The pharyngeal and genitalia-associated muscles of Rhabditolaimus ulmi (Nematoda: Chromodorea: Rhabditida: Diplogastridae)

Abstract

The copulatory organs and pharynx are important for nematode classification. This research aimed to study the musculature of the wood-inhabiting nematode, Rhabditolaimus ulmi, using confocal microscopy. The lip region is hexagonal with enlarged lateral lips; the pharynx is diplogastrid type with two bulbs. The corpus comprises the fused stegostoma, procorpus and metacorpus, with six glands opening in the stegostoma and the corpus limen. The stegostoma has a large dorsal bulge and the posterior bulb is devoid of valve, with two circles of dilators and a basal sphincter. The female genital muscles have a four-radial symmetry around the vaginal opening to the uterus. Two vaginal constrictors and four pairs of dilators of two types are connected to the vagina-uterus opening; four dilators run perpendicular to the uterus axis and are connected to the uterine muscular corset. The sphincter between the intestine and cloaca consists of the middle ring with two pairs of processes connected ventrally with intestinal fasciculi and dorsally with the body wall. The ring contains the inner biconical X-structure. In the male, the gubernaculum has the dorsal erector and a pair of transverse muscles. The wide gubernacular spicule protractor envelops spicules anteriorly. The ventral tail muscle is wide, unpaired, and nine pairs of serial diagonal muscles are located beneath the body wall muscles, followed by three pairs of postcloacal oblique muscles of the tail. Anal depressors comprise a pair of transverse muscles with expanded middle globular parts. The copulatory muscles are of the Rhabditidae and Cephalobidae type modified because of spicules elongation. The muscle characters code of the previously published tabular key for 15 muscle characters is 73422-22144-42223; it can be used for phylogenetic reconstructions.