Saturday 28 June 2014

Gastropod predation on Barnacles in the Late Pleistocene of southern South America.

Muricid Gastropods (Murexes) are carnivorous Snails which are capable of drilling through shells in order to feed on the animals within. The boreholes they produce are distinctive, and are well documented in the fossil record, particularly on Bivalves, which are generally their favoured prey. In some ecosystems in Australia and New Zealand Muricids are known to feed largely on Acorn Barnacles (Balanomorpha), and Barnacle shells with Muricid drill-holes are frequently observed. Such predation is less commonly observed elsewhere, although since many Muricid Gastropods are capable of forcing open Barnacles without drilling into them, Muricid predation on Barnacles may be a lot more common than is recognised.

In a paper published in the journal Alcheringa on 30 May 2013, Sandra Gordillo of the Centro de Investigaciones en Ciencias de la Tierra at the Consejo Nacional de Investigaciones Científicas y Técnicas and the Centro de Investigaciones Paleobiológicas at the Facultad de Ciencias Exactas, Físicas y Naturales at the Universidad Nacional de Córdoba, describes a series of preserved Acorn Barnacles from the Beagle Channel, which separates Isla Grande de Tierra del Fuego from the more southerly Hoste and Navarino Islands, at the southern tip of South America, dated to the last interglacial in the Late Pleistocene.

The Barnacles are referred to the species Balanus laevis, which is still extant in the region. Each has been drilled through the apical part or middle sector of the parietal plate, suggesting a consistent, non-random pattern of predation, rather than occasional, opportunistic attacks.

Pleistocene specimens of Balanus laevis with predatory drillholes. (A) Specimen with a single hole in external lateral view; (B) Specimen with a single hole in external lateral view; (C) Detail of (B) showing drillhole; (D) Specimen with two holes in external apical view; (E) Detail of (D) showing two drillholes; (F) A cluster of acorn barnacles in external view, including specimen with two holes; (G) detail of (F) showing specimen with two holes in apical view; (H) detail of (G) showing one drillhole. Gordillo (2013).

There are six Muricid Gastropods present in the deposits that yielded the drilled Barnacles, Fuegotrophon pallidus, Trophon geversianus, Trophon plicatus, Xymenopsis muriciformis, Xymenopsis buccineus and Lepsiella ukika; two of which, Trophon geversianus and Xymenopsis muriciformis are still present, as is another species, Acanthina monodon, which was not present in the Pleistocene.

Species of the genus Lepsiella are frequent predators of Barnacles in Australia, and are known to be highly flexible predators that switch quickly to new prey species when introduced elsewhere. However the species Lepsiella ukika is extinct, and the genus Lepsiella is no longer found in South America, making its diet hard to assess. Furthermore, examination of modern Barnacles in the Beagle Channel produced several modern specimens, showing similar drill holes, suggesting that if Lepsiella ukika was responsible for the Pleistocene drillings, then either that it was not the sole driller or another species has subsequently taken up the habit in the same location.

(A–C) Schematic maps showing the location of the sampling site in southern South America. (A, B) The Beagle Channel connects the Atlantic and the Pacific oceans; (C) The Pleistocene fossiliferous ite is located on the northern coast of Navarino Island. (D) Stratigraphic section showing the position of the marine layer with calcareous fossil shells. Gordillo (2013).

See also…

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 The Snail that eats Crabs.

Nactid Gastropods (Moonsnails) are predatory snails with a long fossil record. They typically predate smaller Gastropods and Bivalves, drilling through their prey's shells, then injecting digestive juices and sucking out the dissolved soft tissues if their victims. This leaves a distinctive boring, which is often used by palaeontologists...

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