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Friday, November 7, 2014

Curved needles

On 5 November, Emily e-mailed that she had found more pteropods, or sea butterflies — and this time it looked like a different species (i.e., not Hyalocylis striata, the pteropod she identified in September).

These animals were from a plankton tow about 24 km (15 miles) off Bodega Head.

Emily noticed that the shell was smooth and the wings had a different shape and were of different proportions.

When we looked under high magnification, we could see those characteristics.  We also noticed that the wings had two very intriguing features something that looked like small "hooks" about halfway along the inside edge of each wing and two oval rough patches in the middle of each wing just below those "hooks."

After consulting a few sources, we believe this is Creseis virgula.  We've seen one common name for it — Curved Needle Pteropod. 

I was excited to find an older drawing of this species which matched perfectly with what we were seeing:

Modified from Tesch, J.J.  1946.  The Thecosomatous Pteropods. I. The Atlantic.  Dana-Reports, 28, pp. 1-82.

We learned that the "hooks" are wing protrusions and the "rough patches" are ciliated fields.  This pteropod feeds by capturing suspended food particles in a large mucous net.  The ciliated fields aid in hauling in the mucous net.

Creseis virgula is a warm-water species.  Although the CalCOFI Atlas for pelagic molluscs (McGowan 1967) shows one record for 37°N, most are from south of Point Conception (approximately 34°N).

Because it was important to document the occurrence of this pteropod in northern California, Eric captured some wonderful video footage and compiled the best clips.  

There are many things to watch for in this video:

- the way Creseis frequently holds its wings far forward
- at about 20 seconds, a food particle moves between the wings towards the mouth
- when a side view is shown, note the slight curvature of the shell
- there's a close-up of the rhythmic mouth movements
- throughout the video, the heart is visible beating about 1/3 of the way up from the tip of the shell
- and one of the last segments is a bonus — it's a veliger, or the larval stage, of this pteropod.  The veliger doesn't have its wings yet, but instead has a velum, a lobed ciliated swimming organ around the opening of its tiny shell.

P.S.  Nearshore ocean temperatures are still quite warm, especially for this time of year 14-15°C (57-59°F).

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