Life History & Behaviour

Feeding 
Nemerteans are known to be voracious predators often ambushing their prey. Species such as those found in the genus Lineus belong to the class Anopla which lack a stylet, leaving the proboscis unarmed and non-differentiated. Instead of harpooning their prey, they instead lasso it with their sticky proboscis (Rupert, Richard & Barnes, 2004). The proboscis is an important part of prey capture as they are slow-moving and therefore have to evert it quickly in order to be successful. This is helped by the potent toxins they secrete as a mucus and their highly developed chemosensory system to make up for their simple/ non-existent eyes. Once a chemical cue is detected, active pursuit begins allowing them to hunt down their prey like a greyhound on the scent (Thiel & Kruse, 2001).

They can be very selective with what they will eat; with it thought that those in the order Heteronemertea prefer polychaetes over the small crustaceans favoured by the Hoplonemerteans. If their preference is unavailable though they will settle for whatever they can find (e.g. bivalves, dead organisms) (Thiel & Kruse, 2001).

Reproduction
Most nemerteans are gonochoric (one sex per individual) and have a simple reproductive system in which gametes are derived from stem cells and enclosed in an epithelium to form a gonad with a short gonoduct leading from the gonad to the outside. When breeding, contact is not necessary but some species have been known to aggregate and spawn or pair-off into a shared burrow or cocoon. However they reproduce most species fertilise externally with direct development. The larval stage in heteronemerteans is known as a pilidium. This is a free-swimming, planktotrophic stage that is helmet-shaped with apical tuft of cilia, a band of locomotory cilia and a thick gelatinous blastocoel to give it buoyancy (Rupert, Richard & Barnes, 2004).

Fragmentation is a common form of asexual reproduction seen mainly in the larger species, with each piece becoming a new organism. It can be induced if the nemerteans is irritated which can make collection difficult especially as regeneration is species-dependent(Rupert, Richard & Barnes, 2004).  

Locomotion
Three different layers of muscle lay underneath the soft epidermis. The outer layer is comprised of circular musculature, the innermost usually longitudinal and the layer in between of crisscrossed helical musculature. The different muscles allow for different types of movement in the Nemertea. Helical muscles allow twisting and coiling and longitudinal allow bending and turning.  However, both circular and longitudinal muscles are needed to elongate and contract the body producing movement (Rupert, Richard & Barnes, 2004). Smaller nemerteans may rely upon ciliary locomotion instead of muscular (Wright, 2014).

Respiration
Gas exchange is taken care of over the surface of the epidermis and therefore has no need for specialised organs or gills to facilitate oxygen exchange (Rupert, Richard & Barnes, 2004).