Definitions

Anteriormost part of body carrying eyes, not considered to be true cephalic somite.
(syn. ophthalmic somite, presegmental region. [Some authors recognize as protocephalon anterior part of h) [Moore and McCormick, 1969]
Anteriormost part of the body carrying the eyes; not considered true cephalic somite.
(syn. opthalmic somite, presegmental region) [McLaughlin, 1980]
(Taxon-specific: Order Decapoda) Anterior segment of body (although not considered to be a true somite); bears eyestalks (ocular peduncles). Acron and first cephalic somite occasionally interpreted as representing protocephalon.
(syn. ophthalmic somite, pre-segmental region) [Stachowitsch, 1992]
(Taxon-specific: Order Stomatopoda) Anteriormost segment of body (although not considered to be a true somite); divided into three plates-fastigial, ocular, and postocular- of which the median ocular plate bears the eyestalks (ocular peduncles). Not covered by carapace, although rostrum may partially or entirely extend across acron.
(syn. opthalmic somite) [Stachowitsch, 1992]