Mycedium, MILNE EDWARDS & HAIME, 1851: 130

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 : 324-326

GENUS MYCEDIUM MILNE EDWARDS & HAIME, 1851: 130 ( FIG. 17 )

Synonym

Phyllastraea Dana, 1846: 269 (type species: Phyllastraea tubifex Dana, 1846: 270 , pl. 16: figs 4, 4a, b = Madrepora elephantotus Pallas, 1766: 290 ; original designation, Dana, 1846: 270).

Type species

Madrepora elephantotus Pallas, 1766: 290 ; subsequent designation; Verrill, 1901: 133.

Original description

‘Polypier en expansions frondiformes. Calices circonscrits, penchés, submamillaires, et disposés autour de l’individu parent qui reste plus développé que les autres. Plateau commun nu et costulé.’ ( Milne Edwards & Haime, 1851, vol. 15: 130).

Subsequent descriptions

Milne Edwards, 1860, vol. 3: 72, 73; Duncan, 1884: 158; Delage & Hérouard, 1901: 641; Verrill, 1901: 133; Wells, 1936: 121; Yabe et al., 1936: 49; Vaughan & Wells, 1943: 198; Wells, 1956: F419; Alloiteau, 1952: 632; Nemenzo, 1959: 120; Chevalier, 1975: 336, 337; Veron & Pichon, 1980: 319; Scheer & Pillai, 1983: 151; Wood, 1983: 199; Veron, 1986: 382; Chevalier & Beauvais, 1987: 725; Sheppard, 1990: 16; Sheppard & Sheppard, 1991: 109; Veron, 2000, vol. 2: 342.

Diagnosis

Colonial, with intracalicular budding only. Corallites polymorphic and organically united; monticules absent. Coenosteum costate, extensive amount (≥ corallite diameter). Calice width medium (4–15 mm), with medium relief (3–6 mm). Costosepta confluent. Septa in three cycles (24–36 septa). Free septa present but irregular. Septa spaced <six septa per 5 mm. Costosepta unequal in relative thickness. Columellae trabecular and spongy (> three threads), <1/4 of calice width, and discontinuous amongst adjacent corallites (lamellar linkage). Paliform (uniaxial) lobes weak or moderate. Epitheca absent and endotheca abundant (vesicular) ( Fig. 17A, D ).

Tooth base at midcalice circular. Tooth tip at midcalice irregular; tip orientation perpendicular to septum. Tooth height medium (0.3–0.6 mm) and tooth spacing medium (0.3–1 mm), with no more than six teeth per septum. Granules scattered on septal face; irregular in shape. Interarea formed by horizontal bands ( Fig. 17B, E ).

Walls formed by dominant paratheca; abortive septa absent. Thickening deposits microfibrous. Costa centre clusters not distinct; medial lines strong. Septum centre clusters not distinct; medial lines strong. Transverse crosses absent. Columella centres clustered ( Fig. 17C, F ).

Species included

1. Mycedium elephantotus ( Pallas, 1766: 290) ; holotype: lost ( Chevalier, 1975: 338); neotype (designated herein): RMBR ZRC.CNI.0916 (dry specimen; Fig. 17A ); type locality: Raffles Light, Singapore, 8 m depth (‘Oceanus Indicus’; Pallas, 1766: 290); phylogenetic data: molecular and morphology.

2. Mycedium mancaoi Nemenzo, 1979: 48 , fig. 10; holotype: UP CCC-9 (dry specimen); type locality: Pinamungajan , Cebu, the Philippines; phylogenetic data: none .

3. Mycedium robokaki Moll & Best, 1984: 56 , figs 10b, c, 11; holotype: RMNH 15270 (dry specimen); type locality: 150 m offshore of north Lumu Lumu , Spermonde Archipelago, Indonesia, 8 m depth; phylogenetic data: molecular and partial morphology .

4. Mycedium spina Ditlev, 2003: 204 , figs 16, 17; holotype: BMRI 2533 (dry specimen); type locality: Bagahak, Darvel Bay , Sabah, 6 m depth; phylogenetic data: none .

5. Mycedium steeni Veron, 2000 , vol. 2: 347, figs 4–6 (see also Veron, 2002: 120, figs 226–228; ICZN, 2011: 165); lectotype (designated herein): UP MSI-3011- CO (dry specimen); type locality: Calamian Islands, Palawan, the Philippines, 6 m depth; phylogenetic data: none.

