Worm Breeder's Gazette 7(2): 7

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Larva or Juvenile?

A.F. Bird

In recent years there has been some pressure put on authors by one 
or two editors of journals to use the term 'juvenile' when describing 
the developmental stages of nematodes rather than the term 'larva'.
The argument, I believe, goes something like this - In the Insecta 
the term larva is used to describe a particular stage totally unlike 
the adult in form which usually develops into an inert pupal stage 
which in turn metamorphoses into the adult, i.e.  caterpillar pupa 
butterfly, etc.  In exopterygote insects, in which the young stage 
hatches from the egg into a minute sexless and wingless replica of the 
adult, developmental stages are known as nymphs (not an appropriate 
term for nematodes as it refers to forms with wing buds).  Those 
persons who insist that the term 'larvae' should not be applied to 
nematodes point out that these forms do not undergo a complex 
metamorphosis but usually develop stepwise through a series of moults 
into somewhat similar but larger shapes, and thus a term such as 
juvenile is more appropriate.
I cannot find the term 'juvenile' in two biological dictionaries 
that I have consulted (Abercombie et al., 1973, Martin, 1976) Caveness 
(1964) in his 'Glossary of Nematological terms' defines juvenile as 'a 
fourth stage nematode which does not yet have functional gonads' or 
'any immature nematode.' However, juvenile is an old word coming from 
the Latin word juvenis meaning a young person or in the Latin sense 
one in the prime of life (20th to 40th year - Cassell's Latin 
dictionary).  One might say that scientists using the term 'juvenile' 
for nematodes could be accused of anthropomorphism, as all the 
definitions of juvenile or juvenility in the Shorter Oxford Dictionary 
(SOD) relate to persons.  Furthermore, there is no indication that the 
term should imply no sexual capacity.
The term 'larva' on the other hand is found in dictionaries of 
biology where it is defined as 'the immature form in which many 
animals exist after hatching from the egg and before undergoing 
metamorphosis to the adult form'.  The word comes from the Latin larva 
meaning a ghost.  The SOD defines it not only as 'an insect in the 
grub stage' but also as 'the immature form of other animals 
characterized by metamorphosis'.
Metamorphosis is derived from a Greek word meaning 'to transform'.  
The SOD defines it in its physiological state as a 'change of form in 
animals and plants, or their parts, during life' so that whilst the 
term tends to be used in the Insecta it is not precluded from other 
forms of life such as the ammocoete larva of the lamprey or the 
various larval stages of nematodes for instance.  I see no reason to 
forbid the use of the word 'juvenile' as used in nematology just as I 
see no reason for forbidding the use of the term 'larva.'  These terms 
are now synonymous in nematology and whereas some may feel that 
juvenile is the more correct term others may feel, equally strongly, 
that the term 'larva' is more appropriate.