Hydroid Stage Research Articles

On some tropical hydroids (Cnidaria: Hydrozoa), with descriptions of four new species

The present study provides a morphological account of six tropical hydroids, of which four are described as new. Halecium turbinariae sp. nov. grows exclusively on brown algae of the genus Turbinaria (Phaeophyceae: Fucales), and contains numerous zooxanthellae in its coenosarc. Nemalecium caeruleus sp. nov. occurs in a peculiar ecological niche, viz. the crevices of scleractinian corals, and is distinguished from its congeners by its sympodial mode of branching and an original, bluish-fluorescent sheen of its polyps. Antennella flava sp. nov. belongs to the A. secundaria (Gmelin, 1791) species group, but its tissues are abundantly filled with zooxanthellae, conferring it a striking yellow coloration. Macrorhynchia fallax sp. nov. imitates the fine morphology of M. philippina Kirchenpauer, 1872, although live specimens lack the characteristic irisation of the cladia met with in the latter. The peculiar, decapod crab-associated Corymorpha balssi Stechow, 1932, so far only known from the original account, is rediscovered and redescribed based on its hydroid stage and the ready-to-detach medusae. According to the morphological features of the latter, C. bitungensis (Xu, Huang & Guo, 2013), and possibly C. juliephillipsi (Gershwin et al., 2010), are considered the mature medusa stages of the same species, and are regarded as potential junior synonyms. The controversial synonymy of Tridentata borneensis (Billard, 1925) is addressed based on the examination of new material and its comparison with part of the type series, supplemented by the reinspection of the types of several nominal species subjectively assigned earlier to its synonymy. The distinctive sculpture of the hydrothecal wall leaves little doubt that it has a recent junior synonym, viz. Sertularia vervoorti Migotto & Calder, 1998, syn. nov. Conversely, the following taxa are removed from its synonymy upon the reevaluation of their taxonomic statuses: 1) Thuiaria maldivensis Borradaile, 1905 is a valid species that has a junior synonym, namely Pasythea heterodonta Jarvis, 1922 (now Dynamena), syn. nov., the former being henceforth referred to as Dynamena maldivensis (Borradaile, 1905), comb. nov., on the account of its polyps lacking an abcauline caecum; 2) Tridentata westindica Stechow, 1919, syn. nov., is a junior synonym of Tridentata turbinata (Lamouroux, 1816); 3) Sertularia tongensis Stechow, 1919 is a valid species that has a recent junior synonym, viz. Sertularia orthogonalis Gibbons & Ryland (1989), syn. nov.; 4) Sertularia tumida Allman, 1877, whose type is reportedly lost, is removed from the synonymy of Billard’s (1925a) species, on the account on its much longer internodes; 5) Sertularia malayensis var. sorongensis Leloup, 1930 remains a subjective junior synonym; 6) also reexamined was type material of the little-known, not formerly illustrated Tridentata occulta Stechow, 1926, syn. nov. of Amphisbetia distans (Lamouroux, 1816). Additionally, we provide single- (16S rRNA or COI) and multi-locus (16S, 18S and 28S rRNA) phylogenetic analyses for many families of athecate and thecate hydroids, including at least 57 species from Bali, with 25 nominal species characterized genetically for the first time. Halecium halecinum var. minor Pictet, 1893 is raised to species, as H. minor Pictet, 1893, nov. status, on both morphological and molecular grounds. Campanularia spinulosa Bale, 1888 is assigned to the genus Obelia Péron & Lesueur, 1810, as O. spinulosa (Bale, 1888), based on its genetic affinities.

Margelopsid species search taxonomic home within Corymorphidae and Boreohydridae

Planktonic lifestyle of polyps in representatives of Margelopsidae are very different from all other species in the hydrozoan clade Aplanulata. Their evolutionary origin and phylogenetic position have been the subject of significant speculation. A recent molecular study based only on COI data placed Margelopsidae as a sister group to all Aplanulata, an unexpected result because margelopsid morphology suggests affiliation with Tubulariidae or Corymorphidae. Here we used multigene analyses, including nuclear (18S rRNA and 28S rRNA) and mitochondrial (16S rRNA and COI) markers of the hydroid stage of the margelopsid species Margelopsis haeckelii and the medusa stage of Margelopsis hartlaubii to resolve their phylogenetic position with respect to other hydrozoans. Our data provide strong evidence that M. haeckelii, the type species of Margelopsis, is a member of the family Corymorphidae. In contrast, M. hartlaubii is sister to Plotocnide borealis, a member of Boreohydridae. These results call into question the validity of the genus Margelopsis and the family Margelopsidae. The systematic position of M. haeckelii is discussed in light of the phylogeny of Corymorphidae.

