Metamorphosis of the Pedunculate Barnacle Capitulum mitella Linnaeus, 1758 (Cirripedia: Scalpelliformes)

Abstract

In this paper, metamorphosis of laboratory-reared cyprids of the pedunculate cirripede, Capitulum mitella was successfully induced. A timeline and a detailed description of morphological events during metamorphosis were derived from light microscopy and scanning electron microscopy analyses. The metamorphic process of cyprids involves five main events. (1) Triggering of metamorphosis: after 0–6 h of reagent exposure, the epidermis ventral to the compound eyes gradually invaginates. (2) Invagination and separation of epidermis: after 6–36 h, the invagination bypasses the compound eyes, the cypris epidermis separates slightly from the carapace and the nauplius eye gradually migrates ventrally. (3) Formation of juvenile rudiment: after 36–72 h, the metamorphosing specimen shape slightly resembles that of a juvenile. (4) Shedding of thoracopodal exuvium: after 72–96 h, the cyprid finally sheds the thoracopodal exuvium and metamorphoses into a juvenile barnacle. (5) Early development of juvenile barnacle: the juvenile shed the cirrum cuticle for the first, second, third and fourth time at 1.5–2, 1.5–2, 4–5 and 5–6 days, respectively. The newly formed juvenile completely assumes the shape and armature of all shell-plates found in adult barnacle. Rostro-carnal length of the juvenile is 240–260 μm. Tergum, scutum and upper latus are paired, and carina and rostrum are unpaired. Uniform circular depressions are dispersed on the surface of the tergum, scutum and carina. The rostrum and upper latus, which have the shape of small triangle, are not clear. The entire surface of the peduncle is covered with convoluted cuticular ridges. The metamorphosis of C. mitella is similar to that of Lepas.