Chaetal fields and morphological units
We attempt to access the
chaetotaxy of the head and great abdomen of Collembola, by identifying
body segments arranged in each tagma (Figs. 1-2), or whorl in each
appendage (Figs. 3-5) (Hopkin 1997, Jura et al., 1987, Nayrolles 1988,
1990a, 1990b, 1991, Tomizuka & Machida 2015). Each segment has its own
set of chaetae, and more than one chaetal field may occur in a single
body segment. A chaetal field is a group of associated chaetae that are
consistently observed in a given body segment, often associated with
some landmark on the cuticle (Figs. 6-7).
The morphological units are the actual observed character in a given
species. Once recognized all the chaetal fields, the characters are
listed, and its inherent character states are described. Each
morphological unit in the character list is given a code (0, 1, 2) to
each observed condition. It is important to note that it is not a
phylogenetic matrix, once the codes in the resulting matrix are not
supposed to include hypothesis of ordering or polarity, and both
apomorphies and plesiomorphies may be listed as character, instead, it
is a descriptive coded character state matrix.