Zoo 314 Exam #1 Study

Where are choanocytes found in Ascon-grade sponges?

Lining the spongocoel.

Where are choanocytes found in Sycon-grade sponges?

Lining the radial canals.

Where are choanocytes found in Leucon-grade sponges?

Lining the flagellated chambers.

What is the evolutionary progression of sponge body architectures from simplest to most complex?

Ascon → Sycon → Leucon.

Which sponge cells produce/secrete spicules?

Sclerocytes.

Which sponge cells capture food particles?

Choanocytes.

Which sponge cells form the outer surface?

Pinacocytes.

Which sponge cells are responsible for regeneration and can differentiate into other cell types?

Archaeocytes.

What are the smallest and most numerous pores on a sponge's surface called, and what forms them?

Ostia; they are formed by porocytes.

What is found in the mesohyl of a sponge?

Archaeocytes.

What is unique about Hexactinellid (glass) sponges?

They have a syncytial choanoderm and siliceous hexactine spicules.

What type of spicules do Hexactinellida have?

Glass/silicon dioxide (siliceous) spicules.

What type of spicules do Calcarea have?

Calcium carbonate spicules.

What type of skeleton can Demospongiae have?

Spongin.

What are gemmules?

Resistant structures containing totipotent cells that allow freshwater sponges to survive unfavorable conditions such as freezing.

What are the three main functions of choanocytes?

Generate water currents, capture/filter food, and participate in sperm capture/transport.

What protozoans have cells similar to sponge choanocytes?

Choanoflagellates.

Why are choanoflagellates important in understanding sponge evolution?

Their cells resemble choanocytes, supporting their close evolutionary relationship with animals.

What is a totipotent cell?

A cell capable of differentiating into many/all cell types.

What is the path of water through a leuconoid sponge?

Ostia → incurrent canals → flagellated chambers → excurrent canals → osculum.

How does a leuconoid sponge's architecture affect water velocity?

The complex canal system slows water and increases contact with choanocytes for efficient feeding/filtering.

What are the sticky prey-capturing cells of ctenophores called?

Colloblasts.

What structures are unique to Ctenophora?

Ctenes/comb rows and colloblasts.

What do ctenes do?

Beat with cilia to propel the ctenophore through the water.

How do ctenophores capture prey?

Tentacles with colloblasts capture prey, and the prey is moved toward the mouth.

Where are the tentacles of a ctenophore located?

At the aboral end.

What is the largest animal group capable of moving primarily using cilia?

Ctenophores.

What structure helps ctenophores maintain balance?

A statocyst.

What is a statolith?

A calcium carbonate structure within the statocyst that interacts with cilia and helps detect orientation/balance.

What happens when a ctenophore becomes unbalanced?

The statolith shifts against cilia, causing the appropriate comb row to beat differently and restore orientation.

What do Ctenophores and Cnidarians share?

Extracellular digestion, an inner gastrodermis, and an outer epidermis.

What is a key difference between cnidarian nematocysts and ctenophore colloblasts?

Nematocysts are stinging/capturing structures; colloblasts are sticky prey-capturing cells.

What are nematocysts?

Specialized organelles within cnidocytes used for functions such as prey capture and defense.

Are all nematocysts used to inject toxins?

No. Some are sticky and help capture prey.

What are cubozoans known for?

Lensed eyes and a square/cubical medusa.

How can a cubomedusa be distinguished from a true scyphomedusa?

Cubomedusae have lensed eyes.

What is a hydrostatic skeleton?

A body cavity or compartment filled with incompressible fluid against which muscles contract.

What are the two germ layers of cnidarians?

Ectoderm and endoderm.

Are cnidarians diploblastic or triploblastic?

Diploblastic.

What is the manubrium?

A structure associated with the mouth of jellyfish and extending into the gastrovascular region.

What is the difference between a hydromedusa and a scyphomedusa regarding the velum?

Hydromedusae usually have a velum; scyphomedusae generally lack one.

What is unusual about Obelia medusae?

They lack a velum.

What is strobilation?

Asexual production of ephyrae by scyphozoan polyps.

What are ephyrae?

Young medusae produced by strobilation in scyphozoans.

What is polymorphism in cnidarians?

The presence of different specialized forms/individuals within a colony or life cycle.

Give an example of a polymorphic cnidarian colony.

Portuguese Man-O-War (Physalia physalis).

What specialized individuals occur in siphonophore colonies?

Feeding polyps (gastrozooids) and defensive polyps (dactylozooids); some siphonophores also have floats/pneumatophores.

What is the difference between acontia and acrorhagi?

