Exaiptasia pallida

Grajales, Alejandro & Rodríguez, Estefanía, 2014, Morphological revision of the genus Aiptasia and the family Aiptasiidae (Cnidaria, Actiniaria, Metridioidea), Zootaxa 3826 (1), pp. 55-100 : 69-74

Exaiptasia pallida (Agassiz in Verrill, 1864) comb. nov.

( Figs. 8–10 , Table 3)

Actinia diaphana Rapp, 1829

Cribina diaphana: Deshayes & Milne Edwards 1840 Actinia elongata Delle Chiaje, 1841

Adamsia diaphana: Milne Edwards 1857 Dysactis pallida Agassiz in Verrill, 1864

Bartholomea tagetes [sic] Duchassaing de Fombressin & Michelotti, 1864 Bartholomea inula [sic] Duchassaing de Fombressin & Michelotti, 1864 Dysactis mimosa Duchassaing de Fombressin & Michelotti, 1864 Bartholomea inula: Duchassaing de Fombressin & Michelotti, 1866 Dysactis minuta Verrill, 1867 (1866)

Paranthea minuta: Verrill 1868

Paranthea pallida: Verrill 1868

Disactis mimosa [sic]: Duchassaing 1870 Aiptasia saxicola Andres, 1881

Aiptasia diaphana: Andres 1883 ( 1884)

Aiptasia [sic] Agassizii: Andres 1883 ( 1884) Aiptasia inula: Andres 1883 ( 1884)

Aiptasia minuta: Andres 1883 ( 1884)

Aiptasia mimosa: Andres 1883 ( 1884)

Aiptasia tagetes: Andres 1883 ( 1884)

Aiptasia pallida: McMurrich 1887

Aiptasia leiodactyla Pax, 1910

Aiptasia insignis Carlgren, 1941

Aiptasioides pallida: Stephenson 1918

Aiptasiomorpha diaphana: Stephenson 1920 Aiptasiomorpha leiodactyla: Stephenson 1920 Bartholomea tagetes: Stephenson 1920

Aiptasia pulchella Carlgren, 1943

Aiptasia californica Carlgren, 1952

Aiptasia tagetes: Atoda 1954

Aiptasiomorpha minuta: Uchida & Soyama 2001 Aipstasia [sic] pulchella: Reimer et al. 2007

Material examined. (See Appendix 1).

Comparative material examined. Aiptasia insignis Carlgren, 1941 ; SMNH-type 4510 (three syntypes). South Atlantic Ocean, Saint Helena, off Jamestown. Leg. Th. Mortenseni 0 1 Feb 1930.

Aiptasia parva Carlgren, 1938 ; SMNH-type 4053 (six syntypes, only two loaned). South Atlantic Ocean, South Africa, East London. Leg. Swedish South African Expedition 1935.

Aiptasia parva Carlgren, 1938 ; SMNH-type 4054 (three syntypes). South Atlantic Ocean, South Africa, East London. Leg. Swedish South African Expedition 1935.

Dysactis pallida Agassiz in Verrill, 1864; MCZ SCOR-1004 (two syntypes). North America, United States, South Carolina, Charleston. Louise Agassiz.

Description. External anatomy ( Fig. 8 ): Pedal disc to 10 mm diameter, wider than column in living specimens. Column smooth, to 60 mm height and to 30 mm diameter in preserved specimens. Cinclides often conspicuous in mid-column, in 2–3 rows, with ~12 cinclides per row, alternating in height, corresponding with endocoels of first two cycles of mesenteries. Mesenterial insertions visible. Oral disc to 10 mm diameter in preserved specimens. Tentacles to 96, smooth, long, tapering toward tips, all of same length, to 20 mm.

