New record for the distribution of the colonial hydroid Cordylophora caspia (Pallas, 1771) (Cnidaria: Hydrozoa) in Argentina

Cordylophora caspia is a colonial, athecate hydroid inhabiting both in freshwater and brackish habitats. Its global distribution is in part due to its ability to tolerate a wide range of salinity. It is considered an invasive species and its control is widely studied because of the industrial and ecological problems it causes in many environments. We report for the first time the occurrence of this hydrozoan in Nahuel Rucá Lake (Buenos Aires province, Argentina) with some notes on its internal and external morphology.Fil: Deserti, Maria Irene. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Escalante, Alicia Haydee. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Acuña, Fabian Horacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentin

Shared Skeletal Support in a Coral-Hydroid Symbiosis

Hydroids form symbiotic relationships with a range of invertebrate hosts. Where they live with colonial invertebrates such as corals or bryozoans the hydroids may benefit from the physical support and protection of their host's hard exoskeleton, but how they interact with them is unknown. Electron microscopy was used to investigate the physical interactions between the colonial hydroid Zanclea margaritae and its reef-building coral host Acropora muricata. The hydroid tissues extend below the coral tissue surface sitting in direct contact with the host's skeleton. Although this arrangement provides the hydroid with protective support, it also presents problems of potential interference with the coral's growth processes and exposes the hydroid to overgrowth and smothering. Desmocytes located within the epidermal layer of the hydroid's perisarc-free hydrorhizae fasten it to the coral skeleton. The large apical surface area of the desmocyte and high bifurcation of the distal end within the mesoglea, as well as the clustering of desmocytes suggests that a very strong attachment between the hydroid and the coral skeleton. This is the first study to provide a detailed description of how symbiotic hydroids attach to their host's skeleton, utilising it for physical support. Results suggest that the loss of perisarc, a characteristic commonly associated with symbiosis, allows the hydroid to utilise desmocytes for attachment. The use of these anchoring structures provides a dynamic method of attachment, facilitating detachment from the coral skeleton during extension, thereby avoiding overgrowth and smothering enabling the hydroid to remain within the host colony for prolonged periods of time

Tubiclavoides striatum gen. nov et sp nov (Cnidaria : Hydrozoa) a new bathyal hydroid from the Gulf of Cadiz, north-east Atlantic Ocean

Tubiclavoides striatum, a new species of an athecate hydroid, was found on mud volcanoes, inactive carbonate clumneys, and cold-water coral stands in the Gulf of Cadiz (south-western Iberian Peninsula, Atlantic Ocean). The new family Tubiclavoididae and the new genus Tubiclavoides are proposed to accommodate the new species. The new hydroid is characterized by scattered filiform tentacles, sporosacs developing among the tentacles and hydrocauli covered with striated perisarc, often subdivided into imbricating cones. A full description and illustrations are provided, as well as some notes on the ecology and distribution of the new species

A Novel Mode of Colony Formation in a Hydrozoan through Fusion of Sexually Generated Individuals

SummaryColoniality, as displayed by most hydrozoans, is thought to confer a size advantage in substrate-limited benthic marine environments and affects nearly every aspect of a species' ecology and evolution [1,2]. Hydrozoan colonies normally develop through asexual budding of polyps that remain interconnected by continuous epithelia. The clade Aplanulata is unique in that it comprises mostly solitary species, including the model organism Hydra, with only a few colonial species [3,4]. We reconstruct a multigene phylogeny to trace the evolution of coloniality in Aplanulata, revealing that the ancestor of Aplanulata was solitary and that coloniality was regained in the genus Ectopleura. Examination of Ectopleura larynx development reveals a unique type of colony formation never before described in Hydrozoa, in that colonies form through sexual reproduction followed by epithelial fusion of offspring polyps to adults. We characterize the expression of manacle, a gene involved in foot development in Hydra [5], to determine polyp-colony boundaries. Our results suggest that stalks beneath the neck do not have polyp identity and instead are specialized structures that interconnect polyps. Epithelial fusion, brooding behavior, and the presence of a skeleton were all key factors behind the evolution of this novel pathway to coloniality in Ectopleura

Phylogenetics of Aplanulata (Cnidaria: Hydrozoa) and the evolution and development of Ectopleura larynx

