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Thursday, March 22, 2018

At home in the hydrocoral

The Hydrocoral Chronicles continue!

While looking for Polydora on the surface of the hydrocoral Stylantheca papillosa, Eric noticed a small raised blister (~3 mm long) with an opening at one end.  The antennae of a tiny worm were barely visible in the darkened doorway.  [I think the little blister is reminiscent of a pink igloo!  :) ]

We were curious about this worm, and eventually found a reference to a little-known syllid polychaete, Proceraea penetrans, first discovered living on the subtidal hydrocoral Stylaster californicus in southern California (Wright and Woodwick 1977).

In response to the worm, the hydrocoral creates a "blister" that serves as a home for the worm.  Eric was able to coax this worm out of its home for a closer look and it turns out that it was indeed Proceraea penetrans!  Many thanks to Leslie Harris for confirming this identification.

This appears to be the first record of Proceraea penetrans living on the intertidal hydrocoral Stylantheca papillosa, and also the first record of this species north of the Channel Islands. 

Note that Proceraea penetrans is tiny (see photos below).  [Its small size is likely one of the reasons it has been observed so rarely.]  We don't believe any photographs of a live specimen have been published before.  With this post, you get to see photos and a video!

The entire individual was only ~5 mm long:

Here's a magnified view of the anterior end, with 2 pairs of red eyes:

Another fascinating aspect of Proceraea penetrans is its life history.  Some polychaete worms, including this species, produce reproductive individuals called epitokes.  Epitokes are specialized for swimming to the surface of the ocean, often in response to lunar cues, where they release eggs or sperm with other epitokes during mass spawning events. 

To facilitate this journey, epitokes often have enlarged eyes and modified setae (bristles) on their appendages that aid in swimming.  In some species the entire adult worm transforms into an epitoke.  But in other species, including Proceraea penetrans, the adult worm produces epitokes asexually, as genetically-identical buds attached at its posterior end (see photos below).

When the lunar cues are right, the mature epitoke separates from the posterior end and takes a one-way journey to the surface to spawn while the adult worm (formally called an atoke) remains safe and sound on the bottom.  Proceraea penetrans produces just a single epitoke at a time. 

Below, here are two views of the epitoke.  In the first, note the adult worm (the atoke) in the lead, and the epitoke developing at the posterior end of the atoke.  Look for one set of eyes at the head end of the atoke (bottom of photo), and a second set of eyes at the head end of the epitoke (top of photo).

It looks odd to see eyes in what appears to be the mid-section of the worm.  Remember that the portion in front is the benthic adult and the second set of eyes belongs to the reproductive epitoke that will separate and swim to the surface to spawn.

Eric was lucky to capture a short video clip (probably the first ever of this species).  Note that the epitoke is longer than the atoke — watch how long it takes for the epitoke to pass through the view!

Amazingly, some closely-related syllid polychaetes in the same family (Autolytinae) as Proceraea produce a chain of multiple epitokes at one time.  The photo below of Myrianida pachycera from the Indo-Pacific (and introduced to Southern California) is a particularly beautiful species and a striking example of this phenomenon.  Thanks to Leslie Harris for sharing her wonderful photo.


Sue Johnson said...


Anonymous said...

I love an interesting story with a "surprise ending"! --ES