Nemertea from SF Bay

The nemerteans are soft-bodied, unsegmented worms, often with few easily observed, external diagnostic features. This forces taxonomists to rely heavily upon nemertean internal anatomy and histology to make accurate identifications.

Different species vary greatly in size. Some species are as small as 1 millimeter long, but there are true giants that can extend themselves to 30 meters (about 100 ft) in length. Because these worms are extremely flexible and can lengthen their bodies up to five times their minimum lengths, our size estimates can only be just that…estimates!

The most distinctive features of a nemertean are its general shape, which is vermiform (worm-shaped) and unsegmented, as well as its long proboscis (an eversible organ that lies in an anterior, internal cavity called the rhynchocoel). This organ is everted (or shot out) from the mouth or proboscis opening (some nemerteans have these orifices separated) when the animal is hunting, defending itself, or moving along the substrate. Most species of nemerteans are carnivorous, eating small invertebrates (such as annelids and crustaceans) and their eggs. Others live symbiotically in the shells of mollusks, feeding on plankton and microbes that are filtered by their host. There are also omnivorous species. Most commonly, the gonadal systems are simple, and reproduction involves spawning by separate sexes. A few species exhibit internal fertilization. Fragmentation is also possible, allowing broken sections of worm to regenerate a head, tail, or both.

There are about 1,000 known species of nemerteans (and probably several times this number yet to be discovered). Most nemertean worms are marine, although there are a few freshwater and terrestrial species. They are not an especially well known group, as they live relatively concealed lives, and there are few systematists working on them. Many of the less brightly colored species hide by day and emerge to feed only at night. Some species are also capable of forming protective tubes or cysts of mucus during periods of breeding or environmental stress.

Most nemerteans found in San Francisco Bay are very small and not easily identifiable. An exception to this is Tubulanus sexlineatus (see photo and description).

mmm	Baseodiscus sp.
mmm	Carinoma mutabilis Griffin, 1898
mmm	Cerebratulus californiensis Coe, 1905
mmm	Micrura verrilli Coe, 1905
mmm	Paranemertes sp.
	Tubulanus sexlineatus (Griffin, 1898)