Pristionchus nudus, Kanzaki & Herrmann & Weiler & Röseler & Theska & Berger & Rödelsperger & Sommer, 2021

Kanzaki, Natsumi, Herrmann, Matthias, Weiler, Christian, Röseler, Waltraud, Theska, Tobias, Berger, Jürgen, Rödelsperger, Christian & Sommer, Ralf J., 2021, Nine new Pristionchus (Nematoda: Diplogastridae) species from China, Zootaxa 4943 (1), pp. 1-66 : 6-11

Pristionchus nudus n. sp.

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Etymology. The species name is derived from the absence of prominent striation, common in other Pristionchus species ( nudus lat.: naked)

Measurements. See Table 1

Adult. Body cylindrical, stout, i.e., body length-maximum body diam. ratio (a value) is ranging from 12-18, depending on culture condition; cuticle moderate in thickness, smooth with fine annulations, weak but conspicuous longitudinal striations, conspicuous lateral field with two bands, no clear annulation between bands. Head without apparent lips, six mound-like anteriorly directed expansions, one on each sector. Six labial sensilla one on each lip sector, long, bristle-like; two lateral sensilla clearly longer than other four. Cephalic papillae vestigial, probably degenerate and embedded in cephalic tissue. Amphidial apertures located on lateral sector, slightly dorsally shifted, at level of margin of cheilo- and gymnostom. Stomal dimorphism not observed; all individuals examined of stenostomatous form. Dorsal pharyngeal gland penetrating dorsal tooth to gland opening. Anterior pharynx (=pro and metacorpus) twice as long as posterior (=isthmus and basal bulb), muscular composed of tube-shaped procorpus and moderately developed metacorpus (median bulb) with roundish rectangular shape in lateral view; posterior pharynx glandular with nerve ring surrounding anterior end of isthmus. Pharyngo-intestinal junction (cardia) welldeveloped. Intestine simple tube, not forming pre-rectum, extended posteriorly from cardia to rectum; three (two subventral and one dorsal) rectal gland cells at distal end of intestine (margin between intestine and rectum). Secretory-excretory pore not conspicuous, ventrally located at level of isthmus to pharyngo-intestinal junction, excretory duct extending anteriad and reflexed back to position of pore; two large secretory-excretory cells around excretory duct. Deirid observed laterally on lateral field, located around posterior end of basal bulb to pharyngo-intestinal junction to a half body diameter posterior to junction, ca 0.5 body diam. posterior to secretory-excretory pore. Hemizonid not observed. Lateral glands (small pores connected to secretory cell) on lateral body surface, with positions inconsistent among individuals, numbering 5 to 8 for males and 9 to 13 for females. Postdeirid at anterior part of vas deferens in male and posterior end of posterior gonad in female, on the same striation with deirid (= lateral field) or the adjacent striation or the second dorsally neighboring striation to lateral field.

Stenostomatous form. Cheilostom consisting of six per- and interradial plates, each forming small flap at anterior end, posterior part of each plate broad, consisting of translucent and non-sclerotized tissue. Gymnostom short, cuticular ring-like anterior end overlapping cheilostom internally; two layers of metastegostomatal mounds consisting of weakly sclerotized tissue present on dorsal side of inner wall. Pro-meso stegostom forming a weakly cuticularized ring internally overlapping with gymnostom to connect gymnostom and metastegostom; broad and conspicuous in dorsal view. Metastegostom bearing dorsal mounds, small, conspicuous, triangular, movable tooth with clearly observed pharyngeal tube. Left subventral ridge with three minute, rounded adventitious denticles on a plate, and the most ventral denticle masked by remaining two in lateral view. Right subventral ridge with two rounded distal adventitious denticles. Telostegostom weakly sclerotized cup-like cavity connecting stoma and pharynx.

Male. Whole body ventrally arcuate, strongly ventrally curved at tail region when killed by heat. Testis single, ventrally located, anterior part reflexed to right or left side; spermatogonia arranged in three to five rows in reflexed part, well-developed spermatocytes arranged as three to four rows in anterior two-thirds of main branch, mature amoeboid spermatids arranged in multiple rows in proximal part of gonad. Vas deferens not clearly separated from other parts of gonad. Posterior end of vas deferens and rectum fused to form a cloacal tube. Spicules paired, separate; spicules smoothly curved in ventral view, adjacent to each other for distal third of their length, each smoothly tapering to pointed distal end; spicule in lateral view smoothly ventrally arcuate, giving spicule about 100° curvature, oval manubrium at anterior end, lamina/calomus complex smoothly tapering to pointed distal end. Gubernaculum conspicuous, about one-third of spicule length, broad anteriorly such that dorsal wall is slightly recurved with dorsal and ventral walls separate at ca 30° angle at posterior end; dorsal side of gubernaculum possessing single, membranous, anteriorly directed process and lateral pair of more sclerotized, anteriorly and obliquely ventrally directed processes. In lateral view, anterior half of gubernaculum with two successive curves separated by anteriorly and obliquely ventrally directed process, with anterior terminal curvature highly concave and almost closed, with deep posterior curvature being one-third of gubernaculum length; posterior half forming tube-like process enveloping spicules. Cloacal opening (co) slit-like in ventral view; one small, ventral, single genital papilla (vs) on anterior cloacal lip. All nine paired genital papillae relatively long, bristle-like. Tail elongate conoid to sharply pointed tip, i.e., tail does not form a distinct spike. Paired papillae and phasmid are arranged as <v1, v2d, v3, co, v4, ad, (v5, v6, v7), ph, pd>, where v1 located about 1 cloacal body diameter (CBD) anterior to co; v2d a little less than 0.5 CBD anterior to co; v3 adcloacal; v4 at less than 1/10 CBD posterior to co, i.e., v3, co and v4 are very close to each other; ad about 1 CBD posterior to co; v5–v7 forming triplet, but clearly separated from each other, about 1 CBD posterior to ad, i.e., about 2 CBD posterior to co; ph at about 1/4 CBD posterior to v7; and pd about 1 CBD posterior to v7. v1, v4 and ph subventral, v2d and ad lateral, v3, v5–7 ventral, pd subdorsal in male tail. Bursa or bursal flap absent.

