Diploctenium chilensis, Collado & Galleguillos, 2025

? Diploctenium chilensis , new species

Figure 2A–D View FIGURE 2

Holotype. Specimen almost complete ( MGUC PT/01 -L2/C2) ( Fig. 2A–D View FIGURE 2 ).

Description of the holotype. Solitary coral, flabelliform, with a thick triangular pedicel. Thecal edge crest extends to about one quarter of the corallum, corresponding to the summit of the pedicel; columella not observed due to preservation. Calice perimeter dentate, characterized by conspicuous costosepta arranged in four alternating size cycles that extend toward the center. There are at least 33 long septa, each with a fang-like appearance. Outer wall with marked and numerous costae that originate from the base of the pedicel and distinctly bifurcate as they extend to the upper margin of the corallum.

Dimensions of the holotype. Height 2.3 cm (measured as a straight line from the base of the pedicel to the margin of the calice in Figure 2B View FIGURE 2 ), width 2.9 cm (measured as a straight line connecting the two wings of the specimen over the pedicel in Figure 2B View FIGURE 2 ).

Type locality. Millaneco Beach, south of Lebu , Arauco Province, Bío-Bío Region, south-central Chile ( Fig. 1 View FIGURE 1 ) .

Geological horizon. Trihueco Formation of the Lower Paleocene in the Arauco Basin along the coast of the Bío-Bío Region, according to the geological setting described by Becerra et al. (2013) .

Etymology. The name derives from Chile, where the fossil was found.

Comparisons with other species. In terms of general morphology,? Diploctenium chilensis sp. nov. is trianguliform and wider than it is tall, distinguishing it from the type species, Diploctenium cordatum Goldfuss, 1826 , from the Maastrichtian (Upper Cretaceous) of Netherlands, which has a heart shape and is taller than it is wide ( Goldfuss 1826; Alloiteau 1952).? Diploctenium chilensis sp. nov. exhibits a very similar shape when compared to Diploctenium matheroni Michelin, 1847 , Diploctenium simplex Alloiteau, 1952 , and Diploctenium jacobi Alloiteau, 1952 from the Santonian (Upper Cretaceous) of France, as well as Diploctenium zuffardii Maccagno, 1942 ( Fig. 3 View FIGURE 3 ), from the Maastrichtian of Libya ( Michelin 1847; Alloiteau 1952; Maccagno 1942; Manni 2006; GBIF 2024). However, Diploctenium simplex differs from the new species by having thicker costae, a shorter pedicel, and poorly developed thecal edge crests, with the lateral margin of the wall between the base of the pedicel and the edge of the calice being nearly straight ( Alloiteau 1952). Both Diploctenium matheroni and Diploctenium zuffardii are distinguished from the new species by their narrower pedicel and finer costae ( Michelin 1847; Alloiteau 1952; Maccagno 1942; Manni 2006). Diploctenium jacobi is distinguished from? Diploctenium chilensis sp. nov. by its semicircular shape and thicker, trifurcating costae ( Alloiteau 1952).

? Diploctenium chilensis sp. nov. differs from Diploctenium gracile de Fromentel, 1862 (Maastrichtian) and Diploctenium parvum Alloiteau, 1952 , from the Campanian (Upper Cretaceous) of France, which have a conical shape and an acuminate pedicel(de Fromentel 1862; Alloiteau 1952). It also differs from Diploctenium crassicostatum Alloiteau, 1952 (Campanian), which is much wider than it is tall and has thick costae arranged in pairs ( Alloiteau 1952). Diploctenium cureti Alloiteau, 1952 (Campanian), like Diploctenium chilensis sp. nov., is also wider than it is tall, but in the former species the thecal edge crests almost reach the summit of the pedicel ( Alloiteau 1952).

? Diploctenium chilensis sp. nov. differs from Diploctenium lunatum ( Bruguière, 1792) , Diploctenium plumum Goldfuss, 1827 , Diploctenium subcirculare Milne-Edwards & Haime, 1848 , Diploctenium lamellosum d’Orbigny, 1850 , Diploctenium ferrumequinum Reuss, 1854 , Diploctenium pavoninum Reuss, 1854 , Diploctenium affine Felix, 1903 , Diploctenium falloti Bataller, 1936 , Diploctenium arnaudi Alloiteau, 1952 , Diploctenium corbariensis Alloiteau, 1952 , Diploctenium enigma Alloiteau, 1952 , Diploctenium epagnacensis Alloiteau, 1952 , Diploctenium lutaudi Alloiteau, 1952 , Diploctenium mixtum Alloiteau, 1952 , Diploctenium petrocoriensis Alloiteau, 1952 , Diploctenium provincialis Alloiteau, 1952 , Diploctenium toucasi Alloiteau, 1952 , and Diploctenium uxacalcensis Alloiteau, 1952 , which have a semicircular or subcircular outline ( Alloiteau 1952; Gameil 2005; Baron‐Szabo 2006; GBIF 2024). The new species differs from Diploctenium pluma Goldfuss, 1826 , which has a heart shape, with a more pronounced lobe.

