chapter 33 study guide part 1

1. What are sponges and what phylum do they belong to?

Sponges are in phylum Porifera and are considered basal animals because they lack true tisses.

1a. What are the body plan characteristics of sponges

- asymmetrical

- lack true tissues

- lack a body cavity (acoelomate)

- body is full of pores (ostia) that allow water flow

- stationary (sessile)

sponge characteristics

• Body plan: asymmetrical, no tissues, acoelomate, pores (ostia/osculum), sessile

• Digestion: intracellular only (choanocytes + amoebocytes)

• Reproduction: hermaphroditic; sexual + asexual (budding/fragmentation)

• Excretory/Circulatory: none (diffusion)

2a. What is intracellular digestion and what animals use it?

- Intracellular digestion occurs inside cells. Food particles are engulfed by cells via phagocytosis and digested in food vacuoles using lysosomal enzymes.

- Occurs in: sponges (primary method)

2b. Describe how sponges feed.

Sponges are filter feeders:

- Water enters through ostia (pores)

- Moves through canals into central cavity

- Exits through osculum

2b. What are the roles of choanocyte cells and amoebocyte cells in sponges?

Choanocytes create water currents and trap food particles, while amoebocytes digest the food and distribute nutrients throughout the sponge.

2c. What is extracellular digestion and what animals use it?

Extracellular digestion occurs outside cells, within a digestive cavity or tract where enzymes break down food.

- Found in: cnidarians, flatworms, molluscs, annelids, and most animals

- More efficient and allows larger body size

3. What are cnidarians and what phylum do they belong to?

Cnidarians belong to Phylum Cnidaria (eumetazoans). They include hydra, jellyfish, corals, and sea anemones.

cnidarian characteristics

• Body plan: radial symmetry, diploblastic, acoelomate, polyp & medusa forms

• Digestion: gastrovascular cavity (1 opening); extracellular + intracellular

• Structures: tentacles with cnidocytes (nematocysts)

• Reproduction: asexual (budding) + sexual (often medusa stage)

• Excretory/Circulatory: none (diffusion + gastrovascular distribution)

3a. Describe the polyp and medusa forms of cnidarians

The polyp form is sessile (attached), cylindrical in shape, with tentacles and the mouth facing upward, while the medusa form is free-swimming, bell-shaped, with tentacles and mouth facing downward.

Polyp:

- Asexual reproduction common

- Example: Hydra, coral

Medusa:

- Sexual reproduction stage

- Example: jellyfish

3a. Describe the body plan characteristics of cnidarians

- radially symmetrical

- diploblastic

- without a coelom (acoelomate)

- single opening (mouth = anus)

- central digestive cavity: gastrovascular cavity

4. What is a gastrovascular cavity?

A gastrovascular cavity is a central digestive chamber with a single opening that functions in digestion, distribution of nutrients, and gas exchange.

4a. Describe how the hydra uses a gastrovascular cavity to feed.

1. Tentacles capture prey

2. Prey enters mouth

3. Enzymes digest food in cavity

4. Nutrients distributed through branched cavity

4b. What are the function of radial canals in jellies?

Radial canals distribute nutrients from central stomach throughout body and connect to circular canal for circulation of materials.

5. Describe the structure and function of the stinging cells for which cnidarians are named.

Cnidocytes: specialized stinging cells used for defense and prey capture

Nematocysts: organelles inside cnidocytes that explosively fire a barbed thread with toxins

Function:

- Immobilize prey

- Defense against predators

6. Describe the general characteristics of hydrozoans.

Hydrozoans are cnidarians that often alternate between polyp and medusa forms, with the polyp stage typically being dominant, and they commonly reproduce asexually by budding and sexually through medusae.

6. Describe the general characteristics of scyphozoans.

Scyphozoans are cnidarians in which the medusa form is dominant, meaning they are mostly free-swimming jellyfish, and they typically have a reduced or brief polyp stage.

6. Describe the general characteristics of anthozoans.

Anthozoans are cnidarians that exist only in the polyp form and include corals and sea anemones, many of which live in the ocean and form hard skeletons or symbiotic relationships with algae.

