Shellfish
General & History
Echinoderms first appeared in the early Cambrian period over 500 million years ago. They have neither an internal nor an external skeleton but are stiffened by hard calcified plates and spines just under the skin. While this may seem like an exoskeleton it allows the organism to grow without molting it's shell.
These creatures have no muscles to speak of but are hydraulically operated through a system of plumbing called the "water vascular system". Without muscle tissue there isn't a lot to eat in most echinoderms. The exception is the sea cucumber which has a tube like body made of gelatinous material that is a popular food item in the Orient.
Buying, Cleaning & Cooking
Unless you are in a sushi bar you are unlikely to buy edible echinoderms except sea cucumbers. These are available in markets serving Oriental communities. You will find them dried, generally in boxes of pieces, and frozen in bags and trays.
There is very little to do in preparing these. Dried ones you need to soak for an hour or so. Frozen need to be thawed, checked for any gooey stuff that should be washed out, and cut to the size you wish.
If you are in a sushi bar you can order "uni" (sea urchin reproductive organs) but there's still little to do - these are prepared "ready to serve" and put up in little wooden or plastic trays in seafood factories in California, New England (where they are NOT eaten, thank you), Chile, Japan and other places.
Varieties
Sea Cucumber -
[bˆche-de-mer, order Holothuroidea]
Sea cucumbers are known from the Silurian 400 million years ago, but may be
even more ancient. Today they live in every marine environment from tidal to
the deepest trenches, but not in fresh water or on land. They should not be
called "sea slugs" because they are not mollusks.
Most sea cucumbers are less than 12 inches long, but there is one that can grow to more than 7 feet. They are of pharmaceutical interest (interesting toxins, mostly) and are a popular food item in the Orient. They are exported to China from all over the Indo-Pacific region and have been badly overfished in some areas, particularly Pacific islands.
The photo specimens were recruited from markets in San Gabriel serving
a mostly Vietnamese community. The big ones were labeled "U.S.A wild grown"
but no provenance was given for the others. The largest was 9 inches and
weighed 8.6 ounces. The black ones are firmest and have the most flavor.
Prep & Cooking Details.
Sea Urchins -
[class Echinoidea many orders, genera and species]
Sea urchins are a favorite food of sea otters and California spiny lobsters.
Their reproductive organs are eaten by people, sometimes lightly cooked but
most often raw, mostly in Japan, Korea, Chile and California sushi bars.
Sea urchins are highly destructive to our economically important kelp beds
so it would be better if more people ate them. Perhaps they would be more
popular if it were widely known that sea urchin reproductive organs contain
cannabinoids. In Japan these organs are called "Uni" and in Chile they are
called "erizo". Go to your local sushi bar and order Uni, the lobsters and
sea otters can't handle them all without your help (yes, I like uni and
order it often).
Prep & Cooking Details.
Starfish -
[Sea Star, class Asteroidea eight orders and numerous species]
The only culinary importance of starfish is the number of clams they eat
which impacts the price and availability of clams. Starfish are hydraulically
operated rather than muscle operated so they can apply force indefinitely
without tiring. They use this feature to pull open the shells of bivalves,
then exude their stomach into the shell and digest the occupant in place.
There is nothing to eat here.
Health & Nutrition
You are unlikely to depend on echinoderms for a significant part of your nutrition so it's sufficient to say they are safe to eat in any normal amount so long as they lived in unpolluted seawater. They are way too far down the food chain to contain significant amounts of mercury.
Some Sea Cucumbers contain interesting toxins but those sold in general commerce are safe to eat.
Sea Urchin reproductive organs (uni) contain cannabinoids and are traditionally considered aphrodisiac, but neither in harmful amounts.