Acropora herklotsi, (REUSS, 1866)

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 : 708-711

ACROPORA HERKLOTSI ( REUSS, 1866)

FIGURES 14 , 15

Madrepora herklotsi Reuss, 1866: 170 , pl. 2 figs 1a–c

Diagnosis

Colonies probably arborescent with indeterminate growth, composed of thin, cylindrical, terete branches. Branch structure axial dominated. Labellate radial corallites arranged in alternating longitudinal rows. Coenosteum composed of slightly flattened spinules, costate on corallites and reticulate to costate between corallites.

Material studied

Lectotype. NHMW 1959 /334/16, 1 specimen. Type locality: Gunung Selah-Ci-Lanangthale, Java. Tortonian, 8.5–11.6 Ma. Collector F. V. Hochstetter, Novara Expedition 1857–1859.

Paralectotypes. NHMW 1959 /334/16a, Gunung Selah- Ci-Lanangthale , Java, 1 specimen ;

NHMW 1959 /334/15, Gunung Selah-Ci-Lanangthale, Java, 1 specimen. Same data as lectotype .

Other material studied. East Kalimantan: NHMUK PI AZ 6234 , 9 fragments of a colony; NHMUK PI AZ 6275 , 34 specimens ; NHMUK PI AZ 5964 , 24 specimens ; NHMUK PI AZ 6306 , 11 specimens ; NHMUK PI AZ 6324 , 33 specimens .

Description of lectotype

Corallum . One specimen, overall length 18.38 mm, mid branch diameter 6.2–6.74– 7.3 mm, no scars of branching, slightly tapering, branch tip broken.

Corallites. Axial corallite dominates branch structure, visible only on transverse section, inner diameter 1.15 mm, wall porous, primary septa present up to three-quarters R, secondary septa visible as points; radial corallites evenly sized, labellate, round calices, profile length 0.64–0.78– 0.95 mm, outer diameter 1.04– 1.27– 1.49 mm, inner diameter 0.52–0.75– 0.99 mm, wall thickness 0.17–0.26– 0.33 mm, arranged in alternating longitudinal rows, distance between centres 2.75– 3.16– 4.04 mm, primary septa up to two-thirds R, smooth and straight distal border, secondary septa up to onequarter R or visible as points. Corallite arrangement 1–3–3–6–?.

Coenosteum. Flattened simple spinules, arranged into irregular costae on radial corallite walls, reticulate with sparse spinules in intercorallite areas. Coenosteum amount longitudinal 0.89–1.53– 2.33 mm, coenosteum amount between corallites of alternating rows 1.38– 2.42– 2.91 mm.

Description of East Kalimantan fossil specimens Corallum . Some specimens with short broken secondary branches or respective scars interpreted as suggesting small arborescent colony forms as the branches probably arise from basal parts of the colony and also occasionally from primary branches. Mostly broken in small fragments, length 8.9–12.86–17.0 mm, generally with no other scars other than the attachment point; branches slightly tapering, round in transverse section, mid branch diameter 2.39–3.65– 5.60 mm, branch tip diameter 1.70–2.20– 2.59 mm, angles 51.21–51.30– 51.39°, growth probably indeterminate.

Corallites. Axial corallites dominate branch structure, in the present material branches are mostly broken and branch structure is mainly visible on transverse section. Axial corallite 0.45–0.50– 0.55 mm exsert, outer diameter 1.01–1.12– 1.22 mm, inner diameter 0.89– 0.91– 0.93 mm, wall thickness 0.22–0.23– 0.25 mm, primary septa up to one-half R, secondary septa visible as points; radial corallites evenly sized and arranged in alternating longitudinal rows, mostly labellate with flaring lips and oval calices, lip length 0.39–0.59– 0.78 mm, angle 37.26–44.19–54.96°, outer diameter 0.56– 0.75– 1.06 mm, inner diameter 0.54–0.68– 0.87 mm, wall thickness 0.12–0.18– 0.24 mm, distance between centres 1.34–1.46– 1.72 mm, primary septa up to two-thirds R, secondary septa up to one-quarter R or visible as points. Corallite arrangement sequence 1–3–3–6–?.

