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Chapter 27 Review
1 Briefly describe the three classes of sponges, and provide examples of each.
Class Calcarea consists of small marine sponges with spicules composed of calcium carbonate. The
spicules vary from monaxonal (needle-shaped) to triaxonal (three rays), tetraxonal (four rays) and sixrayed. Most sponges in this phylum are vase-shaped and drab in color, although a few bright yellow,
lavender, red, and green species exist. Asconoid, syconoid, and leuconoid body forms are found in class
Calcarea. Sycpha (Grantia) is a vase-shaped syconoid sponge that can live in colonies.
Class Demospongiae is the largest class of sponges, usually brilliantly colored with monaxonal or
tetraxonal siliceous spicules, sometimes bound together by spongin. Members of this class have
leuconoid canal systems.
An example is the bath sponge (Spongilla spp.).
Class Hexactinellida is referred to as the “glass sponge” because of the six-rayed siliceous spicules fused
into an intricate glass-like lattice. Members of this class of sponges are primarily deep-water marine
forms. The body of these sponges is usually cylindrical or funnel-shaped. The flagellated chambers can
be simple syconoid or leuconoid.
The Venus flower basket (Euplectella sp.) is a member of this class.
2 Compare and contrast asconoid, syconoid, and leuconoid sponges.
Sponges that have an asconoid canal system are generally small and tube-shaped. Water enters these
sponges via tiny ostia in the dermis and makes its way to a large cavity called a spongocoel, lined with
choanocytes. The water is filtered and exits via a large opening called an osculum. Asconoid sponges are
placed in class Calcarea. Syconoid sponges resemble large versions of asconoid sponges. These
sponges possess a tubular body with a single prominent osculum. Syconoid sponges, however, have a
more complex canal system than asconoid sponges.
The choanocytes are found in numerous radial canals that empty into the spongocoel, lined with epithelialike cells in syconoid sponges. The water, with its nutrients, enters the sponge through a large number of
ostia into an incurrent canal. The water then passes through prosopyles into the radial canals, where the
food is ingested by the choanocytes. The flagella of the choanocytes force the water through apopyles
into the spongocoel. Finally, filtered water exits the osculum. Syconoid bodies are found in classes
Calcarea and Hexactinellida.
Leuconoid sponges, the most common and complex of the types of sponge, generally form large masses,
each member having its own osculum. Clusters of flagellated chambers receive water from incurrent
canals, and discharged water exits via the excurrent canals and eventually to the osculum.
3 Describe the skeletal elements of sponges.
The skeletal structure of sponges consists of fibrous collagen and calcareous or siliceous crystalline
spicules. These structures can vary from monoaxonal to hexaxonal. Spicules are associated with spongin
in many species.
4 What are five characteristics of cnidarians?
The cnidarians get their name from cells called cnidoblasts (cnidocytes), which contain the stinging cells,
nematocysts, found in members of this phylum. Cnidarians exhibit radial symmetry and are diploblastic.
The cnidarians exhibit two obviously different body forms, termed dimorphism. The medusa form
resembles a swimming upside-down cup with tentacles, and the polyp form consists of a tubular sessile
body. Cnidarians possess a nerve net composed of neurites and sensory organs. Digestion is
extracellular, and they have no coelom. They do not have a respiratory system; gas exchange occurs
through diffusion.
Chapter 27 | Animal Planet: Understanding Creatures from the Sea 8
5 Draw the life cycle of the jellyfish Aurelia.
Sketches will vary.
6 What are the classes of phylum Cnidaria?
In class Hydrozoa, the polyp form is dominant. Representative hydrozoans include Hydra spp., Obelia
spp., and the Portuguese man-of-war, Physalia spp. Most hydrozoans are marine, but a few are
freshwater species. Hydrozoans consist of an asexual polyp and a sexual medusa stage.
Class Scyphozoa (true jellyfish) are solitary organisms in which a polyp stage is reduced or absent, and it
has a dominant bell-shaped medusa stage. The edge of the bell, the umbrella, has eight notches
provided with sense organs. Examples of true jellyfish are Aurelia spp., Chrysaora spp., and Cassiopeia
spp. Class Cubozoa once was considered an order of class Scyphozoa. The medusoid form is prominent,
and the polyp is inconspicuous. The bell is cubical and bent inward. The tentacles are suspended from
four flat pedalia at the corners of the umbrella. These organisms commonly are called box jellyfish, such
as Tripedalia cystophora. Class Anthozoa (flower animals) exists as polyps only. Anthozoans can be
colonial or solitary marine organisms. The pharynx leads into a gastrovascular cavity divided by eight or
more septa. Examples of anthozoans are sea anemones, sea fans, sea pens, sea pansies, and the
7 Describe reproduction in Hydra.
Upon close examination, testes or ovaries, when present, appear as rounded structures on the body.
Hydra can reproduce asexually by budding.
8 Cite the dangers of several cnidarians.
Many beautiful cnidarians, such as fire coral sea anemones, jellyfish, and the Portuguese man-of-war,
can deliver
a painful sting. The box jellyfish can be lethal.
9 Label the Obelia sp. colony.
1. Tentacles
2. Perisarc
3. Coenosarc
4. Medusa buds
5. Hydranth
6. Gonangium
7. Gonotheca
8. Blastostyle
9. Hypostome
10 Discuss the biology of coral.
Most coral species are colonial and made up of many individual polyps connected by living tissue called
the coenosarc. Each coral polyp has a cuplike shape with a ring of tentacles around a central opening
that functions as both mouth and anus. The tentacles are tipped with stinging cells called nematocysts.
There is no skeleton in the polyp. The polyps sit on top of an external skeleton made from the polyp’s
11 What are three characteristics of a ctenophore?
Ctenophores have adhesive cells called colloblasts to capture food and do not possess nematocysts. The
tentacles of ctenophores are solid, consisting of epidermis only. Ctenophores swim by means of rows of
fused cilia known as comb plates. Most ctenophores are monoecious, reproducing only by sexual means.
Many ctenophores are bioluminescent.
12 Sketch and label a longitudinal section of a sea anemone.
Sketches will vary. Make sure students include tentacles, oral disk,
mouth, pharynx, coelenterons, gonads, acontia, and pedal disk.
13 Why can clownfish live in harmony with a sea anenome?
Clownfish secrete a special type of slimy mucus that the sea anemone does not recognize thus not
stinging the clownfish. If the mucus is wiped off of a clownfish, it will get stung and possibly be killed when
it returns home to the anemone.