Muscles of the sex organs of Panagrolaimus detritophagus (Chromodorea: Rhabditida: Panagrolaimidae)

Abstract

Summary The sex organs are important for nematode systematics, but the associated muscles are rarely used as phylogenetic characters. This research aimed to study the musculature of Panagrolaimus detritophagus, using confocal microscopy. The ring-shaped anal sphincter is pierced by a biconical X-structure and connected by two pairs of processes to the subventral stomato-intestinal muscles and dorsal body wall. The female has two pairs of vaginal dilators that are connected to the proximally invaginated vaginal sphincter and subventral body wall. The anal depressor is a pair of dorsoventral muscles. The male has 7-8 pairs of caudal diagonal muscles located beneath the ventral body wall muscles, followed by five pairs of postcloacal oblique muscles. The paired posterior longitudinal muscles are connected to the cloacal opening and tail tip. The paired anterior retractors of the spicule connect the spicule capitula to the lateral body wall; a pair of spicule-gubernacular protractors runs from spicule capitula to the anterior part of gubernaculum, and paired ventral protractors run from spicule capitula to anterior cloacal lip. Two pairs of gubernaculum erectors are attached to the mid-gubernaculum, and the unpaired gubernaculum protractor extends ventrally to attach to the body wall at the posterior cloacal lip. The sex muscle pattern is of the Rhabditidae-Cephalobidae type with a 15-character code for phylogenetic reconstructions: 63313-22234-42243.