As this tongue is pulled back into the hagfish's mouth, the pairs of rasps pinch together. This bite is used to tear into the flesh of dead and dying fish which have sunk to the muddy ocean bottom, or in catching and eating marine invertebrates. By far, the largest part of their diet is polychaete worms , but because of their slow metabolism, hagfish may go for up to seven months without eating any food. Unlike many other fish, the Myxini undergo direct development , with no larval stage. The newly hatched young are practically miniature versions of their parents.
Hagfish eggs are approximately one inch long, and encased in a tough shell.
These eggs are large for a fish, and a female can therefore not produce very many. Despite the low number of eggs laid, hagfish exist in large numbers, with populations of up to 15,000 occurring in a relatively small area. This suggests that hagfish have a low mortality rate. The skeleton is composed of cartilage, and lacks bone. Jawlessness is the primitive state for fish however, and so any such group based on a lack of jaws is paraphyletic .