Electrophoretic evaluation of the taxonomic status of two species of sea anemone

Puerto Rican populations of two species of sea anemones (Bunodosoma cavernata and B. granulifera) which had previously been considered one were assayed electrophoretically for enzymes encoded by 12 loci. The two species shared no common allozymes at 6 of the 12 loci. Genetic distance and identity values based on these allozymes were computed for the Puerto Rican populations and for B. cavernata from Florida and B. granulifera from Panama. The Puerto Rican populations of both species had much higher genetic identities for their geographically distant conspecifics than for each other. These results indicate that the two species are reproductively isolated and should be considered as separate valid species. Average heterozygosities are presented which are the first published for coelenterate species.     

Haeckelia (= Euchlora) and Hydroctena and the phylogenetic interrelationships of Cnidaria and Ctenophora

A scrutiny of the literature shows that the ctenophore Haeckelia (= Euchlora) ruba has only kleptocnidae and that Hydroctena salenskii is a ctenophore without special cnidarian affinities. The “missing links” between cnidarians and ctenophores have thus turned out to be based on misinterpretations and must be excluded from future discussions on phylogeny.     

Regeneration in Hydrozoa: distal versus proximal transformation in Hydractinia

Summary Polyps of mature colonies of Hydractinia echinata obey the rule of distal transformation by regenerating heads but not stolons. However, this rule is not valid for young polyps as these regenerate stolons from proximal cut ends. Also, small cell aggregates and even small fragments excised from full-grown polyps are capable of stolon formation. Aggregates produced from dissociated cells undergo either distal or proximal transformation depending on their size, speed of head regeneration in the donor used for dissociation and the positional derivation of the cells. The latent capability of stolon formation is released under conditions that cause loss of morphogens and depletion of their sources. However, internal regulative processes can also lead to gradual proximal transformation: regenerating segments of polyps sometimes form heads at both ends and the distal pattern is duplicated. Subsequently, all sets of proximal structures, including stolons, are intercalated. In contrast to distal transformation, proximal transformation is a process the velocity of which declines with the age and size of the cell community.     

Confocal laser scanning light microscopy of the extra-thecal epithelia of undecalcified scleractinian corals

The extra-thecal epithelia of cryofixed undecalcified, freeze-substituted polyps of the scleractinian corals Galaxea fascicularis and Tubastrea faulkneri and axial and basal polyps of Acropora formosa have been examined, in anhydrously prepared thick slices, by confocal laser scanning light microscopy. The avoidance of chemical fixation and decalcification makes it possible to determine whether previously seen structures are real or artefactual products of swelling, shrinkage and distortion. All of the epithelia of all the corals examined are characterised by well defined intercellular spaces. Mucocytes are present in all cell layers in Galaxea and Tubastrea but are not present in any cell layers in the axial polyp of Acropora although they are abundant in the oral ectoderm of the basal polyps in this coral. Zooxanthellae are absent in Tubastrea, the epithelia of the exert septa of Galaxea and the axial polyp of Acropora. The calicoblastic ectoderm is generally composed of thin squamous cells with large intercellular spaces. At rapidly calcifying regions such as the tips of the exert septa of Galaxea, the calicoblastic cells are elongated with extensive arborisation of the basal regions of the cells. They are separated by large intercellular spaces and contain numerous fluorescent granules. The apical regions of these cells appear to be closely applied to the surface of the skeleton. There is no evidence of a space between the apical region of the calicoblastic cells and the skeleton.     

Thecate stem medusozoans (Cnidaria) from the early Cambrian Chengjiang biota

Cnidarians are phylogenetically located near the base of the ‘tree of animals’, and their early evolution had a profound impact on the rise of bilaterians. However, the early diversity and phylogeny of this ‘lowly’ metazoan clade has hitherto been enigmatic. Fortunately, cnidarian fossils from the early Cambrian could provide key insights into their evolutionary history. Here, based on a scrutiny of the purported hyolith Burithes yunnanensis Hou et al. from the early Cambrian Chengjiang biota in South China, we reveal that this species shows characters distinct from those typical of hyoliths, not least a funnel-shaped gastrovascular system with a single opening, a whorl of tentacles surrounding the mouth, and the lack of an operculum. These characters suggest a great deviation from the original definition of the genus Burithes, and a closer affinity with cnidarians. We therefore reassign the material to a new genus: Palaeoconotuba. Bayesian inference of phylogeny based on new anatomical traits identifies a new clade, including Palaeoconotuba and Cambrorhytium, as a stem group of sessile medusozoan cnidarians that are united by the synapomorphies of developing an organic conical theca and a funnel-like gastrovascular system. This study unveils a stem lineage of medusozoans that evolved a lifelong conical theca in the early Cambrian.     

