Two New Marine Free-Living Nematodes from Jeju Island Together with a Review of the Genus Gammanema Cobb 1920 (Nematoda, Chromadorida, Selachinematidae)

diversity Article Two New Marine Free-Living Nematodes from Jeju Island Together with a Review of the Genus Gammanema Cobb 1920 (Nematoda, Chromadorida, Selachinematidae) Alexei Tchesunov 1,*, Raehyuk Jeong 2 and Wonchoel Lee 2 1 Department of Invertebrate Zoology, Faculty of Biology, Moscow State University, 119991 Moscow, Russia 2 Department of Life Science, Hanyang University, Seoul 04763, Korea; [email protected] (R.J.); [email protected] (W.L.) * Correspondence: [email protected] http://zoobank.org/urn:lsid:zoobank.org:pub:4C6B07ED-52DB-42A1-80B7-2881F0559E56 Received: 19 November 2019; Accepted: 18 December 2019; Published: 1 January 2020 Abstract: In the context of exploration of meiofauna in a sandy intertidal zone of Jeju Island (South Korea), over 70 nematode species are identified, some which have been proven to be new for science. Two new free-living marine nematode species of the family Selachinematidae (Chromadorida, Selachinematidae, Choniolaiminae) are described from the intertidal sandy sediments of Jeju Island (South Korea). Gammanema okhlopkovi sp. n. is closest to Gammanema anthostoma (Okhlopkov, 2002) and differs by having longer cephalic setae (8.5–19 µm in G. okhlopkovi versus 6–7.5 µm in G. anthostoma) and by the presence of precloacal supplementary organs. The genus diagnosis of Gammanema is updated. The genus includes fourteen valid species, while three species are considered species inquirendae due to incomplete diagnoses and illustrations impeding their correct recognition. An annotated list of valid and invalid Gammanema species is provided. A pictorial key for valid Gammanema species is constructed, which consists of two components: (1) simplified images of heads, and (2) a table summarizing most of the significant measured and numeric characters between species. Latronema obscuramphis sp. n. differs from its related species Latronema aberrans (Allgén 1934), Latronema annulatum (Gerlach, 1953), and Latronema spinosum (Andrássy, 1973) by body size, number of supplementary organs, tail shape, length of spicules, and cuticle ornamentation. Keywords: free-living marine nematodes; pictorial key; taxonomy 1. Introduction Data on Jeju marine free-living nematodes have been presented by Rho and Kim [1,2], Rho et al. [3], and Lim and Chang [4]. However, the exploration of the rich nematofauna of Jeju is still in the early stages. In connection with our project on Jeju intertidal meiofauna, we have recorded almost 70 nematode species at four points along a transect through the sandy intertidal zone at Shinyang, in the eastern corner of Jeju Island. A taxonomic survey of Jeju nematodes started with the family Thoracostomopsidae by Jeong et al. [5,6]. Now, we present a communication on the family Selachinematidae. The selachinematid nematodes are usually characterized by a stout cylindrical body with a truncate anterior end. They have a complicated buccal armament of rhabdions, denticles, or heavy mandibles, enabling them to capture nematode prey. The selachinematids have been known for a long time as carnivores in the strict sense, ingesting other smaller nematodes [7,8]. The percentage of selachinematids and other predator taxa in nematode assemblages are usually low in mud and silty Diversity 2020, 12, 19; doi:10.3390/d12010019 www.mdpi.com/journal/diversity Diversity 2020, 12, x FOR PEER REVIEW 2 of 19 long time as carnivores in the strict sense, ingesting other smaller nematodes [7,8]. The percentage of Diversityselachinematids2020, 12, 19 and other predator taxa in nematode assemblages are usually low in mud and2 silty of 19 sediment, but more abundant in sandy sediment with higher species diversity [9,10]. Particularly, sediment,most species but of more Gammanema abundant and in Latronema sandy sediment are confined with higherto sandy species sedime diversitynts of upper [9,10 shelf]. Particularly, zones. most species of Gammanema and Latronema are confined to sandy sediments of upper shelf zones. 2. Materials and Methods 2. MaterialsQuantitative and Methods samples were taken in June 2018, in the intertidal zone at Shinyang, close to the easternQuantitative corner of Jeju samples Island were (Figure taken 1). Sediments in June 2018, were in fixed the intertidal in 5% neutralized zone at Shinyang, formalin solution close to and the easternbrought corner back ofto Jejuthe Islandlaboratory. (Figure Meiofauna1). Sediments were were extracted fixed in 5%using neutralized the Ludox formalin method solution [11], andand broughtpostfixed back with to 70% the laboratory.ethanol dyed Meiofauna with Rose were bengal. extracted Nematodes using the were Ludox counted method and [11 specimens], and postfixed were withpacked 70% into ethanol a Syracuse