Zoology 10th Edition by Stephen Miller,John Harley

تمرين 7

The phylum Hemichordata includes the classes Enteropneusta and Pterobranchia. The enteropneusts live in U-shaped burrows in intertidal sandy and muddy substrates. They feed on detritus, which clings to their conical proboscis. Reproduction involves external fertilization and the development of a planktonic tornaria larval stage. Pterobranchs live in secreted tubes in shallow marine waters. They filter feed using cilia-covered arms and tentacles. Asexual budding and external fertilization with the development of a planula-like larval stage are common forms of reproduction.
How are the larval stages of enteropneusts similar to those found in the echinoderms? Why might these similarities be important?
FIGURE 16.18 External Structure of the Pterobranch Rhabdopleura. Ciliated tracts on tentacles and arms direct food particles toward the mouth (5 mm).