7. What are flatworms and what phylum do they belong to?

Flatworms belong to Phylum Platyhelminthes within Lophotrochozoa (Bilateria). They include free-living forms like planarians and parasitic forms like flukes and tapeworms.

flatworm charcteristics

• Body plan: bilateral, triploblastic, acoelomate, flattened

• Digestion: gastrovascular cavity (1 opening)

• Gas exchange: diffusion across body surface

• Reproduction: hermaphroditic; sexual + asexual (fission/regeneration)

7a. Describe the body plan characteristics of flatworms

- bilaterally symmetrical

- triploblastic

- without a coelom (acoelomates).

7b. Why are flatworms flat?

Flatworms are flat to increase their surface area, allowing for efficient gas exchange and nutrient distribution by diffusion since they lack a circulatory system.

7b. Describe the digestive system of flatworms.

- Have a gastrovascular cavity

- Only one opening (mouth = anus)

- Highly branched cavity distributes nutrients

- Digestion is extracellular first, then intracellular

7b. Describe the excretory system of flatworms.

- Use protonephridia (flame cells)

- Ciliated cells that push fluid through tubules

- Remove excess water and metabolic waste

- Maintain osmotic balance

7b. Where does gas exchange take place in flatworms?

Gas exchange takes place across the surface, and protonephridia or flame cells, regulate the osmotic balance

7c. What ways can a planarian reproduce?

Sexual reproduction:

- Hermaphrodites (both male and female reproductive organs)

- Cross-fertilization is common

Asexual reproduction:

- Fission (splitting into two)

8. What are rotifers and what phylum do they belong to?

Rotifers belong to Phylum Rotifera. They are microscopic but complex animals found in freshwater, marine, and moist soil environments.

rotifer characteristics

• Body plan: bilateral, triploblastic, pseudocoelom, microscopic, ciliated corona

• Digestion: complete digestive tract (alimentary canal)

• Structures: trophi (jaws)

• Reproduction: parthenogenesis (mostly female), some sexual

• Excretory/Circulatory: no circulatory system; pseudocoelom distributes materials

8a. Why are most rotifers female?

- Most reproduce through parthenogenesis

- Females produce eggs without fertilization

- Males are rare or seasonal in many species

- Allows rapid population growth in stable environments

8a. How do rotifers move and feed?

Movement

- Move using a corona (crown of cilia)

- Cilia beat to:

Pull them through water

Direct food toward mouth

Feeding

- Suspension feeders

- Use cilia to draw in particles

- Food is ground by trophi (jaw-like structures) in the pharynx

8b. Describe the body plan characteristics of rotifers

- bilaterally symmetrical

- triploblastic animals

- complete digestive tract

- pseudocoelom

8c. What is the evolutionary advantage of a complete digestive tract (alimentary canal)?

A complete digestive tract allows food to move in one direction from mouth to anus, making digestion more efficient because different regions can specialize in digestion and absorption.

8c. What are some invertebrate animals that have an alimentary canal?

Rotifers

Molluscs

Annelids

Arthropods

Vertebrates

9. What are molluscs and what phylum do they belong to?

Molluscs belong to Phylum Mollusca. They are soft-bodied animals, many with external or internal shells, and include snails, clams, squids, and octopuses.

phylum mollusca classes

˃ Gastropoda (snails and slugs)

˃ Bivalvia (clams, oysters, and other bivalves)

˃ Cephalopoda (squids, octopuses, cuttlefish,

and chambered nautiluses)

9a. Describe the general body characteristics of molluscs.

- bilaterally symmetrical

- triploblastic animals

- complete digestive tract

- true coelom (eucoelomates).

molluscs characteristics

• Body plan: bilateral, triploblastic, coelomate; foot, visceral mass, mantle

• Digestion: complete digestive tract; radula (except bivalves)

• Reproduction: mostly dioecious; trochophore larva; glochidium (mussels)

• Circulatory: open (most), closed (cephalopods)

• Excretory: nephridia-like organs

9b. Describe the general body plan that all molluscs share.

All molluscs share three main structures:

- Muscular foot: movement or attachment

- Visceral mass: internal organs (digestive, reproductive, excretory)

- Mantle: tissue that secretes shell (if present)

9c. What is the difference between an open and a closed circulatory system?

In an open circulatory system, the circulatory fluid (hemolymph) flows freely through body spaces, while in a closed circulatory system, blood is contained within vessels and remains separate from the interstitial fluid.

9c. Which animal groups have an open circulatory system?

