Showing papers by "Ferdinando Boero published in 1998"

The cnidarian premises of metazoan evolution: From triploblasty, to coelom formation, to metamery

Abstract: The hydromedusan subumbrellar muscle tissues originate from a mass of endo‐ and ectoderm derived cells proliferating inwardly. This mass of cells, called entocodon, is separated by the ecto‐and endoderm through a layer of extracellular matrix, thus forming a locally triploblastic arrangement of tissues. By cavitation and differentiation, the entocodon gives rise to the striated and smooth muscle layers of the subumbrella. The structure of the striated muscle is histologically identical to that described for triploblasts, where striated muscle is mainly mesodermic. Together with the mode of development, this suggests that not all Cnidaria are diploblastic and that the subumbrellar cavity is a coelom‐like structure. The subumbreHar cavity is formed late in ontogeny, whereas the coelom in higher animals is normally formed during embryonic development. Instead of remaining closed, the subumbrella becomes open, with the muscular mesothelium in contact with the environment. This view of cnidarian struc...

The impact of small benthic passive suspension feeders in shallow marine ecosystems: the hydroids as an example

Abstract: Benthic suspension feeders are abundant in littoral and shallow sub-littoral ecosystems, where they feed on the plankton and on organic matter suspended in the water column Recent studies indicate that active suspension feeders with powerful water filtration mechanisms (eg, bivalve molluscs) may exert an important influence on the abundance and production of phytoplankton, and probably zooplankton as well Passive suspension feeders, such as hydrozoans, have received less attention, and their effect on shallow planktonic communities is poorly understood This paper presents evidence that hydrozoans, which make only a minor contribution to benthic community biomass, capture large amounts of zooplankton and seston, and that they may play an important role in transferring energy from pelagic to benthic ecosystems over a wide range of latitudes

Heterochrony, generic distinction and phylogeny in the family Hydractiniidae (Hydrozoa: Cnidaria)

Abstract: The taxonomy of Hydractinia, Stylactaria and Podocoryna is discussed and the three genera are merged into Hydractinia since their diagnostic characters are liable to lead to polyphyly and paraphyly, due to repeated episodes of medusa reduction via heterochrony (paedomorphosis). The phylogeny of the Hydractiniidae is reconstructed by using two outgroups, Clava and Cytaeis, both having some characters in common with the Hydractiniidae. The resulting phylogenetic trees agree in identifying affinities among Hydractinia, Kinetocodium and Hydrocorella, all with polymorphic colonies with gastrozooids having oral tentacles. The position of Clavactinia (characterized by gastrozooids with widely scattered tentacles) is at the root of the tree if Clava is the outgroup, whereas it becomes apical when the outgroup is Cytaeis. The pattern of medusa suppression is different in the two cladograms, since the presence of a medusa is a plesiomorphic feature when Cytaeis is the outgroup, whereas it becomes apomorphic when the outgroup is Clava. These inconveniences are difficult to accommodate, since medusa suppression has occurred many times in the evolution of the hydroidomedusae, and Recent species do not witness past paedomorphic events of medusa reduction properly, so that many intermediate states are probably missing.