Advanced Cambrian hydroid fossils (Cnidaria: Hydrozoa) extend the medusozoan evolutionary history

Primitive cnidarians are crucial for elucidating the early evolution of metazoan body plans and life histories in the late Neoproterozoic and Palaeozoic. The highest complexity of both evolutionary aspects within cnidarians is found in extant hydrozoans. Many colonial hydrozoans coated with chitinous exoskeletons have the potential to form fossils; however, only a few fossils possibly representing hydroids have been reported, which still require scrutiny. Here, we present an exceptionally well-preserved hydroid found in the Upper Cambrian Fengshan Formation in northern China. It was originally interpreted as a problematic graptolite with an uncertain systematic position. Based on three characteristic morphological traits shared with extant hydroids (with paired hydrothecae, regular hydrocaulus internodes and special intrathecal origin pattern of hydrocladium), we propose this fossil hydroid as a new genus, Palaeodiphasia gen. nov., affiliated with the advanced monophyletic hydrozoan clade Macrocolonia typically showing loss of the medusa stage. More Macrocolonia fossils reviewed here indicate that this life strategy of medusa loss has been achieved already as early as the Middle Devonian. The early stratigraphical appearance of such advanced hydroid contrasts with previous molecular hypotheses regarding the timing of medusozoan evolution, and may be indicative for understanding the Ediacaran cnidarian radiation.     

A probable thecate hydroid from the upper cretaceous of southern England preserved by bioimmuration

An inferred thecate hydroid, moulded on the attachment scar of the bivalvePycnodonte vesiculare, is described from the Santonian Chalk of Kent. The living hydroid was evidently overgrown by theP. vesiculare shell and is preserved as a bioimmuration.Eisenackiella thanetensis gen. et sp. nov. is characterized by a hydrorhiza whose stolons bear hydrothecae alternately to the left and right, and a hydrocaulus consisting of several unbranched stems with alternating hydrothecae. The widely spaced stolonal hydrothecae have adnate proximal parts and erect distal parts. Assignment to an extant hydroid family is difficult: whereas the hydrorhiza resembles that of the Family Lafoeidae, the hydrocaulus is reminiscent of the Family Sertulariidae.     

Description and ecology of Cytaeis capitata n. sp. (Hydrozoa,Cytaeididae) from Bunaken Marine Park (North Sulawesi,Indonesia)

Hydrobiologia - A new hydroid species, Cytaeis capitata n. sp. (family Cytaeididae), is described. This species, an epibiont of gastropod shells living in the shallow water of the Bunaken National...     

Reproductive costs of the symbiotic hydroid Hydractinia symbiolongicarpus (Buss and Yund) to its host hermit crab Pagurus longicarpus (Say)

Studies on the interaction between the hermit crab Pagurus longicarpus and its symbiotic hydroid Hydractinia symbiolongicarpus have focused on positive effects of hydroids on their host hermit crabs (e.g., protection from predators). Yet, these benefits may be balanced with reproductive costs, which are rarely studied. Results from field observations, laboratory trials, and a mesocosm experiment indicate that female hermit crabs in hydroid-colonized shells exhibit depressed ovigery, smaller clutch sizes, and increased clutch failure relative to females in bare shells. Frequent switching between bare and hydroid-colonized shells may alleviate negative effects when the density of hydroids in the environment is low, but at high densities Hydractinia may significantly impact hermit crab reproduction.     

Green Fluorescence of Cytaeis Hydroids Living in Association with Nassarius Gastropods in the Red Sea

Green Fluorescent Proteins (GFPs) have been reported from a wide diversity of medusae, but only a few observations of green fluorescence have been reported for hydroid colonies. In this study, we report on fluorescence displayed by hydroid polyps of the genus Cytaeis Eschscholtz, 1829 (Hydrozoa: Anthoathecata: Filifera) found at night time in the southern Red Sea (Saudi Arabia) living on shells of the gastropod Nassarius margaritifer (Dunker, 1847) (Neogastropoda: Buccinoidea: Nassariidae). We examined the fluorescence of these polyps and compare with previously reported data. Intensive green fluorescence with a spectral peak at 518 nm was detected in the hypostome of the Cytaeis polyps, unlike in previous reports that reported fluorescence either in the basal parts of polyps or in other locations on hydroid colonies. These results suggest that fluorescence may be widespread not only in medusae, but also in polyps, and also suggests that the patterns of fluorescence localization can vary in closely related species. The fluorescence of polyps may be potentially useful for field identification of cryptic species and study of geographical distributions of such hydroids and their hosts.     

