Phacelostylophyllum mg. martini (Fromentel, 1860), 1972

Vasseur, Raphaël & Lathuilière, Bernard, 2021, Pliensbachian corals from the Western Tethys, Geodiversitas 43 (22), pp. 1187-1291 : 1258-1260

Phacelostylophyllum mg. martini (Fromentel, 1860)

( Fig. 50 )

Thecosmilia martini Fromentel in Martin, 1860: 92, pl. 8, fig. 8-9. — Fromentel 1861: 142. — Dumortier 1864: 173, pl. 29, fig. 9-10. — Terquem & Piette 1865: 127, pl. 17, fig. 1-3. — Duncan 1868: 45, pl. 12, fig. 1-2. — Tomes 1878: 186. — Koby 1884b: 164, pl. 54, fig. 5; 1894: 16, pl. 4, fig. 3. — Joly 1936: 170.

Phacelostylophyllum sp. 1 – Vasseur 2018: 286-287, fig. 3.74.

TYPE MATERIAL. — Syntype MHNG GEPI 036077 . TYPE HORIZON. — Sinemurian . TYPE LOCALITY. — Semur en Auxois ( France, historical stratotype of Sinemurian ). STUDIED SAMPLES. — Three specimens: CPUN PFPyr7, PFPyr10, PFPyr12 from French Pyrenees . GEOGRAPHIC AND STRATIGRAPHIC RANGES. — Lower Lias of France, Belgium and Great Britain. Pliensbachian of the Estivère pass and surrounding areas ( Pyrenees , France). Cited also from Lower Lias of Northern Scotland ( Hallam 1959; Morton & Hudson 1995; Gretz et al. 2013).

DESCRIPTION

Phaceloid colony with cylindrical corallites multiplying by intratentacular budding. Radial elements are subcompact, free, straight or wavy septa, organized in 3 or 4 distinct size orders. Microstructure typically stylophyllid: septa are made of septal spines linked together by sclerenchyme deposits and generally dissociated at the distal and inner edges. Septa show a rhopaloid aspect in transverse section when a septal spine occurs in its very inner part. The dissociation of the septal spines along the inner edge sometimes produces a weak papillose columella. Endotheca abundant, made of tabular and vesicular dissepiments mostly concentrated in the periphery of the corallites. Wall present, apparently parathecal. An epitheca s.l. seems to wrap the corallites.

Calicular diameter: 10 to 18.3 mm – Number of septa: 39 to 54 – Septal density: 3 for 2 mm.

REMARK

The initial description of the species by Fromentel (in Martin 1860) mentioned 80 septa. The observation of photos of the type material housed in Geneva demonstrates a much lower value (around 50-60) compatible with the present material.

SIMILARITIES AND DIFFERENCES

Differs from Phacelostylophyllum arbustulum n. sp. by the larger size of the calices and the mode of budding.

Dimensions of P. martini are partly overlapping with those of P. medium Roniewicz, 1974 . However the morphology of P. medium is not a fully developed phaceloid growth form. Additionnally, there is a stratigraphic gap of two stages between the two species.

Dimensions of P. caespitosum (Reuss, 1864) are not very far from those of our specimens. However, again, the species is Triassic and with a poor astogenic (= colonial) development. According to the figures in Frech (1890), the septa do not show a detachment of septal spines at their inner edges.

Phacelostylophyllum dentatum (Duncan, 1867) dimensions range within the dimensions of our specimens of P. martini (Fromentel, 1860) but the colonial development is stopped after a very low number of corallites and the distal edge of septa in P. dentatum (Duncan, 1867) is characterized by an extensive development of septal spines even far from the inner edge. Phacelostylophyllum dentatum is Hettangian.

Phacelostylophyllum michelini ( Terquem & Piette, 1865) seems very close in terms of dimensions and is a really a fully developed phaceloid colony. From the original drawing, we do not observe septal spines at the inner edge. P. michelini ( Terquem & Piette, 1865) is known from the Lower Liassic.

Phacelostylophyllum robustum (Roniewicz, 1974) has dimensions partially overlapping with P. martini ( Fromentel, 1865) . However, this Triassic species has very thick tabuloid dissepiments that produce a thick wall.

Phacelostylophyllum peruviana ( Wells, 1953) has a tendency toward the ceroid structure that we never observed in our samples.

All other species have significantly different dimensions: P. rugosum (Laube, 1865) , P. romerloana ( Volz, 1896) , P. pygmaeum (Frech, 1889) , P. affinis (Duncan, 1867) , P. sp. in Roniewicz, 1974, P. karauldyndalaensis Melnikova, 1972 ). Phacelostylophyllum pontebbanae ( Volz, 1896) was reclassified in a new genus Pontebbastraea (in Roniewicz & Michalík: 152) and P. chocolatensis ( Wells, 1953) is not a stylophyllid according to Morsch (1995).

Figures

FIG. 50. — Phacelostylophyllum mg. martini (Fromentel, 1860): A, Distal view of specimen CPUN PFPyr10; B, natural worn longitudinal section of a corallum on specimen CPUN PFPyr7;C, transverse polished section in one corallum of specimen CPUN PFPyr7; D, longitudinal polished section in one corallum of specimen CPUN PFPyr10; E, transverse polished section in one corallum of specimen CPUN PFPyr7;F, transverse thin section in one corallum of specimen CPUN PFPyr7. Scale bars: A, 2 cm; B, D, F, 5 mm; C, 6 mm; E, 4 mm.