Short answers, pulled from the story.
Crustaceans are mandibulate arthropods traditionally placed in the paraphyletic subphylum Crustacea. The group is mainly aquatic and includes decapods such as shrimps, prawns, crabs, lobsters, and crayfish, along with krill, barnacles, copepods, isopods, amphipods, and mantis shrimp.
About 67,000 crustacean species have been described, though this is thought to be a fraction of the total because most species remain undiscovered. They range from Stygotantulus stocki at 0.1 millimetres to the Japanese spider crab, with a leg span of up to 3.8 metres and a mass of 20 kilograms.
Yes, it is now well accepted that hexapods, meaning insects and entognathans, are cladistically crustaceans. The two groups are combined in the monophyletic clade Pancrustacea, and DNA studies suggest Crustacea is paraphyletic with hexapods nested inside it.
The nauplius is the earliest and most characteristic crustacean larval form, and it unites the whole group. It has three pairs of appendages, all emerging from the young animal's head, and a single naupliar eye, and it is often followed by stages such as the zoea, mysis, or megalopa.
More than 7.9 million tons of crustaceans are harvested each year for human food, and nearly 10,700,000 tons were harvested in 2007. Shrimp and prawns account for over 60 percent by weight, nearly 80 percent is produced in Asia, and China alone produces nearly half the world's total.
The scientific study of crustaceans is known as carcinology, also called malacostracology, crustaceology, or crustalogy. A scientist who works in this field is a carcinologist.
Crustaceans are distinguished from insects, myriapods, and chelicerates by their biramous, or two-parted, limbs and by larval forms such as the nauplius stage of branchiopods and copepods. Like other arthropods they have an exoskeleton, which they must moult in order to grow.