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A new free-living nematode, Actinonema falciforme sp. nov. (Nematoda: Chromadoridae), from the continental shelf of the East China Sea
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Benze SHI1, Tingting YU1, Kuidong XU1, 2, 3, *
Acta Oceanologica Sinica | 2018, 37(10) : 152 - 156
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Acta Oceanologica Sinica | 2018, 37(10): 152-156
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A new free-living nematode, Actinonema falciforme sp. nov. (Nematoda: Chromadoridae), from the continental shelf of the East China Sea
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Benze SHI1, Tingting YU1, Kuidong XU1, 2, 3, *
Affiliations
  • 1 Department of Marine Organism Taxonomy and Phylogeny, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
  • 2 Laboratory for Marine Biology and Biotechnology, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266237, China
  • 3 University of Chinese Academy of Sciences, Beijing 100049, China
Published: 2018-10-25 doi: 10.1007/s13131-018-1318-x
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Actinonema falciforme sp. nov. was discovered from the continental-shelf sediments of the East China Sea. It is characterized by six outer labial setae and four cephalic setae in one circle, complex and heterogeneous cuticular ornamentation with lateral differentiation, large and conspicuous amphideal fovea which is transversely oval-shaped, a single anterior testis, two opposed reflexed ovaries, falciform telamon (lateral pieces of gubernaculum), and the lack of spicule and gubernaculum. Within the genus Actinonema, only A. longicaudatum and the new species possess telamon and lack spicule and gubernaculum. Actinonema falciforme sp. nov. can be easily differentiated from A. longicaudatum by its much shorter body length, the peculiar shape of the telamon and a shorter tail.

East China Sea  /  free-living marine nematodes  /  new species
Benze SHI, Tingting YU, Kuidong XU. A new free-living nematode, Actinonema falciforme sp. nov. (Nematoda: Chromadoridae), from the continental shelf of the East China Sea[J]. Acta Oceanologica Sinica, 2018 , 37 (10) : 152 -156 . DOI: 10.1007/s13131-018-1318-x
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1 Introduction
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The family Chromadoridae Filipjev, 1917 can be distinguished by two synapomorphies: males possessing only the anterior testis; females having two antidromously reflexed ovaries, with the anterior gonad right of the intestine and the posterior one left of the intestine (Lorenzen, 1994). Chromadoridae is a large family, containing five subfamilies and 38 genera (Tchesunov, 2014). The five subfamilies can be separated from each other by the shape of the amphideal fovea, the stoma armature, the arrangement of anterior sensilla, the cuticular ornamentation with or without differentiations, and presence or absence of pre-cloacal supplements in males (Decraemer and Smol, 2006). The subfamily Euchromadorinae Gerlach and Riemann, 1973 can be easily distinguished by the cuticle with complex heterogeneous ornamentation (rarely homogeneous), often with lateral differentiation; the amphideal fovea large, transverse slit-like or oval, located posterior to the cephalic setae; the gubernaculum usually with hammer- or L-shaped lateral pieces (telamon); and the absence of precloacal supplements.
Within the subfamily Euchromadorinae, the genus Actinonema Cobb, 1920 is most similar to the genus Rhips Cobb, 1920. Actinonema has simple spicules, while Rhips has long and double-jointed spicules (Tchesunov, 2014). Platt and Zhang (1982) considered the spicules of Actinonema to be homologous to the lateral pieces (telamon) of Rhips and stated that the two genera are very closely related, except for the double-jointed spicules of Rhips. Muthumbi and Vincx (1998) assessed the taxonomic importance of the generic features of the two genera and considered that some species of Actinonema lack spicules totally.
So far, the full scope of nematodes diversity in the sea areas of China is largely unknown due to insufficient investigations, especially in the East China Sea. During the examination of free-living nematode diversity in the East China Sea, we discovered a nematode belonging to the subfamily Euchromadorinae. The species is peculiar in the absence of spicule and gubernaculum. Detailed investigation suggests the nematode is a new species of the genus Actinonema, which is described herein.
