Diagnosis

Corallum solitary, fixed, free, or transversely dividing. Wall epithecal (neotenic condition), sometimes secondarily thickened with stereome. Epitheca usually smooth, lacking costae. Septa imperforate, composed of a single fan system of numerous closely spaced trabeculae, which produces a smooth axial edge. Pali, dissepiments, and synapticulae absent; paliform lobes present on one genus. Columella usually rudimentary or absent, but may be lamellar, papillose, or fascicular. Exclusively azooxanthellate.

Occurrence

Lower Cretaceous to Recent: worldwide, including off Antarctica, 0–3,186 m.

Remarks

The family was most recently revised by Cairns (Reference Cairns1989b, table 4), who tabularized the characteristics of the various genera. Table 1 is an update and expansion of that compilation, the family now consisting of 14 genera: seven exclusively Recent, four exclusively fossil, and three having both components. 100 Recent species are known in the family (Cairns and Hoeksema, Reference Cairns and Hoeksema2015, table 1), making it the fifth-most species-rich family among the 24 families that contain Recent species in the Scleractinia (Cairns, Reference Cairns1999), and containing about 7% of the living species. Approximately 174 fossil species are known (Table 1); however, the total number of fossil species in the approximately 85 families that contain fossil species is not well known, and thus similar ranking cannot be made for the fossil species.

Table 1

Number of species and distribution of the 14 Recent and fossil flabellid genera.

In the first broadly based phylogenetic analysis of the Scleractinia using molecular sequencing, Kitahara et al. (Reference Kitahara, Cairns, Stolarski, Blair and Miller2010) supported the monophyly of the family Flabellidae but found polyphyletic assemblages among the three multispecies genera they analyzed (i.e., Flabellum, Truncatoflabellum, Javania), implying that the morphological distinctions of these genera may not be accurate. However, Kitahara et al. (Reference Kitahara, Cairns, Stolarski, Blair and Miller2010, p. 4), even though professing to include “species representing the full morphological spectrum of the family,” included species from only four of the 10 Recent genera, and of course none from the four exclusively fossil genera. Furthermore, only one mitochondrial gene was used in the analysis, which is usually not considered to be adequate for phylogenetic analyses. Finally, their conclusion that the transversely dividing genera (e.g., Truncatoflabellum) were antecedent to those with a pedicellate base (e.g., Flabellum) contradicts the fossil record, wherein Flabellum has the oldest fossil occurrence. Thus, based on these three reasons, the morphological distinction of genera is favored in this paper and is the only one that can be used with fossils.

Genus Periplacotrochus new genus

1864 Placotrochus; Reference DuncanDuncan, p. 163, 164, 166–167 (in part).

1884 Placotrochus; Reference DuncanDuncan, p. 16 (in part).

1943 Placotrochus; Reference Vaughan and WellsVaughan and Wells, p. 227 (in part).

1956 Placotrochus; Reference WellsWells, p. F432 (in part).

1989b “Placotrochus” deltoideus species complex; Reference CairnsCairns, p. 44, 45.

Type species

Placotrochus deltoideus Duncan, Reference Duncan1864, here designated.

Diagnosis

Corallum solitary, shaped as a laterally compressed fan; edge spines lacking but may have low thecal crests. Transverse division lacking; corallum fixed to fragment of substrate by small pedicel elliptical in cross section; pedicel not stereome reinforced. Pali and paliform lobes absent; lamellar columella prominent. Calicular edge smooth; septa often slightly exsert.

Occurrence

Late Eocene to middle Miocene: Victoria, South Australia, Tasmania.

Etymology

The Greek prefix peri, meaning near, prefaces Placotrochus to show its close relationship to that genus. Gender: masculine.

Remarks

Periplacotrochus differs from Flabellum in having a lamellar columella, and from Placotrochus by being pedicellate (not transversely dividing). Key to the species of Periplacotrochus is shown in Table 2.

