Sagartiogeton erythraios Zelnio, Rodriguez & Daly, 2009
Diagnosis: In live specimens the column is short and rosy pink to white in colour. The tapering tentacles are deep red to pink, becoming lighter at the tip. The tentacles have microbasic p-mastigophores, basitrichs and spirocysts. The microbasic p-mastigophores are not arranged in distinct batteries. There are three cycles of hexamerously arranged mesenteries, with the mesenteries of the first two cycles being perfect.
Oral disc and tentacles: The oral disc is flat, with a broad tentacle free space surrounding a prominent mouth. The musculature of the oral disc is strong and ectodermal. The margin of the oral disc is white in colour. The lips and oral disc of preserved specimens have a deeper red or pink colour than the column, but are not as deeply coloured as the tentacles or the actinopharynx. The sphionoglyphs and actinopharynx of preserved specimens are blood red. There are ca. 48 tentacles in four crowded marginal cycles. The tentacles are typically retracted inside the column in contraction. The distal column covers the oral disc and the base of the tentacles in all of the examined specimens. In contraction the tentacles are blunt and longitudinally furrowed, slightly longer in length than the oral disc radius. The tentacles are ca. 6 mm in length and beige to pink in colour when preserved. In live specimens the tentacles are long and sharply tapering, with those of the inner cycle ca. equal in length to the oral disc diameter, and are deep pink or red at the base, becoming white at the tips. The tentacles of the inner cycles are typically held erect, whilst those of the outer cycle are held out or pointing towards the substrate. The tentacles of preserved specimens are red to brown in colour, with those parts of the tentacles that are inside contacted specimens being more deeply coloured than those parts that are exposed. The ectodermal longitudinal muscles of the tentacles are slightly more developed on the oral side of the tentacles. The endodermal circular muscle is evenly developed.
Base and column: In preserved contracted specimens the column is stout and dome-shaped. The diameter at the base of the column is 13 - 27 mm, and the height of the column is 13 -18 mm. The column is differentiated into a thin walled distal scapulus and a thick walled proximal scapus. The scapus bears a cuticle and small irregularly spaced papillae. The papillae are solid, with a tightly adhering cuticle. There are no cinclides. The mesenterial insertions are not distinct in contracted preserved specimens. Preserved specimens are brownish cream in colour. In live specimens, the column is cylindrical, and the colour of the scapus is obscured by a brownish cuticle. The scapulus is pale pink. Contracted live specimens have a pale ring at the margin because the scapulus lacks a cuticle. The column musculature is concentrated into a strong mesogleal marginal sphincter distally. The sphincter is long, encompassing the entire length of the scapulus. It is stronger distally, closer to the gastrodermis than the epidermis. The pedal disc is adherent, muscular and flat. It is the same colour as the column and retains a thin covering of small particles from the substrate. The basilar muscles are well-developed.
Mesenteries and internal anatomy: The mesenteries are hexamerously arranged in three cycles. There are an equal number of mesenteries distally and proximally, but sometimes there are fewer in the middle. There are two pairs of directives, each attached to a prominent siphonoglyph. All of the mesenteries of the first cycle are perfect. Some of the mesenteries of the second cycle are perfect, whilst none of the mesenteries of the third cycle are perfect. All of the larger mesenteries, including the directives, are fertile with acontia. The longitudinal muscles of the mesenteries are strong. The reactor muscles of all the mesenteries are diffuse but restricted, and span more than half of the distance between the body wall and the filament. The parietobasilar muscles are weak and are not differentiated in the stronger mesenteries. There are globular mesogleal pennons adjacent to the retractor muscle in some of the imperfect mesenteries.
Cnidom: Robust and gracile spirocysts, basitrichs, microbasic p-mastigophores.
(Zelnio et al., 2009)
Ecology and Distribution
Types were collected from hydrothermal vent communities at the Eastern Lau Spreading Center in the south-western Pacific at 2620 m depth from Kilo Moana (20°9`S, 176°12`E), and at 2145 m from ABE (20°45`S, 176°11`E) (Zelnio et al., 2009)
Specimens collected in September were sexually mature, with either male or female gametes present in any single specimen. Oocytes measured bewtween 40 - 120 um in diameter (Zelnio et al., 2009).