Calyptraea aurita (Reeve, 1859)

Holtheuer, Jorge, Aldea, Cristian, Schories, Dirk & Gallardo, Carlos S., 2018, The natural history of Calyptraeaaurita (Reeve, 1859) from Southern Chile (Gastropoda, Calyptraeidae), ZooKeys 798, pp. 1-22 : 1

Calyptraea aurita (Reeve, 1859)

Calyptraea striata (non Say, 1826): Broderip 1834: 38; Broderip 1835: 202, pl. 28, fig. 6.

Crucibulum auritum Reeve, 1859: sp. 17, pl. 6, fig. 17a, b; Tryon 1886: 118 (in part), pl. 32, figs 32, 33.

Type material.

[ Crucibulum auritum ] is housed at NHMUK 197798.

Material examined.

MNHNCL 7570 (female), MNHNCL 7571-7574 and MZUA–UACH 501-505, all specimens from Caleta Yerbas Buenas, 41°40'20"S, 72°39'24"W. All coll. Jorge Holtheuer and Dirk Schories.

Description.

Shell (Figures 3 a–h, 4 b–d, 5 a–h): Limpet–like, circular, conic, with spiral septum in center and right of ventral surface. The shell externally is usually opaque white and internally dark brown porcelaneous. The apex is small, sub–central; protoconch apparently smooth, with a total diameter difficult to measure because the protoconch–teleoconch boundary is not evident, but may have ~500 μm (Figure 6a). Sculpture has ~ 70 to 80 fine radial ribs, of uniform size, aligned concentrically. Inner surface without visible muscle scars. Septum incompletely conical (opened anteriorly), situated obliquely, from shell apex to posterior. Shell size ranged according to the sexual phases, being from 6.6 to 12.4 mm for immature individuals, from 10.6 to 24.9 mm for males, 15.1 to 25.9 mm for intersex individuals and from 21.0 to 39.6 mm for females (Table 2). Septum (Figures 3d, f, 4c, 5b, d, f, h) white brilliant color, beginning in a spiral conic curve and ending in a wide platform curved to the left side of the specimen (seen from below). Fine growth lines are visible on the septum.

Radula (Figure 6b, c, d): Radula with ca. 30 rows. Rachidian tooth broad, approx. 15 cusps, central cusp more elongated than secondary cusps (Figure 6b, d); lateral teeth curved inwards, with approx. 16 sharp cusps, two cusp on inside and ca. 13 gradually decreasing towards lateral on outside of main cusp (Figure 6c, d); marginal teeth long, tall, slender, with approx. seven sharp, sub–terminal cusps in inner edge (Figure 6b, d); outer marginal weakly narrower than inner marginal teeth.

Head–foot (Figures 4a, 7a, b): Head and neck regions somewhat similar to the other Calyptraea species, including neck ventral surface and flaps, penis present in all specimens behind right tentacle, but it is reduced or missing in females. Snout–proboscis very well developed, cephalic tentacles simple, eyes dark and small, located on the tentacle basis at lateral outward position. Foot similar to that of other Calyptraea species, with planar, dorso–ventrally flattened sole compressed by shell septum. Mantle, as in Calyptraea , attached to dorsal surface of foot sole and extending beyond its posterior and lateral borders.

Mantle (Figures 4a, 7a, b): Mantle border very broad, including region surrounding foot, occupying 90% of pallial cavity. Pallial cavity conical and curved, begins just inside shell septum. Pallial aperture proportionally small, if animal compared with a clock, this aperture begins at 10 and finishes at 6 o’clock.

Gill: typical to those of Calyptraea , occupying most of inner pallial space, inserts all along left and anterior pallial margins. Gill filaments also similar to those of Calyptraea , with very long (Figure 7b), rigid rod, mainly of the apical region. Gill posterior end just in posterior end of cavity; gill anterior end in central region of pallial aperture.

