Aiptasia pallida

Natural history. — Aiptasia pallida lives in shallow waters attached to small rocks and submerged lumber, between the patches of sand and seagrass of the lagoon-reef zone, sometimes epiphytic on Thalassia testudinum leaves, between 1 – 6 m depth. It often forms aggregations as a result of asexual reproduction by pedal laceration (Carlgren 1949; Clayton 1985; Cairns et al. 1986).

(Figure 9, Table 2)

Diagnosis. — Fully expanded tentacles and oral disc often to 40 mm in diameter. Oral disc wide, 5 – 15 mm in diameter; mouth often with whitish spots in the edges (Figure 9 A). Tentacles about 48, simple, smooth, long, thin, inner ones longer than outer ones, not completely contractile (Figure 9 B, C). Column cylindrical, 10 – 35 mm in height and 2 – 13 mm in diameter, smooth, divided into capitulum and scapus; one or two rows of cinclides in middle column (Figure 9 B). Column, tentacles and oral disc light to dark brown, oral disc often with white, yellow and bluish spots. Pedal disc well developed, 3 – 8 mm in diameter. Pedal disc and scapus often lighter than column, light brown or beige, semitransparent, with mesenterial insertions visible. Mesenteries hexamerously arranged in two or three cycles (12 – 24 pairs in specimens examined): first cycle perfect, others imperfect and poorly developed (Figure 9 D, E). No gametogenic tissue observed in specimens reviewed. Two pairs of directives each attached to a well developed siphonoglyph (Figure 9 D). Retractor muscles diffuse to restricted; parietobasilar muscles poorly developed. Basilar muscles poorly developed. Marginal sphincter muscle not observed. Longitudinal muscles of tentacles ectodermal. Acontia white (Figure 9 C), with basitrichs and microbasic p - amastigophores. Zooxanthellae present. Cnidom: basitrichs, microbasic p- amastigophores and spirocysts (Figure 9 F – S; see Table 2).

Remarks. — Five of the 16 currently valid species of the genus Aiptasia have been recorded in the Caribbean Sea (Fautin 2011); however, differences between A. pallida and its four Caribbean congeners are unclear based on the scarce information available. Aiptasia inula (Duchassaing & Michelotti, 1864) has only one row of cinclides and the oral disc could be yellow or blue (Duchassaing & Micheloti 1864; Andres 1883); A. mimosa (Duchassaing & Michelotti, 1864) has 50 – 60 tentacles arranged in three cycles and the oral disc is dark red (Duchassaing & Michelotti 1864; Andres 1883); A. leiodactyla Pax, 1910 lacks a marginal sphincter muscle and is reported as a protogynous hermaphrodite. According to Sebens (1998), the most distinctive difference between A. pallida and A. tagetes (Duchassaing & Michelotti, 1864) is the presence of two (rarely one or three) prominent transversal rows of cinclides in the former, and the lack of distinct rows of cinclides in the latter; however, Duchassaing & Michelotti (1864) describe two rows of cinclides in the middle of column of A. tagetes. Some studies consider A. pallida and A. tagetes synonyms (Corrêa 1964; Herrera-Moreno 1981; Cairns et al. 1986); according to Fautin (2011), both species are valid. A thorough revision of Caribbean species of genus Aiptasia is needed to clarify their taxonomic status.

Distribution. — Aiptasia pallida is reported from Bermuda to Brazil, along the entire Caribbean Sea (see Table 1); however, our specimens represent the first record for the Mexican Caribbean (Puerto Morelos and Isla Contoy reefs).

Material examined. — Puerto Morelos (20 ° 54 ’ 28.73 ” N, 86 ° 50 ’ 43.33 ” W; 5 specimens); Isla Contoy (21 ° 28 ’ 23 ” N, 86 ° 47 ’ 22.18 ” W; 5 specimens).