Pristionchus passalidorum, 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 : 45-52

Pristionchus passalidorum n. sp.

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Etymology. The species name is derived from the family name of the host, bess beetle ( Coleoptera : Passalidae ).

Measurements. See Table 5

Adult. General characters are as described above for the triformis -group.

Stenostomatous form. Cheilostom, gymnostom, pro-mesostegostom and telostegostom as described above. 12- plated form not found. Arrangement of tooth and denticles in metastegostom as described above; dorsal movable tooth triangular, anterior end slightly curved, tooth often directed anteriorly; left subventral ridge with three minute, blunt or pointed adventitious denticles on a plate; right subventral ridge with a distal pointed adventitious denticle. Whole stoma including tooth and denticles narrow and more pointed in males.

Eurystomatous form. Cheilostom as described above, anterior half of each cheilostomal plate often split into two tips to form 12-flapped form. Six-flapped form (without split cheilostomal plate) rare. Gymnostom short and thick in both types 1 and 2, forming cuticular ring. Pro-mesostegostom well-developed, internally overlapping with posterior end of gymnostom; type 1 form short flattened with weak serrates at anterior end; type 2 bearing few small spines on inner surface. Arrangement of tooth and denticles in metastegostom as described above; dorsal movable tooth claw-like as typical of the genus; left subventral ridge with three large plates, each often has split tips and extra denticles on middle forming spiny plate; right subventral movable tooth claw-like often with extra peak on ventral side. Telostegostom as described above.

Male. Paired papillae and phasmid are arranged as <v1, v2d, v3, co, v4, ad, (ph, v5, v6, v7, pd)>, where v1 located about 1 CBD anterior to co; v2d just less than 1/5 CBD anterior to co; v3 adcloacal; v4 at 1/3 CBD posterior to co, i.e., v2d, v3, co and v4 are close to each other; ad about 1 CBD posterior to co; ph 2/3 distance from ad and rest of tail spike; v5–v7 forming triplet, just posterior to ph; and pd around the level of v7, i.e., ph, triplet papillae and pd close to each other. v1, v3, v4 and ph subventral, v2d and ad lateral, v5–7 ventral, pd subdorsal in the male tail. General shape of spicule and gubernaculum as described above.

Female. Gonadal characters of female as described above. Tail elongate conoid with slightly filiform terminus, i.e., the posterior half of tail is more elongated compared to anterior part. Phasmid ventro-laterally located at about 1.5 ABD posterior to anal opening.

Diagnosis and relationships. Pristionchus passalidorum n. sp. is characterized by the slightly anteriorly curved triangular dorsal tooth, the right and left subventral plates with one and three denticle(s) in stenostomatous form, right subventral stegostomal tooth without extra peak in eurystomatous form, sparsely serrated pro-mesostegostomal wall in type 2 eurystomatous form, and the arrangement of male genital papillae, <v1, v2d, v3, co, v4, ad, (ph, v5, v6, v7, pd)> where v2d, v3, co and v4 and ph, v5, v6, v7, pd are close to each other, respectively, and a long spike occupying more than 2/3 of tail length of male tail. Pristionchus passalidorum n. sp. is typologically similar to P. hoplostomus and P. musae n. sp. The new species and these two species share a triangular and pointed dorsal tooth with slightly anteriorly curved tip in stenostomatous form and the arrangement of genital papillae, closely located v2d, v3, co and v4. The new species is distinguished from P. hoplostomus by the absence vs. presence of 12- plated stenostomatous form, left subventral ridges of stenostomatous form, clearly pointed vs. bluntly pointed, right subventral plate of stenostomatous form, single vs. multiple peaks, right subventral tooth of eurystomatous form, without vs. with extra peak. 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 MW017223 ), the sequence of which is distinct from that of all other Pristionchus species.

Type host and locality. Bessbug ( Coleoptera : Passalidae ) at Ailaoshan Field Station CAS, Yunnan province, PRC.

Type material and type strain. Type strain RS6031, 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 .

Species description of P. dorci n. sp. and P. purgamentorium n. sp. of the Pristionchus maupasi -group

Adult. Body cylindrical, stout, i.e., body length-maximum body diam. ratio (a value) is usually ranging from 10–14, depending on culture condition; cuticle thick with fine annulation and longitudinal striations. Head without apparent lips, six mound-like anteriorly directed expansions, one on each sector. Six labial sensilla, one on each lip sector (on the mound); four small papilliform cephalic papillae in males on right and left subventral and right and left dorsal sectors; amphidial apertures located on lateral sector, slightly dorsally shifted, at level of margin of cheilo- and gymnostom. Stomal dimorphism present, and detailed morphology of the stoma is described below. Dorsal pharyngeal gland clearly observed, penetrating dorsal tooth to gland opening. Anterior pharynx longer than posterior pharynx; procorpus muscular, stout, occupying half to two-thirds of corresponding body diameter; metacorpus muscular, forming median bulb; isthmus narrow, not muscular; basal bulb glandular. Pharyngo-intestinal junction (cardia) clearly observed, 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 consisting of six per- and interradial plates. Incision between plates not always distinguished. Anterior end of each plate rounded and elongated to project from stomaal opening and form a small flap. Split cheilostomal plate not observed. Gymnostom short, cuticular ring-like anterior end overlapping cheilostom internally; dorsal gymnostomal wall with mound-like expansion probably derived from metastegostom which gives an appearance of thickened dorsal gymnostomal wall compared to ventral side. Stegostom separated into three subsections: pro-meso, meta, and telostegostom. Pro-mesostegostom forming a weakly cuticularized ring internally overlapping with gymnostoma to connect gymnostom and metastegostom. Metastegostom bearing conspicuous and movable triangular or flint-shaped dorsal tooth with strongly sclerotized surface giving an appearance of an inverted V-shape in light microscopy in lateral view; pointed left subventral ridge with three minute adventitious denticles on a plate, most ventral denticle often masked by remaining two in lateral view; pointed right subventral ridge, often with distinct distal adventitious denticle(s). Telostegostom forming weakly sclerotized cuplike cavity connecting stoma and pharynx. Whole stoma including tooth and denticles narrow and more pointed in males.

Eurystomatous form. Cheilostom divided into six well-distinctive per- and interradial plates. Anterior end of each plate rounded and elongated to stick out from stomal opening and form a small flap. Split cheilostomal plate not observed. 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; lacking the serrates at anterior end of gymnostom. Pro-mesostegostom forming a weakly cuticularized ring connecting gymnostom and metastegostom. Metastegostom bearing large claw-like dorsal tooth; claw-like right subventral tooth; and three left subventral denticles, where the tip of each denticle sometimes splits into two or three small ridges. 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 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 40–50° 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 papilliform. Paired papillae and phasmid arranged as <v1, v2, v3d, co, v4, ad, ph, (v5, v6, v7, pd)>, where v1 located about 1.5 CBD anterior to co; v2 about 0.5 CBD anterior to co; v3d less than 1/10 CBD posterior to v2, i.e., about 1/3 CBD anterior to co; v4 at about 1/3 CBD posterior to co; ad about 1 CBD posterior to co; ph midway between ad and root of tail spike; v5–v7 forming triplet, just posterior to ph; and pd level of ventral triplet (v5–v7). v1, v2, v4 and ph subventral, v3d and ad lateral, v5–7 ventral and pd subdorsal in the male tail. General shape of spicule and gubernaculum as described above, spicule relatively thin, gubernaculum relatively low (flattened). Male tail spike long.

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. Tail elongate conoid with long and filiform terminus. Phasmid ventro-laterally located at about 1.5–2.0 ABD posterior to anal opening.