Thoracic (tx) segments fused, forming one segment
that is wider than the abdomen (ab); Thoracic and
abdominal segments with lateral fanlike tufts of
elongated setae (se) and/or anal setal fan (af) located
on the last abdominal segment

Thoracic segments not fused and distinguishable;
Thorax (tx) and abdomen (ab) equal in diameter or
abdomen wider; No setae on thoracic or abdominal
segments and no anal fan on terminal segment