Pharyngonema chinense, Ivanova, Elena S. & Hope, Duane, 2009

Ivanova, Elena S. & Hope, Duane, 2009, A new genus and three new species of Drilonematidae (Rhabditida, Drilonematoidea) from earthworms, Zootaxa 2293, pp. 53-67 : 61-64

Pharyngonema chinense sp. n.

Figs 4–5

Adult: Found in fragments 1000–2000 µm long. Yellowish nematodes. No marked sexual dimorphism except in primary sexual characters. Body length about 3000–4000 µm. Body tapering to both ends, mainly cylindrical, but swollen close to both ends due to the presence of prominent laterally placed circular spots of highly modified tissue lacking cuticle; the anterior pair (amphids? deirids?) situated at mid-pharyngeal level and the posterior one (caudal organs?) at mid-tail. Each spot with a central pore and long duct about 2–3 µm in diameter running through the body of the enlarged portion. Head sensilla not apparent. Body cuticle 1 µm thick, very finely striated. Lateral chords about 10–15 µm wide, with central ridge. Conical lips about 2–4 µm long and 5 µm wide. Mouth terminal; lumen of stoma closed and not enveloped by anterior end of pharynx. Pharynx long, corpus muscular, isthmus short, ill-defined, posterior bulb pear-shaped. Nerve ring thin, surrounding intestine about two pharyngeal lengths from anterior. Excretory pore situated posterior to nerve ring; excretory duct thin and short; excretory cell very large. Cardia short and composed of two cells. Intestine well developed. Rectal glands present. Tail short and curved ventrally in both sexes.

Male: Organs of head end 36–56 µm long and 35–55 wide. Testis long, reflexed in anterior body region, often anterior to nerve ring, and with loop posteriorly from flexure. Spermatocytes spherical, small, in one, then two, then 4 or more rows. Spermatozoa in vas deferens about 6–7 µm x10 µm. Vas deferens long, separated from broader ejaculatory duct by constriction. Enlarged cells, about 24–25 µm in diameter and 15–27 µm long, (spermatids?) present in ejaculatory duct. Spicules stout, curved, with broad bowl-shaped capitula about twice the diameter of the shafts which are tube-like and equal in diameter from capitula to tips. Capitula about 12–16 µm in diameter and 8–10 µm long, shafts 6 µm. Numerous short spikes present on distal, truncate tip of spicule; claw-like, posteriorly curved, blunt process present on anterior side of distal tip. Gubernaculum thick, clavate. Caudal organs 25–30 µm long and 25 µm in diameter.

In specimen USNM 1117728, testis forked posteriorly from flexure into two branches of unequal length; each branch filled with normal-looking spermatocytes; total length of both branches less than length of unbranched testis.

Female: Organs of head end about 45–65 µm in diameter. Ovary with short flexure in tail region near anterior margin of caudal organs; ovary with oocytes in 2–3 files. Ovary anteriorly transforms gradually into oviduct with single file of oocytes; oviduct merges with uterus at about two pharyngeal lengths from anterior of body. Anteriorly directed spermatheca present at distal end of uterus; seminal receptacle filled with spermatozoa 6-7 µm x 10-11 µm in size (similar in size and shape to spermatozoa in male vas deferens). Vulva post-median, distance between vulva and anus 895 µm (estimated in a single specimen only). Intrauterine ova numerous, broadly elliptical, with 1 µm thick very finely mammillated coat. Vagina short, straight. Small post-uterine sac present, about 45 µm long. Anus present. Three large glandular cells in caudal region (caudal glands?). Caudal organs 42–80 µm long and 47-90 µm in diameter.

Type material: Holotype: 2 fragments of male on a slide USNM 1117723, paratypes: male fragments USNM 1117724, female fragments USNM 1117725, 1117726 and mixture of male and female fragments USNM 1117727 and 1117728 deposited in the Smithsonian Institution’s National Museum of Natural History. Further paratype female fragments No 1069 and paratype male fragments No 1070 deposited in the Museum of Helminthological Collections in the Centre of Parasitology of A.N. Severtsov Institute of Ecology and Evolution RAS, Moscow, Russia and paratype male and fragments of male and female are in the first author’s collection.

Type host and locality: Coelomic cavity of Pheretima guillelmi (Michaelsen 1895) Michaelsen 1900 , USNM 20157, collected in Nanking, China, time of collection not indicated; leg. Gates.

Etymology. The species name refers to the locality of the oligochaete host.

Diagnosis and relationships. Pharyngonema chinense sp. n. is characterized by the long cylindrical body swollen laterally close to both ends with circular spots of modified tissue lacking cuticle. The stoma is reduced, and the pharynx is clavate. The nerve ring surrounds the intestine and the excretory pore is situated a short distance posterior to the nerve ring. The tail is short and conical in both sexes. The vulva is postmedian, and there is a short post-uterine sac. A spermatheca is attached to the uterus near its junction with the oviduct and is packed with large, irregularly ovoid spermatozoa. The ovary is reflexed immediately anterior to the caudal organ. Spicules are paired, curved, similar in size, and each with a broad capitulum. Distal truncate tips of spicules bear numerous short spikes and a blunt, posteriorly curved, process. The distinctly clavate gubernaculum is nearly half the length of the spicules.

From the only other member of the genus, Ph. mekongianum Pierantoni, 1923 , this new species is clearly distinguished by the organs at the head end being more anteriorly placed (at mid-pharynx vs at pharynx base), and smaller (36-56 µm x 35 -55 µm vs 104-123 µm x 70 -80 µm) (Spiridonov 1994). In addition, Ph. chinense n. sp. has smaller spicules (37–40 µm) with a blunt claw at the distal tip vs larger spicules (52–57 µm) with an acute distal spine. The smaller gubernacula (25–26 µm) of the present species are clavate vs the longer (38–40 µm), infundibular gubernacula of Ph. mekongianum . Also, the egg shells are ornamented vs smooth.

Figures

FIGURE 4. Pharyngonema chinense sp. n. male. A: forked testis; B: excretory pore; C: head; D: anterior region; E: posterior region; F: gubernaculum; G: cloacal region. All in lateral position. (Scale bars in µm.)

FIGURE 5. Pharyngonema chinense sp. n. female. A: head, ventral view; B: spermatheca; C, D: egg; E: anterior region; F: vulval region; G: caudal organ; H: tail; I: tail tip. If not indicated, in lateral position. (Scale bars in µm.)