sidered according to provisions of the International Code of Zoological Nomenclature (International Commission on Zoological Nomenclature [iczn|, 1985). Some of the nomenclatural problems encountered have been resolved here, while others will require submissions to the commission. Questions regarding the identity, synonymy, and systematic positions of taxa arose repeatedly during the course of this study. One quandary in particular involved the extent to which nominal species should be combined or divided. The hydrozoan literature is replete with extremes of taxonomic "lumping" and "splitting," and the confusion resulting from both. For example, Duchassaing and Michelotti (1864) viewed practically every morphological form of the hydrocoral Millepora Linnaeus, 1758, from the Caribbean as a distinct species, whereas Hickson (1898a, 1898b) recognized only one species in the genus worldwide. Most authors now follow Boschma (1948) in recognizing three species in the Caribbean, and about a dozen worldwide. Nevertheless, determining how far to go in combining or splitting nominal species is largely a matter of personal opinion. Most recent hydrozoan systematists have tended to be "taxonomic lumpers," and generally broad taxa have been recognized here. Reasons why relatively few species of hydroids are believed to exist worldwide were briefly stated by Cornelius (1981). Related to the question of lumping or splitting of taxa is the interpretation of hydroid species distribution. According to literature records, many species of hydroids are virtually cosmopolitan. Admittedly, certain hydroids are well adapted for long-range dispersal, and their rate of speciation seems to be rather slow (Cornelius, 1981). Yet the question arises whether some species are as widely distributed as records indicate, or whether their reported range is partly an artifact of the hydrozoan taxonomist's inability to discriminate distinct but closely related species. Hydrozoan classification is complicated by many factors, including the following: (1) the existence of separate hydroid and medusa generations in many species; (2) the legacy of separate classifications for hydroids and medusae; (3) the production of free medusae and fixed gonophores in closely related species; (4) the differential reduction of male and female gonophores in certain species; (5) the production in some taxa of morphologically dissimilar medusae by virtually indistinguishable hydroids, and vice versa; (6) the morphological variation sometimes displayed within a given taxon; (7) the scarcity of reliable taxonomic characters in various taxa; (8) the general lack of knowledge concerning the biology of these animals, including life cycles of many species. Classification of the order Athecatae Hincks, 1868, in particular is currently in a state of flux. Most authors over the past 30 years have regarded the Capitata Kiihn, 1913, as the most primitive suborder of the Hydrozoa, largely following Rees (1957). Athecate classification has been extensively modified recently by Peters...

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Hydroids investigated in estuaries of Virginia and South Carolina, USA, were characteristically seasonal in occurrence. Of 20 species studied in Virginia, 14 were active only during warmer months and 6 only during colder months of the year. Seven of the 18 species examined in South Carolina were active all year, whereas 9 were active only in warmer months and 2 only during colder months. Reflecting the differing temperature regimes of the two study areas, warm-water species were active for a longer period of time in South Carolina than in Virginia; cold-water species were active longer in Virginia than in South Carolina. Warm-water species commenced activity in late winter or spring at higher temperatures than those coinciding with hydranth regression in autumn or early winter. Activity in cold-water species began at lower temperatures than those observed at regression in spring. Correlations were apparent in the seasonality, water temperature tolerances, and latitudinal distribution of most species. Field observations and laboratory experiments demonstrated that a number of species survived unfavourable periods as dormant coenosarc in stems and stolons. With the return of favourable conditions, new growth began and hydranths were regenerated from dormant tissue. Water temperature is considered the prime factor influencing the seasonal activity–inactivity cycles of hydroids in the two study areas.

