retractile

Decapoda.—Four pairs of ordinary non-retractile arms which are shorter than the body, and one pair of tentacular arms, situated between the third and fourth normal arms on each side and retractile within special pouches.

From Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics" by Various

The single prosthomere carries the retractile tentacles as its “parapodia.”

From Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6 "Armour Plates" to "Arundel, Earls of" by Various

The genital somite is always small and sometimes retractile within the somite bearing the last pair of legs.

From Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 6 "Celtes, Konrad" to "Ceramics" by Various

Sem′i-recon′dite, half-hidden; Sem′i-rē′flex, involuntarily performed, but not entirely independent of the will; Sem′i-reg′ular, pertaining to a quadrilateral having four equal sides, but only pairs of equal angles; Sem′i-retrac′tile, retractile to some extent.—n.

From Chambers's Twentieth Century Dictionary (part 4 of 4: S-Z and supplements) by Various

Most species have sharp, curved claws, often retractile between some of the lamellae or into a special sheath.

From Encyclopaedia Britannica, 11th Edition, Volume 11, Slice 5 "Gassendi, Pierre" to "Geocentric" by Various