Female. Body relaxed or weakly ventrally arcuate when killed by heat. Gonad didelphic, amphidelphic; each gonadal system arranged from vulva/vagina as uterus, oviduct, and ovary; anterior gonad right of intestine, with uterus and oviduct extending ventrally and anteriorly on right of intestine and with totally reflexed (=antidromous reflexion) ovary extending dorsally on left of intestine; oocytes mostly arranged in three to four or more rows in distal two-thirds of ovary and in double or single row in rest of ovary, distal tips of each ovary reaching oviduct of opposite gonad branch; anterior end of oviduct (=junction tissue between ovary and oviduct) consists of rounded cells; anterior part of oviduct consists of rounded cells, forming a simple tube; middle part of oviduct serving as spermatheca, consists of roundish and relatively large cells. Eggs in single to multiple-cell stage or even further developed at posterior part of oviduct (=uterus), in young females being composed of squared or angular cells, long enough to contain one well-developed oocyte. Receptaculum seminis not observed, i.e., the organ is not independent, and a part of oviduct/uterus works as the organ; vaginal glands present but obscure; vagina perpendicular to body surface, surrounded by sclerotized tissue; vulva slightly protuberant in lateral view, pore-like in ventral view; rectum about one anal body diameter (ABD) long, intestine/rectum junction surrounded by well-developed sphincter muscle. Anus in form of dome-shaped slit, posterior anal lip slightly protuberant; phasmid about 2 ABDs posterior to anus. Tail elongate, conoid, with sharply pointed tip.

Diagnosis and relationships. Pristionchus nudus n. sp. has several characteristic typological traits, which have not been found in other species of the genus. The new species is characterized by its long and bristle-like labial sensilla where two lateral sensilla are much longer than the other four, lack of male cephalic sensilla, monomorphic stoma morphology (stenostomatous form only), where thick posterior half of cheilostomal plate is composed by translucent tissue, two-layered dorsal gymno- and stegostomal mound, small and triangular dorsal tooth, roundish rectangular-shaped metacorpus, position of nerve ring surrounding the anterior end of isthmus, long male tail without clear spike and the arrangement of male genital papillae, i.e., <v1, v2d, v3, co, v4, ad, (v5, v6, v7), ph, pd>. The new species can be readily distinguished from all other Pristionchus species with the above species-specific characters, i.e., none of the other species in the genus have these characters.

Phylogenetically, P. nudus n. sp. belongs to the basal species group of the genus, where two monomorphic species, P. elegans Kanzaki, Ragsdale, Herrmann, & Sommer, 2012 and P. bucculentus Kanzaki, Ragsdale, Herrmann, Röseler & Sommer, 2013 ( elegans group), and two dimorphic species, P. fissidentatus Kanzaki, Ragsdale, Herrmann & Sommer, 2012 and P. paulseni Herrmann, Kanzaki, Weiler, Yoshida, Rödelsperger & Sommer, 2019 ( fissidentatus group) have been described. P. nudus n. sp. shares the modification of the cheilostomatal plates with P. elegans and P. bucculentus , which have thin membrane-like cheilostomatal plates. Within these two species, P. nudus n. sp. shares the stoma pattern, monomorphic stenostomatous form with P. elegans . However, the new species is distinguished from P. elegans with its species-specific characters described above. Further, the new species is distinguished from all other species by mating experiments and also characterized by a ca. 1,600-bp fragment of the SSU rRNA gene (GenBank accession number MW017221 ), the sequence of which is distinct from that of all other Pristionchus species.

Type host and locality. Isolated from a longhorn beetle ( Coleoptera : Cerambycidae ) collected at Xishuangbanna Tropical Botanical Garden - Green stone forest, Yunnan province, PRC.

Type material and type strain. Type strain RS6026 frozen at the nematode collection of the MPI Tübingen and available as living culture upon request. Voucher specimens sent to the following museums: Holotype male, Paratype male and female: Museum für Naturkunde Karlsruhe , Germany ; Paratype male and female: Swedish Natural History Museum, Stockholm, Sweden ; Paratype male and female: University of California in Riverside Nematode Collection ( UCRNC), Riverside , CA, USA .