Lobsters, crabs, crayfish, prawns … seafood lovers everywhere relish the mention of such culinary delights. But there’s much more to know about these shellfish than simply how tastily they can be served up on a plate.
They are the largest members of the subphylum known as Crustacea, which has nearly 30,000 species distributed worldwide. Crustaceans range in size from the American lobster, weighing up to 20 kg (44 lb), and the Japanese spider crab—with a leg span of up to 3.7 m (12 ft)—to water fleas that can be less than a millimetre in length.1
Most crustaceans live in either fresh or sea water, although some do live on land, such as Christmas Island Red Crabs (see box below).
These species, however, return to the water when their eggs are ready to hatch. There are few aquatic environments that are not home to some form of crustacean, whether it be in open sea or lakes, sediment at the bottom of the sea, rocks at the water’s edge, or in sand, seaweed or mud. Crustaceans live in oceanic trenches at depths of up to 10,000 m, in mountain lakes at altitudes of 5,000 m, and on sunny tropical beaches.
Scientists find it hard to characterize the ‘standard’ crustacean body because there is such a variety of forms. The most easily recognisable are the decapods—those large crustaceans with 10 legs. They have a number of body segments (known as somites), which are sometimes fused to form rigid areas, or are free but linked to each other by flexible areas. Most crustaceans have some sort of shell (called a carapace), which is periodically moulted because the hard structure prohibits growth.
A number of crustaceans are considered by evolutionists to be ‘living fossils’ because they don’t appear to have changed much over supposedly millions of years. In fact, evolutionists really have no idea how crustaceans evolved, or how so many varied species are related to each other within an evolutionary framework.
There is debate as to what a hypothetical ancestor could have looked like, and disagreement about how crustaceans should be classified.
Evolutionists compare the anatomy among living species and study the fossil record, but neither approach offers any evidence as to how crustaceans evolved. They are still asking themselves if the crustaceans’ shell is a ‘primitive’ structure (because the so-called ‘living fossils’ all have it), or if the structure evolved independently.
The New Encyclopaedia Britannica admits the earliest fossils were already specialized and that: ‘The fossil record, although fairly rich, has not solved any of the questions about the early evolution of the Crustacea.’2
There is no mystery for creationists. Having a common Designer explains the similarities between the creatures, and the fossil record is clearly consistent with the fact that crustaceans have always been crustaceans, and have not evolved from non-crustaceans.
When the wet season starts on Christmas Island (300 km south of Java, and 1,300 km from Singapore), about 120 million red crabs (Gecarcoidea natalis, not pictured) swarm down from the rainforest to the sea to mate. Until the mating season, they live in the forest eating fallen leaves, berries and carrion. Males migrate first, taking 5–7 days to reach the shore, where they burrow into the sand to await the females, who swarm down two weeks later (three nights before the new moon). During this amazing migration, countless millions of crabs must cross the island’s roads; around 700,000 to a million are unavoidably killed by traffic each year (often causing punctures in the process).
Cliffs and beaches are soon covered with red crabs releasing their egg packages. The larvae then live in the deep ocean for a month before they all return—incredibly, at the same time—and make a dash for the rainforest.
Source: Choo, N.B., Christmas Island red crab migration, scubayogi.de; A ‘Christmas’ In June on an island with unique wildlife, post1.com, 22 January 2001.
- Unless otherwise stated, all information in main article is from New Encyclopaedia Britannica 16:840–845, 1992. Return to text.
- Ref. 1, p. 845. Return to text.