Most molluscs

Arthropods

9c. Which animal groups have a closed circulatory system?

Annelids

Cephalopods

Vertebrates

9c. Which group of molluscs have a closed circulatory system?

Cephalopods

9d. What is a trochophore?

Trochophore larva:

- Free-swimming larva

- Dispersed by ocean currents

9d. What is a glochidium?

Glochidium (freshwater mussels only):

- Parasitic larva

- Attaches to fish gills

- Develops while using host nutrients

- Helps spread upstream populations

9d. Explain how freshwater mussels distribute their offspring upstream.

Freshwater mussels release larvae called glochidia that attach to fish gills or fins; the fish then carry them upstream, and the larvae later detach and develop into adult mussels in new locations.

9e. Describe the general characteristics, feeding, and or reproductive methods of class gastropoda.

1. Gastropoda (snails, slugs)

- Move using muscular foot (gliding motion)

- Undergo torsion during development

- Shell present in snails, absent in slugs

- Use radula (rasp-like feeding structure)

- Mostly herbivores, some predators

9e. Describe the general characteristics, feeding, and or reproductive methods of class bivalvia.

2. Bivalvia (clams, oysters, mussels)

- Two-part shell (valves)

- No head or radula

- Suspension feeders

- Feed by filtering water through gills

- Use incurrent and excurrent siphons

- Mostly sedentary

9e. Describe the general characteristics, feeding, and or reproductive methods of class cephalopoda.

3. Cephalopoda (squid, octopus, nautilus)

- Highly intelligent predators

- Foot modified into tentacles and siphon

- Closed circulatory system

- Jet propulsion movement

- Complex nervous system

9e. Which of the cephalopods has retained their external shell?

Nautilus

9e. Which cephalopod has a reduced internal shell?

Squid

10. What are annelids and what phylum do they belong to?

Annelids belong to Phylum Annelida and are segmented worms, polychaetes, oligochaetes (i.e. earthworms), and leeches.

annelid characteristics

• Body plan: bilateral, triploblastic, coelomate, segmented (“tube within a tube”)

• Digestion: complete digestive tract

• Reproduction: mostly hermaphroditic; cross-fertilization; some asexual

• Circulatory: closed

• Excretory: metanephridia

10a. Describe the body plan charcteristics of annelids.

- bilaterally symmetrical

- triploblastic animals

- true coelom (eucoelomates)

- segmented body (metamerism)

10b. Do annelids have a closed or open circulatory system. Explain.

Closed circulatory system

- Blood confined to vessels

- Includes dorsal and ventral vessels

- Pumped by aortic arches ("hearts")

10c. Briefly describe the digestive and excretory system of annelids.

Digestive system

- Complete digestive tract

- Specialized regions (mouth → pharynx → intestine → anus)

- Efficient nutrient absorption

Metanephridia

- Found in each segment

- Collect coelomic fluid

- Reabsorb nutrients

- Excrete waste via pores

10c. How does the digestive and excretory systems of annelids compare to flatworms?

Comparison to flatworms

- Flatworms → flame cells (simpler, less efficient)

- Annelids → metanephridia (more advanced, selective reabsorption)

10c. Annelid anatomy can be described as having "a tube within a tube" body plan. Explain.

Annelids have a “tube within a tube” body plan because the digestive tract is a tube inside the body wall, and it is surrounded by a fluid-filled coelom that separates it from the outer body and allows movement and organ support.

10d. Describe the morphological differences and similarities between polychaetes and earthworms.

Polychaetes

- Mostly marine

- Have parapodia

- Used for movement and gas exchange

- Many bristles (chaetae)

Earthworms (Oligochaetes)

- No parapodia

- Move using two muscle layers:

Circular muscles → elongate body

Longitudinal muscles → shorten body

- Hydrostatic skeleton helps movement

- Hermaphroditic but cross-fertilize

- Important for soil nutrient cycling

10d. What structures do polychaetes use for movement?

Polychaetes have a pair of paddle-like or ridge-like structures called parapodia ("beside feet") on each body segment

10d. Describe how the earthworm uses two sets of muscles to move.

- The longitudinal muscles make up the inner layer of muscle. When they contract, the worm gets shorter.

- The circular muscles surround the longitudinal muscle. When they contract, the worm gets thinner.