MERULINIDAE VERRILL, 1865: 146

Huang, Danwei, Benzoni, Francesca, Fukami, Hironobu, Knowlton, Nancy, Smith, Nathan D. & Budd, Ann F., 2014, Taxonomic classification of the reef coral families Merulinidae, Montastraeidae, and Diploastraeidae (Cnidaria: Anthozoa: Scleractinia), Zoological Journal of the Linnean Society 171 (2), pp. 277-355 : 292-293

FAMILY MERULINIDAE VERRILL, 1865: 146

Synonyms: Pectiniidae Vaughan & Wells, 1943: 196 ; Trachyphylliidae Verrill, 1901: 84 .

Type genus

Merulina Ehrenberg, 1834: 328 .

Diagnosis (apomorphies in italics)

Colonial, with intra- and/or extracalicular budding; attached or free-living. Corallites monomorphic or polymorphic; monticules may be present. Corallites discrete (1–3 mouths), uniserial or organically united. Walls fused, or with varying amount of coenosteum that may be costate or spinose. Calice of varying width (<4 to> 15 mm) and relief (<3 to> 6 mm). Costosepta may be confluent. Septa in varying number of cycles. Free septa may be present, regular or irregular. Septal spacing varies (<6, 6–11, or> 11 septa per 5 mm). Costosepta may be equal or unequal in relative thickness. Columellae of varying sizes relative to calice width, and may be trabecular or lamellar; continuous or discontinuous amongst adjacent corallites. Paliform (uniaxial) lobes may be weak/moderate or well developed. Septal (multiaxial) lobes may be present. Epitheca and endotheca developments vary amongst species.

Tooth base at midcalice circular. Tooth tip at midcalice irregular; tip orientation perpendicular to septum or multiaxial. Tooth height low (<0.3 mm) or medium (0.3– 0.6 mm). Tooth spacing narrow (<0.3 mm) or medium (0.3–1.0 mm). Number of teeth per septum varies amongst species. Granules aligned or scattered on septal face; generally irregular in shape. Interarea smooth, palisade, or with horizontal bands.

Synapticulotheca absent. Septotheca, abortive septa, trabeculotheca and paratheca developments vary amongst taxa. Thickening deposits fibrous without forming concentric rings. Costa centre clusters generally weak; ≤ 0.6 mm between clusters; medial lines present. Septum centre clusters weak or not distinct; ≤ 0.5 mm between clusters; medial lines present. Transverse crosses may be present. Columella centres clustered or aligned.

Genera included

1. Merulina Ehrenberg, 1834: 328 .

2. Astrea Lamarck, 1801: 371 .

3. Australogyra Veron & Pichon, 1982: 138 .

4. Boninastrea Yabe & Sugiyama, 1935: 402 .

5. Caulastraea Dana, 1846: 197 .

6. Coelastrea Verrill, 1866: 32 .

7. Cyphastrea Milne Edwards & Haime, 1848a , vol. 27: 494.

8. Dipsastraea de Blainville, 1830: 338 .

9. Echinopora Lamarck, 1816: 252 .

10. Erythrastrea Pichon, Scheer & Pillai in Scheer & Pillai, 1983: 104 .

11. Favites Link, 1807: 162 .

12. Goniastrea Milne Edwards & Haime, 1848a , vol. 27: 495.

13. Hydnophora Fischer von Waldheim, 1807: 295 .

14. Leptoria Milne Edwards & Haime, 1848a , vol. 27: 493.

15. Mycedium Milne Edwards & Haime, 1851 , vol. 15: 130.

16. Orbicella Dana, 1846: 205 .

17. Oulophyllia Milne Edwards & Haime, 1848a , vol. 27: 492.

18. Paraclavarina Veron, 1985: 179 .

19. Paramontastraea Huang & Budd gen. nov.

20. Pectinia de Blainville, 1825: 201 .

21. Physophyllia Duncan, 1884: 118 .

22. Platygyra Ehrenberg, 1834: 323 .

23. Scapophyllia Milne Edwards & Haime, 1848a , vol. 27: 492.

24. Trachyphyllia Milne Edwards & Haime, 1848a , vol. 27: 492.

Taxonomic remarks

The clade Merulinidae was provisionally named ‘Bigmessidae’ ( Budd, 2009 ) because of the profound confusion that surrounded the classification of four living families comprising it – Faviidae , Merulinidae , Pectiniidae , and Trachyphylliidae – prior to the comprehensive revision by Budd et al. (2012; see also Huang et al., 2011). Molecular phylogenetic analyses unequivocally showed that, other than the monotypic Trachyphylliidae , these families were not monophyletic ( Fukami et al., 2008; Huang et al., 2011; Arrigoni et al., 2012). For instance, Trachyphyllia geoffroyi , the only extant Trachyphylliidae species, was nested within Indo- Pacific Favia (now Dipsastraea ), whereas species of Merulinidae belonged to two separate subclades within ‘Bigmessidae’. Yet, most ‘Bigmessidae’ genera were monophyletic (the exceptions being Favia , Favites , Goniastrea , and Montastraea ) (Fig. 2A; Huang et al., 2011), and well-defined genus-level subclades appeared to be supported by subcorallite morphological features ( Budd & Stolarski, 2011).

