BIOL 1202 Chapter : Chapter 33 Learning Objectives
Learning Objectives
Chapter 33
Concept 33.1: Sponges are basal animals that lack true tissues
• From a diagram, identify the parts of a sponge (including the spongocoel, porocyte, epidermis,
choanocyte, mesohyl, amoebocyte, osculum, and spicules) and describe the function of each.
• Spongocoel- the central cavity of a sponge; water is drawn through the pores into the
spongocoel and then flows out of the sponge through a larger opening called the osculum
• Osculum- a large opening in a sponge that connects the spongocoel to the environment
• Pores- water enters the sponge through pores formed by doughnut shaped cells that span the
body wall
• Epidermis- the outer layer consists of tightly packed epidermal cells
• Choanocyte- a flagellated feeding cell found in sponges. Also called a collar cell, it has a collar-
like ring that traps food particles around the base of its flagellum; these cells engulf bacteria and
other food particles by phagocytosis; the movement of a choanocyte’s flagellum also draws
water through its collar of finger-like projections. Food particles are trapped in the mucus that
coats the projections, engulfed by phagocytosis, and either digested or transferred to
amoebocytes
• Mesohyl- a gelatinous region between the two layers of cells of a sponge- because both cell
layers are in contact with water, processes such as gas exchange and waste removal can occur
by diffusion across the membranes of these cells; also called “middle matter”
• Amoebocyte- an amoeba-like cell that moves by pseudopodia and is found in most animals.
Depending on the species, it may digest and distribute food, dispose of wastes, form skeletal
fibers, fight infections, or change into other cell types; these cells can transport nutrients to
other cells of the sponge body, produce materials for skeletal fibers (spicules), or become any
type of sponge cell as needed; named for their use of pseudopodia. These cells move through
the mesohyl and have many functions. For example, they take up food from the surrounding
water and from choanocytes, digest it, and carry nutrients to other cells. Amoebocytes also
manufacture tough skeletal fibers within the mesohyl. In some sponges, these fibers are sharp
spicules made from calcium carbonate or silica.
Concept 33.2: Cnidarians are an ancient phylum of eumetazoans
• List the characteristics of the phylum Cnidaria that distinguish it from the other animal phyla.
o Diploblastic, radial body plan- a sac with a central digestive compartment, the
gastrovascular cavity. A single opening to this cavity functions as both a mouth and
anus. Cnidarians are carnivores that use tentacles arranged in a ring around their mouth
to capture prey and push the food into their gastrovascular cavity, where digestion
begins. Enzymes are secreted into the cavity, thius breaking down the prey into a
nutrient-rich broth. Cells lining the vacity then absorb these nutrients and complete the
digestive process; any undigested remains are expelled through the mouth/anus.
Movements are coordinated by a nerve net, cnidarians have no brain
• Describe the specialized cells that are found in Cnidarians.
o The tentacles are armed with batteries of cnidocytes, cells unique to cnidarians that
function in defense and prey capture. Cnidocytes contain cnidae, capsule- like
organelles that are capable of exploiding outward and that give phylm Cnidaria its
name. Specialized cnidae called nematocysts contain a stinging thread that can
penetrate the body wall of the cnidarian’s prey. Other kinds of cnidae have long threads
that stick to or entangle small prey that bump into the cnidarian’s tentacles.
• Describe the two basic body plans in Cnidaria and their role in Cnidarian life cycles.
o There are two variations on this body plan: the sessile polyp and the motile medusa.
Polyps are cylindrical forms that adhere to the substrate by the aboral end of their body
(the end opposite the mouth) and extend their tentacles, waiting for prey. Examples of
the poly form include hydras and sea anemones. A medusa resembles a flattened, outh-
down version of the polyp. It moves freely in the water by a combination of passive
drifting and contractions of its bell-shaped body. The tentacles of a jelly dangle from the
oral surface, which points downward. Some cnidarians exist only as polyps or only as
medusa; others have both a polyp stage and a medusa stage in their life cycle.
• List the four classes of Cnidaria.
o Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa
Concept 33.3: Lophotrochozoans, a clade identified by molecular data, have the widest range of animal
body forms
• Distinguish between:
o Diploblastic and triploblastic development
▪ Tribloblastic development: flatworms
o Acoelomates, pseudocoelomates, and coelomates
▪ Acoelomates (animals that lack a body cavity): flatworms
▪ Pseudocoelomates: rotifer
o Gastrovascular cavity and alimentary canal
▪ Gastrovascular cavity: most flatworms
▪ Alimentary canal (digestive tube with two openings- a mouth and an anus):
rotifers
o Protostome and deuterostome
• List the characteristics of the phylum Platyhelminthes and give examples of each.
Document Summary
These cells move through the mesohyl and have many functions. For example, they take up food from the surrounding water and from choanocytes, digest it, and carry nutrients to other cells. Amoebocytes also manufacture tough skeletal fibers within the mesohyl. In some sponges, these fibers are sharp spicules made from calcium carbonate or silica. Concept 33. 2: cnidarians are an ancient phylum of eumetazoans. List the characteristics of the phylum cnidaria that distinguish it from the other animal phyla: diploblastic, radial body plan- a sac with a central digestive compartment, the gastrovascular cavity. A single opening to this cavity functions as both a mouth and anus. Cnidarians are carnivores that use tentacles arranged in a ring around their mouth to capture prey and push the food into their gastrovascular cavity, where digestion begins. Enzymes are secreted into the cavity, thius breaking down the prey into a nutrient-rich broth.
