I was excited to find quite a few squid egg capsules washed ashore on Bodega Head this afternoon. Although it's not a good situation for the squid (they need to stay submerged to survive), it was an opportunity to look for tiny developing squid inside the egg capsules.
The photo above shows a late stage squid embryo. Its external yolk sac (the teardrop-shaped structure above the eyes) is relatively small. The embryo also has functioning chromatophores — the red, yellow, and brown spots scattered across the head and mantle. (The mantle is the hood-like structure used in jet propulsion.)
There were squid embryos in various stages, some more developed than others. Compare the next two images and guess which is younger. Hint: the younger embryos have larger yolk sacs.
Answer: The first photograph shows younger embryos.
As I was searching the egg capsules, a newly hatched squid larva (formally called a paralarva at this stage) swam by! It was very small (only a few millimeters long) and very active. I didn't have much time, but here are a couple of shots.
Note the arms (with tiny suckers!) in front of the eyes.
Squid chromatophores expand and contract via muscles stimulated by nerve signals sent from the brain. Seeing the chromatophores pulsing reminded me of a video circulated this past summer.
The clip shows squid chromatophores responding to music being played on an iPod (the iPod was connected to squid skin with an electrode). Its pretty amazing — check out "Insane in the Chromatophores"!
Along with the egg capsules, there were also several squid pens on the beach (although slightly damaged, see a scan of one below). Squid pens are basically internal shells (squids are molluscs like snails and clams). They're long and slender, often transparent, flexible (made of chitin), and sometimes described as feather-shaped. The pen supports the squid's mantle and serves as a muscle attachment site.
If you're interested in looking for squid eggs, try searching the wrack line at Doran Beach or Dillon Beach.
P.S. I'm not 100% certain of the species of squid illustrated here, but it might be a Market Squid (Doryteuthis (formerly Loligo) opalescens).