11.11.1 Diversity of Deuterostome Species

Question 1

Diversity of Deuterostome Species

Answer 1

• In deuterostome development, the anus is derived from the blastopore, the coelom is derived from the gut (enterocoelous), and the cleavage of the embryo is radial and indeterminant.
• Some of the more common deuterostomes are lophophorates, arrow worms, echinoderms, and chordates.

Question 2

note

Answer 2

• Remember that at the level of the phylum animals are
  classified by both anatomical structures and developmental patterns. Deuterostomes are coelomates; they have a body cavity that is surrounded by mesoderm. Further, the coelom of deuterostomes is enterocoelous, or formed from the gut. (In protostomes, the coelom is formed from tissue between the gut and the epidermis or from the gonads). During the embryological development of deuterostomes, the anus forms from the blastopore and the mouth is formed secondarily. After fertilization, cleavage of the deuterostome embryo is radial and the cell fate is indeterminant.
• The deuterostome phyla emphasized in this tutorial include Echinodermata (echinoderms); Phoronida, Brachiopoda, and Bryozoa (the lophophorates); Chaetognatha (arrow worms); and Chordata (chordates).
• Although the lophophorate phyla are all characterized by a lophophore, which is a ciliated feeding apparatus, their appearance is highly varied. Bryozoans are colonial and stalked. Brachiopods have an external shell like a clam. Phoronids look quite similar to tube worms.
• The chaetognaths, or arrow worms, are highly voracious predators. There are about 70 species of these marine worms, which are very numerous in the plankton. Their name means “bristle-jaw” and it is derived from the long, chitinous spines on either side of the chaetognath’s head.
• The phylum Echinodermata includes five classes: Crinoidea (sea lilies), Asteroidea (star fish), Ophiuroidea (brittle stars), Echinoidea (sea urchins), and Holothuroidea (sea cucumbers). The name Echinodermata means “spiny skin” and these animals are characterized by a calcareous internal skeleton.
  Adult echinoderms exhibit radial symmetry, although their larvae have bilateral symmetry. Echinoderms have a fascinating water-vascular system that is involved in
  locomotion, feeding and defense.
• Chordates are characterized by the presence of a notochord at some point during development, a dorsal hollow nerve cord, pharyngeal slits, and a postanal tail. The chordates include two invertebrate subphyla: Urochordata (tunicates) and Cephalochordata (lancelets), as well as the subphylum Vertebrata

Question 3

True or false?

Humans are deuterostomes.

Answer 3

• true

Question 4

Lancelets are members of phylum

Answer 4

• Chordata

Question 5

The name chaetognath literally translates as

Answer 5

• bristle-jaw

Question 6

Which statement regarding deuterostomes is true?

Answer 6

• Anus develops from the blastopore.

Question 7

Adult echinoderms exhibit _______________ symmetry, although their larvae have _______________ symmetry.

Answer 7

• radial; bilateral

Question 8

True or false?

Chordates are characterized by the presence of a spinal chord.

Answer 8

• false