Table 2

Key to the species of Periplacotrochus.

Periplacotrochus deltoideus (Duncan, Reference Duncan1864) new combination

Figure 2.1–2.4

Figure 2

(1–4) Periplacotrochus deltoideus, USNM 67953, Balcombe’s Bay, Victoria, middle Miocene, lateral, edge, calicular, and oblique calicular views, respectively. (5–7) P. corniculatus, holotype, NMV P27069, lateral, edge, and calicular views, respectively. (8–12) P. elongatus, USNM 10674, Muddy Creek, Victoria, middle Miocene: (8) specimen showing lamellar columella; (9–12) lateral, edge , calicular, and oblique calicular views of same specimen. (13–15) P. pueblensis, holotype, NMV P27106, lateral, edge, and calicular views, respectively. (1–6, 8–14) Scale bars=10 mm; (7, 15) scale bars=5 mm.

1864 Placotrochus deltoideus Reference DuncanDuncan, p. 164, 167, pl. 5, fig. 5a–c.

1870 Placotrochus deltoideus; Reference DuncanDuncan, p. 300, 309, 311, pl. 20, fig. 4a, b.

1875 Placotrochus deltoideus; Reference Tenison-WoodsTenison-Woods, p. 17.

1876 Placotrochus deltoideus; Reference DuncanDuncan, p. 341.

1878b Placotrochus deltoideus: Reference Tenison-WoodsTenison-Woods, p. 315.

1878c Placotrochus deltoideus; Reference Tenison-WoodsTenison-Woods, p. 65.

1927 Placotrochus deltoideus; Reference FelixFelix, p. 417.

1989b Placotrochus deltoideus; Reference CairnsCairns, p. 75, pl. 40, fig. a–c.

Undated Placotrochus deltoideus; Reference Fitzgerald and SchmidtFitzgerald and Schmidt, p. 3 (color illustration).

Types

Five syntypes are deposited at the NHMUK (PI R29269-29273). Type locality: Muddy Creek, Victoria (Balcombian, middle Miocene).

Diagnosis

Corallum with five cycles (96 septa) of hexamerally arranged septa.

Occurrence

Janjukian (=Rupelian, late Oligocene): Torquay, Victoria. Balcombian (=Langhian, middle Miocene): Muddy Creek, Balcombe’s Bay, and Beaumaris, Victoria. Miocene: northwestern Tasmania.

Description

The corallum has a bimodal edge angle, the lower thecal edges making an angle of 71º–87º, the upper thecal edges diverging at only 48º–60º (Fig. 2.1); the lower thecal edges are acute and usually bear a low, discontinuous crest (variety bursarius of Duncan, Reference Duncan1864). The thecal faces are planar (not convex), having a face angle of 30º–39º. The largest corallum (USNM 67953, Fig. 2.1–2.4) is 27.2 mm in height and 27.2 x 19.3 mm in calicular diameter. The calice is elliptical, the GCD:LCD ranging from 1.4 to 1.7; the H:GCD ranges from 1.0 to 1.1. The greater axis of the small (1.5–1.6 x 0.95–1.0 mm), elongate pedicel is aligned with the GCD. Each thecal face is ribbed with low C1–3 (Fig. 2.1).

Above a GCD of 20 mm the septa are consistently arranged in five complete cycles (Fig. 2.3–2.4): S1–3>S4>S5 (96 septa). Below that diameter, coralla have only 20–22 major septa (not 24) and a corresponding lesser number of higher cycle septa. The S1–3 have slightly sinuous axial edges, the lowermost edges fusing with the columella. The S4 are about half the width of the S1–3, and the S5 are rudimentary, but consistently present. The fossa is of moderate depth and contains a prominent lamellar columella, consisting of a single thick lamella.