KIN INTERACTIONS IN A COLONIAL HYDROZOAN (HYDRACTINIA SYMBIOLONGICARPUS): POPULATION STRUCTURE ON A MOBILE LANDSCAPE

Many sessile colonial organisms intensively compete with conspecifics for growing space. This competition can result in either cooperative fusion or aggressive rejection between colonies, and some species have evolved highly polymorphic genetic systems that mediate the outcome of these interactions. Here we demonstrate the potential for interactions among close kin as the basis for the evolutionary maintenance of a genetically polymorphic allorecognition system in the colonial hydroid Hydractinia symbiolongicarpus, which lives on gastropod shells occupied by hermit crabs. Fusion between hydroids in the laboratory is restricted mainly to encounters between full siblings, whereas other encounters result in aggressive rejection. Natural selection acting on the costs or benefits of fusion between colonies could be responsible for the present maintenance of such a highly specific behavioral response, but only if encounters between fusible colonies still occur in contemporary populations. The large size of these hydroid populations and the mobility of the crabs should limit the potential for interactions among closely related hydroids on the same shell. However, RAPD polymorphisms among a large sample of hydroids from a population off the coast of Massachusetts indicate that genetically similar colonies are often found together on the same shell. Some genetic distances between colonies on the same shell were low relative to genetic distances between colonies on different shells or genetic distances between known full siblings from laboratory matings. We conservatively estimate that 2–18% of co-occurring colonies may be full sibling pairs. These observations suggest that encounters between genetically similar hydroids are common, despite the mobile nature of their habitat, and these encounters may provide frequent opportunities for natural selection to influence the evolution of cooperative and agonistic behaviors and their polymorphic genetic basis.     

拟柄突和平水母在中国的首次发现及其生活史观察

报道青岛海洋科技馆培养的和平水母属(软水母亚纲,和平水母科)一种我国的新纪录--拟柄突和平水母西 Eirene lacteoides Kubota and Horita,1992.首次提供该种水母水螅体的形态,并对各期水母体的特征进行描述,为编写水螅水母动物志提供参考.     

Probable advanced hydroid from the Early Ordovician of China

A fossil of a colonial organism with pyritized soft tissues of elongated fusiform zooids, found in the middle part of the early Floian Fenxiang Formation in Hubei Province of China, probably represents the oldest reliable record of a hydroid cnidarian. The preservation of the fossil is sufficiently different from that of associated carbonized skeletons of graptolites to exclude affinities with this group. The fossil is unlikely to be a bryozoan because of the mode of budding from proximal, not distal, parts of parent zooids, which is typical rather of hydroids. Although no thecae are preserved, the fossil, named Sinobryon elongatum gen. et sp. nov., is suggested to be a thecate hydroid, possibly related to the Haleciidae. The apparent presence of an advanced member of the thecaphoran Macrocolonia clade in strata 470 Ma old means that much of the hydroid (and cnidarian) diversification preceded the Middle Ordovician.     

The hydroid fossil record and analytical techniques for assessing the affinities of putative hydrozoans and possible hemichordates

Hydrozoan cnidarians are widespread in modern environments, but their polyps or hydroids, when not biomineralized, are generally rare in the fossil record. To assess the affinities of four hydrozoan taxa previously described on the basis of supposed fossils of non‐biomineralized hydroids, we re‐analysed the type specimens of these taxa using a combination of light and electron microscopic tools, including backscattered electron (BSE) scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDS). New morphological, ultrastructural and taphonomic data were generated for Archaeoantennularia byersi from the Devonian of Michigan, Archaeocryptolaria compacta from the Ordovician of Virginia, and Mazohydra megabertha and Drevotella proteana from the Carboniferous Mazon Creek Lagerstätte of Illinois, which are preserved as carbonaceous fossils, aluminosilicate films and iron carbonate minerals in siderite concretions, respectively. In the context of these results, we provide a review of the fossil record of non‐biomineralized hydroids, describe possible biases and changes through time in their occurrence and preservation, and evaluate the criteria commonly used to identify and interpret their fossils. Although hydroids have been reported from Phanerozoic (particularly lower Palaeozoic) rocks around the world, many putative hydroids from the Palaeozoic are poorly substantiated and may actually be hemichordates. Indeed, none of the type specimens in this study represent unequivocal hydrozoans. As shown in BSE images, metatype specimens of A. byersi possess autothecae, fusellae, stolons, stolothecae and bithecae, which decisively indicate that they are dendroid graptolites rather than hydroids. The analyses yielded no evidence that A. compacta, Mazohydra and Drevotella are hydrozoans, as their holotypes lack the diagnostic morphological, taphonomic and ecological features characteristic of purported hydroid analogues. Consequently, our results suggest that many Palaeozoic hydroids may be hemichordates and that interpretations of hydroid fossils should be tested and refined using data collected via in situ analytical techniques like BSE‐SEM and EDS.     

