11.10.3 Diversity of Protostome Species

Question 1

Diversity of Protostome Species

Answer 1

• The protostomes include the important phylum Mollusca, which are characterized by a muscular foot, soft bodies, a mantle, and often a calcium carbonate shell.
• The major groups of molluscs are the polyplacophora (chitons), gastropoda (snails and slugs), bivalva (clams and scallops), and cephalopoda (octopi and squids).
• The protostomes also include the highly successful group, the arthropods. Arthropods are characterized by the presence of a chitinous exoskeleton and jointed legs. They include crustaceans, insects, spiders, millipedes and centipedes.

Question 2

note

Answer 2

• The protostomes are coelomates; they have a true body cavity that is surrounded by mesoderm. During the
  embryological development of protostomes, the mouth forms from the blastopore and the anus forms secondarily. Three common protostome phyla are the Mollusca (molluscs), the Annelida (segmented worms) and the Arthropoda (crustaceans, insects and spiders).
• Molluscs are characterized by a muscular foot, a soft body, and a mantle that produces a shell and that forms a mantle cavity. Molluscs obtain calcium carbonate from the seawater in order to deposit their shell, which is used for protection.
• Polyplacophyora, commonly called chitons, is a class in the phylum Mollusca. These animals are well adapted to clinging to rocks along the shoreline.
• Gastropods (“stomach foot”) include the snails and slugs. They are the most diverse class of mollusks with over 8,000 species. The spiral shell of a snail makes it possible for it to carry it above its body. In some snails the body undergoes a process known as torsion during development that places its anus above its head.
• Bivalves are molluscs that have paired, hinged shells. They include the clams, oysters, scallops and their relatives. The powerful adductor muscle holds the two valves of the shell together. Bivalves are strictly aquatic and filter the water in order to trap the small plankton on which they feed.
• Cephalopods are the most complex, active, and intelligent molluscs. The word cephalopod means “head foot” reflecting the anatomical structure in which the head has merged with the foot. They include the octopi, squid, nautili, and cuttlefish. Cephalopods have excellent vision, a well-developed brain, and move via jet propulsion.
• Arthropods are an extremely successful group of
  protostomes. There are over a million arthropod species,
  which account for nearly four fifths of all described animal species. They are found in nearly every habitat on Earth. Arthropods are characterized by a segmented body, a chitinous exoskeleton, and paired-jointed appendages. Arthropod appendages include antennae, mouthparts, and legs. The wings of insects are not true appendages but outgrowths of the thorax. Arthropods include crustaceans (shrimp, crabs, lobster, barnacles, and copepods), insects, arachnids (spiders), chilopods (centipedes), and diplopods (millipedes).

Question 3

All but which of the following are protostomes?

Answer 3

• sea urchins

Question 4

Centipedes, spiders, mites, and grasshoppers are all

Answer 4

• arthropods

Question 5

Which class within Phylum Mollusca is characterized by excellent vision, a well developed brain and locomotion via jet propulsion?

Answer 5

• Class Cephalopoda

Question 6

True or false?

Insects, spiders, centipedes, and millipedes are all crustaceans.

Answer 6

• false

Question 7

Which of the following combinations of class and examples is incorrect?

Answer 7

• Gastropoda- snails, oysters, and slugs