Exocoelactis Carlgren, 1925

Arellano, Shawn M. & Fautin, Daphne G., 2001, Redescription and range extension of the sea anemone Exocoelactis actinostoloides (Wassilieff, 1908), with revision of genus Exocoelactis (Cnidaria, Anthozoa, Actiniaria), Zoosystema 23 (4), pp. 645-657 : 647-648

Genus Exocoelactis Carlgren, 1925

TYPE SPECIES. — Polysiphonia tuberosa Hertwig, 1882 , which was collected on the Challenger Expedition; 19 syntypes are in NHM (catalog #1889.11.25.15) and one is in SMNH (catalog #1181) ( Fautin 2001). Hertwig published his findings from the Challenger twice; the German-language version ( Hertwig 1882b) has priority over the English-language version ( Hertwig 1882a) ( Fautin 2001). The other species included by Carlgren (1949) in the genus was described as Exocoelactis valdiviae by Carlgren (1928). Carlgren (1925) renamed Exocoelactis because a sponge preoccupied the name Polysiphonia .

DEFINITION. — Exocoelactiidae with well-developed base. Column smooth or somewhat nodular, thickwalled, and vase-shaped. Sphincter mesogleal, weak, so upper part of column cannot cover the tentacles. Margin tentaculate. Tentacles short to moderately long, in some species some thickened on outer side at the base. At least the 12 first tentacles, and sometimes at least some of those of third cycle, typically arranged; the other tentacles set in two rows, forming triangular groups continuous with one another. Inner tentacles the largest; tentacles decrease in size toward margin. Outermost tentacles communicate with exocoels, inner ones with endocoels. Longitudinal muscles of tentacles and radial muscles of oral disc mesogleal. Two broad siphonoglyphs and two pairs of directive mesenteries. Mesenteries of the two first cycles normally positioned, complete, and sterile. Later mesenteries arranged bilaterally, the youngest ones in the middle of the secondary exocoels. Each later pair consists of a larger and a smaller mesentery: the larger member of each pair may be complete and may be sterile; nearly all incomplete mesenteries fertile. C n i d o m: s p i r o c y s t s, b a s i t r i c h s, m i c r o b a s i c p -mastigophores.

REMARKS

In the definition of Exocoelactis in his catalog to sea anemones of the world, referring to mesenterial arrangement, Carlgren (1949: 86) stated “the stronger partner in each of these [unequal] pairs is perfect and may be sterile, all the other mesenteries are fertile”. However, his original definition did not specify that the stronger partner is perfect ( Carlgren 1928). Having found that in many unequally developed pairs, both partners are incomplete (imperfect), we revise the sentence of the definition referring to that structure. We make two other revisions to bring the definition into conformity with our experience of the animals. The tentaculate margin is not necessarily either “undulating or drawn out in 12 or more lobes”, as Carlgren (1949: 85) stated; this feature is probably due to contraction of the specimen. And the tentacle musculature is not necessarily near the endoderm. We also change the word “perfect” to “complete” (and “imperfect” to “incomplete”) to conform to current usage, make consistent the rendering of numbers, and phrase the entire definition telegraphically. We make no change to the description of tentacles in triangular fields, an arrangement that reflects the mesenterial arrangement, but this feature may not be clear in well-expanded individuals.

Exocoelactis actinostoloides ( Wassilieff, 1908)