Stichodactyla gigantea ( Forsskål, 1775 ),

Titus, Benjamin M., Bennett-Smith, Morgan F., Chiodo, Tommaso & Rodríguez, Estefanía, 2024, The clownfish-hosting sea anemones (Anthozoa: Actiniaria): updated nomenclature, biogeography, and practical field guide., Zootaxa 5506 (1), pp. 1-34 : 24

Stichodactyla gigantea ( Forsskål, 1775) ( Figure 14 ; Figure S7 )

Contrary to its name, the “giant carpet” anemone Stichodactyla gigantea is not the largest clownfish-hosting anemone species, and not even the largest of the “carpet” anemones in the genus Stichodactyla . Although largebodied, this species rarely reaches 500 mm in oral disc diameter and is generally exceeded in size by S. mertensii and R. magnifica . This species is characterized by a deeply folded oral disc, which is covered by densely packed tentacles. Tentacles are typically short (10-20 mm in length), thin, and taper to a blunt point ( Figure 14 , Figure S7 ). The tapered tentacle tips represent one important diagnostic character to differentiate S. gigantea from S. haddoni , S. mertensii , and R. magnifica . The density and thickness of the tentacles give the anemone a “furry” appearance like a shag carpet. Tentacle color is typically tan but can also be tipped with purple or blue. Some individuals are a vibrant blue or violet color ( Figure 14B ). Tentacles are most densely packed surrounding the margin of the oral disc, and typically stop just shy of the mouth ( Figure 14A ; Figure S7D ). Tentacles are extremely sticky to the touch and will tear off easily, some always twitching even in calm waters. The column is usually short and can contrast in color with the tentacles. Column color typically ranges from tan to yellow to pink but can also take on brownishgreen hues. Longitudinal rows of verrucae occupy the upper portion of the column only, and contrast in color from the surrounding column ( Figure 14C ). Verrucae are not strongly adherent and do not hold debris. Verrucae color is typically blue, maroon, or purple. The pedal disc and lower portion of column are typically obscured from view and burrowed in sand pockets or reef crevices.

This species occupies calm, shallow-water habitats and may become exposed at low tides. It occupies both sandy and rocky microhabitats. Molecular evidence suggests this species is capable of asexual reproduction (Gatis 2014). Among the three species of clownfish-hosting sea anemones in the genus Stichodactyla , S. gigantea can be easily differentiated from S. mertensii and S. haddoni by its tapered tentacle tips, more deeply folded/wavy oral disc, and shallow-water habitat.

Geographically, this species ranges from the Andaman and Nicobar Islands in the Eastern Indian Ocean, throughout the Coral Triangle, Northern Australia, Taiwan and Southern Japanese Archipelago, and as far east as New Caledonia and Vanuatu in the South Pacific and Micronesia in the North Pacific ( Figure 15 ). It does not reach Fiji or the Marshall Islands.

Figures

FIGURE 7. Confirmed geographic range of Radianthus crispa in the Indo-West Pacific. Red dots represent species observations from the Global Biodiversity Information Facility (GBIF). Blue shaded area represents shallow water habitat (60 m bathymetry).

FIGURE 14. Representative images of Stichodactyla gigantea encompassing a broad range of geographic and phenotypic variation. A) Wide-angle photograph of S. gigantea in shallow water habitat surrounded by stony corals. Note the strongly wavy oral disc and visible mouth (Kimbe Bay, Papua New Guinea). B) Individual with rare vibrant blue/violet body coloration (Kimbe Bay, Papua New Guinea). C) Macro photograph of S. gigantea column, tentacles, and verrucae. Note the thin tentacles, slightly tapered tentacle tips, and verrucae (arrow) that contrast in color with surrounding column (Kimbe Bay, Papua New Guinea. D) Common tan colored individual (Kimbe Bay, Papua New Guinea). E) Macro photograph of S. gigantea tentacles highlighting tapered tentacle tips (Palawan, Philippines). Photographs by Morgan Bennett-Smith.

FIGURE 15. Confirmed geographic range of Stichodactyla gigantea in the Indo-West Pacific. Red dots represent species observations from the Global Biodiversity Information Facility (GBIF). Blue shaded area represents shallow water habitat (60 m bathymetry).