Dichotomous, Ehrenberg, 1834

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 : 11

Dichotomous Key for Field Identification

1 - Two tentacle types: outer tentacles bulbous, forming a thick, distinct band around the entire circumference of the anemone resembling a pizza crust. Inner tentacles branched Cryptodendrum adhaesivum ( Table 2 )

- All tentacles of same type but might be of different shapes and lengths........................................... 2

2(1) - Verrucae (wart-like blotches) present and conspicuous on column underneath oral disc.............................. 3

- Verrucae inconspicuous or absent on column underneath oral disc.............................................. 4

3(2) - Tentacles heavily beaded, diagnostic for this species. Tentacles in some individuals are variable in shape, with some tentacles smoother or less beaded. Some individuals can have beaded outer tentacles and smoother inner tentacles.............................................................................................. Heteractis aurora ( Table 2 )

- Tentacles not beaded................................................................................... 6

4(2) - Tentacles are short (<2 cm), rounded, and densely packed. Enlarged exocoelic tentacles protrude from the fringe of the oral disc and are diagnostic. Column and pedal disc buried deeply in sandy substrate and not visible. Oral disc lies flat on sandy substrate.................................................................. Stichodactyla haddoni ( Table 2 )

- Tentacles elongate (> 2 cm), rounded, and densely packed. Exocoelic tentacles indistinguishable from endocoelic tentacles. Column not buried in sandy substrate. Oral disc does not lie flat on sandy substrate................................. 5

5(4) Verrucae absent. Column smooth, with thin body wall. Tentacles may have characteristic “bubble-tips” or be elongate and digitiform. Pedal disc attached to hard substrate, typically deep in crevices in the reef. When disturbed, animal retracts rapidly and completely into reef rockwork.............................................. Entacmaea quadricolor ( Table 2 )

- Verrucae on distal (upper) portion of column but not prominent. Verrucae non-adhesive, same color or darker as column, forming longitudinal rows. Body wall thick. Column and pedal disc fully visible. The only host anemone with visible pedal disc. Anemone perched prominently on hard substrate. Cannot retract completely into reef. Instead retracts into a large “ball” leaving only a small tuft of tentacles visible. Typically, the most conspicuous species in fore reef habitats; large body size, up to 1 m in oral disc diameter.................................................... Radianthus magnifica ( Table 2 )

6(3) - Verrucae adhesive, the same color as the surrounding column.................................................. 7

- Verrucae non-adhesive, significantly lighter, or different in color, than the surrounding column........................ 8

7(6) - Tentacles long (> 2 cm) and thinly tapered............................................ Radianthus crispa ( Table 2 )

- Tentacles short (<2 cm), stubby, of unequal shape and length when animal is not disturbed..... Radianthus malu ( Table 2 )

8(6) - Pedal disc and column burrowed deeply in sandy substrate. Verrucae are light in color and contrast sharply against a darker gray/brown column. Tentacles are long and often form corkscrew spirals................ Radianthus doreensis ( Table 2 )

- Pedal disc attached directly to hard reef substrate. Verrucae not white. Tentacles do not form corkscrew spirals........... 9

9(8) - Tentacles around the mouth often longer than peripheral tentacles. Tentacles rounded, adhesive but will not easily rip off or detach. Verrucae pigmented and contrast highly with tan or gray column; verrucae extend to pedal disc. Oral disc diameter can exceed 1 m. Found attached to, and often draped directly over, hard reef substrate in fore reef environments. Typically found in water depths exceeding 5 m. .................................................. Stichodactyla mertensii ( Table 2 )

- All tentacles the same size. Tentacles taper towards the tips taking on a slightly pointed appearance. Tentacles extremely sticky to the touch and easily rip off. Verrucae are typically a lighter color than surrounding column and do not extend to pedal disc. Oral disc deeply folded. Typically found in shallow water (≤ 2 m)..................... Stichodactyla gigantea ( Table 2 )