Merulina, EHRENBERG, 1834: 328

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 : 294-295

GENUS MERULINA EHRENBERG, 1834: 328 ( FIG. 3 )

Synonym

Clavarina Verrill, 1864: 56 (type species: Merulina scabricula Dana, 1846: 275 , pl. 16: figs 2, 2a, b; original designation, Verrill, 1864: 56).

Type species

Madrepora ampliata Ellis & Solander, 1786: 157 , pl. 41: figs 1, 2; original designation, Ehrenberg, 1834: 328.

Original description

‘Fere pedalis, frondibus liberis, subflabellatis, e ramulis coalitis dichotome colliculatis, collibus lamellososerratis, asperrimis, vix lineam altis, stellis in seriebus dichotomis saepe confluentibus positis, sulcis lineam latis, parietibus turgidis, 2′′′ distantibus.’ ( Ehrenberg, 1834: 328).

Subsequent descriptions

Dana, 1846: 271, 272; Milne Edwards & Haime, 1851, vol. 15: 143; Milne Edwards & Haime, 1857, vol. 2: 628; Dana, 1859: 40; Verrill, 1864: 56; Quenstedt, 1881: 1031; Quelch, 1886: 109; Saville Kent, 1893: 168; Vaughan, 1918: 126; Hickson, 1924: 60, 61; Hoffmeister, 1925: 31; Faustino, 1927: 163, 164; Matthai, 1928: 125, 126; Yabe et al., 1936: 41; Vaughan & Wells, 1943: 190; Alloiteau, 1952: 632; Crossland, 1952: 151; Wells, 1956: F416; Nemenzo, 1959: 125; Chevalier, 1975: 208; Veron & Pichon, 1980: 216; Head, 1983: 419; Scheer & Pillai, 1983: 143, 144; Wood, 1983: 186, 187; Veron, 1986: 434; Chevalier & Beauvais, 1987: 720, 721; Veron & Hodgson, 1989: 268, 269; Sheppard, 1990: 14; Best & Suharsono, 1991: 334; Sheppard & Sheppard, 1991: 119; Veron, 2000, vol. 2: 376.

Diagnosis (apomorphies in italics)

Colonial, with intracalicular budding only. Corallites monomorphic and uniserial; monticules absent. Walls fused. Calice width small (<4 mm), with low relief (<3 mm). Costosepta confluent. Septa in <three cycles (<24 septa). Free septa present but irregular. Septa spaced six to 11 septa per 5 mm. Costosepta equal in relative thickness. Columellae trabecular but compact (one to three threads), <1/4 of calice width, and continuous amongst adjacent corallites. Paliform (uniaxial) lobes well developed. Epitheca absent and endotheca sparse ( Fig. 3A, D, G ).

Tooth base at midcalice circular. Tooth tip at midcalice irregular; tip orientation perpendicular to septum. Tooth height low (<0.3 mm) and tooth spacing narrow (<0.3 mm), with> six teeth per septum. Granules scattered on septal face; irregular in shape. Interarea palisade ( Fig. 3B, E, H ).

Walls formed by strong abortive septa and partial septotheca; trabeculothecal elements may be present. Thickening deposits fibrous. Costa centre clusters weak; <0.3 mm between clusters; medial lines weak. Septum centre clusters weak; <0.3 mm between clusters; medial lines weak. Transverse crosses absent. Columella centres clustered ( Fig. 3C, F, I ).

Species included

1. Merulina ampliata ( Ellis & Solander, 1786: 157, pl. 41: figs 1, 2); holotype: GLAHM 104015 (dry specimen; Fig. 3A, D ); type locality: ‘les mers de l’Inde’ ( Lamarck, 1816: 243); phylogenetic data: molecular and morphology.

2. Merulina scabricula Dana, 1846: 275 , pl. 16: figs 2, 2a, b; syntypes: USNM 165 , 167 (two dry specimens); syntypes: YPM IZ 1927 A, B (two dry specimens; Fig. 3G–I ); type locality: Fiji; phylogenetic data: molecular and morphology .

