The longest worm known, Lineus longissimus, belongs to the phylum Nemertea. It is found under boulders at low tide along the North Sea and has been reported to exceed 150 feet in length and commonly exceeds 15 feet.   In contrast, the smallest nemerteans are only 1 mm long and live in the pore-water on coarse sand beaches.  Exact length of nemerteans can't be measured because nemerteans are capable of stretching from 2 to more than 10 times their most contracted length. Nemerteans are common in many intertidal habitats; most are predators and feed on other worms and crustaceans. 

The longest worms on land are some of the earthworms in Australia. These earthworms, belonging to a group called the Megascolecids, are characteristic of the southern hemisphere; they get to be as much as 2-3 m long. At this point most of them are threatened by the modification of the local landscape where they live.

Earthworms need air to be able to get oxygen and come to the surface when it rains because they would drown.

How do worms reproduce?

Most of them have distinct sexes, but earthworms are hermaphrodites, that is, they are simultaneously male and female. However, they do not fertilize themselves, they require the presence of a partner to get the development going. Other worms, especially those living in the oceans, simply release out eggs and sperm in the water where the early part of development takes place. Some worms have very sharply focused periods when reproduction takes place.

The palolos are segmented worms (annelids) that live burrowed into coral reefs in very shallow water. Once a year, over a period of one or two nights, the posterior end of each worm breaks off and swarms to the surface. These posterior ends are filled with either eggs or sperm, and at the surface they burst open releasing their contents. The larvae develop for a few days in the water above the reef and then burrow into the bottom where the front end of their parents may still be living. Interestingly, the front ends regenerate a new posterior end for the next year's spawning and can keep on doing so for several years.

As a rule, the smaller the adult worm is, the shorter the life is; some of the really small ones live only for about 45-60 days, whereas some of the really large ones may become more than 50 years old.

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