Systematic affinities of Zygophylacidae (Cnidaria: Hydrozoa: Macrocolonia) with descriptions of 15 deep-sea species

AbstractHydrozoans (Cnidaria) are distributed worldwide and exhibit alternating benthic polyp (hydroid) and pelagic medusan life-history forms. Zygophylacidae are a hydrozoan family with an exclusive hydroid stage throughout their life cycle. Within Hydrozoa, they are unusual in that a relatively large proportion (50%) of species occur in deep waters, but their validity and systematic affinities have been controversial for more than a century. Here, 97 deep-sea specimens, collected by manned submersible or bottom dredging, were investigated using an integrative taxonomical approach. Molecular data concatenating the 16S, 18S and 28S rRNA genes support the validity of Zygophylacidae and their placement within Macrocolonia, instead of Lafoeida. Fourteen zygophylacids and one relevant lafoeid are described or re-described, including three newly proposed species: Zygophylax lighti sp. nov. and Z. tankahkeei sp. nov. from the South China Sea, Z. pseudosibogae sp. nov. from Portugal and five species introduced by Eberhard Stechow (1883–1959) through the re-examination of type material. Four candidate generic diagnoses are discussed for future Zygophylacidae fine systematics by integrating a taxonomic review of all 74 zygophylacids. Morphological characters such as long hydrothecae and complex protective gonothecal structures mostly present in the deep-sea zygophylacids are heuristic for future functional morphology and evolutionary studies.

Diversity and life-cycle analysis of Pacific Ocean zooplankton by videomicroscopy and DNA barcoding: Hydrozoa.

Most, but not all cnidarian species in the class Hydrozoa have a life cycle in which a colonial, asexually reproducing hydroid phase alternates with a free-swimming, sexually reproducing medusa phase. They are not well known, in part because many of them are microscopic, at least in the medusa phase. Matching the two phases has previously required rearing of the organism from one phase to another, which has not often been possible. Here we show that DNA barcoding makes it possible to easily link life-cycle phases without the need for laboratory rearing. Hydrozoan medusae were collected by zooplankton tows in Newport Bay and the Pacific Ocean near Newport Beach, California, and hydroid colonies were collected from solid substrates in the same areas. Specimens were documented by videomicroscopy, preserved in ethanol, and sent to the Canadian Centre for DNA Barcoding at the University of Guelph, Ontario, Canada for sequencing of the COI DNA barcode. In the order Anthoathecata (athecate hydroids), DNA barcoding allowed for the discrimination between the medusae of eight putative species of Bougainvillia, and the hydroid stages were documented for two of these. The medusae of three putative species of Amphinema were identified, and the hydroid stages were identified for two of them. DNA barcodes were obtained from medusae of one species of Cladonema, one adult of the by-the wind Sailor, Velella velella, five putative species of Corymorpha with the matching hydroid phase for one; and Coryne eximia, Turritopsis dohrnii and Turritopsis nutricula with the corresponding hydroid phases. The actinula larvae and hydroid for the pink-hearted hydroid Ectopleura crocea were identified and linked by DNA barcoding. In the order Leptothecata (thecate hydroids) medusae were identified for Clytia elsaeoswaldae, Clytia gracilis and Clytia sp. 701 AC and matched with the hydroid phases for the latter two species. Medusae were matched with the hydroid phases for two species of Obelia (including O. dichotoma) and Eucheilota bakeri. Obelia geniculata was collected as a single hydroid. DNA barcodes were obtained for hydroids of Orthopyxis everta and three other species of Orthopyxis. One member of the family Solmarisidae, representing the order Narcomedusae, and one member (Liriope tetraphylla) of the order Trachymedusae were recognized as medusae. The results show the utility of DNA barcoding for matching life-cycle stages as well as for documenting the diversity of this class of organisms.

