Circeaster americanus

Circeaster americanus (A.H. Clark 1916)

Figure 7 A–C

Circeaster americanus is a widely occurring species throughout the western North Atlantic, with occurrence recorded throughout the tropical Atlantic to the mid-Atlantic Ridge (Mah 2015). Most Circeaster diversity is known primarily in the Indo-Pacific where it is represented by eight species. Two of the most closely related species to C. americanus, Circeaster pullus Mah 2006 and Circaster sandrae Mah 2006 occur in the north and south Pacific, respectively.

Morphological variation was observed in this species across its range. The Caribbean form (Fig. 7A, 721 m) showed slender arms and demonstrated a closer resemblance to the Pacific species, such as C. pullus and C. sandrae. In contrast, two individuals from the Gulf of Mexico (694-1133 m) displayed massive and strongly developed marginal plate series with thicker and more broadly triangular arms.

Feeding Observations

This species was observed feeding on three occasions. Observations showed predation on two different types of octocoral species. One observation (721 m) showed an individual with an arm upturned adjacent to a denuded Chrysogorgia colony. The other two observations (693 m and 1133 m) showed an individual slightly askew on a rock with a denuded isidid stalk emerging from below its oral region with the deeper observation (1133 m) showing an individual perched upon the upper branches of a denuded isidid coral skeleton.

Circeaster americanus has previously been reported feeding on a fallen soft coral colony in the genus Paragorgia from Manning Seamount in the North Atlantic (Mah 2015). The diversity of prey items suggests this species displays broad variation with regard to its feeding preferences. Alternatively, it is possible that different cryptic lineages may have different feeding preferences but no data is available for the population phylogeography of this species.

Occurrence

Tropical Atlantic, Florida, Louisiana, Gulf of Mexico, North Carolina and the Caribbean, including Columbia, the Grenadines, Leeward Islands, Nicaragua, Netherlands, Antilles, St. Vincent, Suriname and Venezuela. North Atlantic, Manning Seamount, 500–1675 m.

Images Examined

Okeanos Ridge, Gulf of Mexico, 25.68007, -84.62041, 721 m EX1711_IMG_20171202T 150207 Z_ROVHD.jpg (Chrysogorgia)

Okeanos Ridge, Gulf of Mexico, 25.68030, -84.61918, 694 m EX1711_IMG_20171202T 170721 Z_ROVHD.jpg (bamboo)

Mona South Ridge, Caribbean Sea, 17.946907, -67.887304, 1133 m EX1811_IMG_20181117T155851Z_ROVHD.jpg (feeding)