Description of four new species in the hard coral genus Acropora Oken, 1815 (Scleractinia: Astrocoeniina: Acroporidae) from south-east Africa

Four new species in the hermatypic scleractinian coral genus Acropora art described from southeast Africa. Two species, A. natalensis sp. nov. and A. mossambica sp. nov. , occur in both South Africa and Mozambique. Two species, A. sordiensis sp. nov. , and A. branchi sp. nov. , are only known from northern Natal in South Africa. A. branchi sp. nov. and A. mossambica sp. nov. are intertidal species and were collected from permanent tidal pools. A. sordiensis sp. nov. and A. natalensis sp. nov. are strictly subtidal species.     

Reduced color polymorphism in a population of Bunodosoma granulifera

The proportions of carotenoids responsible for column coloration were determined for a population of the sea anemone Bunodosoma granulifera from Grand Cayman using TLC. This population exhibited a very low degree of polymorphism for these proportions, compared to previously sampled populations from Puerto Rico and Curaçao. In addition to the carotenoid pigment system a second system possessing pigments similar to bilins was found for the first time in this genus. This population was also assayed electrophoretically for enzymes encoded by 12 loci. Analysis of these data suggested that the reduced polymorphism for column color may be the result of selection. Although the proportions of carotenoids varied little, the amount of carotenoid per unit of epidermal tissue varied almost four-fold from 0.05 to 0.19 μg/mg dry wt.     

The benthic deep-water siphonophore Rhodalia miranda and other coelenterates in the south-west Atlantic: ecological and oceanographical implications

The benthic deep-water siphonophore Rhodalia miranda was collected for the first time in 1876 by H.M.S. Challenger off the Rio de la Plata estuary beneath the Subtropical Convergence at about 1000 m depth. Rhodalia was reported again about 100 years later from certain distant localities in the subantarctic region of the south-west Atlantic. Hydrographic and topographic features that may be involved in creating this peculiar distribution pattern are discussed together with a likely mode of dispersal of benthic coelenterates. The disjunct distribution of Rhodalia and other benthos of the upper Argentine Slope suggests the subsurface oceanographic régime to be quite different from what we know of the surface layers.     

The form and function of cnidarian spirocysts

Summary The electron-dense capsule tip (apical cap) of sea anemone and coral spirocysts is of a different structure than the capsule wall. The capsule wall is composed of a double layer of fiber-like materials which cross each other at roughly right angles. The innermost layer is characterized by numerous serrations, the tips of which project into the lumen of the capsule. Within each serration, a band of finely cross-striated material encircles the capsule at right angles to its longitudinal axis. The membrane lining the lumen of the capsule appears to be continuous with the wall of the undischarged thread. The outer capsule wall layer consists of closely spaced microfilaments (cnidofilaments) which are oriented in the longitudinal axis of the capsule. The cnidofilaments appear to merge with the apical cap material. Contrary to some previous reports in the literature, it has been found that spirocysts normally discharge by eversion, as do nematocysts. The relationship of the capsule wall sub-structure to the spirocyst discharge process is discussed.Thanks are due Dr. Cadet Hand for the use of the facilities of the Bodega Marine Laboratory of the University of California and B. Miller, F. Doroshow, C. Bigger, G. Chapman and E. Chang for expert technical assistance. The use of the facilities of the Electron Microscope Laboratory and Electronics Research Laboratory of the University of California at Berkeley and the Eelectron Microscope Laboratory of the Florida State University is gratefully acknowledged. Part of this work was made possible by NSF Grant GB-40547 to the senior author     

Anoxia can increase the rate of decay for cnidarian tissue: Using Actinia equina to understand the early fossil record

An experimental decay methodology is developed for a cnidarian model organism to serve as a comparison to the many previous such studies on bilaterians. This allows an examination of inherent bias against the fossilisation of cnidarian tissue and their diagnostic characters, under what conditions these occur, and in what way. The decay sequence of Actinia equina was examined under a series of controlled conditions. These experiments show that cnidarian decay begins with an initial rupturing of the epidermis, followed by rapid loss of recognisable internal morphological characters. This suggests that bacteria work quicker on the epidermis than autolysis does on the internal anatomy. The data also show that diploblastic tissue is not universally decayed more slowly under anoxic or reducing conditions than under oxic conditions. Indeed, some cnidarian characters decay more rapidly under anoxic conditions than they do under oxic conditions. This suggests the decay pathways acting may be different to those affecting soft bilaterian tissue such as soft epidermis and internal organs. What is most important in the decay of soft polyp anatomy is the microbial community, which can be dominated by oxic or anoxic bacteria. Different Lagerstätte, even of the same type, will inevitably have subtle difference in their bacterial communities, which among other factors, could be a control on soft polyp preservation leading to either an absence of compelling soft anthozoans (Burgess Shale) or an astonishing abundance (Qingjiang biota).