records from the Gulf proper are starred in the check list. The Texas records are of exceptional interest, however, as only three hydroids had previously been recorded from those waters; they were included in the writer's account of the hydroids of Louisiana and Texas (Deevey 1950), a zoogeographic discussion that was founded primarily on a small collection made by J. W. Hedgpeth. ZOOGEOGRAPHY The list of 183 species looks impressive, but it would be idle to pretend that the hydroids of the Gulf are well-known. Tropical regions generally have a wealth of species, but hydroid habitats are probably no more extensive in the tropics than elsewhere. The rarity of the rarest species is correspondingly greater, and it is unlikely that more than half the hydroids living in the Gulf have yet been found there. Partly because of inadequate collecting and partly because shallow water hydroids are always under suspicion as fouling organisms, little can be said about the meaning of their geographic distribution. Of the total of 183 hydroid species known from the Gulf of Mexico, 95 are also found in the Caribbean and another 18, though not yet recorded from the Caribbean, are known from the eastern tropical Pacific. The remaining 70 species include some of the most interesting. Some of the 70, of course, are known only from the Gulf, but while a few true endemics are to be expected it is too early to say which ones they are; at any rate, no common species is known to be endemic. The interesting members of the group of 70 are those whose main range is otherwise boreal. The boreal species among the hydroids of Texas and Louisiana have already been discussed (Deevey 1950). They include several, such as Podocoryne carnea, that are unknown in the warmer parts of the Gulf, and at least one, Tubularia crocea, whose ecology is well enough understood to indicate that it could not flourish in southern Florida. To the list of supposed relicts of a glacial age of the Pleistocene given in the earlier paper may be added the name of Cladocarpus flexilis, a moderately deep water species taken at three stations off Mobile but not otherwise known south of Cape May. In several other cases we have the familiar phenomenon of a 0 shallow water boreal species occurring at considerable depths in the Gulf (and Caribbean): Eudendrium tenellum, Lafoea dumosa, L. gracillima. Another way of looking at the facts is this: of 156 species known from the Caribbean, 61 are not known from the Gulf; 29 of them, at least, are common enough in the Caribbean to have been taken at more than one station. Hydroid statistics are scarcely necessary to prove the point, but it is obvious that the Gulf is not a strictly tropical body of water. Low winter temperatures and low and variable salinity, particularly along the northwestern shore, are only some of the factors that must be responsible for maintaining a different "fauna" in the Gulf of Mexico. The 95 species that are common to the Gulf and the Caribbean present different problems. Most of them are definitely warm water types, although a high proportion belong to the tropical flotsam (especially sargassum) fauna and so may not be true residents of the Gulf. Seventy of the Gulf hydroids and 59 of the 156 Caribbean species are represented in the much larger list of 312 species recorded from the eastern tropical Pacific. The richness of the Pacific fauna, which is known almost exclusively from the Allan Hancock collection (Fraser 1948), is another indication that the Caribbean hydroids have been inadequately collected; it is surely correct to suppose that the 18 species common to the Gulf and the eastern tropical Pacific will appear in the Caribbean, along with many others. What is surprising is that nearly half of the tropical Atlantic hydroids cross the Isthmus of Panama without undergoing specific differentiation. If one cares for statistical statements, the "strength of the relationship" between the Gulf and Pacific faunas is nearly as great (38 percent) as is that between the Gulf and Caribbean faunas (52 percent). The Isthmus of Panama is not very old, and many biogeographers have supposed that it is younger than most of the species of marine organisms (Schuchert 1935). The problem is related to that of Tethyan distributions; pan-tropical species (more usually genera) are supposed to have had their ranges established in the Tethys Sea, of Cretaceous and