Internal anatomy and microanatomy ( Fig. 9 ): Mesogleal marginal sphincter muscle diffuse, strong, reticulate, relatively short, restricted to column margin; fibers occupying entire mesoglea ( Fig. 9 G). Mesenteries hexamerously arranged in four cycles ( Figs. 9 A, B). Only first cycle perfect; first two cycles fertile, probably including directives; third and fourth cycles reduced, without filaments or acontia. Two pairs of directives each associated with a well-developed siphonoglyph. Gonochoric. Asexual reproduction by pedal laceration. Retractor muscles restricted, strong. Parietobasilar muscles differentiated, weak ( Fig. 9 E). Longitudinal muscles of tentacles ectodermal ( Fig. 9 C). Strong longitudinal ectodermal muscles in distal end of column ( Fig. 9 D). Basilar muscles well differentiated, with fibers on thin mesogleal pennon ( Fig. 9 F). Acontia numerous, well developed.

Color ( Fig. 8 ): In living specimens, column translucent proximally and greyish-brownish with scattered spots distally; oral disc and tentacles greyish, the latter with scattered white transversal stripes ( Figs. 8 A, B). Whitish mouth and actinopharynx with yellowish circle around ( Fig. 8 A). Preserved specimens uniform tan in color.

Cnidom: Spirocysts, basitrichs, microbasic b -mastigophores and p- amastigophores ( Fig. 10 ). See Table 3 and Appendix 2 for size and distribution.

TABLE 3. Size ranges of the cnidae of Exaiptasia pallida comb. nov. 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.

Geographic and bathymetric distribution. Exaiptasia pallida comb. nov. is a widespread species recorded worldwide along the northwestern Atlantic coast ( Fautin 2013), the Gulf of Mexico (e.g. Cary 1906; Gunter & Geyer 1955) and the Caribbean Sea (e.g. Silbiger & Childress 2008; González-Muñoz et al. 2012), the coast of Brazil in the southwestern Atlantic Ocean (e.g. Corrêa 1964, 1973; Dube 1983; Pires et al. 1992; Castro et al. 1995; Echeverria et al. 1997; Zamponi 1998; Farrapeira et al. 2007), Galapagos Islands (Fautin et al. 2007b), and Australia. As a consequence of this study, we extend the distribution of the species to the Mediterranean Sea and western Africa (geographic distribution of the former Aiptasia diaphana ), the east and west Pacific coasts (e.g. California [geographic distribution of former A. californica ], Japan and Hawaii [geographic distribution of former A. pulchella ]), and Saint Helena Island (geographic distribution of former A. insignis ). We provide new records for Brazil, Australia, and Panama (Appendix 1). Exaiptasia pallida comb. nov. is a tropical and subtropical, shallowwater subtidal species, preferring calm and protected waters, found between 0– 5 m.

Taxonomic remarks. The genus Aiptasia currently includes 13 nominal species ( Fautin 2013). Two of these species ( A. mutabilis and A. prima ) we consider to belong within Aiptasia (see Taxonomic remarks following treatment of Aiptasia , above). Descriptions of most of the other 11 species are incomplete by modern standards, particularly those of species within the Caribbean Sea ( González-Muñoz et al. 2012), and type material is not available in most cases. Differences among these species are usually the lack of several characters—such as rows of cinclides or the marginal sphincter muscle—which are sometimes variable but also difficult to detect in some preserved specimens (e.g. differences between A. tagetes and A. leiodactyla vs. Exaiptasia pallida comb. nov., see González-Muñoz et al. 2012). Despite detailed examination of morphology and cnidae of newly-collected material from almost all localities reported for the 11 putative species (except South Africa, South Trinidad Islands and Saint Helena, see Appendix 1), we did not find any constant morphological features that would distinguish Aiptasia pallida , A. californica , A. diaphana , A. inula , A. leiodactyla , A. mimosa , A. pulchella and A. tagetes . Appendix 2 lists cnida data of examined populations by geographical regions (i.e. east Atlantic and Caribbean Sea, west Atlantic, Pacific Ocean). Although we found slight differences in the size ranges of cnidae among a few localities, most notably longer microbasic p -amastigophores (2) in the filaments of specimens from Hawaii (to 35 Μm vs. to 45 Μm), the ranges always overlap. We do not consider these differences sufficient to distinguish species. Furthermore, molecular evidence supports a single, widely distributed species (Grajales 2014). Thus, we synonymize the former seven species as E. pallida comb. nov.

