Pristionchus paranudus, 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 : 11-20

Pristionchus paranudus n. sp.

urn:lsid:zoobank.org:act:23065D78-DFEB-4739-9C5E-B023DE10F678

Etymology. The species name is derived from its phylogenetic position as tentative sister to P. nudus .

Measurements. See Table 1

Adult. Body cylindrical, moderate to stout, i.e., body length-maximum body diam. ratio (a value) is ranging from 15–22, depending on culture condition; cuticle moderate in thickness, smooth with fine annulations, weak 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, short, papilliform. Four small papilliform cephalic papillae in males on right and left subventral and right and left dorsal sectors. Amphidial apertures located on the lateral sector, slightly dorsally shifted, at level of margin of cheilo- and gymnostom. Stomal dimorphism present, and details are described below. Dorsal pharyngeal gland clearly observed, penetrating dorsal tooth to gland opening. Anterior pharynx 1.5 times as long as posterior pharynx, muscular, composed of tube-shaped procorpus and well-developed oval-shaped metacorpus; posterior pharynx glandular with nerve ring surrounding the middle of isthmus. Pharyngo-intestinal junction (cardia) well-developed. Intestine simple tube, not forming pre-rectum, extended posteriorly from cardia to rectum; three (two subventral and one dorsal) rectal gland cells observed 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 the excretory duct. Deirid observed laterally on lateral field, located at the level around the posterior end of basal bulb to pharyngo-intestinal junction to a half body diameter posterior to the junction, ca 0.5–1 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 the posterior end of posterior gonad in female, on the same striation with deirid (= lateral field) or on the adjacent striation or the second dorsally neighboring striation to lateral field.

Stenostomatous form. Cheilostom with six per- and interradial cuticular plates. Anterior end of each plate rounded and elongated to project from stomal opening and form a small flap. Gymnostom short, cuticular ring-like anterior end overlapping cheilostom internally with, metastegostomal mound consisting of weakly sclerotized tissue present on dorsal side of inner wall. Pro-meso stegostom forming a weakly cuticularized ring internally overlapping with gymnostoma to connect gymnostom and metastegostom, with dorsal side relatively thick and conspicuous, ventral side thin and inconspicuous. Metastegostom bearing dorsal mound, conspicuous, movable triangular or flint-shaped dorsal tooth with strongly sclerotized surface with an inverted V-shape in lateral view. Left subventral ridge with three minute, rounded adventitious denticles on a plate, most ventral denticle is masked by the remaining two in lateral view. Right subventral ridge with two rounded distal adventitious denticles. Telostegostom weakly sclerotized cup-like cavity connecting stoma and pharynx.

Eurystomatous form. Cheilostom divided into six per- and interradial plates. Anterior end of each plate rounded and elongated to project from stomal opening, forming a small flap. Tip of each cheilostomal plate sometimes split into two small flaps. Each cheilostomal plate inclined inwardly, i.e., whole stoma appears to narrow anteriorly. Gymnostom with thick cuticle, forming short, ring-like tube with more heavily sclerotized wall in the posterior; anterior end of gymnostom internally overlapping posterior end of cheilostomatal plates. Pro-mesostegostom forming a weakly cuticularized ring internally overlapping with gymnostoma to connect gymnostom and metastegostom with dorsal side relatively thick and conspicuous, ventral side thin and inconspicuous; metastegostom bearing large claw-like or triangular dorsal tooth; two right subventral serrated plates; three left subventral serrated plates. Separation between serrated plates often inconspicuous. Telostegostom forming 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 expanded slightly (ca 1/4 of blade length) posterior to manubrium, then 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 50 to 60° 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 conoid with long spike occupying more than 2/3 of tail length, possessing filiform terminus. Paired papillae and phasmid arranged as <v1, v2d, v3, co, v4, ad, ph, (v5, v6, v7), pd>, where v1 located about 1.5 CBD anterior to co; v2d midway between v1 and co; v3 adcloacal; v4 at less than 1/10 CBD posterior to co, i.e., v3, co and v4 situated close to each other; ad less than 1 CBD posterior to co; ph at 1 CBD posterior to co; v5-v7 forming triplet, but clearly separated from each other, about 1 CBD posterior to ad, i.e., less than 1/10 CBD posterior to ph; pd about 1/4 CBD posterior to v7. v1, v4 and ph subventral, v2d and ad lateral, v3, v5–7 ventral and 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 2–2.5 ABDs posterior to anus. Tail long, smoothly elongate, conoid, with filiform terminus.

Diagnosis and relationship. Pristionchus paranudus n. sp. is characterized by its cuticle structure with weak longitudinal striation and distinctive lateral field, presence of partially split cheilostomatal plates and right and left subventral metastegostomatal serrated plates of eurystomatous form, long spike of male tail and the arrangement of male genital papillae, i.e., <v1, v2d, v3, co, v4, ad, ph, (v5, v6, v7), pd>. The new species shares partially split cheilostomatal plates with P. paulseni and some of the triformis group species ( P. hoplostomus Ragsdale, Kanzaki, Röseler, Herrmann, Sommer, 2013 ; P. fukushimae Ragsdale, Kanzaki, Röseler, Herrmann, Sommer, 2013 and P. yamagatae Herrmann, Kanzaki, Weiler, Yoshida, Rödelsperger & Sommer, 2019 ), and its surface cuticle structure (moderate in thickness with weak striations and distinctive lateral field) and the structure and arrangement of male genital papillae (long bristle-like and ventrally located v3, co and subventral v4 are very close to each other) with P. nudus n. sp. However, the new species is distinguished from P. paulseni and triformis group by its left subventral stegostomal plate of the eurystomatous form, cuticle structure and the structure and the arrangement of genital papillae, i.e., P. paulseni and triformis group species have claw-like stegostomatous tooth on the left subventral sector of the eurystomatous form, thick cuticle with distinctive longitudinal striations and indistinctive lateral field, and v3 and v4 are clearly separated. The new species is also distinguished from P. nudus n. sp. by its median bulb, which is oval vs. somewhat rectangular in lateral view, the position of the nerve ring, middle vs. anterior end of isthmus, labial sensilla, papilliform vs. bristle-like, stomal morphology in stenostomatous form, with sclerotized chilostomatal plates, flint-shaped dorsal tooth with a metastegostomal mound on the dorsal side vs. thick and seemingly soft cheilostomatal plates, triangular dorsal tooth and two layers of dorsal metastegostomatal mounds, arrangement of genital papillae and phasmid, <v1, v2d, v3, co, v4, ad, ph, (v5, v6, v7), pd> vs. <v1, v2d, v3, co, v4, ad, (v5, v6, v7), ph, pd>, and the male tail shape with vs. without spike. 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 MW017222 ), the sequence of which is distinct from that of all other Pristionchus species.

Type host and locality. Isolated from rotting water hyacinth bulbs ( Eichhornia ) on terraces below Dayutang village, Yuanyang, Yunnan province, PRC .

Type material and type strain. Type strain RS5988 frozen at the nematode collection of the MPI Tübingen and available as living culture upon request. Voucher specimen 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 .