They have a skull but no vertebral column, no skeleton, just a flexible rod of cells, called notochord.
Hagfish found in the north Atlantic and Western Mediterranean can be up to 30in (80cm) in length and weigh up to 1 3/4 lb (750g). While Pacific Hagfih (Eptatretus Stoutii) which are found in shelf waters of the North Eastern Pacific can be found in lengths up to 20 in (50 cm) and weigh up to 3 lb (1.4kg). Depending on the species of Hagfish they can be found at depths as shallow as 65 ft(20m) to depths of over 2,100ft (650m). There are about 64 known species of the Hagfish.
The hagfish spends most of it’s time buried in mud with only the tip of it’s head showing. They mainly eat crustaceans but will also much on whale and fish carcasses. What’s most interesting is that when the hagfsih has latched onto a carcass with its mouth, it will form a knot near the end of it’s tail, then slide the knot forwared in order to provide itself with enough leverage to tear its mouth away fro the carass along with a chunk of food. They have slime pores that run down both sides of their eel-like body, allowing them to produce enough slime to fill a bucket in a matter of minutes. This mostly to deter predators in the oceans.
