Cypris larva in the Crustacea Thecostraca: The role in the life cycle and in phylogeny reconstruction
Jens T. Høeg 博士（Institute of Biology, University of Copenhagen, Denmark）
2003年10月28日（火）15:00～16:00
The Crustacea Thecostraca are all sessile as adults. The larval development, normally starting with series of naupliar instars, terminates with a highly specialized instar, normally called the cyprid, which is specialized for the location of a settlement site and attachment to the substratum. The settlement and metamorphosis is best known within the Cirripedia, where the three subgroups (Thoracica, Acrothoracica, Rhizocephala) have surprisingly similar cyprids despite the fact that this larva develop into vastly different adults ranging from the conventional filter-feeding barnacles to the incredibly specialized rhizocephalan parasites. Recent comparative investigations have demonstrated that only the Cirripedia have a true cypris. The two other thecostracan taxa, the Facetotecta and Ascothoracida, have settlement stages that lack numerous apomorphies characterizing the cirripede cypris. The specialization of the 2 cirripede cypris concerns principally the sensory apparatus, the morphology of the antennules and the glandular systems, all organs that play a key role in the attachment process. Yet, there is no doubt that the facetotectan and ascothoracidan settlement stages are homologous to the cirripede cypris and the recent discovery of the so called lattice organs, which are unique to the Thecostraca, support this contention. Unfortunately, both the internal anatomy of the “Cypris” at the TEM level and the settlement process and the ensuing metamorphosis remain almost unknown in the non-cirripede Thecostraca.
This seminar will focus on the biology and morphology of the cirripede cypris, compare it with the ascothoracidan and facetotectan equivalents, and enumerate which characters can be considered apomorphic for the Cirripedia. It will include videos clips of cypris larvae during the settlement process and during the ensuing metamorphosis.