Anthopleura pallida

Diagnosis. Fully expanded oral disc and tentacles 10 - 19 mm in diameter. Oral disc narrow, smooth, 3 - 8 mm in diameter, pale green or gray (Figure 4 A). Tentacles hexamerously arranged in three cycles (24 in number), smooth, slender, relatively short (to 4 - 9 mm), tapering distally, inner ones longer than outer ones, contractile, whitish or gray, translucent, oral side with opaque white roundish spots (Figure 4 A, B). Fosse well marked (Figure 4 E). Column cylindrical, relatively elongate, 3 - 6 mm in diameter and 6 - 12 mm in height, with 12 longitudinal rows of verrucae from mid-column to distal margin (Figure 4 B, G). Twelve endocoelic marginal projections forming acrorhagi (Figure 4 B, E) with holotrichs, basitrichs, microbasic p-mastigophores, and spirocysts. Pedal disc well-developed, 4 - 8 mm in diameter, slightly wider than column (Figure 4 B). Pedal disc and column white to pale green (Figure 4 B). Mesenteries hexamerously arranged in 2 - 3 cycles: only first cycle perfect or first two cycles perfect and third imperfect; same number of mesenteries distally and proximally (12 - 32 pairs in specimens examined). Only first two cycles fertile (except directives); gonochoric (?), only spermatic cysts observed in specimens examined (Figure 4 F). Two pairs of directives each attached to a well-developed siphonoglyph (Figure 4 C). Retractor muscles diffuse; parietobasilar muscles well-developed with short mesogleal pennon (Figure 4 D). Basilar muscles well-developed (Figure 4 H). Marginal sphincter muscle endodermal, weak and diffuse (Figure 4 E). Longitudinal muscles of tentacles ectodermal. Cnidom: basitrichs, microbasic b- and p-mastigophores, holotrichs, and spirocysts (Figure 4 I-X; see Table 2).

Distribution. Western Atlantic, from Bermuda (Verrill 1900) to Virgin Islands (Duchassaing and Michelotti 1864). This is the first record for the coast of Mexico; found in Alacranes reef (see Table 1).