(Figure 9, Table 2)
Dysactis pallida Agassiz in Verrill, 1864: 26.
Paranthea pallida Verrill, 1868: 322.
Aiptasia Agassizii [sic] Andres, 1883: 183.
Aiptasia pallida McMurrich, 1887: 59 –61.
Aiptasia McMurrich, 1889 b: 102 –104.
Aiptasia tagetes Verrill, 1900: 557.
Aiptasioides pallida Stephenson, 1918: 51.
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).
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).
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).
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).
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.