Aiptasia minuta ( Verrill, 1867) is described from Japan, adjacent to the known range to the former A. pulchella (now E. pallida comb. nov.). Although Verrill (1866) did not mention cinclides in this species, he described small low prominences in the column that might correspond to cinclides. Uchida and Soyama (2001) placed it within Aiptasiomorpha ( Stephenson, 1920) , which implies that they did not see a marginal sphincter muscle (see Carlgren 1949). However, Uchida and Soyama (2001) did not describe the species or provide cnida data because their publication is not a taxonomic work but a guidebook. In addition, cinclides are easily overlooked, and thus we consider this species to correspond to E. pallida comb. nov. (as a synonymy of the former A. pulchella ).

Carlgren (1941) described in brief Aiptasia insignis from Saint Helena Island; he noted that it resembled A. couchii . However, as described, this species fits Exaiptasia gen. nov. better than Aiptasia , especially in the size range of the longer microbasic p -amastigophores of the acontia (55–70.5 µm in length) and the geographic distribution (tropical and subtropical). The marginal sphincter muscle is slightly weaker in A. insignis than in E. pallida comb. nov. (see Carlgren 1941, fig. 8) and there are few differences in cnidae (mainly narrower sizes ranges than those of E. pallida comb. nov. and absence of small categories of cnidae). However, our examination of the type material of A. insignis confirmed that differences in cnidae were probably due to lower numbers of capsules and specimens measured; cnida sizes and categories correspond to those of E. pallida comb. nov. (particularly the microbasic b -mastigophores of the scapus). We found no morphological reason to consider E. insignis a separate species from E. pallida comb. nov.

According to the Principle of Priority (Art. 23, ICZN 1999), Aiptasia diaphana is the senior subjective synonym and thus must be used over the junior synonym, the former A. pallida . Although the species epithet pallida currently has a broader use than diaphana (particularly in non-taxonomic works), this name does not fulfill the requirements for a reversal of precedence of a junior synonym—i.e. Art. 23.9.1 of the Code—ICZN 1999). However, in our opinion, the use of the senior synonym ( diaphana ) will cause confusion and threatens stability, and we wish to maintain the use of the junior synonym ( pallida ). Following Art. 23.9.3 of the Code (ICZN 1999), the matter has been referred to the ICZN (Grajales & Rodríguez 2013: Case 3633) and is awaiting resolution. While the case is under consideration, the junior name is to be maintained (ICZN 1999); thus, here we use Exaiptasia pallida comb. nov.

Figures

FIGURE 8. External anatomy of Exaiptasia pallida comb. nov. A) Oral view of living specimen. B) Lateral view of living specimen. C) Lateral view of preserved specimen; notice cinclides and acontia (arrows). Scale bars: A – C, 10 mm.

FIGURE 9. Internal anatomy of Exaiptasia pallida comb. nov. A) Cross section of the column at the level of the actinopharynx showing the cycles of mesenteries (indicated by roman numerals between pairs). B) Detail of fourth cycle of mesenteries (arrows). C) Cross section through a tentacle showing the ectodermal longitudinal musculature; notice zooxanthellae in gastrodermis. D) Cross section through distal column showing strong ectodermal longitudinal musculature. E) Detail of weak parietobasilar muscles. F) Detail of a longitudinal section of the proximal end showing the basilar muscles (arrows). G) Longitudinal section of the distal column showing reticulate mesogleal marginal sphincter muscle. Abbreviations: ep, epidermis; ga, gastrodermis; me, mesoglea; s, siphonoglyph. Scale bars: A – G, 0.1 mm.

FIGURE 10. Cnidae of Exaiptasia pallida comb. nov. A, C, F, I, K, L, N, O) Microbasic p - amastigophores. B, D, G, J, M, P) Basitrichs. E) Microbasic b - mastigophore. H) Spirocyst.