Stichodactyla haddoni ( Saville-Kent, 1893 )

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 : 26

Stichodactyla haddoni ( Saville-Kent, 1893) ( Figure 16 ; Figure S8 )

Haddon’s carpet anemone, Stichodactyla haddoni , is a sand dwelling species and the most heavily collected carpet sea anemone in the ornamental aquarium trade ( Figure 16 ; Figure S8 ). Although not small (potentially reaching up to 800 mm in oral disc diameter), the overall body size of this species is smaller than the other clownfish-hosting species in the genus Stichodactyla , making them more suited for home aquaria than their congenrs. The tentacles of this species are short, rounded, and globular in shape. They are also densely packed, leaving little of the oral disc visible. Endocoelic tentacles are often white, giving the anemone a radially striped pattern ( Figure 16 A-E). This pattern is common in S. haddoni , but also seen occasionally in S. mertensii and thus should not be used as a diagnostic character for this species. The most important diagnostic character for S. haddoni is the enlarged exocoelic tentacles that protrude from the margin of oral disc ( Figure 16A ). These tentacles are typically 2-3 times longer in total length than endocoelic tentacles. Tentacle color is typically various shades of dull green, tan, and brown, but can also be bright red, blue, or green ( Figure 16 ; Figure S8 ). The brightest individuals are typically targeted by the aquarium trade.

The oral disc of this species is flared widely and often lays flat over the surrounding sandy substrate ( Figure 16 ; Figure S8 ). This species can also form deep folds in the oral disc similar to S. gigantea , but in general, the oral disc of S. haddoni is much more circular in shape than those of any other carpet anemone species ( Figure 16 ; Figure S8 ). The column of S. haddoni is smooth, typically pale, and lacks the conspicuous verrucae seen in other carpet anemones ( Figure 16B ; Figure S8B, E ). The combination of enlarged exocoelic tentacles and lack of conspicuous verrucae are the two most important characters for identifying S. haddoni in the field. As a sand-dwelling species, the column and pedal disc are burrowed deeply in the sediment and typically obscured from view ( Figure 16 ; Figure S8 ). Upon disturbance, this species can retract entirely into the sand. Stichodactyla haddoni is often found on calm sand flats and seagrass beds away from fore reef habitats, at depth rangin from 0.5- 30 m. This species is only found as solitary anemones (it does not form aggregations) and it is expected to sexually reproduce only.

Stichodactyla haddoni is widespread throughout the Indo-West Pacific, and ranges from the Red Sea, throughout the Indian ocean, Coral Triangle, and into the Central Pacific at least to the Marshall Islands ( Figure 17 ). This species extends north to the Japanese Archipelago, and south to Australia and South Africa.

Figures

FIGURE 8. Representative images of the long-tentacled sea anemone Radianthus doreensis encompassing a broad range of geographic and phenotypic variation.A) Whole individual in typical sandy microhabitat (Bali, Indonesia). B) Macro photograph of characteristic curling/spiraling tentacle pattern (Kwajalein Atoll, Marshall Islands). C) Partially retracted individual revealing highly contrasting white verrucae on brown column (arrow; Anilao, Philippines). D) Small purple individual with longitudinally striped tentacles and oral disc (Anilao, Philippines). E) Large individual with longitudinal “zebra-stripe” tentacle and oral disc pattern (Anilao, Philippines). All photographs by Scott and Jeanette Johnson.

FIGURE 16. Representative images of Stichodactyla haddoni encompassing a broad range of geographic and phenotypic variation. A) Tan/olive individual in sandy microhabitat with enlarged exocoelic tentacles (black arrows; Saudi Arabia, Red Sea). B) Exposed upper column revealing pale color and lack of distinctive verrucae (white arrow; Saudi Arabia, Red Sea). C) Macro photograph of striped endocoelic tentacles. Note the rounded globular shape (Kwajalein Atoll, Marshall Islands). D) Individual in typical microhabitat (Majuro Atoll, Marshall Islands). E). Bright yellow individual likely experiencing bleaching stress (Majuro Atoll, Marshall Islands). Photographs by Morgan Bennett-Smith and Benjamin M. Titus.

FIGURE 17. Confirmed geographic range of Stichodactyla haddoni 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).