The Occurrence of Bacterial Colonies in the Epidermis of the Tentacles of the Sea Anemone Aiptasia pallida (Anthozoa: Actinaria)

Light and transmission electron microscopic observations indicate that bacteria in the epidermis of Aiptasia pallida are rod-shaped, possess a thin, undulant cell wall, and occur as a single morphotype in a colony. The absence of visible tissue damage suggests a symbiotic relationship between the bacteria and the anemone. Reports of symbiotes in Cnidaria are few, other than those on the muchstudied photosynthetic dinoflagellates or zooxanthellae; e.g., Zooxanthella microadriatica (see Blank & Trench, 1986). Cheng & Wong (1974) described trematode metacercaria in the scleractinian corals Porites compressa and P. lobata. Trematode metacercaria also were found in P. astreoides from Belize (Peters, unpublished observations). Riggs (1982) reported finding numerous multinucleate surrounded by a thin cuticle in the mesoglea of the mesenteries and pharynx of several specimens of Aiptasia tagetes. Riggs (1982) also discovered an identical in the gastrodermis of a tentacle of A. tagetes. These parasites ranged in size from 24 x 40 ,m to 60 x 86 .m. Carlgren (1943) described a similar parasite that ranged from 31 x 40 Atm to 149 x 187 ,tm in the coelenteron of Aiptasia pulchella. In one specimen of Aiptasia pallida, Riggs (1982) found several round pinkstaining consisting of two or three concentric rings, in the column epidermis. The largest was determined to be 40 ,m in diameter. Riggs (1982) also reported finding pink bodies in the column epidermis of A. pallida, but they did not have the abundant nuclei that were present in the parasites of A. pulchella and A. tagetes. Carlgren & Hedgepeth (1952) noted the presence of numerous round or oval bodies, which they believed were probably gregarines, in the epidermis of the tentacles of a specimen of A. pallida. Protozoan parasites also were found in the scleractinian corals. Gemmocystis cylindrus (Apicomplexa: Agamoccidiorida) occurred in the gastrodermal cells of the lobes of the mesenterial filaments of Agaricia agaricites, Dendrogyra cylindrus, Diploria strigosa, Meandrina meandrites, Montastraea cavernosa, Porites astreoides, P. porites, and Porites sp. (see Peters, 1984; Upton & Peters, 1 We thank Andrea S. Blake for technical assistance. 2 Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, U.S.A. TRANS. AM. MICROSC. SOC., 108(3): 239-244. 1989. ? Copyright, 1989, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.211 on Mon, 08 Aug 2016 06:05:09 UTC All use subject to http://about.jstor.org/terms TRANS. AM. MICROSC. SOC. 1986). Peters (1984) discovered a sporozoon, tentatively identified as Nematopsis sp., in the calicoblast epithelium of P. porites. Peters (1984) further reported the presence of an unidentified amoeba in the calicoblastic epithelium of specimens of Siderastrea sp. Lauckner (1980) stated that there had been no studies of viral or bacterial diseases among cnidarians. However, colonies of bacteria in cnidarians other than Aiptasia have been reported (Peters, 1984; Peters et al., 1983; Peters in manuscript). Various bacterial morphotypes appear in a single and in different cnidarian species. Peters et al. (1983) noted that tissues of specimens of Acropora palmata and A. cervicornis showing symptoms of white band harbored gram-negative bacteria. Similar bacteria were found in diseased and healthy specimens of A. agaricites and healthy specimens of Stephanocoenia michelinii and P. astreoides (see Peters, 1984). Ducklow & Mitchell (1979) and Peters (1984) also found spiral and rod-shaped bacteria, as well as ciliates and cyanobacterial filaments, within the disease line of specimens of Colpophyllia natans, D. strigosa, and Montastraea annularis exhibiting black line disease. The cyanobacterium responsible for black line (=black band) has been identified as Phormidium corallyticum (see Riitzler & Santavy, 1983), but little is known about other bacterial populations associated with cnidarians (e.g., Paul et al., 1986). We report here the occurrence of bacteria in tissues of Aiptasia pallida, discovered during a study of morphological changes resulting from fish predation of the anemone's tentacles. MATERIALS AND METHODS Specimens of Aiptasia pallida (Verrill, 1864) were collected from the Coral Reef Exhibit in the Museum of Natural History at the Smithsonian Institution, Washington, D.C. and maintained in the aquaria of the Coral Reef Microcosm of the Department of Biology, Georgetown University. One anemone was removed from an aquarium and subjected to predation by a four-eyed butterflyfish, Chaetodon capistratus. The fish bit off the tips of several tentacles of the sea anemone. This anemone was returned to the approximate position in the aquarium from which it had been removed. Twenty-four hours later, a visibly normal tentacle and a tentacle undergoing recovery after having been bitten off by the fish were detached with fine pointed forceps and placed in separate vials containing a primary fixative solution consisting of 2.5% glutaraldehyde buffered at a pH of 7.8 with a mixture of Instant Ocean? and distilled water (specific density, 1.0250). Primary fixation was for 1.5 h at 20?C. Three consecutive 15-min primary washes with buffer were followed by a 1.5-h post-fixation using 2% Os04 in the same buffer at 20?C. Three consecutive 15-min secondary washes with buffer were followed by passage, at 15-min intervals, through an ethanol series (25%, 50%, 70%, 85%, 95%, 100%, 100%), followed by two 15-min changes in propylene oxide. Overnight infiltration was accomplished in a 1:1 mixture of propylene oxide and Epon LX-112 (Luft, 1961). A 1:3 mixture of propylene oxide and Epon was allowed to infiltrate the specimens for 8 h. Specimens were embedded in 240 This content downloaded from 157.55.39.211 on Mon, 08 Aug 2016 06:05:09 UTC All use subject to http://about.jstor.org/terms VOL. 108, NO. 3, JULY 1989 241