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Saturday, May 12, 2012

Seeing stars

Four different species of seastars observed during the past two days in Oregon.  All four are also found on Bodega Head.

Six-armed Seastar (Leptasterias sp.)

The Six-armed Seastar pictured above was a large specimen, ~6 cm across.  (It's more common to see Six-armed Seastars ~2-3 cm across.) Photo taken at Cape Arago, OR, on 11 May 2012.

Bat Star (Patiria miniata)

Bat Stars are rare in Oregon and Washington.  We found a few individuals at Cape Arago, OR, on 11 May 2012.  All were a handsome slate blue color; two with narrow orange borders along the arms; the third with some white mottling.  

Below, note the intricate braided pattern created by the crescent-shaped ossicles (calcareous plates) on the upper surface.

Sunflower Star (Pycnopodia helianthoides)

Sunflower Stars are among the world's largest (and fastest) seastars.  They can reach a diameter of 3 feet across.  The individual above was ~2 feet across.

The arms of Sunflower Stars are softer and less rigid than other seastars.  Here's a close-up of several arms and a portion of the central disc.

The white and brown finger-like projections are papulae, sites used for gas exchange.  The purple clusters with white tips are pedicellariae, pincers used for defense.  They often surround white calcareous spines.  

If you look closely (see below), you can also see larger isolated pedicellariae on stalks emerging among the papulae.

These stalked pedicellariae were large enough (at least 1 mm long) that you could see their pincer-like structure (see below).

The lavender-colored hearts are the gaps in between the two halves of the pincer (imagine them opening and closing like scissors).

Ochre Seastar (Pisaster ochraceus)

Like many seastars, Ochre Seastars are broadcast spawners, with spawning occurring primarily in May in Oregon.  Most echinoderms have separate sexes.  The individuals pictured here (above and below) are males in the process of releasing sperm.

We couldn't find any females releasing eggs today, but the eggs would be orange rather than the white of the sperm.  After the eggs are fertilized, the planktonic larvae swim in the open ocean for ~6-8 weeks or longer before undergoing metamorphosis into a benthic (bottom-dwelling) juvenile seastars.

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