Coincident Mass Occurrence of Gelatinous Zooplankton in Northern Norway

In autumn 2015, several sources reported observations of large amounts of gelatinous material in a large north Norwegian fjord system, either caught when trawling for other organisms or fouling fishing gear. The responsible organism was identified as a physonect siphonophore, Nanomia cara, while a ctenophore, Beroe cucumis, and a hydromedusa, Modeeria rotunda, were also registered in high abundances on a couple of occasions. To document the phenomena, we have compiled a variety of data from concurrent fisheries surveys and local fishermen, including physical samples, trawl catch and acoustic data, photo and video evidence, and environmental data. Because of the gas-filled pneumatophore, characteristic for these types of siphonophores, acoustics provided detailed and unique insight to the horizontal and vertical distribution and potential abundances (~0.2-20 colonies∙m-3) of N. cara with the highest concentrations observed in the near bottom region at ~320 m depth in the study area. This suggests that these animals were retained and accumulated in the deep basins of the fjord system possibly blooming here because of favorable environmental conditions and potentially higher prey availability compared to the shallower shelf areas to the north. Few cues as to the origin and onset of the bloom were found, but it may have originated from locally resident siphonophores. The characteristics of the deep-water masses in the fjord basins were different compared to the deep water outside the fjord system, suggesting no recent deep-water import to the fjords. However, water-masses containing siphonophores (not necessarily very abundant), may have been additionally introduced to the fjords at intermediate depths, with the animals subsequently trapped in the deeper fjord basins. The simultaneous observations of abundant siphonophores, hydromedusae, and ctenophores in the Lyngen-Kvaenangen fjord system are intriguing, but difficult to provide a unified explanation for, as the organisms differ in their biology and ecology. Nanomia and Beroe spp. are holopelagic, while Modeeria rotunda has a benthic hydroid stage. The species also have different trophic ecologies and dietary preferences. Only by combining information from acoustics, trawling, genetics, and local fishermen, were the identity, abundance, and the vertical and horizontal distribution of the physonect siphonophore, Nanomia cara, established.

Loss of metagenesis and evolution of a parasitic life style in a group of open-ocean jellyfish

Loss or stark reduction of the free-swimming medusa or jellyfish stage is common in the cnidarian class Hydrozoa. In the hydrozoan clade Trachylina, however, many species do not possess a sessile polyp or hydroid stage. Trachylines inhabiting freshwater and coastal ecosystems (i.e., Limnomedusae) possess a metagenetic life cycle involving benthic, sessile polyp and free-swimming medusa. In contrast, the paradigm is that open ocean inhabiting, oceanic trachylines (in the orders Narcomedusae and Trachymedusae) develop from zygote to medusa via a free-swimming larva, forgoing the polyp stage. In some open-ocean trachylines, development includes a sessile stage that is an ecto- or endoparasite of other oceanic organisms. We expand the molecular-based phylogenetic hypothesis of trachylines significantly, increasing taxon and molecular marker sampling. Using this comprehensive phylogenetic hypothesis in conjunction with character state reconstructions we enhance understanding of the evolution of life cycles in trachyline hydrozoans. We find that the polyp stage was lost at least twice independently, concurrent with a transition to an oceanic life style. Further, a sessile, polypoid parasitic stage arose once, rather than twice as current classification would imply, in the open ocean inhabiting Narcomedusae. Our results also support the hypothesis that interstitial species of the order Actinulida are directly descended from direct developing, oceanic trachylines.

Margelopsis gibbesii (McCrady, 1859) (Cnidaria, Hydrozoa): taxonomic review, and conservation of usage by designation of a lectotype.

The binomen Nemopsis gibbesii McCrady, 1859, originally applied to a species of hydromedusa and its supposed hydroid from South Carolina, USA, has been known for more than a century to encompass two species. The medusa stage is conspecific with that of Nemopsis bachei L. Agassiz, 1849, while the hydroid stage is referable to the genus Margelopsis Hartlaub, 1897. Both that hydroid, and the medusa stage now subjectively linked to it, are commonly assigned to M. gibbesii. With no type having ever been designated for McCrady's species, a lectotype is designated to stabilize nomenclature of the species and serve as the standard for application of the name. In the absence of type specimens, an illustration of the hydroid of N. gibbesii by McCrady is chosen as lectotype, thereby conserving the name Margelopsis gibbesii in its accustomed usage. Hydroids and medusae of the species are re-described from new material, the cnidome of both stages is characterized, and a taxonomic review is given. The hydroid stage is reported for the first time since its original description in the mid-19th century. Medusae of M. gibbesii are also seen infrequently, having been reported only six times earlier.

