New observations and corrections concerning the trio of invasive hydromedusae Maeotias marginata (=M. inexpectata), Blackfordia virginica, and Moerisia sp. in the San Francisco Estuary*

Further observations in low salinity tributaries to San Francisco Bay of hydromedusae and their polyps in the genera Maeotias, Blackfordia, and Moerisia have revealed a number of errors in the Mills and Sommer (1995) paper, which first described the presence of two of these invasive species in California. We take this opportunity to clarify a number of important details concerning the nomenclature and biology of Maeotias marginata (=inexspectata), Blackfordia virginica and Moerisia sp. and to add a few new observations. SCI. MAR., 64 (Supl. 1): 151-155 SCIENTIA MARINA 2000


INTRODUCTION
Further observations in low salinity tributaries to San Francisco Bay of hydromedusae and their polyps in the genera Maeotias, Blackfordia, and Moerisia have revealed a number of errors in the Mills and Sommer (1995) paper, which first described the presence of two of these invasive species in California. We take this opportunity to clarify a number of important details concerning the nomenclature and biology of Maeotias marginata (=inexspectata), Blackfordia virginica and Moerisia sp. and to add a few new observations. SCI. MAR.,64 (Supl. MILLS, F. BOERO, A. MIGOTTO and J.M. GILI (eds.) New observations and corrections concerning the trio of invasive hydromedusae Maeotias marginata (=M. inexpectata), Blackfordia virginica, and Moerisia sp. in the San Francisco Estuary*

Maeotias marginata (Modeer, 1791)
We have recently determined, thanks to a question by Ron Ates of Zaandam in the Netherlands, that Maeotias inexspectata Ostroumoff, 1896 is actually a junior synonym of Maeotias marginata (Modeer, 1791). The intricate early history of the synonomies of this distinct, yet confusing species were enumerated by Hummelinck (1938bHummelinck ( , 1941. Kramp (1961), missing its significance, synonymized the highly distinct M. marginata with Craspedacusta sowerbii Lankester, 1880. Examination of the figures of Baster (1765), republished by Hummelinck (1938bHummelinck ( , 1941 with accompanying detailed description, as well as two specimens in poor condition (COEL. 2046) from the Zoological Museum, University of Amsterdam, collected in there in 1889, leaves little doubt that there is only one species of Maeotias, which should therefore henceforward be called Maeotias marginata (Modeer, 1791). The specimens of Baster, subsequently described by Modeer as Medusa marginata, were up to 40 mm in diameter in life (Hummelinck, 1941). Most of our Petaluma River specimens were less than 35 mm in diameter, but a few exceptional animals reaching 50 mm in diameter have been collected in nearby Suisun Slough (see below), another tributary to San Francisco Bay. In all aspects they agree with the description detailed by Hummelinck (1941) for M. marginata.
With regard to the correct spelling of the junior synonym M. inexpectata, it has been pointed out that Ostroumoff described this species twice in 1896, and although inexspectata (Ostroumoff, 1896b) is better Latin, this spelling of the name is predated by three months by a description using the spelling inexpectata (Ostroumoff, 1896a), which therefore takes precedence as the original and correct spelling of this species name.
Statocysts were not observed around the bell margin of Maeotias marginata (as M. inexspectata) by Mills and Sommer (1995). Further observation of living specimens in August 1995 and on subsequent occasions showed unquestionably that Maeotias does indeed have numerous marginal statocysts (see also Rees and Gershwin, 2000). Such statocysts are clearly described and illustrated by Ostroumoff (1896b), as well as by Borcea (1928), Hummelinck (1941) and Denayer (1973), so any questions about their existence can be laid to rest.
The presence of marginal statocysts undermines placement of Maeotias within the Anthomedusae by Mills and Sommer (1995). At this time, until molecular genetic phylogenies are able to clearly sort out some of these relationships, it seems best to restore Maeotias to the family Olindiidae in the Limnomedusae.
In addition to the locations summarized by Mills and Sommer (1995) for Maeotias marginata in the Black Sea, Sea of Azov, Loire River estuary, Chesapeake Bay, South Edisto River estuary in South Carolina, and the San Francisco Estuary system in California, M. marginata has also been collected at least twice in the Netherlands. It was collected during the summer of 1762 in freshwater environments of the estuarine Spaarne River near Haarlem [making that collection one of the earliest known marine introductions (J.T. Carlton, personal communication)] and during July 1889 in the brackish Plantage Muidergracht canal, Amsterdam (Hummelinck, 1938b(Hummelinck, , 1941. Both of these locations occasionally received salt water from the Zuiderzee at that time (but do not now). The occurrence of live M. marginata in freshwater (Baster, cited by Hummelinck 1938a, 1938b, 1941 is not out of agreement with laboratory observations (C.E.M., unpublished) that San Francisco Bay specimens can survive in pond water [0 psu (practical salinity units)] for five days in good condition, and died only on the eleventh day in entirely fresh water. Maeotias marginata has most recently been collected in August 1999 at several locations in the Moonsund (Väinameri) Sea area of the Baltic Sea in western Estonia in salinity near 6.5 psu (R. Vainola, personal communication;Vainola and Oulasvirta, 1999).
Within the San Francisco Estuary, Maeotias marginata medusae have recently been found in additional low-salinity locations in north San Francisco Bay, including the Napa River and Suisun Slough (Rees and Gershwin, 2000). Additional field and laboratory work revealed another surprise about Maeotias in California. Although Mills and Sommer (1995) reported only male medusae in the Petaluma River, a few female M. marginata (among numerous males) were found in the Napa River in September 1998. Eggs produced by these females were fertilized in the laboratory and developed into tiny, simple, primary polyps without tentacles (see Rees and Gershwin, 2000), very different than those polyps figured as Maeotias by Mills and Sommer (1995) (see below under Moerisia), but not out of character with other known limnopolyps such as Craspedacusta. Growth of these primary polyps did not occur in laboratory culture and they subsequently disintegrated without further development.

