A large species, up to about 140-150 mm in length, with a slender, cylindrical trunk. The oral disk carries a single-tiered circle of paired tentacles surrounding the mouth; the number of tentacles in adults (>30 mm long) varies between 20 and 36, the majority having 24-28, but juveniles may have as few as 8 tentacles. Simple, spine-like hooks are arranged in well separated rings on the anterior part of the introvert; juveniles have up to 20 rings, but adults may have only three or four as a result of wear. The skin of the introvert and trunk is fairly smooth, without prominent papillae. The nephridiopores are ventrolateral and just anterior of the anus on the anterior trunk. The longitudinal muscle layer of the body wall is continuous, not collected into bands.
Internally, four retractor muscles are normally present, the ventral pair inserted in the middle third of the trunk and the dorsal pair at about the level of the anus; one or both of the dorsal retractors may be missing in aberrant specimens (G. elongata-internal). The intestine is tightly coiled in a double spiral supported by a spindle muscle attached anteriorly near the anus but not posteriorly. The rectal caecum is usually conspicuous. Gut-fixing muscles fasten the oesophagus on the left and the rectum on the right to the body wall in the region between the roots of the dorsal and ventral retractors; frequently one (or both) of these muscles is missing. The contractile vessel is simple. Two nephridia; these hang freely in the coelom.
Inhabits muddy sand/gravel from the lower shore to about 170 m depth. Juveniles are occasionally found in rock crevices on the lower shore, together with Golfingia rimicola (not in the North Sea) and Nephasoma minutum .
G. elongata spawns in July and August. Its burrows are occasionally inhabited by the polychaete Harmothoe lunulata and the bivalves Epilepton clarkiae and Mysella bidentata .
A common and widespread species, found from the Skagerrak to the eastern Mediterranean. Also reported from Cuba.