Actinioidea Rafinesque, 1815

Yap, Nicholas Wei Liang, Mitchell, Michela Lee, Quek, Zheng Bin Randolph, Tan, Ria, Tan, Koh Siang & Huang, Danwei, 2023, Tripedalia maipoensis Sun & Tsui & Wong & Cheung & Ng & Or & Qiu 2023, sp. nov., Zoological Studies 62 (29), pp. 1-25 : 5-8

Superfamily Actinioidea Rafinesque, 1815 Family Actiniidae Rafinesque, 1815 Genus Macrodactyla Haddon, 1898

Condylactis [pro parte] – Haddon and Shackleton 1893: 123; Fautin 2016: 105.

Macrodactyla [pro parte] – Haddon 1898: 431 [original description]; Stephenson 1921: 524, 531, 545; Stephenson 1922: 263, 265; Carlgren 1949: 63; Dunn 1981: 28, 35; Fautin et al. 2007: 213; Fautin et al. 2008: 49; Fautin 2016: 104, 105.

Etymology gender: Feminine.

Type species: Condylactis aspera Haddon and Shackleton, 1893 , by monotypy, in agreement with Dunn (1981), Fautin et al. (2007) and Fautin (2016).

Definition of genus modified after Dunn (1981) and Fautin et al. (2008). Substantial changes from our research are indicated in bold; all minor additions are underlined.

Diagnosis: Pedal disc distinct, circular to oval in outline, as wide as oral disc. Column elongated, marginal projections present. Adhesive verrucae present on distal end, often with foreign materials often attached, may be lobed and perforated. Fosse very shallow. Tentacles long and stout, covered with nematocyst batteries or entirely smooth; inner tentacles considerably longer than the outer.

Actinopharynx often everted when alive, with a pair of diametric siphonoglyphs. Symmetrically-arrayed mesenteries; always 12 pairs complete, all remainder incomplete. All fertile. Retractor muscles band-like, diffuse-circumscribed. Endodermal marginal sphincter muscle conspicuous and restricted. Parietobasilar muscles well-developed, with an extended pennon present for lower order mesenteries. Cnidom: spirocysts, basitrichs, microbasic p -mastigophores.

Nomenclatural considerations: Neave (1940) reports that the Macrodactyla , as a name for a sea anemone genus, is a junior homonym to a beetle genus described by TW Harris in Hitchcock (1833). As mentioned at the outset, Fautin (2016) had returned both Macrodactyla species (i.e., M. aspera and M. doreensis ) to the next oldest available generic name applied to them: Condylactis .

We consulted Harris’ contribution in Hitchcock (1833: 575) and found the name Macrodactyla , confirming its appearance in the publication. This listed name is further accompanied by a species epithet, a letter that denotes its taxonomic authority of the species (i.e., ‘F’ = JC Fabricius), and a common name – all of which we render here exactly as (including the way it was stylised; see Hitchcock 1833: 575): ( Macrodactyla ) subspinosa, F. Rose-Bug.

Harris’ entry in Hitchcock (1833) was meant simply to be part of an inventory of the insect biota of Massachusetts, and it lacks an accompanying description to Macrodactyla .

No beetle species is known by the name listed by Harris in Hitchcock (1833). The closest match is the species Macrodactylus subspinosus ( Fabricius, 1775) , which also occurs in Massachusetts, and is known by the common names, ‘Rose-bug’ and ‘Rose-chafer’ (see: Blatchely 1910: 953; Schoolmeesters 2021). Originally described by Fabricius (1775) as a member of the genus Melolontha Fabricius, 1775 , this species was later placed in a new genus, Macrodactylus , created by Latreille (1825: 372) ( Schoolmeesters 2021).

We posit that Harris’ entry in Hitchcock (1833) was a misspelling of the coleopteran genus name Macrodactylus . Nomenclatural information we have found on Ma. subspinosus corroborated with much of those present in Harris’ entry (i.e., taxonomic authority, species epithet, common name, etc.), as with this species’ geographical occurrence. Moreover, Harris’ revised checklist in Hitchcock’s (1835: 565) latter work strongly supports our assertion: in this updated listing, Harris attributed the taxonomic authority of the misspelled beetle genus name (still listed as Macrodactyla ) to PA Latreille. No works of Latreille prior to Harris’ entry in Hitchcock (1833) had mentioned Macrodactyla , only the name Macrodactylus was ever used in Latreille’s (1825) publication.

The name Macrodactyla in Hitchcock (1833) is thus not a senior homonym to the genus name that Haddon (1898) had used for the sea anemones; Harris’ entry is an incorrect spelling of the coleopteran genus name Macrodactylus , and therefore cannot enter homonymy (Article 54.3, the Code). As First Revisers, we retain the name Macrodactyla as a genus name for sea anemones; it is valid and available for use.

