We re-isolated in China a relative of the nematode model Caenorhabditis elegans that was previously referred to informally as C. sp. 5. In spite of its importance for comparative biology, C. sp. 5 has remained morphologically uncharacterized. Therefore, we now provide detailed description of morphology and anatomy, assigning the name of Caenorhabditis sinica sp. n. to this nematode that is found frequently in China. C. sinica sp. n. belongs to the Elegans group in the genus Caenorhabditis, being phylogenetically close to C. briggsae although differing in reproductive mode. The gonochoristic C. sinica sp. n. displays two significantly larger distal parts of uteri filled with sperms in the female/hermaphroditic gonad than does the androdioecious C. briggsae. The new species can be differentiated morphologically from all known Caenorhabditis species within the Elegans group by presenting a uniquely shaped, three-pointed hook structure on the male precloacal lip. The lateral field of C. sinica sp. n. is marked by three ridges that are flanked by two additional incisures, sometimes appearing as five ridges in total. This study ends the prolonged period of the ‘undescribed’ anonymity for C. sinica sp. n. since its discovery and use in comparative biological research. Significant and crossing-direction dependent hybrid incompatibilities in F1 and F2 crossing progeny make C. sinica sp. n. an excellent model for studies of population and speciation genetics. The abundance of nematode species lacking detailed taxonomic characterization deserves renewed attention to address the species description gap for this important yet morphologically ‘difficult’ group of animals.
The genus Phasmarhabditis is an economically important group of rhabditid nematodes, to which the well-known slug-parasite P. hermaphrodita belongs. Despite the commercial use of Phasmarhabditis species as an attractive and promising approach for pest control, the taxonomy and systematics of this group of rhabditids are poorly understood, largely because of the lack of diagnostic morphological features and DNA sequences for distinguishing species or inferring phylogenetic relationship. During a nematode sampling effort for identifying free-living relatives of Caenorhabditis elegans in Huizhou City, Guangdong, China, a novel species belonging to the genus Phasmarhabditis was isolated from rotting leaves. Detailed morphology of the gonochoristic P. huizhouensis sp. nov. was described and illustrated. The adult female has a robust body, a relatively short and wide buccal capsule conjoined by a rhabditiform pharynx. Females are characterized by a short cupola-shaped tail end bearing a slender pointed tip, with the junction flanked by a pair of ‘rod-like’ phasmids. Males have an open peloderan bursa that is supported by 9 pairs of genital papillae and 1 terminal pair of phasmids. P. huizhouensis sp. nov. is morphologically very similar to the type species Phasmarhabditis papillosa but is distinguishable by its male caudal traits. The new species is readily differentiated from other taxa in the genus by its female tail shape. Molecular phylogenetic inferences based on small subunit (SSU) and the D2-D3 domain of large subunit (LSU) ribosomal DNA genes reveal that P. huizhouensis sp. nov. forms a unique branch in both phylogenies which is genetically related to P. hermaphrodita and other parasites such as Angiostoma spp. The host associations of P. huizhouensis sp. nov. and its ability to parasitize slugs are unknown.
Seinura lii n. sp. and S. wuae n. sp. are described and illustrated from dying Pinus massoniana infested with Bursaphelenchus xylophilus in China. Seinura lii n. sp. is characterised by relatively long female and male bodies (763-1146 and 831-1068 µm, respectively), stylet 16-20 µm long and lacking knobs, two rows of developing oocytes in the anterior gonad, welldeveloped postuterine sac (120-182 µm long), three lines or incisures in the lateral field, four pairs of subventral papillae on the male tail region, and an elongate-conoid female tail. Seinura wuae n. sp. is characterised by relatively long female and male bodies (819-1179 and 787-1062 µm, respectively), stylet 15-18 µm long and with small knobs, three lines or incisures in the lateral field, two or three rows of developing oocytes in the anterior gonad, long postuterine sac (103-172 µm long), two pairs of subventral papillae on the male tail region, and an elongate-conoid female tail.
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