On the basis of molecular phylogenies by Fukami et al. (2008) and Huang et al. (2011), as well as detailed examinations of coral morphology at the corallite and subcorallite scales ( Budd & Stolarski, 2011), Merulinidae Verrill, 1865 , was expanded to include all members of ‘Bigmessidae’, Faviidae was demoted to the subfamily Faviinae as a group limited to the Atlantic, and the remaining two families were synonymized ( Budd et al., 2012). The seniority of the name Merulinidae relative to the other families justified this modification under the International Code of Zoological Nomenclature (hereafter referred to as the ‘Code’; ICZN, 1999).

Members of Merulinidae have been closely associated in the past. Its type genus Merulina was initially placed in the family-level taxon Daedalina Ehrenberg, 1834: 315, along with other traditional Faviidae taxa such as Favia and Platygyra ( Ehrenberg, 1834) . It was only later that Verrill (1865) recognized the familylevel morphological distinction between Merulina and the Faviidae taxa, concurred by Vaughan & Wells (1943) and Wells (1956). However, the evolutionary affinity between Merulinidae and Faviidae sensu Wells (1956) was never doubted, and the affiliation of the genus Hydnophora to either family was unclear (see Vaughan & Wells, 1943; Wells, 1956; Chevalier, 1975; Veron et al., 1977; Veron & Pichon, 1980; Wood, 1983; Veron, 1986, 2000). Furthermore, Trachyphylliinae Wells, 1956: F407, was a subfamily within Faviidae , and Pectiniidae was hypothesized to be very closely related ( Vaughan & Wells, 1943). The historic links amongst these taxa are evidently extensive, and thus the incorporation of the entire ‘Bigmessidae’ clade under Merulinidae should hardly be surprising.

Several molecular studies have found Catalaphyllia jardinei ( Saville Kent, 1893: 158, pl. 25: fig. 3, chromo pl. 4: fig. 7) to be nested within the merulinid clade ( Romano & Cairns, 2000; Barbeitos et al., 2010; Huang, 2012; Huang & Roy, 2013). Its initial description of Pectinia jardinei Saville Kent, 1893: 158 , suggests that it is possible to regard the monotypic Catalaphyllia Wells, 1971: 368 , as a part of the present family. However, Saville Kent’s (1893) placement of the species reflects the prevailing interpretation of his time, that Pectinia de Blainville, 1825 , actually referred to morphotypes associated with Meandrina Lamarck, 1801: 372 , and Euphyllia Dana, 1846: 157 , rather than the merulinid species we know of today ( Wells, 1971; note below the lack of subsequent descriptions of Pectinia in the 1800s). For this reason, and also because all the molecular studies have utilized the same single sample of Catalaphyllia jardinei from an unknown location ( Romano & Palumbi, 1996), Catalaphyllia is herein transferred to incertae sedis pending further analyses.

Merulinidae is widely distributed on reefs of the Indo-Pacific, and absent in the eastern Pacific. Only one merulinid genus, Orbicella , inhabits the Atlantic Caribbean.

Morphological remarks

There are five synapomorphies defining Merulinidae (bootstrap support of 72 and decay index of 5): (1) perpendicular or multiaxial tooth tip orientation (likelihood of 0.99 based on the Mk1 model); (2) irregularly shaped granules (likelihood 0.90); (3) weak costa centre clusters (likelihood 0.97); with (4) ≤ 0.6 mm separating costa clusters (likelihood 0.98); and (5) ≤ 0.5 mm separating septum centre clusters (likelihood 0.96). These comprise two micromorphological and three microstructural features, respectively. Only three of these may be considered nonhomoplastic synapomorphies – perpendicular or multiaxial tooth tip orientation (two states), ≤ 0.6 mm separating costa clusters (two states), and ≤ 0.5 mm separating septum clusters (two states) – as changes occur farther away from the root of Merulinidae for all other characters. Weak to strong development of paliform lobes is also a synapomorphy according to the morphological phylogeny and one of the most parsimonious reconstructions on the molecular tree, but the likelihood based on the Mk1 model is low (0.28).

Aside from Merulinidae , paliform lobes are independently acquired in Acanthastrea and Echinophyllia of Lobophylliidae , and Mycetophyllia of Mussidae . The microstructural synapomorphies for Merulinidae are also present in outgroups. Weak costa centre clusters are present in Faviinae and some Lobophylliidae genera ( Cynarina , Echinophyllia , Oxypora , and Parascolymia ), and small separations between costa (≤ 0.6 mm) and septum (≤ 0.5 mm) clusters are found in Faviinae . Only irregular tooth tips that are multiaxial or perpendicular to the septum, and unevenly shaped granules, both micromorphological characters, are unique to Merulinidae .