Metamorphosis in the Cirripede Crustacean Balanus amphitrite

Abstract

Stalked and acorn barnacles (Cirripedia Thoracica) have a complex life cycle that includes a free-swimming nauplius larva, a cypris larva and a permanently attached sessile juvenile and adult barnacle. The barnacle cyprid is among the most highly specialized of marine invertebrate larvae and its settlement biology has been intensively studied. By contrast, surprisingly few papers have dealt with the critical series of metamorphic events from cementation of the cyprid to the substratum until the appearance of a suspension feeding juvenile. This metamorphosis is both ontogenetically complex and critical to the survival of the barnacle. Here we use video microscopy to present a timeline and description of morphological events from settled cyprid to juvenile barnacle in the model species Balanus amphitrite, representing an important step towards both a broader understanding of the settlement ecology of this species and a platform for studying the factors that control its metamorphosis. Metamorphosis in B. amphitrite involves a complex sequence of events: cementation, epidermis separation from the cypris cuticle, degeneration of cypris musculature, rotation of the thorax inside the mantle cavity, building of the juvenile musculature, contraction of antennular muscles, raising of the body, shedding of the cypris cuticle, shell plate and basis formation and, possibly, a further moult to become a suspension feeding barnacle. We compare these events with developmental information from other barnacle species and discuss them in the framework of barnacle settlement ecology.

How do coral barnacles start their life in their hosts?

“…For example, the metamorphosis from initial attachment of the cyprid to shedding of the carapace lasted less than 1 day in the intertidal free-living Amphibalanus amphitrite, 1.5 days in the subtidal free-living Megabalanus rosa (figure 2m) and 3.5 days in the neustonic species Lepas sp. These three species commenced feeding shortly after carapace shedding [8,9]. By contrast, D. angularis completed ecdysis in 2 days but required another 8 days to become a feeding juvenile (figure 2n).…”

The diversity of acorn barnacles (Cirripedia, Balanomorpha) across Thailand’s coasts: The Andaman Sea and the Gulf of Thailand

“…The nauplius larva develops in successive manner with ecdysis or molting to shed their exoskeleton and allow growth of larva, a characteristic used to classify acorn barnacles into Ecdysozoa of Protostomia clade. The metamorphosis (settlement process) alters a cyprid larva to a sessile juvenile and subsequently an adult form growing inside the ring of shell plates (4-8 in number depending on the species), homologous structure to carapace of other crustaceans (Høeg and Møller 2006;Maruzzo et al 2012;Martin et al 2014). The sessile body of adult barnacles has six…”

Barnacle biology before, during and after settlement and metamorphosis: a study of the interface

“…Cyprids were settled and allowed to develop through the six stages previously defined via morphological characteristics (Maruzzo et al, 2012). In accordance with previously established techniques, cyprids were aged for 3 days in aged filtered seawater (FSW) at 4°C prior to settlement (Rittschof et al, 1984(Rittschof et al, , 1992.…”

“…Coverslips with larvae were housed individually in Falcon ® 1006 polystyrene Petri dishes in a 28°C incubator and observed and sampled as larvae underwent settlement and metamorphosis. We used the six stages following previous descriptions, but combined stages 3-5 into one group, as those transitions occur too rapidly to detect without video observation, which was how they were originally described (Maruzzo et al, 2011(Maruzzo et al, , 2012. In brief, stage 1 corresponded to cyprids immediately after irreversible attachment and stage 2 was a cyprid with the carapace drawn closer to and in parallel with the surface (Maruzzo et al, 2012).…”

“…Barnacles have a complex life cycle involving drastic changes from a planktonic free-swimming nauplius and cypris larva, to a sessile juvenile barnacle with adult morphology (Crisp, 1955;Crisp and Meadows, 1963;Barnes and Blackstock, 1974;Aldred and Clare, 2008;Gohad et al, 2012;Maruzzo et al, 2012). Adhesion is critical for survival during the transition from cyprid to juvenile and necessary to maintain permanent attachment as the juvenile grows into an adult.…”