early Tertiary age, only to have them sundered by the rise of central Asia (see Ekman 1934, 1935, for review). If disjunct distributions in the Mediterranean and the Indian western Pacific regions have had this origin, there is no reason to doubt that the Isthmus of Panama was crossed about the same time by the same species, or some of them. The species that are perhaps most likely to have spread so widely and to have crossed modern land barriers so freely are now truly pan-tropical species, but the evidence they provide, according to the conventional canons of biogeography, is ruled invalid by the possibility that they are spreading today. Unhappily, if one chooses to follow the rules and exclude the pan-tropical species, it can only be said that the remaining species prove nothing, at least as far as hydroids are concerned. The reason is not so much biogeographic as taxonomic. The number of hydroids common to the two sides of Central America is large, but an even larger number is common to the two coasts of North America taken as a whole. According to Fraser's tabulation (1944), 123 species are known from east and west coasts of the Americas, and by no means all of these are circumpolar. Neither are the tropical species all pan-tropical. The "American" distribution pattern is far too common to be accidental, but its commonness raises doubts about the taxonomy. Fraser was a sound, careful worker with a "good eye" for specific differences. However, his experience, though enormous, was largely confined to the Americas. When one remembers that the hydroids of the East Indies are poorly known (only three families of the Siboga hydroids having been reported by Billard before his death), one cannot escape the suspicion that many species apparently endemic to the American tropics are still to be collected, or are already known under other names, from other parts of the world. Apart from this taxonomic difficulty, inadequate knowledge of the hydroids of the western Pacific and Indian Oceans imposes another limitation on the case for Tethyan paleogeography, for western Atlantic-western Pacific disjunctions have often been used (however unwisely) in building such a case, and we know of no certain examples among hydroids. Until the hydroids of the world have been given much more study and some monographic revision, then, it is unsafe to use them for many zoogeographic purposes. CHECK LIST OF GULF OF MEXICO HYDROIDS Geographic distribution is indicated by the following symbols: K, Florida Keys, including Cay Sal Bank and southern Florida as far east as Miami, but not the Bahamas. T, Tortugas. C, Cuba. Y, Yucatán. NW, northwestern Gulf (Texas, Louisiana). EP, eastern tropical Pacific Ocean, south of United States-Mexico boundary, and including the oceanic islands. *, starred names are new records for the Gulf of Mexico, found in the Woods Hole Oceanographic Institution fouling collection. Suborder GYMNOBLASTEA (Anthomedusae), athecate hydroids K; EP. EP. Cordylophora lacustris Allman, 1844. NW; Ca. K. Turritopsis fascicularis Fraser, 1943. *Turritopsis nutricula McCrady, 1856. K; Ca, EP. Syncoryne eximia 1 (Allman, 1859). NW. Syncoryne mirabilis L. (Agassiz), 1862. K; EP. Zanclea costata Gegenbaur, 1856. T, NW; Ca, EP. Zanclea gemmosa McCrady, 1858. T; EP. Bimeria franciscana Torrey, 1902. NW; B. Bimeria humilis Allman, 1877. T, NW; Ca. Bougainvillia carolinensis (McCrady, 1858). T, NW. Bougainvillia inaequalis Fraser, 1944. NW. Bougainvillia rugosa Clarke, 1882. NW; Ca. Eudendrium album Nutting, 1898. Eudendrium attenuatum Allman 1877. Eudendrium carneum Clarke, 1882. Eudendrium distichum Clarke, 1879. Eudendrium exiguum Allman, 1877. Eudendrium eximium Allman, 1877. Eudendrium fruticosum Allman, 1877. Eudendrium gracile Allman, 1877. K. Eudendrium hargitti Congdon, 1906. Eudendrium laxum Allman, 1877. K; Ca. Eudendrium speciosum Fraser, 1945. Eudendrium tenellum Allman, 1877. Eudendrium tenue A. Agassiz, 1865. Hydractinia echinata Fleming, 1828. K, NW. Podocoryne carnea Sars, 1846. NW. T; Ca, EP. K. K; Ca, EP. K, NE; EP. K. T. NE. K; Ca, EP. NW?; Ca, EP. Pennaria tiarella (Ayres, 1854). K, T, C; Ca, EP. 1 N. J. Berrill, in a letter to the author, has given good reasons for suspect ing that the species reported under this name from Texas and from western. Florida (Deevey 1950), is an undescribed species. Suborder CALYPTOBLASTEA (Leptomedusae), thecate hydroids