Posted by: genghisprawn | November 9, 2008

More Freshwater Barnacles

This is a photo submitted by one Peter to Avril Bourquin’s Man and Mollusc web page.  The freshwater snail was purchased complete with living hitchhikers from a pet store in New York (collection site unknown).  Vigorous discussion on the CONCH-L mailing list identified the snail as Vitta usnea (Röding, 1798), a member of the family Neritidae familiar to aquarists and shell-collectors as the olive nerite.

V. usnea is often found in flowing freshwater with tidal influence, but is quite able to tolerate low-salinity conditions and in at least some cases occurs far upstream.  Say (1822, who christened this species Theodoxus reclivatus), is quoted as writing the following: “I found this species in great plenty, inhabiting St. John’s river in East Florida, from its mouth to Fort Picolata, a distance of one hundred miles, where the water was potable.”

Vitta usnea egg capsules on the shell of a captive Pomacea caniliculata (channeled apple snail, a South American freshwater Ampullariid). Photo by "Burnt Umber" (Flickr).

There appears to be some controversy about larval development — Andrews (1935) reported direct development into benthic miniature adults, bypassing the typical veliger stage, but “the reported maximum diameter of the egg capsules (~1 mm) is too small to hold 40 metamorphosed juveniles,” as he reported, “of any neritid species” (Kano, 2006).  What’s more, Holthuis (1995) reported V. usnea to have what Kano (2006) terms a “type A” opercular nucleus — an operculum morphology typically associated with floating, planktotrophic veliger larvae.  (The operculum is the calcareous lid that seals the aperture of the shell when the snail’s body is withdrawn.)  The geographic distribution of this species (Florida to Colombia, including Trinidad and the Greater Antilles), for my part, makes me inclined to rule against Andrews.

Larval development, at any rate, appears to require saline conditions — although captive specimens will strew the aquarium glass with hard, salt-grain-like egg capsules, the larvae uniformly perish in freshwater.  This carries the curious implication that V. usnea populations sufficiently upstream from the ocean would be unable to recruit except through upstream migration.  I don’t know whether any research on larval tolerance for freshwater in diadromous nerites has yet been done, but it seems to me that there may be physiological/developmental differences between estuarine V. usnea and the upstream populations reported by Say.  Some more discussion on that at CONCH-L.

As for the barnacles, they seem to be Balanus improvisus (Darwin, 1854).  Darwin himself, according to Southward and Crisp (1987, p. 127) “noted that Balanus improvisus was found in a small stream in the estuary of La Plata, near Monte Video, where at high water specimens apparently were covered by the brackish and occasionally almost fresh waters of the estuaries.”  Branscomb (1976) reports that a population in the Chesapeake Bay “appeared unaffected by unusually high freshwater run-off in June which lowered salinities in the bay for 1972.”

So what salinity parameters do these relate to?  Southward and Crisp continue (emphasis mine):

Balanus improvisus occurs in the Baltic Sea to salinities 3-5‰ (Segerstrâle 1957, Barnes & Barnes 1962).  Specimens collected from British estuarine localities could be acclimated to function in salinities less than 3‰, at which salinities they hyperregulate the body fluids at a constant osmotic pressure corresponding to about 3‰ (Foster 1970, Fyhn 1976).  B. improvisus has been recorded on the elytra of water beetles by Tarasov & Zevina (1957), a novel dispersal situation for any barnacle, and there are specimens in the British Museum (Natural History) from the shell of a freshwater crayfish collected in northern Iran (Southward, pers. comm.).

The specimens depicted above, of course, were living in full freshwater, but how long they held out was not reported.  I have personally seen the same species-combination, but can’t recall whether the crustaceans were still alive.


Andrews EA. 1935. The egg capsules of certain Neritidae. J Morphol 57:31–59.
Barnes, H. & M. Barnes 1957.  Resistance to desiccation in intertidal barnacles. Science 126: 358.
Barnes, H. & M. Barnes 1962.  The distribution and general ecology of Balanus balanoides together with some observations on Balanus improvisus in the waters around the north coasts of Denmark, Southern Sweden and North-east Germany. Acta Univ. Lund. (N.F.) Adv.2, 58 Nr.8: 1-41.
Branscomb, E. (1976). Proximate causes of mortality determining the distribution and abundance of the barnacle Balanus improvisus Darwin in Chesapeake Bay. Chesapeake Science, 17(4), 281-288. doi: 10.2307/1350515.
Foster, B. A. (1970). Responses and Acclimation to Salinity in the Adults of Some Balanomorph Barnacles. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences (1934-1990), 256(810), 377-400. doi: 10.1098/rstb.1970.0001.
Fyhn, H. J. (1976). Holeuryhalinity and its mechanisms in a cirriped crustacean, Balanus improvisus. Comparative Biochemistry and Physiology. A, Comparative Physiology, 53(1), 19-30. doi: 179.

Holthuis BV. 1995. Evolution between marine and freshwater habitats: a case study of the gastropod suborder Neritopsina. PhD dissertation, University of Washington.

Kano, Y. (2006). Usefulness of the opercular nucleus for inferring early development in neritimorph gastropods. Journal of Morphology, 267(9), 1120-1136.

Segerstrâle, S.G. 1957. Baltic Sea. In J.W. Hedgpeth (ed.), Treatise on Marine Ecology and Paleoecology 1: 751-800.  New York: Geol. Soc. America.

Southward, A. J., & Crisp, D. J. (1987). Barnacle Biology (p. 443).

Tarasov, N.I. & G.B. Zevina 1957. Cirripedia Thoracica of the seas of the USSR. Fauna SSSR 6(1): 1-267 (in Russian).


  1. First thing. Thank you for properly crediting my photo. No evryone does.

    I have olive nerites I have cultivated from the wild in my freshwater tanks. The area they were removed from as a salinity of only 500PPM.

    I have had them in my freshwater tank for almost 2 years with no effect on their health.

  2. […] wrote about freshwater barnacles here. This sort of thing isn't unheard of with olive nerites (and, elsewhere in the world, has involved […]

  3. […] wrote about occurrences of barnacles in freshwater here. This sort of thing isn't unheard of with olive nerites (and, elsewhere in the world, has involved […]

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