2 Materials and methods
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Sediment samples were collected from sediments on the continental shelf of the East China Sea in July 2012, using box corer, from which the samples used for meiofaunal analysis were taken using a modified syringe tube and preserved with formalin (5% final concentration) on board. In the laboratory, the fixed samples were stained with 0.1% Rose Bengal for 12 h, washed on a 500 μm sieve to remove large particles and a 31 μm sieve to retain meiofauna. The silica sol Ludox HS 40 was used to extract meiofauna from the remaining sediments by centrifugation. The extracted samples were sorted out under a dissecting microscope. Nematodes were transferred into 9:1 (v/v) solution of 50% alcohol-glycerol in an embryo dish to slowly evaporate to pure glycerol, and then mounted into permanent slides (Platt and Warwick, 1983).
The descriptions were made from the glycerin mounts (Platt and Warwick, 1983) using differential interference contrast (DIC) microscope (Nikon E80i). Line drawings were made with the aid of a drawing device. Type specimens are deposited in the Marine Biological Museum of Chinese Academy of Sciences (MBMCAS) at Qingdao, China. All measurements are in μm, and all curved structures are measured along the arc. The terminology used for describing the arrangement of morphological features follows Coomans (1979).
Abbreviations used in the paper are as follows: L, body length; T, tail length; abd, anal body diameter; cbd, corresponding body diameter; mbd, maximum body diameter; a, L/mbd; b, L/pharynx length; c, L/T; c′, T/abd; V, distance from anterior end to vulva; and V%, V×100/L.
3 Taxonomy
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Order Chromadorida Filipjev, 1929
Family Chromadoridae Filipjev, 1917
Subfamily Euchromadorinae Gerlach and Riemann, 1973
Genus Actinonema Cobb, 1920
Actinonema falciforme sp. nov.
(Figs 1 and 2; Table 1)
3.1 Diagnosis
Six outer labial setae and four cephalic setae in one circle. Cuticular ornamentation heterogeneous and complex, regular lateral differentiation beginning just anterior to pharyngeal base. Buccal cavity conical, with a distinct sharply pointed dorsal tooth. Amphideal fovea conspicuous, transversely oval, with a central slit. Posterior pharyngeal bulb present. Single anterior testis, reflexed. Spicule and gubernaculum absent. Telamon (lateral piece of gubernaculum) falciform and cuticularized. Two opposite and reflexed ovaries. Tail conical with pointed tip.
3.2 Type materials
Holotype: one male on slide DH3-4-05-07-07. Paratypes: four males on slides DH3-4-04-03-02, DH2-4-03-16-2, DH2-4-05-13-3, and DH3-2-04-9-3; two females on slides DH2-4-06-8-3 and DH2-4-07-20-3.
3.3 Type locality and habitats
Benthic sediments at Stas DH3-4 (30°00′N, 124°01′E), DH2-4 (31°00′N, 124°31′E) and DH3-2 (30°00′N, 123°00′E) in the East China Sea. Station DH3-4, water depth 64.1 m, water temperature at the sediment-water interface 18.2°C, salinity 34.4, median particle diameter 3.7 μm, silt-clay 44.6%. Station DH2-4, water depth 50 m, water temperature at the sediment-water interface 21.7°C, salinity 33.2, median particle diameter 6.3 μm, silt-clay 41.3%, organic matter 0.26%. Station DH3-2, water depth 52 m, water temperature at the sediment-water interface 19.0°C, salinity 34.3, median particle diameter 3.9 μm, silt-clay 48.9%, organic matter content 0.31%.
3.4 Etymology
Derived from the Latin adjective falciformis (falciform), referring a main feature of the species, i.e., the falciform telamon.
3.5 Description
Measurements shown in Table 1. Body cylindrical and gradually tapering towards tail end, with head region narrower than body trunk (Fig. 1c). Buccal cavity conical, with a distinct sharply pointed dorsal tooth (Figs 1a and 2c). Six inner labial papillae, minute and inconspicuous. Six outer labial setae and four cephalic setae in one circle, almost of same length, 25%–43% of head diameter (Figs 1a and 2c). Amphideal fovea conspicuous, transversely oval, with a central slit; occupying 76%–95% of corresponding body diameter (Figs 1a, 2a and b).
Cuticular ornamentation heterogeneous and complex (Figs 1a, b, 2e and f): transverse dots in the anterior part of pharynx, with irregular lateral differentiation beginning just anterior to the nerve ring (about 41 μm to anterior body end); regular lateral differentiation beginning just anterior to pharyngeal base (about 80 μm to anterior body end); and lateral differentiation beginning to disappear at anterior quarter of the tail (about 18 μm to cloaca).
