Heteronemertea

Heteronemertea is a monophyletic order of about 500 species of nemertean worms. It contains genera such as Lineus and Cerebratulus, and includes the largest and most muscular nemerteans.

Heteronemertea
An example of Heteronemertea, the Parborlasia corrugatus
Scientific classification
Kingdom:	Animalia
Phylum:	Nemertea
Class:	Pilidiophora
Order:	Heteronemertea Bürger, 1892
Families
See text.

Almost all heteronemerteans have three primary body-wall muscle strata: an outer longitudinal, a middle circular, and an inner longitudinal. The lateral nerve cords are outside the circular muscle, as in palaeonemerteans, but separated from the epidermis by the usually well-developed outer longitudinal muscle.^[1]

Illustration of Gorgonorhynchus repens, a species within the family Gorgonorhynchidae, discharging its proboscis in response to a perceived threat.

Taxonomy

Families within the order Heteronemertea include:^[2]

• Baseodiscidae
• Cerebratulidae
• Gorgonorhynchidae
• Lineidae
• Mixolineidae
• Panorhynchidae
• Poliopsiidae
• Polybrachiorhynchidae
• Pussylineidae
• Riseriellidae
• Valenciniidae