Exam 3 Porifera, Platyhelminthes, Cnidaria, Mollusca

What is the level of complexity of poriferans?

Poriferans fall between cellular and cell-tissue levels of organization and do not have true tissues.

What type of symmetry do poriferans display?

Asymmetry and radial symmetry.

What are choanocytes?

Flagellated collar cells that trap food particles suspended in water.

What role do pinacocytes play in sponges?

They line the external surface and some internal spaces, forming the pinacoderm, a sort of proto-tissue.

What are porocytes?

Cells that form passageways in asconoid sponges.

What are archaeocytes?

Amoeboid cells found within the mesohyl of sponges.

What do sclerocytes do?

They form spicules.

What is the function of collencytes?

They form collagen fibers.

What do spongocytes produce?

They form spongyn fibers.

How do sponges feed?

They are filter feeders; choanocytes trap food particles, which are engulfed and digested intracellularly.

How do sponges reproduce?

They reproduce both asexually (budding and fragmentation) and sexually (hermaphroditism with internal fertilization).

What is a gemmule?

A dormant structure produced by freshwater sponges, containing numerous archaeocytes, adapted to survive harsh conditions.

What characterizes the asconoid body form?

It is the simplest body form with choanocytes lining the spongocoel and a single osculum.

Describe the water flow in syconoid sponges.

Water flows through ostia to incurrent canals, then to prosopyles, radial canals, apopyle, spongocoel, and out through a single osculum.

What is the leuconoid body form?

The most complex body form characterized by multiple oscula fed by excurrent canals, with choanocytes lining flagellated chambers.

What are the four taxonomic classes of sponges?

Class Calcarea, Class Demospongiae, Class Hexactinellida, Class Homoscleromorpha.

What defines Class Calcarea?

Calcareous spicules with 1-4 rays; can be asconoid, syconoid, or leuconoid.

What is unique about Class Demospongiae?

It is the most speciose class, comprising about 80% of known sponges, characterized by siliceous spicules, spongin, or both, and all are leuconoid.

What are the characteristics of Class Hexactinellida?

Glass sponges with siliceous spicules having six rays, found in deep sea habitats, exhibiting radial symmetry.

What is notable about Class Homoscleromorpha?

It includes flat, encrusting sponges that adhere closely to substrates, with an absent or simple skeleton.

What is the evolutionary significance of sponges?

Sponges represent an early branch in the evolution of multicellular organisms, showcasing simple body plans and cellular organization.

What is the significance of choanoflagellates in the evolution of multicellularity?

Choanoflagellates are single-cell protists that resemble choanocytes in sponges and provide insight into the origins of multicellularity.

What is a syncytium?

A large cell containing multiple nuclei within a common cytoplasm that behaves as a single coordinated unit.

What are the two phyla often grouped together with radial symmetry?

Phyla Cnidaria and Ctenophora.

What is the body plan of cnidarians?

Cnidarians have a gelatinous sack with an incomplete digestive tract that has only one opening for materials to enter and exit the gastrovascular cavity.

What type of symmetry do cnidarians display?

Cnidarians display radial symmetry.

What are the tissue layers present in cnidarians?

Cnidarians are diploblastic, having only two germ layers: endoderm and ectoderm.

What are the cellular components of a cnidarian?

The epidermis (derived from ectoderm), gastrodermis (derived from endoderm), and mesoglea (a gelatinous layer between the two tissue layers).

How do cnidarians capture and digest their prey?

They are carnivorous, using tentacles with stinging cells (cnidocytes) to capture prey. Digestion begins extracellularly in the gastrovascular cavity and is completed intracellularly by cells lining the cavity.

How do cnidarians reproduce?

They reproduce both sexually and asexually. Sexual reproduction occurs via the medusa or polyp stage by releasing eggs or sperm into the water, while asexual reproduction occurs through budding or fission.

Where are cnidarians typically found?

Cnidarians are mostly marine but can also be found in freshwater, in shallow and deep waters, as well as in warm and cold environments.

What is a nematocyst?

