The Crustacean Metamorphosis

Crustacean; an anthropod class, from Latin ‘crusta’, literally meaning “crust, rind, bark, hard shell”. But what makes a crustacean a crustacean? A crustacean has the following features: a segmented body with a hard exterior (known as an exoskeleton), jointed limbs, each often with two branches (termed biramous) and two pairs of antennae―crabs and shrimps and prawns for example! Ever seen a developing one in a tank or aquarium? The unlikeliness of their metamorphosis  surely deserves a whole article.

Of course, everything varies from species to species. Nonetheless, we are going to focus on the three examples above, because if we are to enumerate all of them, we’ll be up until their next molting.

How do you get in touch with a crab? I don’t know, man. Call it on its shell-phone? Kidding. Oh crab! That was a lame joke wasn’t it? Blame it on those super hard shells that make it difficult to enjoy, especially a seafood mukbang. Did you know that the thick shells covering their bodies do not grow in size? So the animal has to keep shedding its shell several times as it grows! As with other arthropods (such as insects), growth in crustaceans, given the hardened exoskeleton, must proceed through series of molts (ecdysis), where the old exoskeleton is shed and a new cuticle is secreted.  

In what looks like a dance, females brace themselves at the waters edge, and release their eggs. How many eggs can a female crab produce? A female crab can produce up to 100,000 eggs. Crabs brood their eggs for about two weeks and will hatch once the spongy egg mass darkens from yellow into a chocolate brown color. In their first stage, crabs hatch into zoea larvae. They spend about 40 days in this microscopic state and feed off of phytoplankton, a microscopic plant. 

In some crustaceans, such as crayfish, growth from juvenile to adult involves no dramatic changes, but rather a gradual shift of proportions. However, many crustaceans have changes of form at several molts, which are termed metamorphosis. As some crustaceans undergo metamorphosis, they gain more legs with each ecdysis. 

Meanwhile, shrimp’s Life Cycle starts from: a) egg, b) Nauplius, c) Protozoea, d) Mysis, e) Postlarva, f) Juvenile, g) Sub-adults, h) adults. It usually takes about 7 to 8 months from the time the shrimp hatch to the time they are harvested and you can EAT them! 

4There are five naupliar stages. The first stage is about the size of the egg and succeeding stages are slightly larger. Nauplii have limited swimming ability and usually are a part of the oceanic plankton. The three protozoeal stages are planktonic forms found in oceanic waters. Protozoea have undergone development of their mouth parts and the abdomen has begun to develop. Mysids have early development of legs and antennae. The walking and swimming legs have developed and the postlarvae appear as miniature shrimp. The second postlarval stage rides the flood tides into the estuaries, apparently becoming active during flood tide and settling to the bottom during ebb tides. Postlarval shrimp develop directly into juvenile shrimp similar to adults except they are characterized by a much longer rostrum (horn). Sub-adults move into the deeper waters of the estuaries and may remain there for a month or more before moving seaward. Adults may be 5 to 8 inches in length. Adults are usually found in the ocean, but in dry years may delay migration until cold weather occurs. Spawning females are characterized by brightly colored ovaries that can be seen under the shell on the upper side of the body.