Pharynx with distinct posterior bulb (Figs 1c and 2d). Cardia small. Nerve ring located in the middle portion of pharynx. Excretory pore just anterior to pharyngeal bulb, about 61 μm to anterior body end (Fig. 1c). Ventral gland about 48 μm long (Fig. 1c). Three caudal glands (Fig. 1b). Tail conical, with tapering tip (Figs 1b and 2h).
Males. Single anterior testis, reflexed (Fig. 1c). Spicule and gubernaculum absent (Figs 1b and 2h). Telamon (lateral pieces of gubernaculum) falciform with distal end pointed and a large conspicuous hook in the proximal end (Figs 1b, 2h and i). Precloacal supplement absent.
Females. Overall features similar to males. Two opposite and reflexed ovaries, about 67 μm long. Vulva located in the middle portion of the body (Fig. 2g). Spermatheca present (Figs 1d and 2g).
4 Discussion
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Actinonema falciforme sp. nov. is characterized by six outer labial setae and four cephalic setae in one circle, complex and heterogeneous cuticular ornamentation with lateral differentiation, large and conspicuous amphideal fovea transverse oval-shaped, a single anterior testis, two opposed reflexed ovaries, a falciform telamon (lateral pieces of gubernaculum), and the lack of spicule and gubernaculum. These main features match the generic diagnosis of Actinonema within the family Chromadoridae (Tchesunov, 2014).
Within the genus Actinonema, only the species A. longicaudatum Steiner, 1918 has only telamon and lacks spicule and gubernaculum (Muthumbi and Vincx, 1998). The new species also possesses these peculiar features, by which the two species can be easily differentiated from the other congeners. Actinonema falciforme sp. nov. differs distinctly from A. longicaudatum by its much shorter body length (428–560 μm vs. 840–1 251 μm) and the peculiar falciform telamon with distal end pointed and a large conspicuous hook in the proximal end (vs. flat with a broad proximal end and a narrow distal end). In addition, Actinonema falciforme sp. nov. has a relatively shorter tail (c=5.3–7.1 vs. c=3.8–4.1).
Since Wieser (1954) provided a diagnostic key of Actinonema, six further species including the new species have been added in the genus (Boucher, 1976; Jensen, 1991; Muthumbi and Vincx, 1998; Vitiello, 1970). Accordingly, we provide an updated key to nine species of the genus.
Key to nine species of the genus Actinonema
1. Amphids in female half the head diameter wide………......... ......................................................A. chitwoodi (Chitwood, 1951)
– Amphids in female wider than half the head diameter….......2
2. Spicule absent……………....................................……………………3
– Spicule present……………………………....……………......……5
3. Gubernaculum and telamon present…................................. ...................................A. smolae Muthumbi and Vincx, 1998
– Gubernaculum absent, only telamon present………...………4
4. Telamon flat with a broad anterior end and a narrow posteri or end, tail very long with the ratio c=3.8–4.1…….........….... .................…………………A. longicaudatum (Steiner, 1918)
– Telamon falciform with distal end pointed and a large con spicuous hook in the proximal end, tail short with the ratio c=5.3–7.1…...............................................A. falciforme sp. nov.
6. Telamon absent……….......…………........………....…………………7
– Telamon present……………...............………………………………8
7. Spicules with weakly sclerotized proximal portion................... .....................................................A. grafi Jensen, 1991
– Spicules rod-like, without weakly sclerotized proximal por tion……..........................……………A. fldata Vitello, 1970
8. Lateral differentiation with ‘V’ markings………………......……... ................................A. paraceltica Muthumbi and Vincx, 1998
– Lateral differentiation without ‘V’ markings………………………9
9. With six cones at anterior end…………….............................. .....................................……A. pachydermatum (Cobb, 1920)
– Without corns at anterior end…………………………………... .................................................A. celtica Boucher, 1976
Acknowledgements
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Special thanks are given to the crew of R/V Kexue Sanhao for their assistance in the sample collection.
