Calliactis tricolor

Diagnosis. Fully expanded oral disc and tentacles 9 - 48 mm in diameter. Oral disc smooth, wider than column, 3 - 20 mm in diameter, pale-brown translucent, with small white stripes in endocoelic spaces, sometimes forming a white ring; some specimens also with pink flashes (Figure 9 A). Mouth bright yellow, orange, or white; often with purple ring around lips (Figure 9 A). Tentacles hexamerously arranged in 5 - 6 cycles (96 - 192 in number), smooth, thin, short (2.5 - 15.5 mm), inner ones longer than outer ones, contractile (Figure 9 A, B), tapering distally, pale-brown with a longitudinal row of white dots along entire length (Figure 9 A, B); some specimens also with bright-pink flashes mainly at tips. Column trumpet-shaped in extended position, dome-shaped when contracted, 5 - 24.5 mm in diameter and 4 - 31 mm in height, divided into narrow, smooth capitulum and wrinkled-texture scapus (Figure 9 B). Capitulum pale-brown to yellowish, scapus bright to dark orange often with small white stripes or white flashes slightly above limbus (Figure 9 B). Pedal disc well-developed, circular to irregular, wider than column, 6 - 36 mm in diameter, with mesenterial insertions visible, pale-brown and translucent (Figure 9 C). One or two rows of cinclides proximally, near limbus; dark-red or brown (Figure 9 B). Mesenteries hexamerously arranged in four cycles; same number of mesenteries proximally and distally (to 48 pairs in specimens examined): first cycle perfect, others imperfect; third and fourth cycles poorly developed, without filaments or acontia. Gametogenic tissue not observed in specimens examined. Two pairs of directives each attached to a well-developed siphonoglyph (Figure 9 E). Retractor muscles weak and diffuse; parietobasilar muscles poorly developed (Figure 9 E, F). Basilar muscles poorly developed (Figure 9 H). Marginal sphincter muscle mesogleal, strong, transversally stratified (Figure 9 G). Longitudinal muscles of tentacles ectodermal. Acontia numerous, bright orange (Figure 9 C), with basitrichs. Zooxanthellae present. Cnidom: basitrichs, microbasic p-mastigophores, and spirocysts (Figure 9 J-Q; see Table 2).

Distribution. Western Atlantic, from the northern coast of USA to the northern coast of Brazil, along the Caribbean Sea and Gulf of Mexico (Carlgren and Hedgpeth 1952, Zamponi et al. 1998). This is the first record for the coast of Mexico; found in Serpientes and Alacranes reefs.