The model organism Hydra belongs to the hydrozoan clade Aplanulata. Despite being a popular model system for diverse fields of biological research, the morphology and development of Hydra are atypical of most hydrozoans. For example, most hydrozoans develop gonophores (structures housing gametes) on the body of the polyp, or release free-swimming medusae that spawn in the water column. In contrast, Hydra produce no gonophores or medusae and instead form gametes directly in the epithelia of the body column. Additionally, Hydra embryos are difficult to isolate for developmental studies (embryos encyst and are thus difficult to study), so there is currently no model species in Aplanulata for examining gene expression in developing polyps. In this dissertation, I examine the phylogenetic relationships of Aplanulata and the clade Capitata sensu stricto, originally thought to group with Aplanulata, and examine the evolution and development of the Aplanulata species Ectopleura larynx. This close relative of Hydra is ideally suited for evolutionary developmental studies because it develops directly in brooding structures, and produces attached gonophores. Because Ectopleura larynx broods on the body of the polyp, its juveniles and gonophores are easily procured for gene expression and developmental studies. My examination of Ectopleura larynx development reveals a unique type of colony formation that has never before been described in Hydrozoa in that Ectopleura larynx colonies form through sexual reproduction followed by epithelial fusion of offspring polyps to adult colonies. I characterize the expression of the paired-like homeobox gene manacle to determine polyp-colony boundaries, and suggest that stalks beneath the neck of Ectopleura larynx polyps do not have polyp identity and instead are specialized structures that interconnect polyps (stolons). Lastly, I characterize the canonical Wnt pathway in Ectopleura larynx, and examine its role in axial patterning of polyp and gonophore structures. My results are consistent with the Wnt pathway playing a role in patterning oral structures of the polyp and gonophore, and suggest that changes in expression patterns of Wnt pathway genes could explain the sexually-dimorphic morphologies of male and female gonophores of Ectopleura larynx, and the truncation of medusa development in this species

Regeneration in the lower metazoa

This item was digitized by the Internet Archive. Thesis (M.A.)--Boston UniversityThe problem of regeneration has to do with the phenomenon of growth resulting in a restoration of an old form of a mutilated organism. The process, the stimuli and factors causing it, and the effect of agents upon regeneration in the lower metazoa were discussed. The sponger, the simpxest multicellular animals, can after dissociation reconstitute the whole organism again. The arcnaeocytes were found to have tne most important role in regeneration, differentiating into gonocytes, scieroblasts, colienocytes and desmacytes, thus giving rise to the mesenchyme ana skeleton of the new sponge. The pinacocytes formed the dermal membrane and lining of the canals, while the choanocytes gave rise to the flagellated chamoers. Aggregates were formed by the amoeboid activity of the arcnaeocytes within eighteen to twenty-four hours after dissociation. On the third day after dissociation the flagellated chambers appeared, and on the fourth and fifth aays, canals appeared. Development after dissociation was then completed. Dissociated cells from different species (Microciona and Clicna) coalesce and form aggregates only with cells of their own species. The dissociated cells will not coalesce and form aggregates in pure sodium or potassium chloride solutions. The cells were also found to be sensitive to increases in osmotic pressure. Hydra, turned inside out, will regain their normal organization of the rearrangement of endoaermal ana ectodermal cells migrating in opposite directions through the mesoglea. Ectodermal or endodermal layers of hydra cultured alone do not regenerate due to the inability of one cell type to differentiate into the cell type of the other layer. Dissociated cells of hydra will fuse and form aggregates only when the three body layers are present. The pieces of a hydra must measure more than one-sixth of a millimeter in diameter to regenerate. Size also determines the number of tentacles, and the size of the hypostome formed on the regenerant. Various sections of hydra and grafts also form regenerated individuals, although in some cases the results are abnormal. The determination and organization of new polarities depended upon the rate of metabolism incorporated in the regenerating mass. In Tubularia, removal of the perisarc stimulates regeneration, as the cut end is then cathed with more oxygen. The more coenosarc exposed to oxygen the greater is the activation to form hydranth tissue. When there is an increase in the oxygen consumption there is also an increase in the rate of regeneration. The hydranth forms in relation to the oxygen supply with the oral end of the regenerant at the point of highest oxygen tension. The rate of regeneration can be measured at any level under various conditions wnen the formula R=πr^2n/t is used. Exposure of the coenosarc to sea water obliterates the already existing gradients in the stem and thus the regenerating coenosarc fragments form new polarities. The theory of dominance seems to be best explained by the transportation of substances theory, in whicn there are differences in the stem, "E", present in highest concentration at the distal end and lowest at the proximal end. There is also another factor in the stem "S", which may or may not inhibit regeneration depending on the rate of regeneration when "E" is forming new hydranths. Eudendrium and Pennaria cells fuse after dissociation in much the same manner as sponges and hydra. Light is essential for the regeneration of hydranths in Pennaria, but not for Eudendrium. Direct x-radiation inhibited regeneration of Pennaria, but screened colonies connected to those colonies radiated, did regenerate new hydranths. Podocoryne and Hydractinia are also capable of regenerating polyps. Gonionemus shows incomplete regeneration. Mnemiopsis leidyi, a ctenophore, regenerated plate rows, canal connections, and apical organs, depending on the manner in which they were cut. There was found to be no physiological gradient in Mnemiopsis. Polychoerus is the simplest flatworm to stimulate to regenerative activity as these worms have no central nervous system to influence regeneration. Many types of regeneration have been produced from stimulation of planarians to regenerate. The smallest and most irregular pieces have the capability of forming new individuals. The extensive powers of regeneration of this group are due to the localization and differentiation of the formative cells, which are found in the mesoderm. The polyclads will regenerate complete individuals from pieces taken from any part of the oody. The triclads will restore missing anterior parts onxy when the cephalic ganglia are present. Anesthetics and strychnine inhioit regeneration in the flatworms as doeo exposure to x-radiation.https://archive.org/details/regenerationinlo00gof

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

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