Ctenella Matthai, 1928

Arrigoni, Roberto, Stolarski, Jarosław, Terraneo, Tullia I., Hoeksema, Bert W., Berumen, Michael L., Payri, Claude, Montano, Simone & Benzoni, Francesca, 2023, Phylogenetics and taxonomy of the scleractinian coral family Euphylliidae, Contributions to Zoology 92 (2), pp. 130-171 : 153-154

Ctenella Matthai, 1928

Type species: Ctenella chagius Matthai, 1928 ; holotype: bmnh 1928.3.1.61; paratypes: bmnh 1928.3.1. 60, bmnh 1928.4.18.591; type locality: Chagos.

Not: Ctenella C. Carré & D. Carré, 1993 (phylum Ctenophora), junior homonym; invalid name.

Original description: ‘Encrusting, massive or explanate, light. Growth-size small. Base of attachment broad or pedunculate. Valley sinuous, continuous or discontinuous at places, up to 14 mm. in width, depth up to 10 mm. Colline swollen to varying extent (up to 8 mm.) by endothecal deposition, ridged or with rounded edge. Septa in 1 cm. up to 20, of which up to 8 meeting columella, with margins vertical (sometimes curving to right or left) and entire, sides granular or spinulose, those of opposite sides of colline either alternating or continuous over colline. Columella lamellar, comparatively thin but solid, usually continuous (occasionally discontinuous) along middle of valley, and with sharp somewhat wavy ridge above. Ctenella has some resemblance to Pectinia , since the septa have vertical entire margins and granular or spinulose sides, and since the columella is lamellar, comparatively thin but solid, usually continuous along the middle of the valley with a sharp wavy ridge above. But in Ctenella each septum does not appear to be composed of a pair of lamellae, as is often the case in Pectinia , the valleys do not attain to the same width, colline is never grooved, and the corallum is not massive or heavy’ ( Matthai, 1928: 171).

Diagnosis: Colonial. Budding intracalicular and extracalicular. Corallites monomorphic and uni- or multi serial. Fused walls. Calice of width medium (4–15 mm) and relief medium (3–6 mm). Septa in Ẑ 4 cycles (Ẑ 48 septa). Free septa regular. Septal spacing medium (6–11 septa per 5 mm). Costosepta equal in relative thickness. Columellae lamellar, with size small relative to calice width (<1/4), with linkage continuous. Paliform lobes absent. Endotheca abundant (vesicular). Polyp tentacles partially/fully extended at daytime, of shape simple.

Species included: Ctenella chagius Matthai, 1928 .

Taxonomic remarks: Matthai (1928) established Ctenella to include two species, C. chagius and Ctenella laxa Matthai (1928) . To date, the latter species is considered as a taxon inquirendum (Hoeksema & Cairns, 2023). On the basis of meandroid colony and lamellar columella, Ctenella has been historically considered a member of either Meandrinidae or Eusmiliidae (junior synonym of Meandrinidae ) (see table 1; Vaughan & Wells, 1943; Alloiteau, 1952; Wells, 1956; Chevalier & Beauvais, 1987; Veron, 2000).With sequences from mitochondrial markers coi and cytB, Fukami et al. (2008) showed that C. chagius belonged to clade V sensu Fukami et al. (2008). Following the molecular phylogenetic tree of Fukami et al. (2008), Budd et al. (2012) assigned all members of clade V sensu Fukami et al. (2008), thus including Ctenella , to Euphylliidae .Although Ctenella was not collected for this study, we included this taxon in both molecular and morphological phylogeny reconstructions by using the coi sequence of C. chagius published by Fukami et al. (2008) (accession number AB441208) and investigating macromorphology of the holotype of C. chagius (bmnh 1928.3.1.61) and the polyp structure. Both analyses corroborated Ctenella as a member of Euphylliidae and showed a sister relationship with Gyrosmilia .

Morphological remarks: Ctenella displays 15 out of the 18 investigated macromorphological characters identical to Gyrosmilia of which one shared character, i.e., uni-or multi serial corallites, is unique within the family. Nevertheless, a lamellar columella, with continuous linkage, unambiguously tells apart Ctenella from Gyrosmilia and it has narrower valleys. No micromorphological/microstructural characters have been investigated for Ctenella in this study.

Distribution: Ctenella is restricted to the reefs of Chagos Archipelago and Mauritius ( Rosen, 1971; Sheppard et al., 1983; Veron, 2000; Pillay et al., 2002; Obura, 2012).