A systematic account is given of 17 families, 25 genera, and 32 species of anthoathecate hydroids and limnopolyps reported from Hawaii. Applying Reversal of Precedence provisions in zoological nomenclature, the familiar hydrozoan genus names Hydractinia Van Beneden, 1844a, Bimeria Wright, 1859a, and Porpita Lamarck, 1801 are designated as valid and as nomena protecta, while seldom-used older names threatening them (the synonyms Echinochorium Hassall, 1841 and Manicella Allman, 1859a, and the homonym Porpita Soldani, 1789 respectively) are relegated to nomena oblita. Also designated a nomen oblitum is the name Pyxidium Leuckart, 1856, threatening its junior but widely used synonym Ectopleura L. Agassiz, 1862. The species name Bimeria vestita Wright, 1859a is rendered valid and a nomen protectum, while its virtually unused senior synonym Manicella fusca Allman, 1859 becomes a nomen oblitum. Hydrodendrium Nutting, 1905 is reinstated as a valid genus, distinct from Hydractinia and replacing its junior objective synonym Nuttingia Stechow, 1909. The spelling of Hydrodendridae Nutting, 1905 is emended to Hydrodendriidae, but that family name is retained as a synonym of Hydractiniidae. Usage of the familiar generic name Sphaerocoryne Pictet, 1893 is upheld by recognizing it and its former senior subjective synonym Corynetes Haeckel, 1879 as valid. The correct spelling of the family name originally founded as Olindiadae Haeckel, 1879 is taken to be Olindiidae, and spelling of the species name Solanderia misakinensis (Inaba, 1892), first established as Dendrocryne (sic) misakii, is stabilized. One new species, Stylactaria munita, is described from shallow waters at Hawaii Kai, Oahu. Lectotypes are designated for Corydendrium corrugatum Nutting, 1905 and Corydendrium minor Nutting, 1905 (=Turritopsis minor), both originally described from Hawaii. Type material of Balea mirabilis Nutting, 1905 (=Balella mirabilis), originally described from waters between the islands of Molokai and Maui, could not be located. Six anthoathecate species [Corydendrium parasiticum (Linnaeus, 1767), Bimeria vestita, Amphinema sp., Eudendrium carneum Clarke, 1882, Ectopleura viridis (Pictet, 1893), and Sphaerocoryne bedoti Pictet, 1893] are recorded from Hawaii for the first time.

Based largely on collections from the Calanus–Salvelinus expeditions, 54 species of thecate hydroids were identified from the shelf waters of northern Canada between northeastern Newfoundland and the Alaska–Yukon border. Common species included Halecium muricatum, Calycella syringa, Campanularia integra, C. speciosa, C. volubilis, Gonothyraea loveni, Filellum serpens, Lafoea gracillima, Sertularella polyzonias, S. tricuspidata, Sertularia schmidti, and S. similis. Halecium groenlandicum, H. scutum, Cuspidella procumbens, Calycella gracilis, and Sertularia schmidti are new records for North America; Ptychogena lactea is previously known from this continent only as the medusa. Twenty-two species are reported in northern Canada for the first time, bringing to 71 the number of thecate species recorded from the region. Nearly half of the 71 species recorded are circumpolar in distribution, and over two-thirds transgress both arctic and subarctic zones.Most samples had a paucity of hydroids, particularly those from the high arctic. Collection records indicate that the most favourable regions for hydroids in northern Canada are the Strait of Belle Isle, eastern Ungava Bay, eastern Hudson Strait, northern and southeastern Hudson Bay, Foxe Channel, and northern Foxe Basin.

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Sixty species of hydroids, assigned to 24 families and 39 genera, are recognized and discussed in a collection of material from the southwest coast of Florida. One new species (Clytia joycei) is described from turtlegrass (Thalassia testudinum) and reported as well from the Caribbean coast of Panama. Under provisions of the First Reviser Principle in the International Code of Zoological Nomenclature, Antennopsis nigra Nutting, 1900 is assigned precedence over its simultaneous synonym A. longicorna Nutting, 1900. Also included as a synonym of A. nigra is A. sinuosa Fraser, 1947b. The species is now assigned to Nemertesia Lamouroux, 1816, as N. nigra. Following Reversal of Precedence provisions in the code, the well-known name Halecium nanum Alder, 1859 is designated as valid and conserved as a nomen protectum, while Hydra articulata Bosc, 1797 is relegated to a nomen oblitum. The genus Monotheca Nutting, 1900 is upheld as valid on the basis of both morphological and molecular evidence. Sertularia pourtalesi Nutting, 1904, a seldom-reported species, is assigned to Dynamena Lamouroux, 1812 and recognized as distinct from D. disticha (Bosc, 1802). Calyptospadix cerulea Clarke, 1882 and Bimeria franciscana Torrey, 1902 (also known as Garveia franciscana) are taken to be conspecific, with Calyptospadix Clarke, 1882 treated as a valid genus. Confusion over the identity of Lovenella gracilis Clarke, 1882 in literature on North American hydroids is addressed, and topotypic specimens from the Chesapeake Bay region are illustrated to document characters that distinguish the species. Campanularia colombiana (Wedler, 1976) is reported for the first time outside the Caribbean coast of Colombia. The fauna studied here consists largely of species known to occur in the tropical and subtropical western Atlantic. [Zoobank URL: urn:lsid:zoobank.org:act:4C926BE2-D75D-449A-9EAD-14CADACFFADD]