Aiptasia mutabilis ( Gravenhorst, 1831 )

Grajales, Alejandro & Rodríguez, Estefanía, 2014, Morphological revision of the genus Aiptasia and the family Aiptasiidae (Cnidaria, Actiniaria, Metridioidea), Zootaxa 3826 (1), pp. 55-100 : 64-68

Aiptasia mutabilis ( Gravenhorst, 1831)

( Figs. 5 –7, Table 2)

Actinia mutabilis Gravenhorst, 1831

Cribina punctata Schmarda, 1852

Sagartia Penoti [sic] Jourdan, 1880

Aiptasia turgida Andres, 1881

Aiptasia carnea Andres, 1881

Aiptasia mutabilis: Andres 1883 ( 1884) Aiptasiomorpha mutabilis: Carlgren 1949 Aiptasia mutabilis bicolor Andres : Pax & Müller 1953 Aiptasia mutabilis maculata Andres : Pax & Müller 1953 Aiptasia mutabilis Form II: Schmidt 1972

Material examined. (See Appendix 1).

Description. External anatomy ( Fig. 5 ): Pedal disc to 15 mm diameter, wider than column in living specimens. Column smooth, more or less cylindrical, to 30 mm height and 28 mm diameter in preserved specimens ( Fig. 5 C). Cinclides in mid-column, inconspicuous, in three rows, corresponding with endocoels of first two cycles of mesenteries. Oral disc to 10 mm diameter. Tentacles to 192, smooth, tapering towards tips; inner tentacles longer than outer ones, to 30 mm and 20 mm length, respectively.

Internal anatomy and microanatomy ( Fig. 6 ): Mesogleal marginal sphincter muscle diffuse, moderately strong, short, restricted to column margin, alveolar ( Fig. 6 G). More mesenteries distally than proximally. Mesenteries hexamerously arranged in five cycles (fifth cycle only distally) ( Figs. 6 A, B). Only first cycle perfect; first four cycles fertile, including directives. Two pairs of directives each associated with a well-developed siphonoglyph. Gonochoric. Retractor muscles slightly restricted. Parietobasilar muscles weak ( Fig. 6 C). Longitudinal muscles of tentacles ectodermal ( Fig. 6 E). Strong longitudinal ectodermal muscles in distal end of column ( Fig. 6 F). Basilar muscles weak, poorly differentiated ( Fig. 6 D). Acontia numerous, well developed.

FIGURE 7. Cnidae of Aiptasia mutabilis . A, C, F, I, K, L, N, O) Microbasic p -amastigophores. B, D, G, J, M, P) Basitrichs. E) Microbasic b -mastigophore. H) Spirocyst.

Color ( Fig. 5 ): In living specimens, column translucent brownish; tentacles translucent brownish with distinct pattern of whitish longitudinal marks ( Figs. 5 A, B). Mouth and actinopharynx whitish. Preserved specimens uniform tan in color; pattern on tentacles not visible in preserved specimens ( Fig. 5 C).

Cnidom: Spirocysts, basitrichs, microbasic b -mastigophores and p- amastigophores (Fig. 7). See Table 2 for size and distribution.

Geographic and bathymetric distribution. Known only from the Mediterranean Sea ( Schmidt 1972), from 0 to 30 m, in protected rocky habitats (e.g. crevices).

Taxonomic remarks. Stephenson (1918) thoroughly described Aiptasia prima ; however, he does not provide data on cnidae for the species because it was not a common practice at the time. According to Stephenson (1918), A. prima differed from other species of the genus. It has two rows of conspicuous perforated vesicles in the scapus (although Stephenson (1918) was unsure if these were cinclides) and only three cycles of mesenteries; however, A. prima has up to 96 tentacles, and thus a forth cycle of mesenteries should be developing ( Stephenson 1928). Although the type material of this species is available at the British Museum of Natural History (BMNH- 1918.5.12.22, two syntypes) ( Fautin 2013) we were unable to obtain this material through loan. Thus, the generic position and identity of this species remains unclear pending an examination of the cnidae. However, based on the geographic distribution of the species (South Trinidad Island, 51°S 60°W, temperate climate) we think it probably corresponds better with Aiptasia rather than with the widely-distributed Exaiptasia pallida comb. nov.

TABLE 2. Size ranges of the cnidae of Aiptasia mutabilis . x, mean; SD, standard deviation; S, ratio of number of specimens in which each cnida was found to number of specimens examined; N, Total number of capsules measured; F, frequency; +++, very common; ++, common; +, rather common; Abbreviations: M, Microbasic.

Figures

FIGURE 5. External anatomy of Aiptasia mutabilis. A) Oral view of living specimen. B) Detail of the color pattern of the tentacle. C) Lateral view of preserved specimen. D) Detail of pedal disc of preserved specimen. Scale bars: A – D, 10 mm.

FIGURE 6. Internal anatomy of Aiptasia mutabilis. A) Cross section of the column at the level of the actinopharynx showing the cycles of mesenteries (indicated by roman numberals between pairs). B) Detail of fifth cycle of mesenteries (arrows). C) Detail of parietobasilar muscles (arrows). D) Detail of a longitudinal section of the proximal end showing the basilar muscles (arrows). E) Cross section through a tentacle showing the ectodermal longitudinal musculature. F) Cross section through distal column showing the ectodermal longitudinal musculature. G) Longitudinal section of the distal column showing the mesogleal marginal sphincter muscle. Abbreviations: ep, epidermis; ga, gastrodermis; me, mesoglea. Scale bars: A – G, 0.1 mm.