Taxonomic considerations for the genus Macrodactyla : Historically, sea anemone systematists have considered Haddon’s (1898) report of mesentery number and its arrangement in Macrodactyla to be ambiguous. Based only on the type species, C. aspera, Haddon defined Macrodactyla to have “six pairs of imperfect [= incomplete] mesenteries, and a second and third cycle of imperfect mesenteries” ( Haddon 1898: 431; additions in square parentheses, our own). Stephenson (1921) later revised this feature to denote the presence of only six complete mesenteries, elaborating further that Haddon (1898) may been mistaken on this feature ( Stephenson 1922: 263). Later definitions of Macrodactyla retained Stephenson’s assertions (e.g., Carlgren 1949). By including a second species to the genus, M. doreensis, Dunn (1981: 28) had amended its definition to include, “… six or more pairs of mesenteries perfect,… ” because this second species had more than six complete pairs of mesenteries. However, in Dunn’s [as Fautin] later publication of this genus, its diagnosis was changed, indicating that only six pairs of complete mesenteries were present in Macrodactyla (see Fautin et al. 2008: 49). In studying the type specimen of the type species for Macrodactyla (i.e., C. aspera ; MZC.I.33665), we found that it has 12 pairs of complete mesenteries instead of six, a feature that is consistent across all voucher and fresh material. Here, we have revised the definition of the genus to reflect this.

No data concerning the cnidom for the type species of Macrodactyla (i.e., C. aspera ) have ever been reported, it being absent in earlier descriptions of the genus (i.e., Haddon and Shackleton 1893; Haddon 1898; Stephenson 1921 1922). In recent definitions of Macrodactyla , which had included M. doreensis, Fautin et al. (2008: 49) simply reported the types of cnidae present in sea anemones of the genus, stating the presence of, “spirocysts, basitrichs, microbasic p -mastigophores”. We confirmed that these cnidae were present in the name-bearing type specimen of C. aspera .

We deemed Macrodactyla to be the most appropriate genus to place the new species, M. fautinae sp. nov., in the light of both morphological, ecological and genetic evidence gathered from this study. Both M. fautinae sp. nov. and M. aspera share the same number and arrangement of complete mesenteries. Both species also have visible adhesive verrucae on their column, and harbour the same types of cnidae in their tissues (see below, in their respective species description). Like M. aspera , we did not find any symbiotic micro/ macro-organisms associated with M. fautinae sp. nov. Our placement of this new species in Macrodactyla is further supported by genetic evidence we have gathered: we had repeatedly recovered both M. fautinae sp. nov. and M. aspera to be sister to each other, within a clade, with strong support (bootstrap> 80; Fig. 1 ). Our revised diagnosis of Macrodactyla now includes traits of this second species, thereby expanding on its definition.

We failed to recover M. doreensis and M. aspera as a monophyletic clade ( Fig. 1 ). Genetic evidence from this study, as with observations from recent studies, have repeatedly recovered M. doreensis to be nested among clownfish and dinoflagellate-associated sea anemones of the genus Heteractis ( Titus et al. 2019; Yap et al. 2021; Fig. 1 ). Apart from genetic evidence, both M. aspera and M. doreensis also do not share many morphological and ecological traits that would characterise them to be classified in the same genus. While both have verrucae on the distal end, those of M. aspera are always adhesive, whereas verrucae of M. doreensis are not ( Dunn 1981; Fautin et al. 2008). Mesentery number and arrangement between them also differ; those in M. aspera are arranged in up to three cycles while those of M. doreensis may go up to seven ( Dunn 1981). Furthermore, we found microcnemes to be present in M. doreensis , consistent to its depiction in Dunn (1981: Fig. 13), a trait that is absent in M. aspera . Ecologically, M. doreensis is a host to photosynthetic dinoflagellates and macro-fauna such as clownfishes ( Dunn 1981; Fautin and Allen 1992). In contrast, we have not encountered nor observed M. aspera to be involved in any symbiotic relationships with other micro/macro-organisms.

Given the genetic, morphological and ecological evidence presented, we place M. doreensis in the genus Heteractis , under a new combination: Heteractis doreensis ( Quoy and Gaimard, 1833) . In revising the diagnosis of Macrodactyla , we removed all characters that had extended to M. doreensis (e.g., presence of deep fosse).

Figures

Fig. 1. Phylogeny reconstruction of Macrodactyla aspera and Macrodactyla fautinae sp. nov. among actiniid sea anemones. Tree topology a result of maximum likelihood (ML) analysis, using a concatenated dataset (i.e., cox3, 12S, 16S, 28S). At the branches, bootstrap ML resampling values, and Bayesian inference (BI) posterior probability values, are presented as ML/BI. Only bootstrap values> 50, and posterior probability> 0.8 are indicated here; those less than 50 and 0.8 are denoted by (-). Taxa indicated in bold denotes the presence of new sequences obtained for this study. Indicated by an asterisk (*), we retain the name Macrodactyla doreensis in this figure to aid with the discussion within the main-text. For sequences used and the full tree, refer to table S1 and figure S3, respectively.