?

Two germ layers (ectoderm and endoderm); they are diploblastic.

Name the three germ layers found in triploblastic animals.

Ectoderm, mesoderm, and endoderm.

Which body-cavity condition describes flatworms (Platyhelminthes)?

Acoelomate (no body cavity).

In protostome development, what does the blastopore become?

The mouth.

What type of embryonic cleavage pattern do protostomes show?

Spiral, determinate cleavage.

Which cleavage pattern is typical of deuterostomes?

Radial, indeterminate cleavage.

Name the two ecdysozoan phyla that molt a cuticle.

Arthropoda and Nematoda.

What is the chief role of choanocytes in a sponge?

They create water currents and perform intracellular digestion of food particles.

What are spicules in sponges?

Rigid structural elements (of silica, calcium carbonate, or spongin) that support the sponge body.

What is the large opening at the top of a sponge through which water exits?

The osculum.

What term is used for the tiny pores through which water enters a sponge?

Ostia (singular = ostium).

Which mobile sponge cells transport nutrients and wastes?

Amoebocytes.

What term describes an organism that produces both eggs and sperm?

Hermaphroditic.

List the three canal-system types of sponges from simplest to most complex.

Asconoid, syconoid, and leuconoid.

Which animal group contains the greatest number of described species?

Arthropods, particularly insects.

What is the literal meaning of the name “Porifera”?

“Pore bearer” (from Latin porus = pore, ferre = to bear).

What gelatinous matrix lies between the pinacoderm and choanoderm in a sponge?

The mesohyl.

Which sponge cells secrete spicules?

Sclerocytes.

What stinging organelle is housed inside a cnidarian cnidocyte?

A nematocyst.

Name the two main body forms found in cnidarians.

Polyp and medusa.

Hydras belong to which cnidarian class?

Class Hydrozoa.

Which cnidarian class includes the classic “true” jellyfish?

Class Scyphozoa.

What gelatinous layer gives jellyfish their “jelly” consistency?

The mesoglea.

How many digestive openings do cnidarians possess?

One; the mouth also serves as the anus for the gastrovascular cavity.

Describe how most cnidarians reproduce sexually.

They release eggs and sperm into water for external fertilization.

What is a planula?

The free-swimming, ciliated larval stage of cnidarians.

Why is the Portuguese man o’ war not a true jellyfish?

It is a colonial hydrozoan with a gas-filled float (pneumatophore), not a single medusa individual.

Define cephalization.

Evolutionary concentration of sensory structures and nervous tissue at an anterior “head” end.

What is a pseudocoelom?

A body cavity partially, but not completely, lined by mesoderm.

Which larval form is typical of many lophotrochozoans such as molluscs and annelids?

The trochophore larva.

What structure is a lophophore?

A horseshoe-shaped crown of ciliated tentacles used for filter feeding.

What unites members of Ecdysozoa?

They undergo ecdysis—periodic molting of a cuticle or exoskeleton.

Which flattened cells form the outer “skin” (pinacoderm) of a sponge?

Pinacocytes.

What is the gas-filled float of the Portuguese man o’ war called?

A pneumatophore.

Which sponge cells regulate water flow by contracting around ostia?

Porocytes (or “contractile cells” controlling the pore openings).