Isoaulactinia stelloides (McMurrich, 1889)

Gonzalez-Munoz, Ricardo, Simoes, Nuno, Tello-Musi, Jose Luis & Rodriguez, Estefania, 2013, Sea anemones (Cnidaria, Anthozoa, Actiniaria) from coral reefs in the southern Gulf of Mexico, ZooKeys 341, pp. 77-106 : 84-85

Isoaulactinia stelloides (McMurrich, 1889) Figure 6, Table 2

Aulactinia stelloides McMurrich 1889: 28-31.

Aulactinia stella : Duerden 1897: 454-455.

Bunodella stelloides : Verrill 1899: 43-44.

Bunodes stella : Duerden 1898: 455.

Bunodactis stelloides : Verrill 1900: 556.

Anthopleura catenulata : Cairns, den Hartog and Arneson 1986: 177-178; Pl. 51.

Anthopleura carneola : Cairns, den Hartog and Arneson 1986: 177-178; Pl. 51.

Isoaulactinia stelloides : Belém, Herrera-Moreno and Schlenz 1996: 77-88.

Material examined.

La Gallega reef (19°13'20"N, 96°07'39"W; six specimens).

Diagnosis.

Fully expanded oral disc and tentacles to 24-38 mm in diameter. Oral disc smooth, slightly wider than column, 9-11 mm in diameter, light- or olive-green, sometimes with small white stripes near tentacles bases (Figure 6A, B). Tentacles hexamerously arranged in four cycles (about 48 in number), simple, smooth, moderately long (9-14 mm in length), conical, tapering distally, inner ones longer than outer ones, contractile, olive-green with white bands along entire length (Figure 6A, B). Deep fosse (Figure 6G). Twenty-four endocoelic marginal projections (Figure 6C, G) with basitrichs and macrobasic p-mastigophores. Column cylindrical, 8-12 in diameter and 13-22 mm in height, with approximately 48 longitudinal rows of verrucae along entire column, but more conspicuous distally (Figure 6C). Pedal disc well-developed, 9-16 mm in diameter (Figure 6C). Column, verrucae, and pedal disc light-brown or beige (Figure 6C). Mesenteries hexamerously arranged in three cycles (24 pairs in specimens examined): all cycles perfect; same number of mesenteries distally and proximally. First and second cycles fertile (except directives); hermaphroditic (?), only oocytes observed in specimens examined (Figure 6E). Developing polyps in coelenteron (Figure 6F). Two pairs of directives each attached to a well-developed siphonoglyph (Figure 6D). Retractor muscles strong and restricted; parietobasilar muscles well-developed with relatively long and thick free mesogleal pennon (Figure 6E). Basilar muscles well-developed (Figure 6H). Marginal sphincter muscle endodermal, strong and circumscribed, palmate (Figure 6G). Longitudinal muscles of tentacles ectodermal (Figure 6I). Zooxanthellae present. Cnidom: basitrichs, microbasic b-mastigophores, macrobasic and microbasic p-mastigophores, and spirocysts (Figure 6 J–Y; see Table 2).

Natural history.

Isoaulactinia stelloides inhabits shallow waters in the lagoon reef zone, at 1-2 m, near Actinostella flosculifera , Stichodactyla helianthus , and the zoanthid Palythoa caribaeorum (Duchassaing & Michelotti, 1860). It lives with the column burrowed in the sand but the pedal disc attached to rocks and coral rubble. Although we only observed developing oocytes in the two specimens histologically examined, Isoaulactinia stelloides has been reported as a simultaneous hermaphroditic, internally brooding, often with developing polyps in the coelenteron ( Belém et al. 1996, Daly and den Hartog 2004); the latter have also been observed in the present study (Figure 6F).

Distribution.

Western Atlantic, from Bermuda to Barbados, and along the Caribbean Sea ( Belém et al. 1996, Daly and den Hartog 2004). This is the first record for the coast of Mexico; found in the VRS (see Table 1).

Remarks.

Currently Isoaulactinia has two valid species ( Daly 2004, Fautin 2013): Isoaulactinia hespervolita Daly, 2004, and Isoaulactinia stelloides . According to Daly (2004) Isoaulactinia hespervolita differs from Isoaulactinia stelloides in having an unmarked oral disc and tentacles, spinose holotrichs in the column and being gonochoric rather than hermaphroditic. In addition, Isoaulactinia hespervolita has a reddish-orange to greenish-brown column, oral disc and tentacles; approximately 80 tentacles arranged in up to five cycles, and macrobasic p-mastigophores only in the column and tentacles ( Daly 2004). We found additional microbasic b-mastigophores in the actinopharynx of Isoaulactinia stelloides but they were not abundant (Table 2). This category of nematocyst has not been previously reported in the actinopharynx of either of the species ( Belém et al. 1996, Daly and den Hartog 2004).