Acropora lutkeni, CROSSLAND, 1952

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 : 703-705

ACROPORA LUTKENI CROSSLAND, 1952

FIGURE 11

Acropora lutkeni Crossland, 1952: 229 , pl. 41 fig. 1, pl. 46 fig. 2

Diagnosis

Sturdy branches, radial corallites in mixed sizes, touching or closely arranged, tubular with rounded or slightly nariform openings. Dense coenosteum with flaky spinules, laterally flattened spinules on corallite walls ( Wallace & Wolstenholme, 1998; Wallace, 1999).

Material studied

Java: RGM 3989 , Ci Ansana, 1 specimen .

Modern comparative material: Holotype, NHMUK 1934.5 .14.16, June Reef , Great Barrier Reef ; RMNH, 34733, Pulau Ayer Kecil , Bay of Jakarta, Java Sea, Indonesia; MTQ G49647, Karang Masimbung, East Kalimantan, Indonesia.

Skeletal characteristics

Corallum . Fossil specimen is a well-preserved branch tip, overall length 17 m, mid branch diameter 6.53–7.28– 8.43 mm, branch tip diameter 5.59–5.75– 5.91 mm.

Corallites. Axial corallite exsert 1.5 mm, outer diameter 2.98–3.45– 4.06 mm, inner diameter 1.06–1.08– 1.09 mm, wall thickness 0.75–0.76 mm, primary septa up to two-thirds R, secondary septa present up to onethird R; radial corallites with thick wall around the calices, in two different sizes, larger radial corallites tubular with slightly nariform calices, profile length 1.44–1.73– 1.97 mm, angle 25.65–28.60–36.15°, outer diameter 1.02–1.33– 1.81 mm, inner diameter 0.56–0.75– 0.94 mm, wall thickness 0.31–0.44– 0.64 mm, distance between centres 2.77–3.29– 4.14 mm, smaller radial corallites slightly immersed, mostly touching the base of larger radial corallites, profile length 0.67–0.77– 0.93 mm, angles 30.33–31.61–35.01°, outer diameter 0.53–0.71– 0.99 mm, inner diameter 0.34–0.40– 0.47 mm, wall thickness 0.15–0.17– 0.20 mm, primary septa up to two-thirds R, secondary septa up to one-third R. Corallite arrangement sequence irregular,?spiral, 1–[3–5]–8–?.

Coenosteum. Dense arrangement of laterally flattened spinules aligned costae-like on radial corallite walls, reticulate with flaky spinules in intercorallite areas. Coenosteum amount 0.36–0.93– 2.31 mm.

Occurrence

Middle Miocene to Recent. Previous fossil record includes the specimen MTQ G55170 from the Upper Pleistocene of Niue, South Pacific Ocean ( Wallace, 1999). The studied specimen represents the earliest occurrence of A. lutkeni from the Middle Miocene, 12.4–15.5 Ma.

Palaeoenvironment

This specimen was collected in clay-rich deposits, in a sample characterized by isolated corals together with molluscs ( Gerth, 1921). Other fossil corals from Ci Ansana include branching specimens of Seriatopora spp. and poritids ( Leloux & Renema, 2007).

Remarks

This specimen was previously identified by Gerth (1921: 430–431, pl.56, fig. 11) as A. duncani amongst several specimens collected at Ci Ansana, Java. Morphological traits of RGM 3989 including corallite size, shape and arrangement of radials, and characteristic flattened spinules on coenosteum (see plate 18.I in Wallace, 1999) correspond to A. lutkeni . The colony shape cannot be inferred from the small available specimen, but the uniform arrangement of corallites suggests that this branch was upright. Comparison with the modern specimens MTQ G49647 from East Kalimantan and RMNH 34733 from Java (identified by J. van de Brugge), and the holotype NHMUK 1934.5.14.16 from the June Reef, Great Barrier Reef, suggests that the specimen could correspond to a terminal branch of a corymbose or caespitose colony.

Figures

Figure 11. Acropora lutkeni, RGM 3989, Ci Ansana, Central Java, Middle to Late Miocene (8.5–13.5 Ma). A, whole specimen. B, upper view of axial corallite, radial corallites and septal arrangement. C, lateral view of radial corallites in two sizes, larger tubular–nariform and smaller partially immersed. D, detail showing thickened corallite outer margin. E, detail of coenosteum in between corallites formed of flattened spinules in reticular arrangement.