Root-knot nematode perineal pattern development: a reconsideration.

The perineal pattern, a unique and complex structure located at the female posterior body region, comprises the vulva-anus area, tail terminus, phasmids, lateral lines and surrounding cuticular striae. Little is known about the development of this important but variable character complex. Published information together with scanning electron and light microscopical observations on female development and perineal patterns were used to explain in detail the perineal pattern. The basic pattern, with fine striae, is formed just after the last moult when the vulva is induced above the anus at the posterior ventral body side. This process is likely to be influenced by the previous feeding stage. The vulva-anus region moves posteriorly, while the female is still enclosed by the old cuticle layers. After resuming feeding, the female diameter increases rapidly and pattern striae become folded and coarser. The role of the expanding rectal glands and perineal pattern structures as lateral lines, anus, tail terminus and punctations are discussed in detail. Major origins for pattern variation are developmental and aging factors in both feeding stages, a vulva-anus shift and the observation of patterns of different age, in combination with variable interpretation and description. [ABSTRACT FROM AUTHOR]