Family Aiptasiidae Carlgren, 1924

Diagnosis (after Carlgren 1949 and Rodríguez et al. 2012). Metridioidea with well developed pedal disc and basilar muscles. Column sometimes distinctly divided into regions. Tentacles and distal column with ectodermal longitudinal muscles. Cinclides in mid-column, margin tentaculate. Mesogleal marginal sphincter muscle. Mesenteries not divisible into macro- and micro- cnemes. Six to eight pairs of mesenteries perfect and fertile. Two siphonoglyphs. Acontia with basitrichs and microbasic p -amastigophores. Cnidom: Spirocyst, basitrichs, and microbasic b-mastigophores and p -amastigophores.

Type genus. Aiptasia .

Included genera. Aiptasia; Aiptasiogeton; Bartholomea; Bellactis; Carlgreniella Watzl, 1922 (?); Exaiptasia gen. nov.; Paranthea Verrill, 1868 (?); Laviactis gen. nov.

We modified the familial diagnosis to reflect the recent changes in the higher-level classification of the order (see Rodríguez et al. 2012, 2014). We also noted that the column is not always clearly divided into regions in all the taxa, the mesogleal marginal sphincter muscle is not always weak, and that the cnidom of the family includes microbasic b -mastigophores (in the column) and microbasic p -amastigophores but not microbasic p -mastigophores (p -rhabdoids B2 but not p -rhabdoids A sensu Schmidt (1969), respectively).

Aiptasiodes Stephenson, 1918 was previously placed within Aiptasiidae (Fautin 2013) . Stephenson (1918) erected the genus for forms related to Aiptasia but having a mesogleal sphincter muscle because at the time, the type species of Aiptasia ( A. couchii) was described as lacking a marginal sphincter muscle. After a mesogleal marginal sphincter muscle was recognized in A. couchii (Stephenson 1920), Aiptasioides became a junior synonymy of Aiptasia and Aiptasiodes is no longer considered a valid genus (Fautin et al. 2007a).

Watzl (1922) erected Carlgreniella for C. robusta Watzl, 1922, distinguishing it from Bartholomea by the 24 longitudinal rows of papillae in the column and a fairly strong mesogleal marginal sphincter muscle in Carlgreniella . Although Watzl (1922) illustrated and described in detail the papillae of C. robusta, Carlgren (1949) synonymized this species with B. annulata; Carlgren (1949) added the putative presence of papillae in the column (marking it with a question mark) to the diagnosis of Bartholomea . Current data (type material is not available, see Fautin 2013) are insufficient to determine whether C. robusta represents a different species from B. annulata and if the presence of rows of papillae in the column warrants a genus-level distinction within these taxa. Pending further revision, we consider the synonymy of C. robusta and B. annulata and the generic status of Carlgreniella unresolved.

The genus Neoaiptasia Parulekar, 1969 currently includes two species (Fautin 2013): N. comensali Parulekar, 1969 (types species of the genus) and N. morbilla Fautin & Goodwill, 2009 . The original assignment of both species of Neoaiptasia to the family Aiptasiidae was suspect (Parulekar 1969; Fautin & Goodwill 2009). As in Paraiptasia England, 1992, members of Neoaiptasia lack cinclides and the cnidom of both described species of Neoaiptasia does not correspond to those of other members of Aiptasiidae (see Parulekar 1969: 60–61; Fautin & Goodwill 2009: fig. 5). Furthermore, molecular evidence clearly shows that N. morbilla does not belong within Aiptasiidae (Rodríguez et al. 2012, 2014). We do not consider Neoaiptasia to belong to Aiptasiidae; however, the familial position of this genus remains uncertain until additional data from the type species are available.

England (1992) erected the genus Paraiptasia for P. radiata (Stimpson, 1856) and modified the diagnosis of Aiptasiidae to accommodate it within the family (England 1992). Paraiptasia has catch tentacles and lacks cinclides (England 1992); these features are not common to the rest of the genera within Aiptasiidae . The distribution and size ranges of cnidae among tissues within members of Aiptasiidae are relatively uniform (see Tables 1–7). However, the cnidom, cnidae distribution and sizes of Paraiptasia are quite different from the other genera within the family (see England 1992: fig. 18 and table 11). For example, Paraiptasia does not have microbasic b -mastigophores in the column or the smaller microbasic p -amastigophores (1) in the acontia, and the large microbasic p -amastigophores (2) in the acontia are considerably shorter than those of the other aiptasiid genera with non-overlapping length ranges (to ~20–36 Μm vs. 41–80 Μm). Furthermore, according to the size and shape of the capsule Paraiptasia has p -rhabdoid B1a (specific category of microbasic p -amastigophores) in the filaments (see England 1992: fig. 18), although it is not possible to identify the type with total confidence due to poor image quality; this category of nematocyst is not present in any other member of Aiptasiidae (Reft pers. com.). Additionally, England (1992) does not mention the longitudinal muscles in the distal column in his redescription of P. radiata, a distinctive character for the family. Paraiptasia seems unlikely to belong within Aiptasiidae and thus we do not consider it within the family. The appropriate placement of this genus among other families remains uncertain until further revision.

Paranthea originally included three species (Fautin 2013); however, currently it only includes P. a r m a t a Verrill, 1868; the other two species have been synonymized as species of Aiptasia (see below). The description of P. a r m a t a is incomplete by modern standards and the type material of the species is not available (Fautin 2013). Based on existing data (only color of the specimen and the approximately length and number of tentacles are provided: see Verrill 1868), it is not possible to determine the identity of P. ar m at a and thus the familial placement of the genus Paranthea is unclear.