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Monday, July 2, 2012

Purple pelagic cyprids

Early summer is a good time of year to look for pelagic gooseneck barnacles, Lepas anatifera, washed up on beaches.  They're often attached to driftwood, seaweed, or plastic debris.

The adult barnacles may look familiar, but it's also worth examining specimens closely for a view of the larvae.  On 1 July 2012, I encountered them attached to a few different species of seaweeds (e.g., Sea Palm, Feather Boa Kelp, Bull Kelp, Chain Bladder Kelp, and Sea Sacs).

Here's a newly settled larva (next photo).  This stage is called a cyprid.  You can see how the larva attached to the substrate (in this case, the stipe of a floating Sea Palm) head-first with its antennules.

The cyprids often settle gregariously (see below).  Some had very obvious "gold bodies", or oil droplets that serve as lipid reserves in this non-feeding stage.

Once attached to the substrate, the cyprid undergoes a dramatic metamorphosis to become a juvenile barnacle.  In the photo below, note that the shed cyprid carapace is still visible at the base (and just above) the newly transformed juvenile.  It has the same shape of the cyprid, but is transparent.

Hoeg et al. videotaped this process and published some helpful photos illustrating the stages of metamorphosis.

Modified from Hoeg et al.  2012.  Metamorphosis in balanomorphan, pedunculated, and
parasitic barnacles: A video-based analysis.  Integrative and Comparative Biology.  doi:10.1093/icb/ics053

Once transformed, the barnacle is now a filter-feeder, sweeping the water for food.  Here's a close-up of the expanded feeding appendages, also known as a cirral net.

P.S.  When researching the development of these barnacles, I came across a paper with an entertaining title.  Being pelagic, but needing to attach to something, Lepas sp. are found on a variety of floating objects:

Barnes, D.K.A. et al.  2004.  Polar pedunculate barnacles piggy-back on pycnogona, penguins, pinniped seals, and plastic.  Marine Ecology Progress Series 284: 305-310.

These researchers in Antarctica found pelagic gooseneck barnacles attached to a sea spider (pycnogonid), Macaroni Penguins, Antarctic Fur Seals, plastic debris, as well as the leg band of a Wandering Albatross!

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