Class XI, BIOLOGY, "Phylum Hemichordata"

GENERAL CHARACTERS

• It is a small group of animals, which include about 90 species.
• They are soft-bodied animals, which usually live in shallow “U” shaped burrows in the sandy or muddy sea bottom.

EXTERNAL FEATURES

• They are cylindrical or vase shaped animals, bilaterally symmetrical and lack any segmentation.
• They may be solitary or colonial and usually range between a few millimeter and 250 cm in length.
• Sexes are separate in hemichordates.

INTERNAL FEATURES

• Circulatory system is open and coelom is divided into three chambers.
• A dorsal and a ventral nerve cord are present.

LARVA
Tornaria larva
EXAMPLE