Actinostella digitata ( McMurrich, 1893 )

Barragán, Yamaly, Rodríguez, Estefanía, Chiodo, Tommaso, Gusmão, Luciana C., Sánchez, Carlos & Lauretta, Daniel, 2024, Revision of the genus Actinostella (Cnidaria: Actiniaria: Actinioidea) from tropical and subtropical western Atlantic and eastern Pacific: redescriptions and synonymies, American Museum Novitates 2024 (4014), pp. 1-48 : 25-26

Actinostella digitata ( McMurrich, 1893)

Figures 10–12, tables 1, 4

Cradactis digitata McMurrich, 1893 .

Phyllactis digitata ( McMurrich, 1893) : Carlgren, 1949.

Actinostella digitata ( McMurrich, 1893) : Häussermann, 2003.

DIFFERENTIAL DIAGNOSIS: Actinostella with three cycles of mesenteries, all perfect and fertile, including directives. Marginal ruff with p -mastigophores A and basitrichs; column only with basitrichs.

EXAMINED MATERIAL: Actinostella digitata : MACN-In 43521; Cradactis digitata : USNM 17776 (syntypes). See table 1 for material details.

DESCRIPTION: External anatomy (fig. 10): Well-developed pedal disc, to 35 mm diameter. Column elongate, to 70 mm height and 30 mm diameter, with 48 longitudinal rows of verrucae distally in each endo- and exocoel. Marginal ruff with rows of vesicles. Oral disc to 17 mm diameter. Fosse deep. Tentacles, 48, arranged in four cycles; simple, smooth, all of similar length, to 12 mm, with terminal pore. Mesenterial insertions not visible in pedal disc or column.

Internal anatomy (fig. 11): Same number of mesenteries distally and proximally. Twenty-four pairs of mesenteries hexamerously arranged in three cycles (6 + 6 +12 = 24). All cycles perfect. All mesenteries fertile including directives. Two pairs of directives attached to two clearly distinct siphonoglyphs (fig. 11B). Gonochoric, developed spermatic cysts to 0.15 mm in diameter (fig. 11E) in specimen collected in February 2010. Retractor muscles strong, bandlike, restricted. Parietobasilar muscles well developed, with short, free mesogleal lamella (fig. 11F). Basilar muscles poorly developed, processes short and thin (fig. 11G). Endodermal marginal sphincter muscle strong, circumscribed with thin central lamella of mesoglea (fig. 11A). Longitudinal muscles of tentacles ectodermal (fig. 11D). Zooxanthellae present in tentacles and marginal ruff.

Color (fig. 10): Newly collected specimen from Chubut ( Argentina) with beige pedal disc with irregular bright orange spots. Column orange over a beige base color, with verrucae darker orange. Oral disc beige with darker radial lines. Marginal ruff same color as column with beige vesicles. Tentacles translucent brownish, with darker longitudinal lines. Preserved material beige, oral disc and marginal ruff lighter.

Cnidom (fig. 12): Basitrichs, b -mastigophores, p -mastigophores A, p -mastigophores B1, and spirocysts. Sizes and distribution in table 4.

GEOGRAPHIC AND BATHYMETRIC DISTRIBUTION AND NATURAL HISTORY: Actinostella digitata can be found in the southern Atlantic Ocean off the coast of Argentina ( McMurrich, 1893). This is the second record of the species, and it was collected in Paraná Beach , Chubut, southward to the type locality ( La Plata River ) in Argentina. The single specimen from Paraná Beach was found attached to a rolling stone with only the oral disc above the substratum. Despite working in the area for several years, this was the first and only time the collectors noticed this species. It can be found from 5 to 10 meters (Paraná Beach) .

REMARKS: Actinostella digitata is distinguished by the combination of having three cycles of perfect and fertile mesenteries and only small basitrichs in the column; it shares having p -mastigophores A and basitrichs in the marginal ruff with A. flosculifera and A. bradleyi . It was originally described by McMurrich (1893) as Cradactis digitata . We analyzed the type specimens and one newly collected specimen from Paraná Beach (in Chubut, Argentina), southward of the type locality in La Plata River ( Argentina). In the type specimens, the perfect second cycle was hard to discern because of the state of preservation; Carlgren (1934) had analyzed the same specimens and suggested that the three cycles might be perfect, a characteristic we confirmed in the newly collected specimen, which clearly has the three cycles perfect and fertile, including directives.