A nematocyst is a harpoon-like structure within cnidocytes that injects venom, entangles prey, or produces an adhesive.

What triggers the discharge of a nematocyst?

A modified cilium called the cnidocil triggers the opening of the operculum and the discharge of the nematocyst.

Compare the polyp and medusa body forms of cnidarians.

Medusa is free-floating and bowl-shaped with the mouth on the inferior surface, while polyp is sessile and vase-shaped with the mouth on the superior surface.

What is the role of the gastrovascular cavity in cnidarians?

The gastrovascular cavity serves as the site for digestion and distribution of nutrients.

What is the developmental stage of fertilized eggs in cnidarians?

Fertilized eggs develop into planula larvae.

What are the five taxonomic classes of cnidarians?

The five taxonomic classes of cnidarians include Hydrozoa, Scyphozoa, Cubozoa, Anthozoa, and Staurozoa.

What is the ecological role of cnidarians in marine environments?

Many cnidarians form colonies, such as corals, which contribute to reef structures and marine biodiversity.

What is the significance of the incomplete digestive tract in cnidarians?

The incomplete digestive tract allows for the capture and digestion of prey larger than a single cell.

How do cnidarians adapt to different aquatic environments?

Cnidarians can thrive in various aquatic environments, including shallow and deep waters, and can adapt to both warm and cold temperatures.

What is the function of the mesoglea in cnidarians?

The mesoglea provides structural support and buoyancy between the epidermis and gastrodermis.

What is the largest class of cnidarians that includes sea anemones and corals?

Class Anthozoa.

What is the dominant body form of Class Anthozoa?

The polyp form is dominant; no medusa form is present.

What type of association do many Anthozoans form with algae?

They form mutualistic associations with algae known as zooxanthellae.

What are the two subclasses of Class Anthozoa?

Subclass Zoantharia and Subclass Octocorallia.

What is the body plan of Zoantharians?

Hexamerous body plan with tentacles and septa in multiples of six.

What type of skeleton do stony corals have?

An exoskeleton composed of calcium carbonate.

What is the body plan of Octocorallians?

Octamerous body plan with 8 pinnate tentacles and 8 septa.

What is the composition of the endoskeleton in Octocorallians?

It is composed of protein fibers and calcium carbonate spicules.

What class of cnidarians is known for having a hybrid polyp-medusa form?

Class Staurozoan.

What is the dominant form in Class Scyphozoa?

The medusa form is dominant.

What is a unique feature of Class Cubozoan jellyfish?

They have a square cross-section with a tentacle at each corner.

What ecological roles do cnidarians play?

They serve as a food source for some organisms, are important predators, form mutualistic associations, and support diverse marine communities.

What is coral bleaching?

It occurs when reef-building corals expel their zooxanthellae mutualists.

What has increased the rate of coral bleaching?

Global warming.

How does increased atmospheric CO2 affect corals?

It changes the pH and impacts the precipitation of calcium carbonate for coral skeletons.

What is the basic body form of cnidarians considered to be?

The sessile, attached polyp form is considered the most ancient form.

What is the role of jellyfish blooms in marine ecosystems?

Blooms can shut down fisheries and beaches.

What is the sense organ of balance found in Class Scyphozoa?

Rhopalium.

What are the two main forms of cnidarians?

Polyp and medusa forms.

What is a characteristic feature of medusae in Class Hydrozoa?

They are characterized by the presence of a velum.

What is the ecological and economic importance of coral reefs?

They support diverse marine communities.

What is the approximate number of species in the phylum Ctenophora?

Approximately 150 species.

How do ctenophores move?

They move using longitudinal rows of cilia that beat in coordinated waves.

What are the transverse comb plates in ctenophores called?

Ctenes.

What type of symmetry do ctenophores exhibit?

Biradial symmetry.

What type of digestive tract do ctenophores have?

Complete digestive tract.

What specialized cells do ctenophores lack?

Cnidocytes/nematocysts.

What is a key characteristic of flatworms in the phylum Platyhelminthes?

