Ranella bicoronata Bronn 1862
Creators: name: Sacchetti, Claudia
name: Landau, Bernard
name: Ávila, Sérgio P.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Littorinimorpha
Bursidae
Ranella
Ranella bicoronata

description: Ranella bicoronata Bronn, 1862 species inquirenda
Plate 6 M, N
* Ranella bicoronata Bronn in Reiss 1862: 27, pl. 1, fig. 8.
Ranella bicoronata Bronn — Mayer 1864: 72, pl. 7, fig. 53.
Type material. Two specimen, maximun height 19.0 mm, width 15.0 mm, Pinheiros, Santa Maria Island, Azores, Touril Complex, Lower Pliocene; whereabouts unknown (Beu 2017:165).
Original description. “ Drei Gewinde-Theile der Schaale, woran 5 Windungen kenntlich sind, aber der letze Umgang gr̂sstentheils fehlt. Den 3-4 ersten Umgängen nach w̧rde man, was Form, Spiralstreifung un Scwäche der Mundw̧lste betrifft, glauben k̂nnen eine junge R. marginata vor sich zu haben; doc hist das Gewinde Treppenf̂rmig und steht die Kn̂tchen-Reihe mit etwa 16 Kn̂tchen auf den Umgang nicht vor, sondern hinter der Mitte des freien Theils der Umgänge, anfangs dicht a der Naht, dann etwas davon entfernt, einen abgerundet fast rechtkantigen Kiel bildend, welcher 2—3 gerundete Spiral-Streifen hinter (̧ber) und 6—7 dergleichen vor sich hat. Die so gestreifte freie Fläche vor ihm ist anfangs rechtwinkelig, dann auswärts gekŗmmt und mithin konkav; sie erhebt sich vom vorletzten Umgange an in der Nah tzu einer zweiten Kn̂tchen-Reihe, deren Kn̂tchen etwas weiter aus einander geŗckt sind. Die ganze äussre Oberfläche des letzten Umganges scheint ebenfalls spiralstreifig gewesen zu seyn, mit 2—3 stärkeren Streifen darunter, auf denen sich auch noch einzelne undeutlichere Kn̂tchen erheben. Die M̧ndung scheint am obern oder hinter Ende der wulstigen äusseren Lippe der von R. marginata ähnlich und mit eben solchem Kanale versehen gewesen zu seyn (Fig. a stellt den hinter-untern Theil dar; am Rande rechts springen beide Kn̂tchen-Reihen vor.) [Three spire fragments are preserved from which we can tell it has at least 5 whorls, but the last whorl is largely missing. According to the first 3 to 4 whorls, one would believe that it is a young specimen of R. marginata, as far as the shape, spiral striations and the weak apertural callus is concerned; but the suture is scalate and there is a row of sixteen protruding nodules not in front, but behind the middle of the free part of the whorls, initially close to the suture, then slightly distant from it, forming a rounded almost rectangular keel, which has 2-3 rounded spiral cords behind (above) and 6-7 similar one in front of it. The striated space in front [of the nodule] is initially rectangular, then convex and later concave; it rises from the penultimate suture at the suture to a second row of nodules, the nodules of which have moved a little further apart. The whole outer surface of the last whorl also seems to have been spirally striated, with 2-3 thicker cords underneath, on which also individual indistinct nodules develop. The aperture seems to have been similar at the upper or behind the end of the bulging outer lip to that of R. marginata and provided with such a canal (Fig. a represents the lower dorsal part (?); at the edge right both rows of nodules protrude.)]” (Bronn in Reiss 1862: 27-28).
Latin description. “ Testa rotundato-ovata, ventricosa; spira brevissima, subscalata; anfractibus transversim regulariter striatis, ad suturam angulatis et tuberculosis, postea concavis, paulum ante medium altera tuberculorum majorum series cinctis, inferne tuberculis minoribus, inseriebus 2-3 dispositis, ornatis; columella paulum rugosa; canali brevissimo; apertura ampla, utrinque canaliculata; labro varicoso.” (Mayer 1864: 72).
Discussion. The specimen illustrated by Bronn (1862: 27, fig. 8) represents either an apical fragment or a juvenile shell. The spire is extremely low, with a very characteristic sculpture of finely beaded cords with a more strongly beaded cord bordering the suture. The dorsal view is not illustrated but suggests that there are two strong elevated cords, one at the shoulder and one just below, by the spines produced on the outer lip. The original generic assignment Ranella Lamarck, 1816 seems unlikely, as Ranella specimens are large, with much taller spire. Both Bronn in Reiss (1862) and Mayer (1864), likened it to R. marginata [now placed in the genus Aspa; see under A. marginata (Gmelin, 1791)]. Unfortunately, we cannot place this species at either genus or family level and no further specimen have been found. The low ornate spire is more suggestive of the conoidean family Borsoniidae Bellardi, 1875 but again is much lower than any known species. The figured fragment is certainly intriguing, and we have reproduced both the original illustrations (Fig. 6 M) and Mayer’s (1864) drawing (Fig. 6 N). We hope further specimens might come to light.
Distribution. Lower Pliocene: Atlantic, Santa Maria Island, Azores (Bronn in Reiss 1862; Mayer 1864).
Species recorded in historical literature excluded from the Santa Maria assemblages
description: Published as part of Sacchetti, Claudia, Landau, Bernard & Ávila, Sérgio P., 2023, The Lower Pliocene marine gastropods of Santa Maria Island, Azores: Taxonomy and palaeobiogeographic implications, pp. 1-150 in Zootaxa 5295 (1) on pages 99-100, DOI: 10.11646/zootaxa.5295.1.1, http://zenodo.org/record/7965273