The non-Siphonophoran Hydrozoa (Cnidaria) of Salento, Italy with notes on their life-cycles: an illustrated guide.

The majority of Hydrozoa is represented by not readily noticeable, small species. In recent decades, however, taxonomic knowledge of the group has increased worldwide, with a significant number of investigations focused on the Mediterranean Sea. Over more than two decades, 115 species of hydrozoans were recorded from coastal waters along nearly 300 km of the Salento Peninsula (Apulia, Italy). For each species, records from different collections were merged into single sheets of a general database. For each species, the following information is reported: description, cnidome, biology, occurrence in Salento, worldwide distribution, and bibliography. Descriptions refer to the benthic hydroid stage and, when present, also to the planktonic medusa stage. The 115 species of Hydrozoa, recorded along the Salento coastline, represent 25% of the Mediterranean Hydrozoa fauna (totaling 461 species), and nearly 3% of 3,702 world's known species covered in a recent monograph. Four species are non-indigenous, three of them with invasive behavior (Clytia hummelincki, Clytia linearis, and Eudendrium carneum), and one species now very common (Eudendrium merulum) in Salento. The complete life cycle of Clytia paulensis (Vanhöffen, 1910) is described for the first time.

On a collection of hydroids (Cnidaria, Hydrozoa, Hydroidolina) from the west coast of Sweden, with a checklist of species from the region

An account is given of 48 species identified in a small collection of hydroids from the west coast of Sweden. Assigned to39 genera and 18 families, most are well-known from boreal waters of the North Atlantic Ocean. Campanulina paniculaG.O. Sars, 1874 is referred to Racemoramus, a new genus of leptothecates distinguished in part by having monopodialgrowth, rigid and non-segmented hydrocauli, and grape-like clusters of hydrothecae that arise at irregular intervals fromthe stem. The name Sertularia dumosa (now Lafoea dumosa) is taken to have been made available by Fleming (1820), notFleming (1828). As such, it is not threatened by a virtually unused subjective synonym (Lafoea cornuta Lamouroux,1821). Aselomaris michaeli Berrill, 1948 and Rhizorhagium navis Millard, 1959 are regarded as synonyms and combinedunder the binomen Pachycordyle michaeli (Berrill, 1948). Confusion in the literature over the identity of Sertularia teneraG.O. Sars, 1874 is addressed, and distinctive characters of the species are discussed. A species often misidentified as S.tenera is assigned to Sertularia spitzbergensis (Jäderholm, 1909); the name spitzbergensis is elevated in rank from sub-specific to specific, and assigned priority over its simultaneous synonym siberica Jäderholm, 1909 under the First ReviserPrinciple. Gonothecae of Clytia gigantea (Hincks, 1866) (type locality: Lamlash Bay, UK) are reported for the first timein material from Europe. Although much like Clytia hemisphaerica, this species is retained as valid due to its remarkablyrobust colony form, elongate and gradually tapered hydrothecae, and linguiform rather than wavy or pointed marginalcusps. Eudendrium album Nutting, 1896, Pachycordyle michaeli (Berrill, 1948), and the hydroid stage of Halitholus cir-ratus Hartlaub, 1913 are reported for the first time from the study area. A checklist of hydroids from the study area is included.

