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

Abstract

Summary 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.

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

“…The vaginal muscles are promising, because of the deeply invaginated vaginal sphincter and the four-radial symmetry of the vulval and vaginal dilators. The four-radial symmetry of vulval area pattern corresponds to that already known for Caenorhabditis, Chiloplacus and Rhabditolaimus (Lints & Hall, 2009a, b;Ryss & Petrov, 2021;Ryss & Polyanina, 2023), but relatively more complicated because of the three-dimensional differentiation of muscle attachment points on the invaginated vaginal sphincter, dorsal body wall and around the vulval opening.…”

“…A commonly held view is that nematodes lack a specialised intestinal musculature and that peristalsis is accomplished by the wavelike locomotion of their slender body compensating for the lack of intestinal muscles. However, the presence of extensively branched stomato-intestinal musculature in the phylogenetically distant families of the class Chromadorea (Rhabditidae: C. elegans; Telotylenchidae: T. dubius; Diplogastridae: Rhabditolaimus ulmi -see Ryss & Polyanina, 2023;Panagrolaimidae: P. detritophagusthis study) indicates that these nematodes have a modified system of peristalsis caused by intrinsic musculature rather than by the body-wall muscles. A highly branched structure of stomato-intestinal muscles, their structural integrity with the anal sphincter and the three-ring struc-ture of the latter can all be potentially useful in phylogenetic analyses; it is possible that the branching pattern of the stomato-intestinal muscles can be used as taxonomically informative characters, in the same way as the pattern of wing veins are for insect taxonomy.…”

“…Both dgl and ob muscles can therefore be categorised as homotypic organs that have apparently evolved by polymerisation from a single organ. Their numbers (7-8 pairs of the dgl muscles and five pairs of the ob muscles) may be used as diagnostic characters vs three ob muscles in Chiloplacus and nine dgl pairs and three ob pairs in Rhabditolaimus (Ryss & Polyanina, 2023).…”

“…These muscles may be derivates of the anal depressor (adp). The gp muscle presumably corresponds to the ventral expansion (ame) of the adp muscle in Rhabditolaimus (Ryss & Polyanina, 2023). The paired anterior gubernacular erector (ave) extends to the lateral body wall; it corresponds to the transverse gubernacular erector (tsm) in Rhabditolaimus and the transverse saddle muscle (tsm) in the Bursaphelenchus male (Ryss & Petrov, 2021;Ryss & Polyanina, 2023).…”

“…Previously we have examined the muscle systems of three nematode species using phalloidin staining in conjunction with confocal microscopy: Bursaphelenchus mucronatus Mamiya & Enda, 1979;Chiloplacus sp. and Rhabditolaimus ulmi (Goodey, 1930) Susoy & Herrmann, 2012 (Ryss & Petrov, 2021;Ryss & Polyanina, 2023). Panagrolaimus detritophagus Fuchs, 1930 is a new subject for our comparative analysis.…”