ABSTRACT
Larvae of pedunculate barnacles fall into three distinct groups: 1) generalised nauplii of certain intertidal lepadomorphs with brief planktotrophic life; 2) highly specialised oceanic larvae of Lepas spp. and close relatives, in which an extended planktonic phase, involving exaggerated naupliar growth increments produces large cyprids from small eggs; and 3) non-feeding (lecithotrophic) nauplii of a diversity of species, mostly from abyssobenthic habitats, in which there is a small number of large yolky eggs and an abbreviated naupliar life, often with some of the stages telescoped. All the larvae of two species of Lepas are described here for the first time. Antennules of Lepas nauplii have a more specialised role in feeding than those of the generalised nauplii. In the related Octolasmis spp. (which have returned to epibenthic habitats) this antennular feeding function of the nauplii is retained but the usual mandibular role is uniquely reduced. The lecithotrophic condition in lepadomorph larvae is considered to be apomorphic and non-reversible; intertidal barnacles with such larvae have probably passed through an abyssal phase. Extreme specialisation in lepadomorph nauplii has occurred principally in exploitation of the ocean surface and abyssobenthic habitats, in response to plankton and settlement conditions that differed from those of coastal waters. The major change in adult thoracican form, from lepadomorph to balanomorph, was not accompanied by correspondingly profound modification of the larvae.