Sympagohydra tuuli gen. nov. and sp. nov. (Cnidaria: Hydrozoa) a cool hydroid from the Arctic sea ice

A new interstitial hydroid, Sympagohydra tuuli, has been collected from the three-dimensional brine channel system of the coastal fast ice off Barrow, Alaska (71°N 156ºW) in 2003 to 2006. This is the first cnidarian species described from the sea ice interstitial habitat. A morphological and systematic account of the new species is provided here. The hydroid stage is represented by solitary naked polyps, which become almost spherical under contraction. Body length can vary from 200 µm to >1 mm according to the degree of relaxation. The aboral side is extensible into a tubular foot-like projection made by epidermal tissue only, a typical feature of representatives of Protohydridae, order Capitata. However, in contrast to the other two known Protohydridae species, S. tuuli is characterized by three to four solid filiform tentacles, armed with microbasic mastigophore and desmoneme cnidocysts, and located at the base of a short hypostome bearing stenoteles. A small number of mastigophores are also scattered along the body column. Due to its unique combination of features, this taxon is designated here as a new species, and the new genus Sympagohydra is established as a new member of the class Hydroidomedusa, subclass Anthomedusae, order Capitata, family Protohydridae, to accommodate S. tuuli.

Phylogeny of Capitata and Corynidae (Cnidaria, Hydrozoa) in light of mitochondrial 16S rDNA data

New sequences of the partial rDNA gene coding for the mitochondrial large ribosomal subunit, 16S, are derived from 47 diverse hydrozoan species and used to investigate phylogenetic relationships among families of the group Capitata and among species of the capitate family Corynidae. Our analyses identify a well‐supported clade, herein named Aplanulata, of capitate hydrozoans that are united by the synapomorphy of undergoing direct development without the ciliated planula stage that is typical of cnidarians. Aplanulata includes the important model organisms of the group Hydridae, as well as species of Candelabridae, Corymorphidae, and Tubulariidae. The hypothesis that Hydridae is closely related to brackish water species of Moerisiidae is strongly controverted by 16S rDNA data, as has been shown for nuclear 18S rDNA data. The consistent phylogenetic signal derived from 16S and 18S data suggest that both markers would be useful for broad‐scale multimarker analyses of hydrozoan relationships. Corynidae is revealed as paraphyletic with respect to Polyorchidae, a group for which information about the hydroid stage is lacking. Bicorona, which has been classified both within and outside of Corynidae, is shown to have a close relationship with all but one sampled species of Coryne. The corynid genera Coryne, Dipurena, and Sarsia are not revealed as monophyletic, further calling into question the morphological criteria used to classify them. The attached gonophores of the corynid species Sarsia lovenii are confirmed as being derived from an ancestral state of liberated medusae. Our results indicate that the 16S rDNA marker could be useful for a DNA‐based identification system for Cnidaria, for which it has been shown that the commonly used cytochrome c oxidase subunit 1 gene does not work.

A checklist of the Medusae (Hydrozoa, Scyphozoa and Cubozoa) of Mexico

A list of 169 medusae species in 45 families recorded in Mexican waters is presented for the first time. 86 species (50.8%) were found in the Pacific Ocean, 75 species (44.3%) in the Gulf of Mexico, and 88 (52%) in the Mexican Caribbean Sea. Only 17 species (10%) were common to the three regions. The superclass Hydrozoa, the most diverse one, is represented by 151 species (89%), the Scyphozoa by 16 species (9.5%) and the Cubozoa by 3 (1.8%). Among the Hydrozoa, up to 6 new species have been described from Mexican waters. It is expected that the number of species will grow as surveys that include the hydroid stages and their laboratory-released medusae, as well as benthic and deep-living medusofauna are undertaken in both the Atlantic and the Pacific coasts of Mexico.

The hydroid and medusa of <i>Sarsia bella</i> sp. nov. (Hydrozoa, Anthoathecatae, Corynidae), with a correction of the life cycle of <i>Polyorchis penicillatus</i> (Eschscholtz)

