Acasta vesiculosa, Carriol, René-Pierre, 2008

Carriol, René-Pierre, 2008, New genus and new species of Cirripedia (Chthamalidae, Tetraclitidae, Archaeobalanidae and Balanidae) from the Middle Miocene of the faluns of Touraine (France), Zootaxa 1675, pp. 31-48 : 44-45

Acasta vesiculosa sp. nov.

Fig. 3 (3–6)

Etymology: Morphologic, an allusion to the calcareous vesicles of the sheath.

Occurrence: Ferrière-Larçon and Pauvrelay (Paulmy commune), Indre-et-Loire, France, faluns of Middle Miocene age.

Diagnosis: Shell with carinal and lateral sheath vesicular; carinal sheath adhering to the wall in the middle of its basal edge.

Material: Type material. Holotype: MNHN A24752 carina. Paratypes: MNHN A24753 carino-lateral; MNHN A24754 lateral; MNHN A24755 carino-lateral. Additional material. Fragments of 8 carinae, 11 carino-laterals and 6 laterals.

Measurements: Paratype MNHN A24753 height of the middle of the plate 5.9 mm. Paratype MNHN A24754 height of the middle of this broken plate 3.1 mm.

Description: Shell white; parietes externally with knobs, basis of much longer, hollow, upward curving thorns sloping downward, internally slightly ribbed; radii and alae not very wide, upper edge very oblique; sutural edge of radii smooth; sheath broad, transversally striated, with basal edge free from wall in laterals and carino-laterals, not in carinae where central part of basal edge goes down, adhering to wall; sheath of carinae and laterals composed of irregular, thin-walled calcareous vesicles.

Whole specimen unavailable, general shape and relative proportional width of parietes of carino-laterals unknown; Opercular plates and rostrum unknown.

Affinities: Extinct Acasta may be distinguished from A. vesiculosa sp. nov. in the lack of a vesicular sheath. They also differ as follows: A. sarda is higher with external surface of the parietes with horizontal thorns; A. formae is higher, with upper edge of the radii parallel to the basis; A. undulata , a large species, has compartments rather externally smooth; A. muricata lacks striae on the internal surface of the parietes; A. fischeri has the upper edges of the radii and alae parallel to the basal edge of the plates; A. spongites has edges of the radii slightly crenated, A. cyathus has very wide radii.

In light of the absence of the holotype and an incomplete description, the taxonomic placement of A. hebertiana cannot be confirmed.

Figures

FIGURE 3. 1 – 2, Actinobalanus collinsi Zullo & Perreault, 1989, external and internal side of plates: 1, scutum, MNHN A 24750; 2, tergum, MNHN A 24751. 3 – 7, Acasta vesiculosa sp. nov., external and internal side of plates: 3 a, b, carinolateral, paratype MNHN A 24753; 4, carina with broken sheath showing calcareous vesicles, holotype MNHN A 24752; 5, carino-lateral, paratype MNHN A 24755; 6, lateral, paratype MNHN A 24754. 7, Actinobalanus bisulcatus (Darwin, 1854 a), external side of a scutum, MNHN A 24749. 8, Tesseropora dumortieri (Fischer, 1866), internal side of a scutum MNHN A 24748. 9 – 10, Chthamalus grazianii sp. nov.: 9, magnified part showing protuberances on the external side of a rostro-lateral, paratype MNHN A 25741; 10, lateral showing punctuations on the internal side, paratype MNHN A 25742.