Remarks

Periplacotrochus deltoideus is very similar to P. magnus, resembling a smaller version of that species. However, P. deltoideus can be distinguished by having a smaller corallum, straight (not convex) thecal faces and thus a less full corallum, consistently 96 hexamerally arranged septa (vs. three size classes of septa, the largest counting 28–32), consistently crested lower thecal edges, and ribbed C1–3.

Periplacotrochus corniculatus (Dennant, Reference Dennant1899) new combination

Figure 2.5–2.7

1899 Placotrochus corniculatus Reference DennantDennant, p. 115, pl. 2, fig. 3a–b.

1927 Placotrochus corniculatus; Reference FelixFelix, p. 416.

1981 Placotrochus corniculatus; Reference BellBell, p. 11 (type deposition).

1989b Placotrochus corniculatus; Reference CairnsCairns, p. 75 (mentioned).

Types

Holotype deposited at the NMV (P27069); paratype NMV P27070 (Blanche Point); Dennant (Reference Dennant1899) mentioned a third specimen, which would also be a paratype. Type locality: Adelaide bore, South Australia, Miocene according to Felix (Reference Felix1927).

Diagnosis

Corallum with four cycles (48 septa) of hexamerally arranged septa; corallum cornute.

Occurrence

Known only from the type locality.

Description

This species is known only from three specimens. The holotype is a cornute specimen (Fig. 2.5), curved about 75º. It is 20 mm in height and 9.0 x 6.5 mm in calicular diameter, having a H:GCD of 2.2. The GCD:LCD range of the type series is 1.21–1.56. The edge angle is about 13º; the face angle could not be computed from the figures or text. The septa are arranged in four complete cycles: S1–2>S3>S4 (48 septa). The S1–2 are slightly exsert with strongly sinuous axial edges. The S3 are almost as wide as the S1–2, and the S4 are relatively small. The fossa contains a typical lamellar columella.

Remarks

This species is distinguished from the others in the genus by having a regularly curved (cornute) corallum (see Key in Table 2).

Periplacotrochus elongatus (Duncan, Reference Duncan1864) new combination

Figure 2.8–2.12

1864 Placotrochus elongatus Reference DuncanDuncan, p. 163, 167, pl. 5, fig. 4a–e.

1870 Placotrochus elongatus; Reference DuncanDuncan, p. 300, 311, 312, 313, pl. 20, fig. 3a–c.

1878b Placotrochus elongatus; Reference Tenison-WoodsTenison-Woods, p. 314.

1927 Placotrochus elongatus; Reference FelixFelix, p. 417.

1989b Placotrochus elongatus; Reference CairnsCairns, p. 75.

Types

The holotype is deposited at the NHMUK (PI R29274). Type locality: Muddy Creek, Victoria (middle Miocene).

Diagnosis

Corallum with four cycles (48 septa) of hexamerally arranged septa; corallum straight to irregularly bent (but not cornute); calice elliptical in cross section.

Occurrence

Janjukian (late Oligocene): Torquay, Victoria. Balcombian (middle Miocene). Muddy Creek, Aire River, Grice’s Creek, Victoria. Miocene: Table Cape, Tasmania, Mount Gambier, Cape Otway, Victoria.

Description

The corallum is shaped as an isosceles triangle (Fig. 2.9), the edge angle ranging from 17º–29º and the thecal edges being straight. The thecal faces are planar (not convex), having a face angle of 12º–22º (Fig. 2.10). The lower thecal edges are acute but not crested; the upper thecal edges are evenly rounded, producing an elliptical calice having a GCD:LCD of 1.50–1.67. The H:GCD ranges from 1.6 to 3.2, thus the name elongatus. One of the larger coralla (USNM 77069) measures 11.3 x 7.3 mm in calicular diameter and 22.3 mm in height. The pedicel is small, about 1.9 x 1.0 mm in diameter, the longer axis aligned with the GCD.