A new hydrozoan, Sarsia bella sp. nov. is described in both its hydroid and medusa stage from north of Puget Sound, Washington in the San Juan Islands, USA and off the southernmost tip of Vancouver Island, Canada. The medusa is distinguished from other Sarsia species by 16 exumbrellar nematocyst patches and in being more transparent or glass like when living than any other known species of the genus. The exumbrellar nematocyst patches become indistinct in mature specimens and in those crowded in culture, with single nematocysts increasingly spaced out. The hydroid, both field-collected and raised in culture from its medusa, forms small, upright stolonal colonies not more than 1.5 mm high. The hydranths bear an oral whorl of four to five capitate tentacles, and immediately below a second whorl of slightly shorter capitate tentacles. In thriving colonies there is occasionally a whorl of small filiform tentacles on the lower part of the hydranth. Medusa buds develop in the middle of hydranth below the capitate tentacles and above the reduced filiform tentacles, if present. Young medusae are liberated with the typical 16 exumbrellar nematocyst patches. The hydroid of this species was originally mistaken for the hydroid of Polyorchis penicillatus . Brinckmann-Voss (1977) reported a small corynid hydroid living on the margin of rock scallop shells. Medusae liberated from this hydroid were at that time believed to be those of Polyorchis penicillatus (Eschscholtz) present in the plankton. Immature medusae of these two species appear strikingly similar, especially with regard to their exumbrellar nematocyst patches, four tentacles and abaxial ocelli. Since then however, this connection has been proven wrong, because an identical hydroid was raised from the medusae of the new species Sarsia bella . Second generation medusae raised in the laboratory were carefully compared with medusae liberated from field collected hydroids (thought to have been Polyorchis penicillatus ), and these were found to be identical with meduse of Sarsia bella. Young medusae of P. penicillatus from the plankton can be clearly distinguished from S. bella medusae by the number of their exumbrellar nematocyst patches. Both P. penicillatus and Sarsia bella have eight adradial rows of exumbrellar nematocyst patches when young, however each row in P. penicillatus consists of at least three vertically alligned patches whereas each row never has more than two patches in S. bella . In both species the patches consist of microbasic p-mastigophores, but capsules in the case of P. penicillatus are larger than those in S. bella . Later stages of the two species are easily distinguished using other morphological characters with only four tentacles in S. bella and more than four in P. penicillatus . No hydroid of the genus Polyorchis has been described to date.

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

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.

Invertebrate introductions in marine habitats: two species of hydromedusae (Cnidaria) native to the Black Sea, Maeotias inexspectata and Blackfordia virginica, invade San Francisco Bay

The hydrozoans Maeotias inexspectata Ostroumoff, 1896 and Blackfordia virginica Mayer, 1910, believed to be native to the Black Sea (i.e. Sarmatic) and resident in a variety of estuarine habitats worldwide, were found as introduced species in the Petaluma River and Napa River, California, in 1992 and 1993. These rivers are mostly-estuarine tributaries that flow into north San Francisco Bay. Both species appeared to be well-established in this brackishwater habitat. Salinities at the collection sites were about 11‰ during the summer, rising to nearly 20‰ in the early autumn and falling to near 0‰ in the winter. Large numbers of all sizes of both species of medusae were observed and collected, indicating that the hydroid stages of the life cycles of the two are also well-established in these rivers. In the Petaluma River, populations of both species were at maximum in late July, with numbers of individuals declining through August and into September; the Napa River was sampled only in October, and at that time only B. virginica was found. Examination of full guts of M. inexspectata and B. virginica medusae revealed that both species had fed nearly exclusively on small crustaceans, principally barnacle nauplii, copepods and their eggs and nauplii, and crab zoea larvae (M. inexspectata only). All the M. inexspectata medusae were males, indicating that the population has probably developed from the introduction of perhaps only a single male polyp or polyp bud. In spite of its inability to reproduce sexually, this population appears to be maintained by the prodigious ability of the polyp to bud and reproduce asexually, and is fully capable of invading additional low-salinity habitats from its present Petaluma River site. Male and female B. virginica medusae were collected in both the Petaluma River and the Napa River, indicating that B. virginica may have been introduced by either the polyp or medusa stage (or both), but that multiple individuals (of both sexes) must have arrived from another port in one or more invasions. As indicated for M. inexspectata, the B. virginica population will also probably seed new populations in San Francisco Bay and elsewhere. Based on its cnidome as well as the morphology of both medusa and polyp, M. inexspectata has been reclassified by moving it from the family Olindiidae, Limnomedusae, to the family Moerisiidae, Anthomedusae.