6. Mycedium umbra Veron, 2000 , vol. 2: 342, figs 1–3 (see also Veron, 2002: 118, figs 224, 225; ICZN, 2011: 165); lectotype (designated herein): MTQ G55783 (dry specimen; Fig. 17D ); type locality: Ras Mohammed National Park, Sharm al-Sheikh, Sinai Peninsula, Egypt, 10 m depth; phylogenetic data: none.

Taxonomic remarks

Mycedium was originally described by Oken (1815: 68). According to ICZN Opinion 417 ( ICZN, 1956), names proposed by Oken (1815) are rejected, so authority of this taxon is assigned to Milne Edwards & Haime (1851, vol. 15: 130), the second authors who used the name.

This genus has commonly been regarded to be similar to Echinophyllia (Lobophylliidae) , because of its laminar growth form ( Vaughan & Wells, 1943: 198; Wells, 1956: F419; Veron & Pichon, 1980: 319; Veron, 1986: 382; 2000, vol. 2: 342). The lack of distinct corallite walls, or corallites being ‘organically united’ ( Vaughan & Wells, 1943: 196), is a distinguishing feature of Pectiniidae , the family in which Mycedium and Echinophyllia were placed prior to revision by Budd et al. (2012). It is now clear based on molecular phylogenetics that this genus is closest to and also nested within Pectinia de Blainville, 1825: 201 ( Fukami et al., 2008; Huang et al., 2011; Arrigoni et al., 2012; Huang, 2012). As only two of the six Mycedium spp. have been sampled for phylogenetic analysis, we maintain its genus-level status until more data are available.

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

Morphological remarks

Organically united corallites appear to have independently evolved twice, within Merulinidae in Mycedium + Pectinia (likelihood of 1.0 based on the Mk1 model), and within Lobophylliidae in Echinophyllia + Oxypora ( Budd et al., 2012: fig. 2b). Other synapomorphies of the Mycedium + Pectinia clade are polymorphic corallites (likelihood 1.0), extensive coenosteum (≥ corallite diameter; likelihood 1.0), unequal costosepta thickness (likelihood 1.0), discontinuous columellae (lamellar linkage; likelihood 1.0), not more than six teeth per septum (likelihood 1.0), interarea made up of horizontal bands (likelihood 1.0), and microfibrous deposits (likelihood 1.0). Transverse crosses are also lost in this lineage (likelihood 1.0). The clade is highly supported, with a bootstrap of 100 and decay index of 9.

Mycedium and Pectinia share all morphological traits examined here, as opposed to the paraphyletic Pectinia recovered by molecular data. Physophyllia is also extremely similar on the basis of macromorphology. The lack of distinction amongst these three genera, and the paraphyly of Pectinia , may be grounds for regarding Mycedium as a synonym of Pectinia and/or Physophyllia , but as Mycedium elephantotus remains the only species placed on the morphology tree, no changes are proposed here.

Note that quantitative measurements were based on peripheral corallites as structures of the central corallite may be extremely large in comparison.

Figures

Figure 17. Mycedium Milne Edwards & Haime, 1851, has organically united corallites, extensive coenosteum (≥ corallite diameter), septa spaced <six septa per 5 mm and abundant (vesicular) endotheca. Septal teeth with medium height (0.3– 0.6 mm) and spacing (0.3–1 mm), no more than six teeth per septum and interarea formed by horizontal bands. Walls formed by dominant paratheca, with microfibrous deposits and strong costal and septal medial lines. A–C, Mycedium elephantotus (Pallas, 1766), type species of Mycedium; macromorphology, neotype (designated herein) RMBR ZRC.CNI.0916, Raffles Light, Singapore (A); micromorphology (scanning electron microscopy; B) and microstructure (transverse thin section; C), hypotype UF 2062 (FA1082), Palau. D, Mycedium umbra Veron, 2000; macromorphology, holotype MTQ G55783, Sharm al-Sheikh, Egypt. E, F, Mycedium elephantotus (Pallas, 1766); micromorphology (E) and microstructure (F), hypotype UF 2062 (FA1082), Palau.