Symbiosis between gastropods and bryozoans in the late Ordovician of Cumbria, England

Five examples of symbiosis between gastropods and trepostome bryozoans are described from the Ashgill (late Ordovician) of Cumbria (England). The gastropods are invariably found associated with the bryozoans. whereas the bryozoans may be free-living. Encrustation is considered to have taken place, in most cases, on mature, living gastropod shells, resulting in the trepostome utilizing the shell as a surrogate basal disc. Three specimens show encrustation on an empty gastropod shell, causing the trepostome to develop a basal disc similar to non-encrusting forms. The bryozoan colony probably benefited from the symbiotic relationship by increased water flow over the colony, caused by gastropod locomotion, whereas the gastropod was afforded protection from predators. The new species Spiroecus nidhoeggi. Diplotrypa hvergelmi and Monotrypa fontinalis are described.     

Fine structure of the investing layer on the gymnoblastic hydroid Syncoryne tenella (farquhar, 1895)

The hydranth of the gymnoblastic hydroid Syncoryne tenella is invested by a cuticle approximately 530 mμ thick which is continuous with the periderm of the hydrocaulus. The ectodermal cells of the hydranth possess regularly spaced microvilli orientated with their long axis perpendicular to the ectodermal surface. The microvilli project into the cuticle, and probably serve to anchor the cuticle to the ectoderm. In the hydrocaulus the periderm is loosely applied to the ectoderm: in this region microvilli are absent from ectodermal cells. The periderm is a layered structure composed of finely filamentous material. No structural basis is found for the previously reported differential staining of peridermal layers in the hydrocaulus.     

Susceptibility to Antibiotics of Vibrio sp. AO1 Growing in Pure Culture or in Association with its Hydroid Host Aglaophenia octodonta (Cnidaria, Hydrozoa)

Vibrio harveyi is the major causal organism of vibriosis, causing potential devastation to diverse ranges of marine invertebrates over a wide geographical area. These microorganisms, however, are phenotypically diverse, and many of the isolates are also resistant to multiple antibiotics. In a previous study, we described a previously unknown association between Vibrio sp. AO1, a luminous bacterium related to the species V. harveyi, and the benthic hydrozoan Aglaophenia octodonta. In this study, we analyzed the susceptibility to antibiotics (ampicillin, streptomycin, tetracycline, or co-trimoxazole = mix of sulfamethoxazole and trimetoprim) of Vibrio sp. AO1 growing in pure culture or in association with its hydroid host by using microcosm experiments. The results of minimum inhibitory concentration (MIC) experiments demonstrated that Vibrio sp. AO1 was highly resistant to ampicillin and streptomycin in pure culture. Nevertheless, these antibiotics, when used at sub-MIC values, significantly reduced the hydroid fluorescence. Co-trimoxazole showed the highest inhibitory effect on fluorescence of A. octodonta. However, in all treatments, the fluorescence was reduced after 48 h, but never disappeared completely around the folds along the hydrocaulus and at the base of the hydrothecae of A. octodonta when the antibiotic was used at concentration completely inhibiting growth in vitro. The apparent discrepancy between the MIC data and the fluorescence patterns may be due to either heterogeneity of the bacterial population in terms of antibiotic susceptibility or specific chemical–physical conditions of the hydroid microenvironment that may decrease the antibiotic susceptibility of the whole population. The latter hypothesis is supported by scanning electron microscope evidence for development of bacterial biofilm on the hydroid surface. On the basis of the results obtained, we infer that A. octodonta might behave as a reservoir of antibiotic multiresistant bacteria, increasing the risk of their transfer into aquaculture farms.     

Regression and replacement of hydranths in thecate hydroids,and the structure of hydrothecae

In 1953 the author described a regression and replacement cycle of hydranths in Laomedea flexuosa and proposed that this is a common feature of thecate hydroids. Here examples are presented of replacement of hydranths in species from 5 families of thecates, but it has not been demonstrated that this is as common as had been thought. More continuous studies are needed. A brief consideration is given to the origin of hydrothecae and their development.     

MOLECULAR AND GEOLOGIC EVIDENCE OF SHARED HISTORY BETWEEN HERMIT CRABS AND THE SYMBIOTIC GENUS HYDRACTINIA

The paleobiogeographic histories of three North Atlantic hermit crab lineages were compared with a single-copy DNA-DNA hybridization phylogeny of their symbiotic hydroid genus Hydractinia to test hypotheses of shared history between these host and symbiont lineages. A survey of the geologic literature suggests that two vicariance events in the Quaternary are responsible for existing range disjunctions of the host hermit crab lineages. The Hydractinia phylogeny revealed two distinct clades, one with a primarily northern and the other with a primarily southern distribution. In two of three cases, hydroids associated with closely related hermits on both sides of the range disjunction appear as sister taxa in the phylogeny. A linear scaling between a measure of hydroid sequence divergence and independent geologic estimates of the timing of the vicariant events believed to have established the hermit crab range disjunctions is consistent with the claim of temporal coincidence of cladogenic and vicariance events. These findings provide evidence for shared history of symbiotic associations in two of the three cases.     

