Research Study 1

Fig. 1. The penis of Balanus glandula can extend up to 8 body diameters

Courtesy Chris Neufeld & Rich Palmer, University of Alberta, Edmonton

Fig. 2. Life cycle of a barnacle.  The bivalved cyprid larva is the settlement stage

Barnacles are hermaphroditic and one individual usually cross-fertilises with another individual. The penis in a barnacle is extensible, highly maneuvreable, and can extend several body diameters (Fig. 1).  If one individual is out of penis-reach of another then it may be reproductively sterile, as self-fertilisation is found in only a few species¹. The life cycle of a barnacle involves three phases (Fig. 2): 1) a pelagic, suspension-feeding nauplius² larva, 2) a pelagic, non-feeding cypris larva, which is the settlement³ stage, and 3) a bottom-dwelling, suspension-feeding adult.

NOTE¹ if separated by more than about 5cm, both the small species Chthamalus dalli and C. fissus are apparently capable of self-fertilisation

NOTE² (lit. “a kind of mollusc” G.). The name reflects an early belief that barnacles are related to snails and bivalves, presumably based on the nature of their calcareous shell-plates. This idea persisted until the mid-1800s, when scientists recognised distinctive arthropodan features in the barnacle larvae

NOTE³ the term settlement describes the behaviour of a larva of a marine invertebrate dropping out of the plankton, selecting a place to live, and adopting a juvenile way of life usually after passing through metamorphosis. Recruitment refers to the addition of this individual to the population

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