3. Merulina scheeri Head, 1983: 420 , figs 1–6; holotype: NHMUK 1981.4 .1.1 (dry specimen); paratypes: NHMUK 1981.4 .1.2, 1981.4.1.3 (two dry speci- mens); type locality: West Harvey , Sudan, Red Sea, 23 m depth; phylogenetic data: none .

Taxonomic remarks

The genus was first described as part of the family Daedalina Ehrenberg, 1834: 315, and subsequently Astraeidae Dana, 1846: 154 , which incorporated a diversity of genera including Lobophyllia de Blainville, 1830: 321 , Favia Milne Edwards & Haime, 1857, vol. 2: 426, and Mycedium Milne Edwards & Haime, 1851 , vol. 15: 130. The designation of Merulina as the type of Merulinidae Verrill, 1865 , was unclear because the family name was only listed and not defined ( Verrill, 1865: 146), but this had thereafter been assumed. Even as Daedalina’s constituent genera were redistributed into newly erected families such as Mussidae Ortmann, 1890: 315 , Faviidae Gregory, 1900: 29 , Trachyphylliidae Verrill, 1901: 84 , and Pectiniidae Vaughan & Wells, 1943: 196 , the placement of Merulina remained ambiguous according to some authors ( Vaughan, 1918; Hoffmeister, 1925), whereas Hickson (1924), Faustino (1927), and Matthai (1928) continued to recognize Dana’s (1846) Astraeidae . The separation of Merulina from Faviidae Gregory, 1900 , was only complete in the comprehensive treatise by Vaughan & Wells (1943).

Molecular data support Merulina as nested within the largest clade of Goniastrea but the latter is not monophyletic as it minimally excludes G. aspera and G. palauensis ( Fukami et al., 2004 a, 2008; Kitahara et al., 2010; Huang et al., 2011; Arrigoni et al., 2012; Huang, 2012). In contrast, the morphological tree supports Merulina as sister taxon to Scapophyllia , which together are sister group to the main clade of Goniastrea that includes G. retiformis , its type species.

Merulina is widely distributed on reefs of the Indo- Pacific, present as far east as the Austral Islands in the Southern Hemisphere ( Glynn et al., 2007), but absent eastwards from Hawai’i in the north.

Morphological remarks

Only one synapomorphy has been found for Merulina : septa in <three cycles (<24 septa; likelihood of 1.0 based on the Mk1 model). It shares all other analysed characters with Scapophyllia . The loss of epitheca and sparse endotheca occur at the base of the Merulina + Scapophyllia clade on the morphology tree (bootstrap support of 72), and all subcorallite character transitions occur at or before the most recent common ancestor of Merulina , Scapophyllia , and Goniastrea . They are therefore plesiomorphic with respect to Merulina .

Examination of the type material of Merulina scheeri at the Natural History Museum, London, suggests that this species shares all macromorphological characters with the other species in the genus, except for a thick thecal structure on the underside of the corallum. Although the number of septa often exceeds 24, they clearly form two alternating cycles and the lower range is under 24. With its molecular phylogenetic affinity unknown, we hereby preserve its generic placement.

Figures

Figure 3. Merulina Ehrenberg, 1834, has uniserial corallites with few centres, fused walls, small (<4 mm) and lowrelief (<3 mm) calices, septa in <three cycles (<24 septa), compact columellae, well-developed paliform (uniaxial) lobes and no epitheca. Septal teeth are low (<0.3 mm) and narrowly spaced (<0.3 mm). Walls formed by strong abortive septa and partial septotheca. A–F, Merulina ampliata (Ellis & Solander, 1786), type species of Merulina; macromorphology, holotype GLAHM 104015, unknown locality (A, D; photo by K. G. Johnson); micromorphology (scanning electron microscopy; B, E) and microstructure (transverse thin section; C, F), hypotype UF 2051 (FA1056), Palau. G–I, Merulina scabricula Dana, 1846; macromorphology (G), micromorphology (H), and microstructure (I), syntype USNM 165, Fiji.