Acropora valida

Santodomingo, Nadiezhda, Wallace, Carden C. & Johnson, Kenneth G., 2015, Fossils reveal a high diversity of the staghorn coral genera Acropora and Isopora (Scleractinia: Acroporidae) in the Neogene of Indonesia, Zoological Journal of the Linnean Society 175 (4), pp. 677-763 : 702-703

ACROPORA VALIDA ( DANA, 1846)

FIGURE 10

Madrepora valida Dana, 1846: 461 , pl. 35 fig. 1 Madrepora variabilis Klunzinger, 1879: 17 , pl. 1 fig. 10, pl. 2 figs 1,5, pl. 5 figs 1–3, pl. 9 fig. 14 Madrepora coalescens Ortmann, 1889: 509 , pl. 13 fig. 5 Acropora dissimilis Verrill, 1902: 226 , pl. 34 fig. 9

Diagnosis

Radial corallites evenly distributed, appressed to partially appressed tubular with nariform openings. Coenosteum reticulated, simple or laterally flattened spinules ( Wallace & Wolstenholme, 1998; Wallace, 1999).

Material studied

Sumatra: RGM 791826 , Mola Valley, Nias , 3 specimens .

Modern comparative material: Holotype USNM 272 , Fiji; MTQ G47980, Lucipara Island, Banda Sea, Indonesia; MTQ G47985, Manuk Island , Banda Sea , Indonesia; MTQ G49600, Kakaban Island , East Kalimantan, Indonesia.

Skeletal characteristics

Corallum .?Corymbose or caespitose, three branches, tapering, length 16.10–19.02– 24.52 mm, middle branch diameter 4.59–6.41– 7.89 mm, branch tip diameter 3.87– 4.06– 4.25 mm.

Corallites. Axial corallite exsert 2.04 mm, outer diameter 2.08 mm, inner diameter 1.09 mm, primary and secondary septa present but degraded; radial corallites evenly sized, round tubular, some subimmersed radials touching at their bases, round calices, profile length 2.42–2.49– 2.59 mm, exsert in acute angles of 32.66– 42.70–51.80°, outer diameter 1.08–1.36– 1.70 mm, inner diameter 0.53–0.69– 0.80 mm, wall thickness 0.21– 0.30– 0.36 mm, distance between centres 2.65–2.96– 3.4 mm, primary septa up to one-quarter R, secondary septa visible as points. Corallite arrangement irregular and asymmetric 1–[4–5]–6–[8–10]–?.

Coenosteum. Dense reticulate throughout, on some radial corallite walls elaborated spinules arranged into costae. Coenosteum amount 0.60–0.92– 1.17 mm.

Occurrence

Gelasian to Recent. The previous fossil record of A. valida includes Late Pleistocene specimens from North Stradbroke Island, Australia, of 119–132 ka age ( Pickett et al., 1985) and from marine platforms up to 48.6 ka in the Marquesas, a region in which Acropora is now absent ( Cabioch et al., 2011). The three recovered specimens of A. valida from Mola Valley, Nias, Sumatra, are the earliest known occurrence of the species at 2.588 –0.781 Ma (Early Pleistocene); A. valida is one of the most widely distributed and common species in modern reefs, with records from the Red Sea and the entire Indo-Pacific, including one record from the Eastern Pacific of Colombia ( Von Prahl & Mejia, 1985). In Indonesia the species has been found in most islands, including nearby localities in East Kalimantan ( Table 4).

Palaeoenvironment

The Nias Formation has rich well-preserved coral and mollusc faunas that resemble modern shallow-water coral reefs ( Gerth, 1925). Fossil A. valida specimens were found together with Seriatopora specimens.

Remarks

These specimens were previously identified as the collective name of A. duncani by Gerth (1925). They are re-interpreted here as A. valida based on their tapering branches, rounded tubular to appressed tubular corallites and dense reticulate coenosteum through- out. Fossil specimens resemble the morphology and dimensions of the modern material MTQ G47980 and MTQ G47985 from the Banda Sea, and the specimen MTG G49600 from East Kalimantan, Indonesia. The lack of secondary branching of the three specimens suggests a colony of corymbose or caespito-corymbose shape.

Figures

Figure 10. Acropora valida, RGM 791826, Mola Valley, Sumatra, Pleistocene (0.8–2.6 Ma). A, three specimens, showing two branch tips (left and middle) and middle part of a branch (right). B–D, RGM 791826a: upper view of axial and radial corallites. C, detail of a tapering branch tip. D, detail of tubular rounded corallites and subimmersed corallites with reticulate coenosteum throughout. E, detail of axial corallite and branch tip showing asymmetric arrangement of radial corallites.