Jean Bouillon

Zoogeography and life cycle patterns of Mediterranean Hydromedusae (Cnidaria)

The distribution of the 346 hydromedusan species hitherto recorded from the Mediterranean is considered, dividing the species into zoogeographical groups. The consequences for dispersal due to possession or lack of a medusa stage in the life cycle are discussed, and related to actual known distributions. There is contradictory evidence for an influence of life cycle patterns on species distribution. The Mediterranean hydromedusan fauna is composed of 19.5% endemic species. Their origin is debatable. The majority of the remaining Mediterranean species is present in the Atlantic, with various world distributions, and could have entered the Mediterranean from Gibraltar after the Mcssinian crisis. Only 8.0% of the fauna is classified as Indo-Pacific, the species being mainly restricted to the eastern basin, some of which have presumably migrated from the Red Sea via the Suez Canal, being then classifiable as Lessepsian migrants. The importance of historical and climatic factors in determining the composition of the Mediterranean fauna of hydromedusae is discussed.

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...

A survey of Zanclea, Halocoryne and Zanclella (Cnidaria, Hydrozoa, Anthomedusae, Zancleidae) with description of new species

Abstract The genera Zanclea, Halocoryne and Zanclella are surveyed, with description of all known species, including eight new ones of Zanclea (Z. bomala, Z, divergens, Z. fanella, Z. giancarloi, Z. medusopolypata, Z. retraduis, Z. gilii, Z. hirohitoi), two new species of Halocoryne (H. frasca, H. pirainoid), and two new ones of Zanclella (Z. diabolica, Z. glomboides). For most species, the description covers the whole life cycle. The hydroids of this group can be symbiotic with either bryozoans, bivalves, or corals and only few species are not substrate‐specialist. Symbiotic relationships led to polymorphism and colony integration with the hosts. The morphologies of hydroid and medusa stages are often not consistent, so that species with very derived hydroids have non‐derived medusae (e.g., Halocoryne pirainoid), or species with very derived medusae have non‐derived hydroids (e.g., Zanclella diabolica). The architecture of the newly released medusae of Zanclella is exceptional due to a sharp compression of the exumbrella and of the presence of just two radial canals. A phylogenetic scenario is suggested, in spite of the inconsistencies in the rates of change in the two main stages of the cycle.

The rediscovery of Codonorchis octaedrus (Hydroidomedusae, Anthomedusae, Pandeidae), with an update of the Mediterranean hydroidomedusan biodiversity

Abstract Codonorchis octaedrus is recorded for the first time since its discovery by Haeckel in 1879. A hydroid colony collected in a cave of the Apulian Coast (between the Ionian and the Adriatic Seas) produced several medusae which have been reared to maturity. This is the first complete description of the species, which was previously considered as doubtful, as was the genus Codonorchis. The diagnostic features for the genus are: hydroid small, naked, sessile, with a single row of few tentacles, gono‐phores on hydrorhiza, medusa with apical projection with apical process from the manubrium, perradial, interradial and adradial ocellate bulbs, two perradial tentacles, horseshoe‐shaped interradial gonads, small mesenteries. The list of Mediterranean hydroidomedusae is updated with the new (or overlooked) records since the last published list (1993). The increase in species number is great (about 10%), showing that the knowledge of biodiversity of even a well‐studied sea as the Mediterranean is far from be...

Hydromedusae of the New Zealand Oceanographic Institute (Hydrozoa, Cnidaria)

The collection of Hydromedusae of the New Zealand Oceanographic Institute comprises 47 species, 15 of which are new records for New Zealand waters. A new genus and two new species are described (Boeromedusa auricogonia and Bougain- villia vervoorti), and a new family of Tubularioidea, the Boeromedusidae, is proposed. Several specific diagnoses are revised.

The life cycles of Ocfotiara russelli and Sfomofoca atra (Cnidaria, Anthomedusae, Pandeidae)

The previously unknown life cycles of Ocioiiara russelli and Stomoroca alru are described. Both species present differentiated hydroids and medusae. From the morphology of the newly liberated medusae both species are referred to the Pandeidae and, from the presence of a manubrial peduncle, to the subfamily Stomotocinae. together with Timoides. Some aspects of feeding and gonad growth are described and discussed.

