Describe how sponges feed.
The flagella of choanocytes draw water through their collars, which trap food particles. The particles are engulfed by phagocytosis and digested, either by choanocytes or by amoebocytes.
Some molecular evidence suggests that the sister group of animals is not the choanoflagellates, but rather a group of parasitic protists, Mesomycetozoa. Given that these parasites lack collar cells, can this hypothesis be correct? Explain.
The collar cells of sponges bear a striking resemblance to a choanoflagellate cell. This suggests that the last common ancestor of animals and their protist sister group may have resembled a choanoflagellate. Nevertheless, mesomycetozoans could still be t
Compare and contrast the polyp and medusa forms of cnidarians.
Both the polyp and the medusa are composed of an outer epidermis and an inner gastrodermis separated by a gelatinous layer, the mesoglea. The polyp is a cylindrical form that adheres to the substrate by its aboral end; the medusa is a flattened, mouth-dow
Cnidarians today retain the same diploblastic, radial body plan found in cnidarians 560 million years ago. Are cnidarians less successful or less "highly evolved" than other animal groups? Explain.
Evolution is not goal oriented; hence, it would not be correct to argue that cnidarians were not "highly evolved" simply because their form has changed relatively little over the past 560 million years. Instead, the fact that cnidarians have persisted for
Explain how tapeworms can survive without a coelom, a mouth, a digestive system, or an excretory system.
Tapeworms absorb food from their environment and release ammonia into their environment through their body surface because their body is very flat, due in part to the lack of a coelom.
Annelid anatomy can be described as "a tube within a tube." Explain.
The inner tube is the alimentary canal, which runs the length of the body. The outer tube is the body wall. The two tubes are separated by the coelom.
Explain how the molluscan foot in gastropods and the excurrent siphon in cephalopods represent examples of descent with modification.
All molluscs have inherited a foot from their common ancestor. However, in different groups of molluscs, the structure of the foot has been modified over time by natural selection. In gastropods, the foot is used as a holdfast or to move slowly on the sub
How do nematode and annelid body plans differ?
Nematodes lack body segments and a true coelom; annelids have both.
Describe two adaptations that have enabled insects to thrive on land.
The arthropod exoskeleton, which had already evolved in the ocean, allows terrestrial species to retain water and support their bodies on land. Wings allow insects to disperse quickly to new habitats and to find food and mates. The tracheal system allows
Could traditional and molecular hypotheses be tested by studying the Hox genes that control body segmentation? Explain.
Yes. Under the traditional hypothesis, we would expect body segmentation to be controlled by similar Hox genes in annelids and arthropods. However, if annelids are in Lophotrochozoa and arthropods are in Ecdysozoa (as current evidence suggests), body segm
How do sea star tube feet attach to substrates?
Each tube foot consists of an ampulla and a podium. When the ampulla squeezes, it forces water into the podium, which causes the podium to expand and contact the substrate. Adhesive chemicals are then secreted from the base of the podium, thereby attachin
Describe how the features and diversity of echinoderms illustrate the unity of life, the diversity of life, and the match between organisms and their environments.
Echinoderms include species with a wide range of body forms. However, even echinoderms that look very different from one another, such as sea stars and sea cucumbers, share characteristics unique to their phylum, including a water vascular system and tube
Lacking tissues and organs, how do sponges accomplish tasks such as gas exchange, nutrient transport, and waste disposal?
The sponge body consists of two layers of cells, both of which are in contact with water. As a result, gas exchange and waste removal occur as substances diffuse into and out of the cells of the body. Choanocytes and amoebocytes ingest food particles from
Describe the cnidarian body plan and its two major variations.
The cnidarian body plant consists of a sac with a central digestive compartment, the gastrovascular cavity. The single opening to this compartment serves as both a mouth and an anus. The two main variations on this body plan are sessile polyps and motile
Is the lophotrochozoan clade united by unique morphological features shared by all of its members? Explain.
No. some lophotrochozoans have a crown of ciliated tentacles that function in feeding, while others go through a distinctive developmental stage known as trochophore larvae. Many other lophotrochozoans do not have either of these features. As a result, th
Describe some ecological roles of nematodes and arthropods.
Many nematode species live in soil and in sediments on the bottom of bodies of water. These free-living species play important roles in decomposition and nutrient cycling. Other nematodes are parasites, including many species that attack the roots of plan
You've read that echinoderms and chordates are closely related and have evolved independently for over 500 million years. Explain how both of these statements can be correct.
Echinoderms and chordates are both members of Deuterostomia, one of the three main clades of bilaterian animals. As such, chordates (including humans) are more closely related to echinoderms than we are to animals in any of the other phyla covered in this
A land snail, a clam, and an octopus all share A) a mantle B) a radula C) gills D) distinct cephalization
A) a mantle
Which phylum is characterized by animals that have a segmented body? A) Cnidaria B) Platyhelminthes C) Arthropoda D) Mollusca
C) Arthropoda
The water vascular system of echinoderms A) functions as a circulatory system that distributes nutrients to body cells B) functions in locomotion and feeding C) is bilateral in organization, even though the adult animal is not bilaterally symmetrical D) m
B) functions in locomotion and feeding
Which of the following combinations of phylum and description is incorrect? A) Echinodermata - bilateral symmetry as a larva, coelomate B) Nematoda - roundworms, pseudocoelomate C) Platyhelminthes - flatworms, gastrovascular cavity, acoelomate D) Porifera
D) Porifera - gastrovascular cavity coelomate