Coenosteum. As described for the lectotype. Coenosteum amount longitudinal 0.91–1.89– 2.73 mm, between corallites of alternating rows 0.63–0.89– 1.19 mm.

Occurrence

Middle to Late Miocene. The lectotype locality is Gunung Sela, Ci-Lanangthale, Rongga District , of Tortonian age, 8.5–11.6 Ma ( Johnson et al., 2015b). New material from East Kalimantan includes the Bontang localities TF102 , TF154 , TF505 and TF508 of Tortonian age, 9.4–9.8 Ma .

Palaeoenvironment

This species occurs in low abundances in environments interpreted as shallow-water coral carpets. It co-occurs with A. duncani and A. borneoensis in coral settings dominated by the extinct poritid genus Dictyaraea . Other branching corals include Seriatopora and Porites . Typical coral-associated molluscs were abundant among the accompanying fauna, such as Tridacna shells of about 20 cm length and the corallivorous Coralliophilla. Preservation of original aragonite in both corals and molluscs was observed ( Kusworo et al., 2015).

Remarks

Acropora herklotsi ( Reuss, 1866) was considered to be a junior synonym of A. duncani ( Martin, 1880) . Martin (1880) questioned the validity of A. herklotsi arguing that the identification of Acropora species is one of the most difficult tasks of systematic zoology for modern well-preserved specimens and even less reliable in fossils due to the loss of morphological characters. We examined the three syntypes of A. herklotsi and compared them with the two syntypes of A. duncani . The best-preserved specimen of the A. herklotsi syntype series (NHMW 1959/334/16) has labellate radial corallites and uniform arrangement of corallites in alternating longitudinal rows. In contrast, A. duncani has relatively smaller radial corallites that are randomly distribut- ed. Based on these differences, the resurrection of A. herklotsi as a valid species is proposed in this study. We designated the specimen NHMW 1959/334/16 as the lectotype of A. herklotsi and the specimens NHMW 1959/334/15 and NHMW 1959/334/16a as paralectotypes in order to include the variation of skeletal characteristics of the species. Quantitative characters and images of well-preserved specimens from East Kalimantan are also provided to complement the description of the species and support its removal from synonymy of A. duncani . Acropora herklotsi is morphologically similar to the extant species Acropora spicifera ( Dana, 1846) , from which it can be distinguished by its widely spaced radials that are mostly touching in A. spicifera .

Figures

Figure 14. Acropora herklotsi. A, syntypes figured in Reuss (1866, pl. 2 fig. 1a-c). B and C, lectotype, NHMW 1959/334/ 16, Gunung Selah, Ci Lanangthale, Java, Late Miocene (8.5–11.6 Ma): B, transverse section showing axial corallite; C, lateral view of the whole specimen showing radial corallites arrangement. D and E, paralectotype, NHMW 1959/334/ 16a, Gunung Selah, Ci Lanangthale, Java, Late Miocene (8.5–11.6 Ma): D, upper view of the bent branch; E, lateral view of the whole specimen showing radial corallites arrangement. F and G, paralectotype, NHMW 1959/334/15, Gunung Selah, Ci Lanangthale, Java, Late Miocene (8.5–11.6 Ma): F, transverse section showing axial corallite; G, lateral view of the whole specimen showing radial corallites arrangement.

Figure 15. Acropora herklotsi. NHMUK PI AZ6234, TF 154, Bontang, East Kalimantan, Late Miocene (9.4–9.8 Ma). A, four fragments recovered in the same sample, clockwise AZ6234a–d. B, AZ6234a, detail of a branch showing flaring lips of radial corallites and scar of a broken secondary branch. C, AZ6234c, electron micrograph of radial corallites with flaring lips. D–F, AZ6234a. D, electron micrograph of a branch tip showing corallite arrangement. E, electron micrograph of radial corallites with flared lips. F, electron micrograph of flattened simple spinules on coenosteum.