PROC. BIOL. SOC. WASH. 99(3), 1986, pp. 472-477 EPIZOIC BARNACLES ON PLEURODIRAN TURTLES: IS THE RELATIONSHIP RARE? J. G. Frazier Abstract.— The occurrence of epizoic Balanus improvisus on a side-necked turtle in Argentina illustrates the southern extent of this barnacle's wide geo-graphic range, and the diversity of habitats and substrates used. Preferred settling sites for epizoa are similar on all non-marine turtles described as hosts; barnacles concentrate on the posterior of the carapace. The present account of epizoa on a pleurodiran turtle raises questions as to whether the lack of records reflects a true lack of epizoic bamacle-Pleurodira relationships, or a lack of observations. Because the symbiotic relationship is dependent on the turtles' occurrence in estuarine habitats, a better understanding of pleurodiran distri-butions is needed. The little data there are suggest that recent Pleurodire turtles are generally restricted to fresh water, but a few species may inhabit saline waters and they are therefore likely to host epizoic barnacles. Epizoic barnacles have been reported on few species of Testudines. There is an ob-ligate relationship between several barna-cles of the Chelonibiinae and half a dozen marine species in the families Cheloniidae and Dermochelyidae (Ross 1963a, b; Zullo and Bleakney 1966; Ross and Newman 1 967; Ernst and Barbour 1 972; Zullo 1 979). In some populations of marine turtles che-lonibiine infestations are common (Frazier, unpublished data). At least five species of "freshwater" tur-tles (Chelydridae and Emydidae) have been reported to carry epizoic barnacles, but such reports are rare, for they evidently represent an opportunistic relationship. An adult male alligator snapping turtle, Macwclemys tem-minckii (Troost), near Mobile Bay, Ala-bama, had 43 Balanus improvisus Darwin, mostly on its posterior carapace (Jackson and Ross 1971b). The carapace of an adult male Alabama red-belly turtle, Chrysemys {=Pseudemys) alabamensis (Baur), also from Mobile Bay, Alabama, carried more than 600 Balanus improvisus (Jackson and Ross 1972), as well as Bryozoa (Jackson and Ross 1975). Carr (1940) mentioned barnacles being on several discarded shells of Chrys-emys concinna suwanniensis (Carr) at Cedar Key, Florida. An adult female red-belly tur-tle, Chrysemys r. rubriventris (Le Conte), near the mouth of the Delaware River had 12 Balanus improvisus on the posterior of its carapace (Amdt 1975). There are numerous records of epizoic barnacles on diamondback terrapins, Mal-aclemys terrapin (Schoepff), from eastern and western Rorida. Ross and Jackson (1972) reported two Balanus improvisus at-tached to epizoic oysters (Jackson and Ross 1971a) that were on the posterior of the carapace, and two Chelonibia patula (Ran-zani) that were on a posterior ventral mar-ginal surface, of an adult female. Jackson et al. (1973) found a vacant Balanus eburneus Gould, occupied by a bivalve mollusk, on the posterior carapace of an adult female terrapin. Seigel (1983) has done the only detailed study on levels of infestation, re-porting three species of epizoic barnacles on two populations of diamondback terrapins: Chelonibia manati Gruvel infested 47.9% of the total; Balanus eburneus, 42.4%; and Chelonibia testudinaria (L.), 9.5%.
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