Funding
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  • The Strategic Priority Research Program of the Chinese Academy of Sciences under contract No. XDA11030201; the National Natural Science Foundation of China under contract No. 41706163; China Postdoctoral Science Foundation under contract No. 2016M602201.
References
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Boucher G. 1976. Nématodes des sables fins infralittoraux de la Pierre Noire (Manche Occidentale): II. Chromadorida. Bulletin du Muséum National d’Histoire Naturelle, 245(352): 26–30
Coomans A. 1979. Addendum I. A proposal for a more precise terminology of the body regions in the nematode. Annales de la Societe Royale Zoologique de Belgique, 108: 155–117
Decraemer W, Smol N. 2006. The chromadorida, desmodorida and desmoscolecida. In: Eyualem A, Andrássy I, Traunspurger W, eds. Freshwater Nematodes: Taxonomy and Ecology. Wallingford, UK: CABI Publishing, 497–573
Jensen P. 1991. Nine new and less known nematode species from the deep-sea benthos of the Norwegian Sea. Hydrobiologia, 222(1): 57–76, doi: 10.1007/BF00017500
Lorenzen S. 1994. The Phylogenetic Systematics of Freeliving Nematodes. London: Ray Society, 383
Muthumbi A W, Vincx M. 1998. Chromadoridae (Chromadorida: Nematoda) from the Indian Ocean: Difficulties in morphological identification of Actinonema Cobb, 1920 and Rhips Cobb, 1920. Hydrobiologia, 364(2): 155–167
Platt H M, Warwick R M. 1983. Free-living marine nematodes: I. British enoplids: pictorial key to world genera and notes for the identification of British species. In: Barnes R S K, Crothers J H, eds. Synopses of the British Fauna (New Series), no. 28. Cambridge: Cambridge University Press, 169–171
Platt H M, Zhang Z N. 1982. New species of marine nematodes from Loch Ewe, Scotland. Bulletin of the British Museum (Natural History), 42: 227–246
Tchesunov A. 2014. Order Chromadorida Chitwood, 1933. In: Schmidt-Rhaesa A, ed. Handbook of Zoology. Gastrotricha, Cycloneuralia, Gnathifera. Volume 2: Nematoda. Berlin, Boston: De Gruyter, 373–398
Vitiello P. 1970. Nématodes libres marins des vases profondes du Golfe du Lion: II. Chromadorida. Tethys, 2: 449–500
Wieser W. 1954. Reports of the Lund University Chile Expedition 1948–49. 17. Free-living marine nematodes II. Chromadoroidea. Lunds Universitets Årsskrift, Ny Foljd, Avdelningen 2, 50(16): 1–148
Appendix
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Year 2018 volume 37 Issue 10
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Article Info
doi: 10.1007/s13131-018-1318-x
  • Receive Date：2017-08-13
  • Online Date：2026-04-14
  • Published：2018-10-25
Article Data
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History
  • Received：2017-08-13
  • Accepted：2017-12-03
Funding
The Strategic Priority Research Program of the Chinese Academy of Sciences under contract No. XDA11030201; the National Natural Science Foundation of China under contract No. 41706163; China Postdoctoral Science Foundation under contract No. 2016M602201.
Affiliations
    1 Department of Marine Organism Taxonomy and Phylogeny, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China
    2 Laboratory for Marine Biology and Biotechnology, Pilot National Laboratory for Marine Science and Technology (Qingdao), Qingdao 266237, China
    3 University of Chinese Academy of Sciences, Beijing 100049, China

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表12种不同金属材料的力学参数
科
Family		 属数
Number of
genus		 种数
Number of
species		 占总种数比例
Percentage of
total species (%)		 属
Genus		 种数
Number of
species		 占总种数比例
Percentage of total
species (%)
鹅膏菌科Amanitaceae 2 11 5.26 鹅膏菌属 Amanita 10 4.78
小菇科 Mycenaceae 2 12 5.74 丝盖伞属 Inocybe 5 2.39
多孔菌科 Polyporaceae 8 14 6.70 蜡蘑属 Laccaria 5 2.39
红菇科 Russulaceae 3 23 11.00 小皮伞属 Marasmius 6 2.87
小菇属 Mycena 11 5.26
光柄菇属 Pluteus 5 2.39
红菇属 Russula 17 8.13
栓菌属 Trametes 5 2.39
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