E. lineata is a small, delicate-looking, white or brownish anemone with a typical length of 15-20 millimeters as an adult polyp.

The body of an adult is composed of four distinct regions defined by tissue type: the oral disc containing the tentacles, the capitulum which houses the actinopharynx or "gut", the scapus, and the aboral end.

[3] It possesses various types of cnidae, including acontia (threadlike defensive organs thrown out of the mouth or special pores when irritated).

[7] E. lineata is genetically almost indistinguishable from its close relative E. carnea, which is native to the Northeast Atlantic and whose life cycle is currently unknown.

[8] E. lineata has a simple internal structure and is unusual among sea anemones in that it can divide by transverse fission.

[3] It can also reproduce sexually through broadcast spawning and the resulting planula larva has recently evolved a partially parasitic lifestyle [citation needed] The planula larvae are sometimes the cause of a form of irritating dermatitis in humans known as seabather's eruption.

[9] When the larvae get trapped under swimwear they defend themselves by firing their venomous nematocysts into the skin, causing a red blotchy rash that may blister.