They have a flattened body.

What type of digestive tract do flatworms possess?

Incomplete digestive tract with one opening.

What does it mean that flatworms are acoelomates?

They lack any internal cavity other than the digestive tract.

What is the function of the branched gastrovascular cavity in flatworms?

It fulfills some functions of a circulatory system.

What excretory structure do flatworms have?

Protonephridia with flame cells.

How do flatworms reproduce?

Both sexually and asexually; most are hermaphroditic.

Where do many free-living flatworms live?

Mostly in freshwater, some in damp soil or under rocks.

What are the major classes of flatworms?

Class Trematoda, Class Monogenea, Class Cestoda, Class Turbellaria.

What is a defining characteristic of Class Trematoda?

They are parasitic flukes with complex life cycles.

What is the first intermediate host for Class Trematoda?

Gastropod mollusk.

What is the attachment organ in Class Monogenea called?

Opisthaptor.

What is a unique feature of Class Cestoda?

They have a loss of the digestive tract and special sense organs.

What are proglottids in Class Cestoda?

Body segments specialized for absorption of food and reproduction.

What is the Clade Neodermata?

It includes Trematoda, Monogenea, and Cestoda, named for the presence of non-ciliated syncytial tegument.

What type of locomotion do free-living flatworms (Class Turbellaria) use?

Locomotion through ciliated epidermis.

What are rhabdites in flatworms?

Specialized structures that swell to produce a mucous sheath.

What are Trematoda, and what are their key characteristics?

Trematoda, or flukes, are endoparasites with unsegmented bodies and a complex life cycle.

What are Cestoda, and what distinguishes them from Trematoda?

Cestoda, or tapeworms, are endoparasites with segmented bodies and require both an intermediate host and a definitive host.

What are Monogenea, and how do they differ from Trematoda and Cestoda?

Monogenea are ectoparasites with unsegmented bodies and a direct life cycle involving a single host.

What is the difference between ectoparasites and endoparasites?

Ectoparasites live on the external surface of the host (e.g., lice, fleas, ticks), while endoparasites live inside the host's systems (e.g., tapeworms, flukes).

How do parasitic flatworms compare to free-living flatworms?

Free-living flatworms are independent predators or scavengers with regenerative abilities, while parasitic flatworms need a host to survive and have simpler body structures.

What are the key features of rotifers?

Rotifers have over 2000 species, mostly freshwater, with a ciliated corona for feeding, a mastax for chewing, and a telescoping foot.

What is the reproductive strategy of some rotifer species?

Some rotifer species are dioecious, while others can reproduce parthenogenetically or are haplodiploid.

What is the Clade Lophotrochozoa, and what are its defining characteristics?

Lophotrochozoa is a monophyletic group of invertebrates characterized by the presence of a lophophore and trochophore larva.

What is a lophophore, and what is its function?

A lophophore is a specialized feeding structure with a crown of ciliated tentacles surrounding the mouth, used for filter-feeding in aquatic environments.

What is a trochophore larva?

A trochophore larva is a free-swimming larval stage with a distinctive ring of cilia around the body that aids in movement and feeding.

What are the main components of a mollusc's body plan?

Molluscs have a head-foot for locomotion and attachment, a central visceral mass containing organs, and a mantle that forms a cavity for gills or lungs.

What type of circulatory system do most molluscs have?

Most molluscs have an open circulatory system, while cephalopods have a closed circulatory system.

How do molluscs respire?

Molluscs respire through gills or lungs located in the mantle cavity, and the mantle can also function as a respiratory structure.

What is the structure of the nervous system in molluscs?

Molluscs have a nervous system consisting of paired ganglia and ventral nerve cords, with development varying widely depending on their mode of life.

What types of diets do molluscs have?

Molluscs can be filter feeders (plankton), predators (fish, crustaceans), or herbivores (algae, plants, organic matter).

How do molluscs reproduce?

Molluscs mostly reproduce sexually, with some hermaphrodites, and can also reproduce asexually through parthenogenesis.