A common nematode presents 2 body openings (excretory pore and anus/cloaca) for males and juveniles and 3 (excretory pore, vulva and anus) for females.
All the openings are in the ventral region helping in the determination of left and right sides of the body. This information is very important for the correct positioning of diverse structures (i.e. teeth).
On the slides, when correctly mounted, the animals are layed down on one of laterals (left or right) permitting the visualization of the body openings.
The body openings determine the body regions:
Pharyngeal region: from the mounth to the excretory pore
Median region: between the excretory pore and the anus (or cloaca)
Tail region: from anus (or cloaca) to the tail end.
The tail format is important to distinguish some genera and its length is one of the measures used to diferenciate and describe species!!!
In this figure can be seen the openings and the regions of a common nematode body:
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