The life cycle of Gastroblasta raffaelei (Cnidaria, Hydrozoa, Leptomedusae, Campanulariidae) and a review of the genus Gastroblasta

The genus Gastroblasta was proposed by Keller in 1883 for a campanulariid medusa from the Red Sea, G. timida, with round umbrella, multiple radial canals and multiple manubria. A second species, G. raffaelei, with elliptic umbrella, multiple manubria and radial canals, and a great tendency to fission, was subsequently described from the Mediterranean Sea by Lang in 1886. A third species with multiple manubria was described by Mayer in 1900 from Tortugas: Multioralis ovalis (currently ascribed to Gastroblasta). The complete life cycle of a species of Gastroblasta, whose polyp stage was collected inside sponges from the Ligurian Sea and the Ionian and Adriatic Seas, is described. The first stage of medusa development is a typical Clytia with four radial canals and four tentacles, then the medusa becomes similar to G. ovale, to subsequently acquire the typical morphology of G. raffaelei. The species G. timida and G. raffaelei are considered as valid representatives of the genus, sharing the characters of multiple manubria and radial canals. The medusa of G. ovale has a diagonal canal system, instead of multiple radial canals, sharing with Gastroblasta the presence of multiple manubria only: it is proposed to resurrect the genus Multioralis to accommodate it.

The life cycle of Laodicea indica (Laodiceidae, Leptomedusae, Cnidaria)

The life cycle of Laodicea indica is described. In the Bismarck Sea this species shows a normal alternation of generations in the wet season; but in the dry season the cycle is contracted, and planulae give rise to gonothecae without formation of a hydroid colony. Medusae are liberated about 3 d after planula settlement. This life cycle pattern is previously unreported in hydromedusae. The possible adaptive value of such a life cycle and the evolution of polyp reduction in hydromedusan life cycles are discussed.

Four new species of Hydromedusae (Cnidaria, Hydrozoa) from the coast of south‐western Africa

Four previously unknown species of hydromedusae are described from plankton samples collected during oceanographic cruises undertaken along the south‐western coast of Africa. The Anthomedusa Bythotiara capensis sp.n., known from a single specimen, was found in shallow waters of the Cape region (South Africa). The Leptomedusa Margalefia intermedia gen. et sp.n. collected in Namibian waters, possesses desmoneme cnidocysts. This category of cnidocysts is previously unreported in the Leptomedusae, but is common in Anthomedusae and in the limnomedusan family Proboscidactylidae. Margalefia seems to occupy a position intermediate between the families Tirannidae and Laodiceidae. Two species of Limnomedusae, Aglauropsis edwardsii sp.n. and Proboscidactyla menoni sp.n. were frequent at several stations in Namibian waters between depths of 50 m and the surface.

The role of Cnidaria in evolution and ecology

Abstract The recent setting of specific features of the Cnidaria into evolutionary and ecological frameworks suggests the centrality of this phylum in many fields of the life sciences. From an evolutionary point of view, the Cnidaria, with their diploblastic planulae, might represent the ancestral state of higher Metazoa in the light of a peramorphic origin of animal complexity from a simple, individual organism. Medusan development in the Hydroidomedusae via a medusary nodule, furthermore, implies the formation of a third tissue layer (the muscle layer lining the subumbrellar cavity). Cnidarian polyps are diploblastic, whereas at least some of their medusae are triploblastic: the evolutionary enigma of the passage from a diplo‐ to a triploblastic organisation takes place every time hydrozoan polyps bud medusae! Cnidarian polyps have also the premises of the skeletal architecture of higher animals: their chiti‐nous or carbonatic skeletons are similar to those of arthropods and vertebrates respectively. From an ecological point of view, the coelenterates probably play roles that are much more important than usually perceived. Both Cnidaria and Ctenophora feed on the eggs and larvae of most benthic, planktonic and nektonic organisms and might be crucial (with a keystone role?) in maintaining biodiversity high, by feeding on potentially monopolising species. The efficiency of gelatinous predators becomes evident during periodic outbreaks of their populations, with serious implications even on fisheries yields, demonstrating that their impact can be higher than ours!