Acontia are long threads containing mucus/nematocysts used for defense; acrorhagi are offensive structures used in interactions with other organisms/colonies.

What are acrorhagi used for?

Offensive interactions, especially fighting other clones/colonies.

What are acontia used for?

Defense against predators.

What is the function of zooxanthellae in corals?

They photosynthesize and provide carbon/energy to their coral hosts.

Are all Symbiodinium species equally good at photosynthesis and transferring carbon to hosts?

No.

Which cnidarian groups can contain symbiotic algae?

Some Hydrozoa, Scyphozoa, and Anthozoa.

What is coral bleaching?

The loss/expulsion of symbiotic algae from coral tissues, often associated with environmental stress.

What is the rhynchocoel?

A mesoderm-lined cavity that houses the eversible proboscis.

How does the rhynchocoel develop?

Through schizocoely.

What structure do nemerteans use to capture prey?

An eversible proboscis, sometimes equipped with stylets.

Which nemertean class has stylets?

Enopla.

What is a stylet?

A hard, pointed structure associated with the proboscis and used in prey capture.

Do nemerteans have a complete digestive tract?

Yes.

How many embryonic tissue layers do nemerteans have?

Three; they are triploblastic.

What is a pilidium?

A larval form found in some nemerteans with indirect development.

Do all nemerteans have a pilidium larva?

No.

What type of circulatory system do nemerteans have?

A closed circulatory system.

What type of circulatory system do flatworms have?

None; they lack a circulatory system.

What is the primitive excretory system of flatworms called?

Protonephridia.

What are flame cells?

Specialized cells of protonephridia that use cilia to drive fluid through the excretory system.

What is the function of protonephridia?

Osmoregulation and removal of metabolic wastes.

Which animals commonly have protonephridia?

Flatworms and some other small invertebrates.

What are neoblasts?

Regenerative cells in free-living flatworms.

What is paratomy?

Asexual reproduction in which new zooids form at the tail end and are nearly fully developed before separating.

What is architomy?

Asexual reproduction in which an organism divides first and the resulting pieces regenerate missing structures.

What is an advantage of paratomy?

The offspring are more developed before separating.

What is an advantage of architomy?

Rapid fragmentation can allow reproduction when conditions are favorable.

What is Acoela's digestive system like?

They lack a gut altogether.

What type of gut do polyclad flatworms have?

A highly branched digestive tract.

What does it mean that some flatworms lack a gut?

Some groups have no digestive tract and may represent a distinct evolutionary lineage.

What are rhabdites?

Rod-like structures found in some flatworms, associated with mucus production/protection.

Which molluscs have a closed circulatory system?

Cephalopods; the exam material also identifies Polyplacophora/chitons in its closed-circulation questions.

Do all molluscs have a radula?

No; bivalves lack a radula.

Do all molluscs have a shell?

No.

What is torsion?

A developmental process characteristic of gastropods in which the body rotates approximately 180°.

Which molluscan class undergoes torsion?

Gastropoda.

What larval form undergoes torsion in gastropods?

The torsion occurs during gastropod development; the veliger is the later larval stage associated with this development.

What larval form is characteristic of chitons?

Trochophore.

What is a radula?

A rasping feeding structure found in many molluscs.

How do some chitons use magnetite?

Magnetite strengthens their radula teeth, allowing some species to drill into hard prey.

What is the hemocoel of a mollusc?

A blood-filled space associated with its reduced coelom.

What shell traits can protect gastropods from shell-crushing predators?

Short spires, narrow apertures, larger size, and spines.

How does natural selection act on defensive shell traits?

Predation favors shell characteristics that make gastropods harder to crush or extract.

What is coevolution in the context of gastropod shells?

Predator adaptations can create selection for defensive shell traits, which can in turn create selection for improved predator abilities.

What is a genet?

The genetic individual produced from a single zygote.

What is a ramet?

A physically distinct unit produced asexually by a genet that can function as an individual.

What does natural selection primarily act upon: genets or ramets?

Genets.

What is the advantage of producing many ramets?

Asexual production allows a successful genotype to spread rapidly and occupy more space/resources.

What does it mean for an organism to be colonial?

It consists of multiple connected or associated individuals/units derived from reproduction.

What does polymorphic mean?

Having different specialized forms within a species or colony.

What cnidarian groups contain colonial and polymorphic species?

Especially Hydrozoa; examples include siphonophores and Hydractinia.

What is asexual reproduction advantageous for?

Rapid population increase and producing genetically identical offspring when environmental conditions are favorable.

What is a disadvantage of asexual reproduction?

It produces little genetic variation, potentially making populations less adaptable to environmental change.