Remarks. The classification of the genus Diploctenium at the family group has historically posed challenges. Goldfuss (1826) established the genus to include two species from the Netherlands, but he did not assign it to any family or other suprageneric category. Milne Edwards & Haime (1848) placed the genus informally between the “Eusmiliens” in the family of the “Astréides”. Reuss (1854) placed the genus in the subfamily Eusmilinae Milne-Edwards & Haime, 1857 , family Astraeidae Dana, 1846 , a classification accepted by Milne Edwards (1857). Duncan (1884) recognized this classification at the family level but placed the group in the subfamily “Astraeide simplices”, “alliance” Trochosmilioida. In the 20th century, Felix (1903) classified Diploctenium in the tribu “Phillosmiliaceae”, subfamily Trochosmilinae Milne-Edwards, 1857 , family “ Turbinolidae ” Milne Edwards & Haime, 1848. Siemiradzki (1925) grouped the genus in the family Trochosmilidae Milne-Edwards, 1857 , while Wells (1956) relocated it to the subfamily Meandrininae Gray, 1847 , family Meandrinidae Gray, 1847 . Subsequently, Baron-Szabo (1998, 2000) included the group in the family Dendrogyridae Alloiteau, 1952 , but it was soon reclassified back to Meandrinidae ( Baron-Szabo 2006; Baron-Szabo & Leloux 2024). The Paleobiology Database ( Uhen et al. 2023) currently assigns the genus to this last family.

Meandrinidae has been shown to be polyphyletic according to molecular analysis ( Fukami et al. 2008). The polyphyletic nature of the family may be attributed to character convergence, a phenomenon frequently observed in corals ( Fukami et al. 2004, 2008; Budd & Stolarski 2009), as well as to the poor initial definition of the taxon ( Löser et al. 2010). For this reason, different species assigned to this family may occupy distinct clades within the Scleractinia tree ( Fukami et al. 2004, 2008). Consequently, Diploctenium may need to be assigned to another family. Another candidate is the family Trochosmilidae de Fromentel, 1861 , which includes taxa with a lamellar columella, a pseudocolumella, or without columella ( Ogilvie 1896; Yabe & Eguchi 1941). The family Phyllosmiliidae Felix, 1903 may also be a candidate.

The presence of a columella in Diploctenium has historically been controversial. In Goldfuss’s (1826) generic concept, he does not mention the presence of a columella, nor does he refer to it in the two newly described species that accompanied the original description of the genus.According to Milne Edwards (1857), in Diploctenium “...n’existe pas de columelle,” a character he recognized in other corals but not in the 11 Diploctenium species he treated. Reuss (1854) also did not mention the presence of a columella in the six species he characterized. Similarly, Siemiradzki (1925) and Wells (1956) did not observe a columella in their brief characterizations of the genus. Conversely, Felix (1903), Alloiteau (1952), and Baron-Szabo (1998, 2000, 2006) recognized a well-formed columella in all the species they examined, including some that were addressed by earlier authors where this character was not found.

Based on the fan-like shape, the pedicel being shorter than the thecal edge crests, and the similarities between the new species and the type species of Diploctenium (see Fig. 6 in Baron-Szabo 2006, p. 68), as well as other congeners, we assign the new species to this taxon, with the understanding that this classification may be reconsidered if additional material becomes available. It is important to note that Diploctenium zuffardii , which is very similar to? Diploctenium chilensis sp. nov. ( Fig. 3 View FIGURE 3 ), was previously considered a potential synonym of Rennensismilia inflexa ( Reuss, 1854) ( Baron‐Szabo 2006) , a species from Africa, Asia, and Europe. However, we regard the two species as distinct. Further studies, preferably based on material beyond the type specimen, are needed to confirm that? Diploctenium chilensis sp. nov. belongs to this genus. For this reason, we use the symbol ‘?’ to tentatively classify the new species within Diploctenium .