Family CAMPANULARIDAE Campanularia amphora (L. Agassiz, 1862). T? Clytia coronata (Clarke, 1879). Family LAFOEIDAE K; Ca. T, C; Ca, EP. K, T; Ca. K, T; Ca. K; EP. C; Ca, EP. T, NW; Ca, EP. C; Ca. Acryptolaria abies (Allman, 1877). K. T; Ca, EP. T; Ca, EP. K; Ca. K, T, C; Ca. K, NW; Ca, EP. K, NW; Ca, EP. T, NW; Ca. Family SYNTHECIDAE K, T; EP. Synthecium? gracile Fraser, 1937. T; Ca, EP. K, T, NW; Ca, Synthecium? rectum Nutting, 1904. K; Ca, EP. Sertularia exigua Allman, 1877. Sertularia mayeri Nutting, 1904. K, T; Ca, EP. K, T; Ca. K; Ca, EP. K. T. C; Ca, EP. C. Aglaophenia rigida Allman, 1877. K, NW; Ca, EP. Cladocarpus longipinna Fraser, 1945. K. C. T. K, T. NE. NE. Cladocarpus obliquus Nutting, 1900. C. K, NE. K; Ca. K, T; Ca. A total of 183 species of hydroids, 31 athecate and 152 thecate, are known from the Gulf of Mexico, mostly from the Tortugas and the Florida Keys. Medusae are not considered. The Gulf and the Caribbean have 95 species in common, but 61 Caribbean species are unknown in the Gulf. Seventy Gulf species also occur in the eastern tropical Pacific, including 18 not yet known from the Caribbean. Taxonomic difficulties, as well as inadequate collecting, make hydroid geography an unsatisfactory subject, and it is uncertain how far the apparently common "American" distribution pattern should be taken seriously. What is especially interesting is the occurrence in the Gulf of a significant number of boreal species, some of them seemingly disjunct in the northwestern Gulf. LITERATURE CITED ALLMAN, G. J. 1877. Report on the Hydroida collected during the exploration of the Gulf Stream by L. F. de Pourtalès, Assistant United States Coast Survey. Mem. Mus. Comp. Zool., Harvard College 5 (2): 1-66, 34 pls. CLARKE, S. F. 1879. Report on the Hydroida collected during the exploration of the Gulf Stream and Gulf of Mexico by Alexander Agassiz, 1877-78. Bull. Mus. Comp. Zool., Harvard College 5 (10): 239–252, 5 pls. DEEVEY, E. S. 1950. Hydroids from Louisiana and Texas, with remarks on the Pleistocene biogeography of the western Gulf of Mexico. Ecology 31: 334-367. EKMAN, SVEN. 1934. Indo-Westpazifik und Atlanto-Ostpazifik, eine tiergeographische Studie. Zoogeographica 2: 320 374. 1935. Tiergeographie des Meeres. Leipzig: Akademische Verlagsges. xii+542 pp. FEWKES, J. W. 1881. Reports on the results of dredging under the supervision of Alexander Agassiz . . . by the U. S. Coast Survey steamer Blake. XI. Report on the Acalephae. Bull. Mus. Comp. Zool., Harvard College, 8: 127-140. FRASER, C. McL. 1943. Distribution records of some hydroids in the collection of the Museum of Comparative Zoology at Harvard College, with description of new genera and new species. Proc. New England Zool. Club 22: 75 98, pls. 15-20. 1944. Hydroids of the Atlantic coast of North America. 451 pp., 94 pls. Toronto: Univ. Toronto Press. 1945. 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Carnegie Inst. Washington Pub. 109, 3 vols. NUTTING, C. C. 1900. American hydroids, Part I. The Plumularidae. Smithsonian Inst., U. S. Nat. Mus., Spec. Bull., 142 pp., 34 pls. 1904. American hydroids, Part II. The Sertularidae. Smithsonian Inst., U. S. Nat. Mus., Spec. Bull., 151 pp., 41 pls. 1915. American hydroids, Part III. The Campanularidae and the Bonneviellidae. Smithsonian Inst., U. S. Nat. Mus., Spec. Bull., 118 pp., 27 pls. PERKINS, H. F. 1908. Notes on medusae of the western Atlantic. Carnegie Inst. Washington, Pap. Tortugas Lab. 1 (8): 133-156, pls. 1–4. DE POURTALÈS, L. F. 1869. Contributions to the fauna of the Gulf Stream at great depths. Bull. Mus. Comp. Zool., Harvard College, 1 (6): 103-120. SCHUCHERT, CHARLES. 1935. Historical geology of the Antillean-Caribbean region or the lands bordering the Gulf of Mexico and the Caribbean Sea. John Wiley, New York: 811 pp. STECHOW, E. 1912. Hydroiden der Münchener Zoologischen Staatssammlung. Zool. Jahrb., Abt. Syst. 32: 333-378, pls. 12, 13. 1919. Zur Kenntnis der Hydroidenfauna des Mittelmeeres, Amerikas, und anderer Gebiete. I. Zool. Jahrb., Abt. Syst. 42: 1-172. 1923. Zur Kenntnis der Hydroidenfauna des Mittelmeeres, Amerikas, und anderer Gebiete. II. Zool. Jahrb., Abt. Syst. 47: 1–270. 1926. Einige neue Hydroiden aus verschiedenen Meeresgebieten. Zool. Anz. 68: 96-108. WALLACE, W. S. 1909. A collection of hydroids made at the Tortugas, during May, June, and July, 1908. Carnegie Inst. Washington Yearbook 7 (1908): 136–138. |