The multinucleated syncitial morphology is the distinguishing characteristic of this type of larval stage. The presence or absence of a sheath, general size and position of nuclei are used to identify the genus to which they belong when found in blood. This image clearly shows the three large lips that surround the mouths of all ascarid species. The lips are specific to ascarids as a group and are usually obvious when viewing a gross specimen with low magnification. This image shows an adult female pinworm demonstrating the large double-bulbed esophagus charateristic of all species with the group.
Females posses a sharply pointed tail from which the common name is derived.
Male pinwoms are smaller than females and do not have a pointed tail.