Bougainvillia aberrans (Cnidaria, Hydrozoa), a new species of hydroid and medusa from the upper bathyal zone off Bermuda

Bougainvillia aberrans n.sp. is described from Bermuda in the western North Atlantic Ocean. Specimens were collected at a depth of 150 fathoms (274 m) from the polypropylene buoy line of a crab trap. The hydroid colony of B. aberrans is erect, with a polysiphonic hydrocaulus, a smooth to somewhat wrinkled perisarc, hydranths having a maximum of about 16 tentacles, and medusa buds arising only from hydranth pedicels. Medusae liberated in the laboratory from these hydroids differ from all other known species of the genus in having a long, spindle-shaped manubrium, lacking oral tentacles, having marginal tentacles reduced to mere stubs, and being very short-lived (surviving for a few hours at most). Gonads develop in medusa buds while they are still attached to the hydroids, and gametes are shed either prior to liberation of the medusae or shortly thereafter. The eggs are surrounded by an envelope bearing nematocysts (heterotrichous microbasic euryteles). The cnidome of both hydroid and medusa stages consists of desmonemes and heterotrichous microbasic euryteles. The diagnosis of the genus Bougainvillia is modified to accommodate this new deep-water species.

Evolution in leptolid life-cycles (Cnidaria: Hydroida)

The medusae of many hydroids remain attached to the colony, often in a vestigial state. Evolutionary origins are sometimes thus obscured. Some authorities have considered these derived hydroid life-cycles as paedomorphic; and regarded the hydroid stage as a prolonged larva. In some genera, for example in the familiar but unusual Obelia, a re-evolution of the medusa stage has been proposed. These theories are evaluated. Primitively, the larval stage throughout the Cnidaria is the planula. Some possible processes in the re-evolution of the medusa are discussed but the hypothesis is discounted. The origin of medusoid coelenterates is taken to be wholly polypoid, medusae being evolved later as modified and released reproductive polyps. The subsequent evolutionary retention and suppression of the medusa stage is discussed and some physiological processes perhaps leading to it are considered. This direction of evolution is related to the advantages of perennation in large, iterated colonies and consequent larva...

Motile sexual stages and evolution of Leptomedusae (Cnidaria)

Abstract The production of free medusoids is considered to be a transition from the production of medusae to the abolition of this stage of the life cycle, within a generalized process of paedomorphosis occurring within hydromedusae, in which the hydroid stage is the larva and the medusa stage the adult. The discovery of a species of Haleciidae producing free medusoids allows the reconstruction of the phylogeny of this family according to the following sequence of genera: Campalecium (producing medusae); Hydrantbea producing free medusoids); Hydrodendron (with sporosacs and nematophores); Scoresbia (with sporosacs and nematothecae); Ophiodissa (with sporosacs and nematothecae, branched); Phylactotbeca (with sporosacs, differentiated nematothecae and hydrothecae, branched). The affinities of the medusa stages between Campalecium and Eucbeilota indicate that the Haleciidae originated by the evolution of hydroids of the family Campanulinidae s.l. The Haleciidae evolved further, giving rise to the Plumulariid...

HYDROID AND YOUNG MEDUSA STAGES OFDIPURENA STRANGULATA(HYDROZOA, CORYNIDAE)

The hydroid stage in the life history of Dipurena strangulata, a relatively well-known medusa along the United States east coast, is described for the first time. A previous description of the young medusa does not accord with observations recorded here, but is similar to and may have been based on young Linvillea agassizi rather than D. strangulata. Of the described hydroids of Dipurena, D. strangulata is most like D. reesi morphologically, but differs in the position of the filiform tentacles and the number of endodermal cells in the capitate tentacles. The status of the various species of Dipurena described from the North American Atlantic coast is reviewed.

OBSERVATIONS ON THE BIOLOGY AND DEVELOPMENT OF STAUROCLADIA PORTMANNI SP. N. (ANTHOMEDUSAE, ELEUTHERIDAE)

A new species of Anthomedusae, Staurocladia portmanni sp. n. (Anthomedusae, Eleutheridae), is described. The medusa and hydroid stages were collected from the sea and cultivated in the laboratory. Location: Gulf of Naples, Italy. The medusa differs from other species of the genus Staurocladia in possessing two additional lateral cnidocyst bulbs on the main branch of the tentacles, cnidocyst bulbs around the mouth, and protuberances of the radial canals into the exumbrella. The hydroid differs from other species of the genus Staurocladia only in having less medusae buds per polyp. The medusa is found at a depth of 15 to 30 m in Posidonia beds; the hydroid at a depth of 30 m in algae material of Halimeda sp. and Udothea sp.