The septa are hexamerally arranged in four complete cycles: S1–2>S3>S4 (48 septa), even in coralla as small as 6.0 mm GCD. S1–2 are exsert, their axial edges quite sinuous, and their lower axial edges fused to the lamellar columella. The S3 are about four-fifths the width of the S1–2, much less sinuous, and they fuse with the columella. The S4 are two-thirds the width of the S3, their axial edges not attaining the columella. The fossa is deep and contains a prominent sharp lamellar columella, characteristic of the genus (Fig. 2.11, 2.12).

Remarks

Periplacotrochus elongatus is easily distinguished from other species by its elongate slender corallum (GCD:H=1.6–3.2) (see also the Key in Table 2).

Periplacotrochus pueblensis (Dennant, Reference Dennant1903) new combination

Figure 2.13–2.15

1903 Placotrochus pueblensis Reference DennantDennant, p. 212, pl. 2, fig. 1a–b.

1981 Placotrochus pueblensis; Reference BellBell, p. 11 (type deposition).

1989b Placotrochus pueblensis; Reference CairnsCairns, p. 75 (mentioned).

Types

The holotype is deposited at the NMV (P27106). Type locality: Spring Creek (The Ledge), Victoria, Janjukian (late Oligocene).

Diagnosis

Corallum with four cycles (48 septa) of hexamerally arranged septa; corallum straight to irregularly bent (but not cornute); calice round in cross section.

Occurrence

Known only from the type locality.

Description

The species is known from only one specimen, the holotype. It is essentially conical (Fig. 2.13, 2.14): 17.8 mm tall (as measured from the figure) and 10.4 x 10.2 mm (as measured from the figure) in calicular diameter (GCD:LCD=1.02, essentially circular). The angle of thecal divergence is uniformly about 27º. The epitheca is porcellaneous. The septa are arranged in four complete cycles: S1–2>S3>S4 (48 septa). The S1–2 are slightly exsert, whereas the S3 are about three-fourths the width of the S1–2, and the S4 are about half the width of the S3. The fossa is deep, containing a somewhat unusual (?aberrant) double-lamellar columella (Fig. 2.15).

Remarks

Periplacotrochus pueblensis is distinctive in having a circular calice and 48 septa, although it is very similar to P. inflectus, as described in the account of that species (see also Key to species in Table 2).

Periplacotrochus inflectus (Dennant, Reference Dennant1903) new combination

Figure 3.1–3.4

Figure 3

(1–4) Periplacotrochus inflectus: (1, 2, 4) NMV P27107, syntype, lateral, edge, and calicular views, respectively; (3) calicular view of specimen NMV P134078. (5–8) P. cudmorei, holotype, USNM 1283876, lateral, edge, calicular, and oblique calicular views, respectively. (9–16) P. magnus: (9–11) holotype, NMV P27114, lateral, edge, and calicular views, respectively; (12) USNM 67954, damaged specimen showing its lamellar columella; (13–16) USNM 67954, lateral, edge, calicular, and oblique calicular views of same specimen, respectively. (1, 2, 5–16) Scale bars=10 mm; (3, 4) scale bars=5 mm.

1903 Placotrochus inflectus Reference DennantDennant, p. 213, pl. 2, fig. 2a–c.

1981 Placotrochus inflectus; Reference BellBell, p. 11 (type deposition).

1989b Placotrochus inflatus (sic); Reference CairnsCairns, p. 75.

Types

Four syntypes are deposited at the NMV (P27107 and 27108), see Bell (Reference Bell1981). Two additional specimens (?syntypes) are also deposited at that museum: P134078 and P146120. Type locality: “Eocene clays at Brown’s Creek, Aire R. district” (Dennant, Reference Dennant1903, p. 213), Victoria, middle to late Eocene.

Diagnosis

Corallum with four cycles of hexamerally arranged septa but lacking eight S4, resulting in 40 septa; corallum straight to irregularly bent (but not cornute); calice round in cross section.

Occurrence

Known only from the type locality.

