Acropora fennemai (Gerth, 1921)

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 : 718-720

ACROPORA FENNEMAI ( GERTH, 1921)

FIGURE 20

Madrepora fennemai Gerth, 1921: 431 , pl. 56 fig. 12; 1923: 115, pl. 9 fig. 5

Diagnosis

Colony hispidose, slender axis with short branches; radial corallites mainly clustered around the branchlets, or irregularly and sparsely distributed, evenly sized, coenosteum with lateral flattened simple spinules aligned into costae throughout.

Material studied

Lectotype. RGM 3997 , 1 specimen. Type locality: Tjadasngampar, Java, Tortonian age, 5.6–8.3 Ma. Collector R. D. M. Verbeek and R. Fennema.

Paralectotypes. RGM 40959, 5 specimens, Tjadasngampar, Java, Tortonian age, 5.6–8.3 Ma. Collector R. D. M. Verbeek and R. Fennema. Figured in Leloux & Renema, 2007: pl. 23 figs 13, 14 .

Other material studied. East Kalimantan: NHMUK PI AZ 7100, 37 fragments from the same colony.

Additional material. East Kalimantan: RGM 17703, 1 specimen , figured in Gerth, 1923: pl. 9, fig. 5; RGM 167803 , 1 specimen ; RGM 791834 , 1 specimen , previously misidentified as Hydnophora tenella ; RGM 791835 , 1 specimen ; NHMUK PI AZ5526 , 1 specimen ; NHMUK PI AZ8869 , 1 specimen . Java: RGM 883448 , 4 specimens ; RGM 791819 , 4 specimens . Sumatra: RGM 791824 , 2 specimens .

Description of lectotype

Corallum . Overall length of specimen 38.65 mm, fragment of a main branch, mid branch diameter 8.61– 9.21– 9.92 mm, with multiple short branches or branchlets suggesting a simple hispidose growth form; branchlets arising regularly from main branch, distance between branchlets 7.66–9.02– 11.48 mm, with branch tips mostly abraded, tapering, length 2.56–3.59– 4.91 mm, angle 57.97–66.27–85.29°, basal branchlet diameter 4.73–5.58– 6.75 mm, middle branchlet diameter 2.88–3.18– 3.69 mm, portions in between branches with a few sparse or devoid of radial corallites.

Corallites. Axial corallites visible at some branch tips, 0.45–0.62– 0.78 mm exsert, outer diameter 1.76– 2.08– 2.43 mm, inner diameter 1.18–1.41– 1.62 mm, wall thickness 0.34–0.44– 0.54 mm, primary septa threequarters R, secondary septa up to one-quarter R, arranged as S1>>S2; radial corallites mostly crowded around axials in short branches, mostly not touching, tubular with thick lower wall, almost labellate, profile length 0.43–0.55– 0.71 mm, angle 37.22–41.95– 51.11°, outer diameter 1.01–1.21– 1.46 mm, inner diameter 0.66–0.81– 0.94 mm, wall thickness 0.24–0.26– 0.30 mm primary septa up to two-thirds R, smooth and straight axial margins, secondary septa up to onequarter R. Corallite arrangement sequence 1–1–[2– 3]–up to 6.

Coenosteum. Simple flattened spinules evenly distributed and aligned into costae both on and between radial corallites.

Description of East Kalimantan fossil specimens Corallum . Thirty-seven specimens, including complete or fragmented branches, all from the same colony, at least 40 cm long and 25 cm wide; largest specimens length 68–74.8– 86 mm, basal branch diameter 12.50–15.98– 20.40 mm, mid branch diameter 8.90– 10.32– 13.40 mm, branch tip diameter 6.60–8.72– 11.10 mm, most of specimens show a few short branchlets, arising in open wide angle 50.54–67.79– 88.32°, indicating a simple hispidose growth form, branchlet length 5.0– 8.5–11.2 mm, mid branch diameter 2.80–4.28– 5.20 mm.

Corallites. Axial corallites visible at some branch tips or through cross sections of broken branches, angle 37.45–41.40–47.88°, outer diameter 2.20–2.55– 2.82 mm, inner diameter 0.98–1.27– 1.73 mm, wall thickness 0.52– 0.54– 0.55 mm; surface partially worn, radial corallites mainly grouped around short branchlets, tubular with thicker lower wall, almost labellate, profile length 0.97– 1.07– 1.15 mm, outer diameter 1.14–1.55– 1.89 mm, inner diameter 0.82–0.94– 0.98 mm, a few corallites sparse on main branches. Corallite arrangement sequence as described for the holotype.

Coenosteum. Radials widely spaced, mostly worn, formed of simple flattened spinules, reticulate in some preserved intercorallite areas, aligned into costae on corallites.

Occurrence

Early Miocene to Calabrian. Earliest occurrence from locality TF56 , Badak, NHMUK PI AZ8869 , of Langhian to Burdigalian age, 14.8–17.9 Ma. Acropora fennemai has a widespread fossil record from Java (Ci Livat, Cadasngampar, Ngembak) and East Kalimantan (Sungai Gelingseh, Gunung Batu, Kari Orang) of Tortonian to Burdigalian age, 5.3–17.9 Ma. Last occurrence is from Sumatra ( Mola Valley ) of Calabrian to Gelasian age, 0.781 –2.588 Ma .

Palaeoenvironment

This species was found in outcrops characterized by a high richness of species and growth forms, including representatives of the genera Cyphastrea , Pavona , Stylophora , Pachyseris , Echinophyllia , Porites , Fungia , Cycloseris and Heliopora , among others. Specimens from East Kalimantan, TF107, were found in orange silty sediments interbedding with platy colonies of Porites in an environment that has been interpreted as a small patch reef influenced by siliciclastic input ( Renema et al., 2015).

Remarks

This species resembles the extant Acropora florida ( Dana, 1846) , but differs in having slender branches and radial corallites that are scarce or almost absent from the surface of main branches. Collections from the Naturalis museum were examined and some specimens were re-interpreted according to the redescription of the lectotype presented in this study. The specimen RGM 167574 included in the syntype series and figured in the original description of Gerth (1921: pl. 56, fig. 12 right) could not be found among the specimens examined from Naturalis collections. Therefore, the specimen RGM 3997 was designated as the lectotype.

Figures

Figure 20. Acropora fennemai. A–C, lectotype, RGM 3997, Tjadasngampar, Java, Late Miocene (5.6–8.3 Ma): A, whole specimen; B, detail of a branchlet showing corallite arrangement; C, detail of a branchlet showing axial and radial corallites. D, RGM 791834, Kari Orang, Bengalon, East Kalimantan, Middle Miocene (13.77–15.1 Ma), whole specimen. E, RGM 167803, Gunung Batu, East Kalimantan, Middle to Late Miocene (10.7–12.4 Ma), whole specimen. F, RGM 17703, Sungai Gelingseh, East Kalimantan, Middle to Late Miocene (10.7–12.4 Ma), whole specimen, probably from a basal part of a colony. G–I, NHMUK PI AZ 7100, TF107, Bontang, East Kalimantan, Late Miocene (9.4–9.8 Ma). G, colony in the field showing hispidose growth; it overlies platy colonies of Porites. H, specimens from the same colony in the lab showing slender branches and short branchlets. I, detail of a branchlet.