ecdysone A juvenile steroid hormone that affects
arthropods and that belongs to the larger class of ecdy-
steroids, sterol derivatives that as a whole affect a variety
of conditions relating to molting and metamorphosis,
including eliciting molting, regulating growth of motor
neurons, controlling choriogenesis, stimulating growth
and development of imaginal discs, initiating break-
down of larval structures during metamorphosis, and
eliciting the deposition of cuticle by the epidermis. In
insects, ecdysone primarily elicits and stimulates molt-
ing. It acts on specific genes, stimulating the synthesis of
proteins involved in these bodily changes, and is pro-
duced by prothoracic glands in insects and Y-organs (a
gland near the external adductor muscles) in crus-
taceans. Ecdysone—formerly called alpha ecdysone, and
beta ecdysone, or ecdysterone (now called 20-hydroxy-
ecdysone [20-HE])—is believed to be the active form.
Ecdysone is not the active molting hormone. Various
tissues, including the fat body, convert ecdysone to 20-
hydroxyecdysone, the active form of molting hormone.

echinoderm Diversified marine animals (phylum
Echinodermata) that include the classes Crinoidea (sea
lilies), Asteroidea (starfish), Ophiuroidea (brittle stars
or snake stars), Echinoidea (sea urchins and sand dol-
lars), and Holothuroidea (sea cucumbers).

echolocation Aform of sensory perception used by
animals like bats to orient themselves in flight, detect

objects, seek food, and communicate. Bats, for exam-

ple, send out a series of short, high-pitched sounds,

called echoes, that travel, hit an object, and bounce

back, giving the bat the ability to judge distance, size,

shape, and motion.

eclosion The emergence of an adult insect from the

pupa case or, less commonly, the hatching of an egg.

EC nomenclature for enzymes Aclassification of

ENZYMEs according to the Enzyme Commission of the

International Union of Biochemistry and Molecular

Biology. Enzymes are allocated four numbers, the first

of which defines the type of reaction catalyzed; the next

two define the SUBSTRATES; and the fourth is a catalog

number. Categories of enzymes are EC 1, OXIDOREDUC-

TASEs; EC 2, TRANSFERASEs; EC 3, HYDROLASEs; EC 4,

LYASEs; EC 5, ISOMERASEs; EC 6, LIGASEs (synthetases).

ecological efficiency Each transfer of energy from

one trophic level to another has an ecological efficien-

cy associated with it. Ecological efficiency refers to

the transfer of energy up trophic levels; it is the ratio

of secondary productivity to primary productivity

consumed.

Ecological efficiency goes down as you move up the

trophic levels. Ecological efficiencies generally range

from 5 to 20 percent, meaning that this percentage of

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