Male (Figure 7c): Only small specimens (up to 10.58 mm) are functional males, all mobile. Penis is very long (approx. three times head length), originating dorsally and extending to right tentacle. Papilla on penis tip, very long, approx. 1/3 of penis length. The penis sperm groove runs along middle region of the ventral surface of penis. The male of Calyptrea aurita is always attached onto a female, and is never found directly attached on primary substrate.

Female (Figures 4 a–d, 7 a–c): Very similar to other Calyptraea species, the female is sessile. Only specimens larger than 20.98 mm were present in our material. During field work the presence of egg capsules in the pallial cavity of the females could be seen. The females always settle on the rock surface where they attach and protect their egg capsules up to larvae release (Figure 8).

Reproduction and development.

Calyptraea aurita (Reeve, 1859) is a protandric hermaphrodite producing a maximum of 16 egg capsules per female which contain an average of 119 eggs each (Figure 8). Up to three individuals were observed stacked together, always with a female at the base and up to a maximum of two male individuals on her shell. Brooding was observed during the months March (38 of 100 females studied below water), April (38 of 100), August (44 of 55), September (150 of 199), October (36 of 50) and December (10 of 19). In May 2009 none of 100 observed females were brooding. Weather conditions did not allow for the verification of brooding during the other months.

The females of Calyptraea aurita deposit their eggs in thin–walled brooded capsules directly attached to hard substrates. These capsules have a triangular, flattened morphology and are fixed with a fine stem to the substrate. The eggs are concentrated at the distal end of the sac embedded in an uncoloured liquid. All eggs are able to develop into planktonic veliger stages which are liberated into the water column. The veliger has a bilobed ciliated and pigmented velum and two small black–coloured eyes between the velar lobes, a circular mouth, and a transparent protoconch. The mean initial egg size is ca. 150 μm and the size of the veliger, when liberated into the water column is ca. 300 μm. The intracapsular development up to the larval release took ca. 42 days in the laboratory.

Size: A total of 180 individuals were collected in October 2010 in 30 m depth. Shell length, height, and width were measured. Shell length distribution was two peaked, the first peak corresponded to males and intersex individuals and the second peak to females (Figure 9). Mean shell length was 23.9 ± 8.3 mm, mean width 23.6 ± 8.5 mm and mean height 9.1 ± 2.7 mm. Shell width to length relation was close to 1 (0.99 ± 0.10) and shell height to length relation was 0.39 ± 0.05.

Symbionts.

Four samples with 38 to 77 females were taken in October 2010 and were checked underwater for the presence of the pinnotherid decapod Calyptraeotheres politus (Smith, 1870). A total of 4.5 ± 1.3 % of females were infested by C. politus . None of the infested females deposited eggs.

Distribution and habitat.

Calyptraea aurita occurs at Valparaíso at depth of 82-110 m ( Broderip 1834). In this study it was found exclusively on hard substrates in the Reloncaví Sound between 26 to 48 m depth showing a patchy distribution. The species was present in three of four study sites using vertical transects down to 30 m depth. 37.6 ± 14.4 % of the rocks were covered by C. aurita at the location Caleta Yerbas Buenas at 30 m depth. This represented a density of 743 ± 307 ind. m-2. The highest observed density was 1475 ind m-2 covering 50 % of the primary substrate. Coverage at the locations Caleta Gutiérrez and the Reloncaví Estuary were low with 1.8 ± 2.7 and 0.8 ± 1.8 % at the same depth. In none of the locations C. aurita was present along transects in shallower depths (5 to 25 m).

Transplantation experiment.

The experiment was realized for a total time span of 326 days. Several individuals got lost during transport from the experimental depth to the shore, died during course of time, or did not reattach once unintentionally detached from the acrylic plate. Nevertheless all remaining individuals grew several mm in both depths (Figure 10). Additionally some individuals deposited egg capsules, which were visible from the reverse of the acrylic plate. A t–test did not show differences between the growth rates in 10 and 20 m depth after 165 days, t(32) = t– 1.555, p = 0.13. Mean growth rate in 10 m depth was 1.11 mm (n = 20) and 1.68 mm (n = 14) in 20 m depth, respectively.