Blackfordia virginica Mayer, 1910
The first Blackfordia virginica specimens (medusae) were collected in the Napa River and the Petaluma River in the San Francisco Estuary, in 1970 and 1974 respectively, and were deposited in the California Academy of Science (Mills and Sommer, 1995). B. virginica polyps (Fig. 1a, b) were first discovered in the field in September 1997, densely covering living nonindigenous barnacles, Balanus improvisus, collected near the water line on floating docks in the Napa River at the public boat launch in John F. Kennedy Park (although a fragment of a B. virginica hydroid colony was tentatively identified and figured by Mills and Sommer (1995) from the gut of a Maeotias marginata medusa collected in 1993). Salinity in the Napa River was 19 psu and temperature about 16°C at the time of collection. The polyps were growing both on the outer valves and on opercular valves of the barnacles. Individual polyps and gonophores (each containing a single medusa) arise directly from creeping stolons. Both are very small, not exceeding 0.5 mm in height. The polyps have webbing between the tentacles. Positive identification of B. virginica was accomplished by raising medusae produced by these polyps to maturity in the laboratory. A newly-released medusa and older juvenile medusa are shown in Figure 1c and 1d.
Other than the San Francisco Bay estuary, the only other American west coast location known for Blackfordia virginica is Coos Bay, Oregon, where medusae were collected in both July 1998 (one specimen) and July 1999 (thousands seen) by James Carlton and identified by C.E.M. No polyps were located.  1. -Blackfordia virginica. (a) polyp colony growing on glass slide, ( b) single polyp showing webbing between tentacles, 0.5 mm tall measured from substrate to tip of tentacles, (c) newly-released medusa with four perradial marginal tentacles and four developing interradial tentacle bulbs, 0.8 mm bell height and diameter. (d) 16tentacle juvenile medusa, bell 1.3 mm high and 1.6 mm diameter.

Moerisia sp.
Solitary polyps similar to those described as Maeotias by Mills and Sommer (1995) from the Petaluma River (collected in 1993, the first record of this hydroid in the San Francisco Estuary) have now also been found in the field in the San Francisco Estuary in the Napa River amongst the float-fouling community. These polyps have been identified through laboratory rearing as those of Moerisia [whose description they match, as noted by Mills and Sommer (1995)] rather than Maeotias (see Rees and Gershwin, 2000). Furthermore, the newlyreleased medusae of Moerisia have ocelli, which are not present in Maeotias, and only 4 tentacles rather than the 24 tentacles on newly-released Maeotias marginata (see Rees and Gershwin, 2000). Adult Moerisia sp. medusae have subsequently been collected in the same Suisun Slough site in the San Francisco Estuary where M. marginata was also present (Rees and Gershwin, 2000).
The San Francisco Bay system is now at least the third region in which all three genera of invasive hydromedusae, Maeotias, Blackfordia and Moerisia have become established. All are considered to be native to the Black Sea region (Calder and Burrell, 1969) and have also all been reported in the Chesapeake Bay (Calder and Burrell, 1969). The three genera are tolerant of very low salinities, but there may be other variables that cause them to move together. Maeotias and Blackfordia appeared together with the Atlantic American and European hydromedusa Nemopsis bachei in the Loire estuary (Denayer, 1973). [Nemopsis bachei has also been collected in the Zuiderzee (Kramp, 1961), not far from the region where Maeotias was found there, and is common in the Chesapeake Bay (Calder, 1971)]. A fourth "Sarmatic" hydroid (thought native to the Black and/or Caspian Seas), Cordylophora caspia (Pallas, 1771) which does not produce medusae, is also found in very-low salinity sites in the San Francisco estuary (Cohen and Carlton, 1995). C. caspia is apparently the most invasive of the group, and is known to be established in a large number of very-low salinity sites worldwide.

ACKNOWLEDGEMENTS
Several people contributed to the corrections and observations reported here. Most recently, Ron Ates inquired whether Modeer's Medusa marginata might be the same as Maeotias inexspectata. The 1997 collections of the polyps of Blackfordia virginica and Moerisia sp. were made during the Fourth San Francisco Bay Expedition, a rapid assessment inventory for nonindigenous marine species organized by Andrew Cohen. The 1998 collection of the female M. marginata and subsequent development of primary polyps occurred during the Fourth Workshop of the Hydrozoan Society at the Bodega Marine Laboratory, University of California. Thanks to Jim Carlton for sharing his collections of Blackfordia virginica from Oregon and to Shin Kubota for help in collecting in the Napa River. Thanks to Lisa Gershwin, who followed up the tip for Maeotias in Suisun Slough and for noting the precedence of inexpectata over inexspectata. Thanks to Dale Calder, who was the first to see the likelihood that our large solitary polyps were Moerisia rather than Maeotias, and for providing helpful comments on this manuscript. Thanks to Rob van Soest for supplying Dutch material from 1889 for study, and to Risto Vainola, who apprised us of the discovery of Maeotias in the Baltic Sea in 1999. J.T.R. wishes to acknowledge aid from the Interagency Ecological Program and the California Department of Water Resources (DWR agreement #B-81818) to California State University, Hayward and the CSUH Bay/Delta Shore Institute. We are sorry to preside over the demise of yet another imaginative species name with this paper.