Description

The species is known from only four specimens, two of them poorly preserved. The specimen described and illustrated by Dennant (Reference Dennant1903) is ceratoid (almost conical, Fig. 3.1, 3.2), 7.5 x 6.5 mm in calicular diameter (GCD:LCD=1.15), and 16 mm in height (H:GCD=2.13). The edge angle is about 23º. The epitheca is porcellaneous and the C1–2 are slightly raised. The pedicel attachment is elongate, as is typical for the genus. The septa are arranged in four cycles (S1–2>S3>S4), but the fourth cycle is incomplete, lacking four pairs of S4 in the lateral half systems, thus resulting in only 40 septa. The S1–2 are thick, their axial edges fused to the columella. The S3 and S4 are much thinner, the S3 about three-fourths the width of the S1–2, and the S4 small. The lamellar columella is prominent (Fig. 3.3, 3.4).

Remarks

Periplacotrochus inflectus is very similar to P. pueblensis and may simply represent an earlier ontogenetic stage in which the corallum is slightly smaller and thus has an incompletely developed fourth cycle of septa. Most other characters are similar or the same. However, the stratigraphic occurrence of P. inflectus is much earlier (middle to late Eocene) than that of P. pueblensis (late Oligocene). Clearly, more specimens are needed to resolve this distinction.

Periplacotrochus cudmorei new species

Fig. 3.5–3.8

Types

Holotype: Clifton Bank, Muddy Creek, Victoria, Balcombian (middle Miocene), USNM 1283876. Paratypes: same locality as holotype, two, USNM 1283875. Bird Rock Cliffs, Torquay, Victoria, Janjukian (late Oligocene), four, USNM M353583. Spring Creek, Torquay, Victoria, Janjukian (late Oligocene), three, USNM 1283874. Type locality: Clifton Bank, Muddy Creek, Victoria, Balcombian (middle Miocene).

Diagnosis

Septa arranged in three size classes, having 20 primary septa and thus 80 septa.

Occurrence

Balcombian (middle Miocene): Muddy Creek, Victoria. Janjukian (late Oligocene): near Torquay, Victoria.

Description

The corallum is triangular in lateral view (Fig. 3.5), the thecal edges forming an angle of 38º–62º and the planar faces forming a lesser angle of 30º–38º (Fig. 3.6). The lower thecal edges are acute and bear low crests, whereas the upper thecal edges are rounded. The holotype measures 18.2 x 11.7 mm in calicular diameter and is 20.0 mm in height. The GCD:LCD ranges from 1.42 to 1.68, and the H:GCD ranges from 0.8 to 1.1 but is usually over 1.0. The greater axis of the elongate (1.6–1.9 x 0.7–1.1 mm in diameter) pedicel attachment is aligned with the GCD. The 20 costae on the thecal faces are sometimes slightly elevated.

The septa are consistently arranged in three size classes: 20:20:40, resulting in 80 septa. The primaries are exsert as much as 1.5 mm and have moderately sinuous axial edges, their lower axial edges fusing to the lamellar columella. The secondary septa are about two-thirds the width of the primaries, have less sinuous axial edges, and do not reach the columella. The tertiaries are rather small. The fossa is shallow and contains a prominent lamellar columella (Fig. 3.7, 3.8).

Etymology

Named in honor of Francis Alexander Cudmore (1892–1956), enthusiastic marine paleontologist who collected in Victoria and Tasmania and provided most of the Australian Tertiary corals donated to the Smithsonian in 1923.

Remarks

This species is unique in having decameral septal symmetry (see Key in Table 2).

Periplacotrochus magnus (Dennant, Reference Dennant1904) new combination

Figure 3.9–3.16

1904 Placotrochus magnus Reference DennantDennant, p. 54, pl. 22, fig. 4a–c.

1981 Placotrochus magnus; Reference BellBell, p. 11 (type deposition).

1989b Placotrochus magnus; Reference CairnsCairns, p. 75 (mentioned).

