Exam 31: Animal Phylogeny, Acoelomates, and Protostomes

The ____ is the initial opening between the developing gut and the outside environment for most animal embryos.

Members of the ____ flatworm lineage are vertebrate endoparasites; some, called blood flukes, cause an often deadly disease in humans called schistosomiasis.

Members of the ____ lineage have a pair of hinged shells that can be closed by contraction of one or two adductor muscles.

Most contemporary animal lineages first appeared between 530 and 520 million years ago, the time period referred to as the ____ explosion.

Ringlike patterns on an earthworm and "six-pack abs" in humans are evidence of ____ in an animal's body plan.

Flatworms have specialized cells called ____ that function in osmoregulation.

Members of the ____ flatworm lineage are parasites of vertebrates, characterized by modified heads for attaching to the intestinal wall of hosts, and a series of reproductive units called proglottids.

The members of the ____ Cnidarian lineage exist only as polyps as adults, and most build calcium carbonate exoskeletons and have mutualistic relationships with photosynthetic protists.

Members of the ____ Ecdysozoan phylum, commonly called roundworms, are so plentiful in soil and other places that they may be the most abundant animals on Earth.,

Molecular sequence analysis has revealed that Crustacea is paraphyletic, because it includes an ancestor but not all of its descendants; the descendants not included in this clade are the ____.

Most biologists now agree that the common ancestor of all animals was probably a eumetazoan.

In most protostomes, the ____ is the developmental origin of the body cavity between the gut and muscles of the body wall.

Most biologists agree that the most recent common ancestor of all animals was probably a ____, an idea first proposed by Ernst Haeckel in 1874.

More than half of the known animal species comprise the ____ Ecdysozoan phylum.

Members of the ____ subphylum are now all extinct, but they were extremely numerous in shallow Paleozoic seas. Most of them were dorsoventrally flattened and heavily armored, with two deep longitudinal grooves that gave their body a three-lobed appearance.