Hydroid epifaunal communities in Arctic coastal waters (Svalbard): effects of substrate characteristics

The knowledge of cryptic epifaunal groups in the Arctic is far from complete mostly due to logistic difficulties. Only recently, advances in sample collection using SCUBA diving techniques have enabled to explore delicate hydroid fauna from shallow waters. This study is the first attempt to examine the relationship between substrate property (such as size of rock, morphological characteristics of algal or bryozoan host) and hydroid community composition and diversity in the Arctic. Samples of substrates for hydroid attachment including rocks, algae, bryozoans and other hydrozoans were collected around the Svalbard. Examination revealed no substrate-specific species. The substrate property did not have a strong influence on hydroid community. Both species composition and richness were not related to colonized rock surface area and to morphological characteristic of algal host. Therefore, results indicate the opportunistic nature of hydroid fauna in terms of substrate preference. However, the presence or absence of hydroids depended on the surface area of rocky substrate. Hydroids were more often present on rocks of larger surface area. Erect hydroids and bryozoans were important attachment surface for stolonal hydroids.     

A new species of Poly dor a (Polychaeta: Spionidae) from the Indo-West Pacific and first record of host hermit crab egg predation by a commensal polydorid worm

A new spionid polychaete, Polydora robi, is described from intertidal and shallow subtidal areas in the Philippine Islands and Bali, Indonesia. Polydora robi belongs to the Polydora ciliata/ websteri species group and is characterized by a rounded prostomium, triangular occipital tentacle, needlelike posterior notosetae, and a pygidium with digitiform composite cirri surrounding the anus. Adults burrow into empty gastropod shells inhabited by hermit crabs. The burrows of the worms typically extend from an external opening in the apex of the shells to an opening in the central body whorls along the columella. The species was found to ingest the fertilized eggs and developing embryos attached to the pleopods of host hermit crabs. The occurrence of egg predation and the symbiotic relationship between polydorids and hermit crabs is discussed. Known egg predators of hermit crabs are reviewed.     

Mode of life of the Silurian uncoiled gastropod Semitubina sakoi n. sp. from Japan

Semitubina sakoi n. sp. from the late Silurian of Japan represents the second species of this genus and also the first record of a Silurian gastropod in Japan. The gastropod shells occur in a thin mudstone bed and were found to be encrusted exclusively by corallites of ? Favosites sp. These corallites reveal that encrustation proceeded as the gastropod shells grew. The ecological relationship between the two organisms is considered to be symbiotic. This mode of life allowed the coral to live on a muddy substrate because clear sea water passed over the colony as the gastropod moved along. The gastropod benefited from this relationship by being protected from shell-boring or shell-crushing predators by the encrusting corallite. In Semitubina sakoi the body whorl is separated from the penultimate one by a considerable gap in a later growth stage and S. sakoi has been cited as one of the uncoiled gastropods. The uncoiling of this gastropod results primarily from rapidly increasing whorl translation rate in the latest growth stage. Taking the symbiotic relationship with ? Favosites sp. into consideration, a deposit feeding or benthic scavenging mode of life is suggested for this gastropod.     

Paläogene Eischalenreste von Hainin (Belgien)

From Paleocene deposits from Belgium fossil egg shells of turtles are reported. A systematically not interpretable form(Testudinarum ovum) is described, together withHaininchelys curiosa n. g. n. sp. as a new genus organus for fossil eggs. Egg shells from Dinosauna, Aves, Testudines, Crocodylia and Squamata are discussed for comparison.     

Fossilized soft tissues in a Silurian platyceratid gastropod

Gastropod shells are common in the fossil record, but their fossil soft tissues are almost unknown, and have not been reported previously from the Palaeozoic. Here, we describe a Silurian (approx. 425 Myr) platyceratid gastropod from the Herefordshire Lagerst?tte that preserves the oldest soft tissues yet reported from an undoubted crown-group mollusc. The digestive system is preserved in detail, and morphological data on the gonads, digestive gland, pedal muscle, radula, mouth and foot are also available. The specimen is preserved three-dimensionally, and has been reconstructed digitally following serial grinding. Platyceratids are often found attached to echinoderms, and have been interpreted as either commensal coprophages or kleptoparasites. The new data provide support for an attached mode of life, and are suggestive of a coprophagous feeding strategy. The affinities of the platyceratids are uncertain; they have been compared to both the patellogastropods and the neritopsines. Analysis of the new material suggests that a patellogastropod affinity is the more plausible of these hypotheses.