Types

The holotype (P27114) and paratype (P27115) are deposited at the NMV. Type locality: Spring Creek (16 miles south of Geelong), Victoria, Australia, Janjukian (late Oligocene).

Diagnosis

Septa arranged in three size classes, but with 27–32 primary septa, resulting in 104–128 septa.

Occurrence

Janjukian (late Oligocene): Torquay and Spring Creek (near Geelong), Victoria, Australia.

Description

The corallum has a bimodal edge angle, the lower thecal edges making an angle of 91º–98º (Fig. 3.9, 3.13), whereas the upper thecal edges diverge at only 34º–46º; the lower thecal edges are acute and bear a low crest, whereas the upper thecal edges are less acute and rounded near the calice. The thecal faces are planar to slightly convex, making a face angle of 36º–45º (Fig. 3.10, 3.14). The largest corallum (the holotype) is 37 x 26 mm in calicular diameter and 33 mm in height. The calice is elliptical, the GCD:LCD ranging from 1.36 to 1.66; the H:GCD ranges from 0.89 to 1.21. The pedicel is small (1.8–2.0 x 0.75–1.05 mm), the greater axis aligned with the GCD.

The septa are arranged in three size classes, the holotype having septa arranged as 28:28:56 (112 septa), but other coralla have 27–32 primaries and a total of 104–128 septa. The primary septa are slightly exsert and have slightly sinuous axial edges, the lowermost edges fusing to the lamellar columella. The secondaries are about half the width of the primaries and do not attain the columella. The tertiaries are small to rudimentary but consistently present over a GCD of about 30 mm. The fossa is of moderate depth and contains a prominent lamellar columella, usually consisting of a single, thick (0.5 mm) lamella (Fig. 3.12), but sometimes as two or three aligned lamellae (Fig. 3.15, 3.16).

Remarks

Periplacotrochus magnus is compared to the closely related P. deltoideus in the account of the latter species.

Periplacotrochus elegans Tenison-Woods, Reference Tenison-Woods1878a, nomen dubium

1878a Placotrochus elegans Reference Tenison-WoodsTenison-Woods, p. 189, pl. 1, fig. 1, 1a.

1927 Placotrochus elegans; Reference FelixFelix, p. 417.

1971 Placotrochus elegans; Reference FletcherFletcher, p. 32.

1989b Placotrochus elegans; Reference CairnsCairns, p. 75.

Types

Holotype deposited at the Australian Museum (F.1697) (Fletcher, Reference Fletcher1971). Type locality: Muddy Creek, Victoria, Balcombian (middle Miocene).

Diagnosis

The species cannot be diagnosed as it is probably a juvenile stage of another species.

Occurrence

Known only from the type locality.

Description

The holotype is only 3 mm tall, with a compressed calice (3.0 x 1.5 mm in diameter, GCD:LCD=2; H:GCD=1) and an elongate basal attachment (1.65 mm in greater diameter). The edge angle is about 21º. According to Tenison-Woods’ (Reference Tenison-Woods1878a) illustration, there are 16 larger septa and 16 smaller septa and a prominent lamellar columella.

Remarks

The species is known from only one small specimen, undoubtedly the juvenile stage of a larger specimen, which shows the characteristic basal attachment of a Periplacotrochus. Three species of Periplacotrochus are known from the fossil beds of Muddy Creek, Victoria (P. elongatus, P. deltoideus, and P. cudmorei), and this juvenile specimen could be any of these three. A specimen of similar size and shape is shown herein as Figure 4.1 and 4.2. It is therefore suggested to treat the name as a nomen dubium, as defined by the International Code of Zoological Nomenclature (article 75.5).

Figure 4

Juvenile specimen of Periplacotrochus, similar to that described as P. elegans, USNM 67999, Muddy Creek, Victoria, middle Miocene: (1) lateral view of specimen showing characteristic broad attachment to a shell fragment; (2) stereo view of calice showing 32 septa. Scale bars=1 mm.