dyed withglass Rosefilled bengal. with mixture Nematodes of glycerin, were counted 95% etha andnol, specimens and distilled were water packed (1:29:70). into a SyracuseThe glass glasswas placed filled with in a mixturedrying oven of glycerin, set to 40 95% °C ethanol,for 1–2 days and distilleduntil completely water (1:29:70). dehydrated, The glass as in was the placedglycerin-ethanol in a drying method oven set [12]. to 40 Specimens◦C for 1–2 dayswere until mounted completely in a drop dehydrated, of anhydrous as in the glycerin glycerin-ethanol within a methodwax-paraffin [12]. ring. Specimens Specimens were were mounted identified, in a measured, drop of anhydrous photographed, glycerin and within drawn a under wax-para a Leicaffin ring.DM5000 Specimens light microscope were identified, equipped measured, with Leica photographed, Application andSuite drawn Version under 3.8.0 a software Leica DM5000 and a Leica light microscopeDFC 425 C digital equipped camera. with LeicaAll the Application measured Suitesizes are Version given 3.8.0 in μ softwarem. For scanning and a Leica electron DFC 425microscopy, C digital camera.specimens All were the measureddehydrated sizes in a areseries: given 40% in ethanol,µm. For 70% scanning ethanol, electron 95% ethano microscopy,l, 95% ethanol specimens + acetone were dehydrated(50:50), acetone in a I, series: and ac 40%etone ethanol, II, and 70% then ethanol, critical 95%point ethanol, dried. Once 95% ethanol dried, specimens+ acetone (50:50),were mounted acetone I,on and a stub acetone to be II, coated and then with critical platinum–palladium point dried. Once alloy dried, and examined specimens with were Cam mounted Scan S-2. on a stub to be coatedType with specimens platinum–palladium were deposited alloy in and National examined Institute with of Cam Biological Scan S-2. Resources (South Korea). Figure 1. MapMap of of sampling sampling locality. locality. This This map map is made is made with with QGIS QGIS software software v.2.18.14, v.2.18.14, a free aand free open- and open-sourcesource geographic geographic information information system system (https://qgis.org). (https://qgis.org ). Type specimens were deposited in National Institute of Biological Resources (South Korea). 3. Results—Systematics 3.1. Review of Genus Gammanema Order Chromadorida Chitwood, 1933 Family Selachinematidae Cobb, 1915 Subfamily Choniolaiminae Schuurmans-Stekhoven and Adam, 1931 Genus Gammanema Cobb, 1920 Diversity 2020, 12, 19 3 of 19 3.1.1. Diagnosis Updated after Leduc 2013 and Tchesunov 2014 [13,14]. Selachinematidae, Choniolaiminae. Cuticle with homogenous annulations, without longitudinal ridges or lateral differentiation. Six inner and six outer labial sensilla, either setose or papillose; four cephalic setae, often slender and longer; outer labial and cephalic sensilla combined in common circle of 10, with dorso- and ventrosublateral sensilla arranged in four pairs with cephalic sensilla. Amphideal fovea spiral or loop-shaped, usually noticeably larger in males than in females. Somatic setae in irregular longitudinal rows; anterior cervical setae may be as long as cephalic setae. Mouth opening surrounded by partly fused lips shaping a circumoral membrane with fine longitudinal striation. There are twelve projections, from small and inconspicuous to prominent and elaborate, at the rim of the mouth opening. Buccal cavity (pharyngostome) consists of two chambers, anterior cup-shaped and posterior cylindrical; walls of each chamber are strengthened with three cuticularized rhabdions; the rhabdions of the anterior chamber terminate posteriorly in minute denticles. Pharynx cylindroids, evenly muscular and devoid of a terminal bulb. Alimentary tract terminates by rectum and anus. Precloacal midventral supplementary organs sucker-like, cup-shaped, tubular, or absent. Tail short, conical, cuticle of its terminal cone levigated or smooth. Type species: Gammanema ferox (Cobb, 1920). Annotated species list (valid species in bold) 1. Gammanema agglutinans Leduc, 2013. Leduc 2013:21–25, Figures 11–13, Table 2 [13] (males, females); SW Pacific, region to the east of New Zealand, Chatham Rise, depths 350–1238 m. 2. Gammanema anthostoma Okhlopkov, 2002. Okhlopkov 2002:42–45, Figures 2 and 3 [15] (males and females); White Sea (Northern Russia), Kandalaksha Bay, depth 14 m. 3. Gammanema cancellatum Gerlach, 1955. Gerlach 1955:271–272, Abbildung. 6 [16] (female); San Salvador, coastal groundwater. Remark: the species is retained here as valid, despite the absence of males in diagnosis, since it can be distinguished sound from other congeners by peculiar cuticle ornamentation with rods. 4. Gammanema conicauda Gerlach, 1953. Gerlach 1953:553–555, Abbildungen 17 a-f [17] (males, females, juvenile); Tyrrhenian Sea, area of Naples, surf zone; North Sea coast.

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