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**)


#### 3.1.2. Remarks on the Species List and Synonymy

Murphy (1965:179 [25]) considered the species *Gammanema rapax* (Ssaweljev, 1912) as dubious because the original description is not depicted, and type specimens are evidently lacking. Gerlach (1964 [20]) synonymized *Gammanema menzelii* (Ditlevsen, 1918), *Gammanema ferox* Cobb, 1920, and *Gammanema fennicum* (Gerlach, 1953) with *G. rapax*. We find this broad synonymization questionable. *G. rapax* is a large species, measuring 5800–6100 μm in body length (Ssaweljev 1912 [26]), while all other species and specimens are at least half the size (except *G. menzelii*) and found far from the type locality. *G. menzelii* corresponds to *G. rapax* in body length (male 5900 μm) but differs in its higher number of preanal midventral supplementary organs (35 versus 20–22). Diagnosis of *G. menzelii* also lacks some important details, such as sizes of anterior sensilla, amphideal fovea, and spicules. Descriptions of *G. ferox* (New Hebrides [21]), *G. rapax* (North Sea [20]), and *G. rapax* (White Sea [15]) differ from the original diagnosis of Ssaweljev (1912 [26]) in their much smaller body size. Hence, we do not accept all these described specimens to be conspecific. Okhlopkov [15] redescribed females of *G. fennicum* and for the first time described males of *G. fennicum*. Though the specimens have not been sampled in the area of the type locality (Gulf of Finland, east Baltic Sea), but instead in the White Sea, the newly found females correspond to the original diagnosis in most details and morphometrics. Hence, *G. fennicum* is restored as a valid species.

#### 3.1.3. Identification of Species of *Gammanema*

Since *Gammanema* species show evident sexual dimorphism in size and shape of amphids and other structures, it is highly desirable to have both sexes (or at least males) for species identification. Due to deficiency of material, identification based on males is more reliable than identification solely based on females, since the males possess additional significant characteristics, such as supplementary organs and spicules.

For species identification of *Gammanema*, we propose a pictorial key constructed according to the principles of Platt [29], who first introduced pictorial keys in marine nematology. The pictorial key consists of two components, simplified images (caricatures) of heads (Figures 2 and 3), and Tables 1 and 2, with some metric and numeric characters being most important for species differentiation. Because of considerable sexual dimorphism, male and female head images are arranged in two separate plates, where the species are ordered in rows of gradual decrease of amphideal fovea (males) and cephalic setae (females), from top left to bottom right position.

**Figure 2.** Caricatured male heads of valid *Gammanema* species arranged from top left to bottom right along decrease of amphid size and cephalic setae in relation to head diameter.


**1.** *Gammanema* valid species, comparison of males.

**Table** 


 **2.** *Gammanema* valid species, comparison of females.

**Table**

**Figure 3.** Caricatured female heads of valid *Gammanema* species arranged from top left to bottom right along decrease of cephalic setae in relation to head diameter.

*3.2. Description of New Species of* Gammanema

*Gammanema okhlopkovi* sp. n. Figures 4–7, Table 3. http://zoobank.org/urn:lsid:zoobank.org:act:3B8336E6-9F74-4861-BCD3-94B27F52697B

### 3.2.1. Etymology

The species is named in honor of Yuri R. Okhlopkov, a PhD student who published a few papers on Selachinematidae, but unfortunately passed away in 2014 by mischance.

**Figure 4.** *Gammanema okhlopkovi* sp.n., entire view and anterior body: (**A**) holotype, male, entire view; (**B**) apical view, male, scanning electron micrograph; (**C**) subapical view, female, scanning electron micrograph; (**D**) head, lateral view, female, scanning electron micrograph; (**E**) head, sublateral view, male, scanning electron micrograph; (**F**) mouth opening, male, scanning electron micrograph. Scale bars: (**A**) 100 μm, (**B**) 10 μm, (**C**) 10 μm, (**D**) 10 μm, (**E**) 10 μm, (**F**) 3 μm.

#### 3.2.2. Material Examined

One holotype and seven paratype males were deposited in the National Institute of Biological Resources (South Korea). Inventory numbers of the holotype and paratypes are NIBRIV0000861671 and NIBRIV000086172-NIBRIV0000861677, respectively.

Type locality: Intertidal zone at coast of Jeju Island, South Korea (33◦26 05" N, 126◦55 15" E), sandy beach, June 2018.

**Figure 5.** *Gammanema okhlopkovi* sp. n., head of the holotype male: (**A**) surface view; (**B**) optical section. Scale bars: 20 μm.

#### 3.2.3. Description

Body cylindrical, with truncate anterior end and short conical tail. Cuticle annulated and punctuated. There are ca. 13 annules within a 20 μm area, everywhere along the body. Cuticle punctuation homogeneous, without lateral differentiation, the dots arranged in chessboard order. The dots are actually struts in the median zone of the cuticle; the struts are composed of two elements, as seen in sites of damaged cuticles.

**Figure 6.** *Gammanema okhlopkovi* sp. n., posterior body, males: (**A**) hind body; (**B**) spicule tips, precloacal seta, and supplementary organs, lateral view, scanning electron micrograph; (**C**) posterior-most supplementary organ, scanning electron micrograph; (**D**) cloacal opening and precloacal seta, subventral view, scanning electron micrograph; (**E**) tail with sensory papillae; (**F**) damaged cuticle near a supplement displays struts in the median zone, scanning electron micrograph. Scale bars: (**A**) 50 μm, (**B**) 10 μm, (**C**) 3 μm, (**D**) 3 μm, (**E**) 10 μm, (**F**) 3 μm.

Truncate anterior end bordered by a membranous fringe with indistinct sectioning in lips. The fringe is marked by longitudinal striations, with about 15 fine, short ribs or rugae between lateral outer labial sensilla and cephalic seta. There are twelve prominent peg-like projections around the rim of the anterior end.

Anterior sensilla arranged in 6 + 10 pattern. Six inner labial sensilla as pointed conical papillae situated just outside or the peg-like projections. Six outer labial sensilla situated at the base of the striated fringe; they are nearly equal in shape and size to the inner labial sensilla. Four cephalic setae at the same level with latero-median outer labial sensilla in tight pairs; within pair, the cephalic seta disposed laterally of the adjacent outer labial sensilla. Somatic sensilla represented by a few irregular postamphideal setae and two subsequent lateral papillae further posteriad. Somatic sensilla on the posterior body and tail region are represented by papillae sparsely arranged in latero-ventral, lateral, and dorso-lateral rows. Amphideal fovea large, transversally oval in outer outline, spirally coiled in three turns.

**Figure 7.** *Gammanema okhlopkovi* sp. n., posterior body of the holotype male. Scale bar: 20 μm.

The mouth opening is situated on the bottom of a funnel-shaped depression on the truncate anterior end. Acute teeth arranged in three radiating groups are visible, even in a semi-open mouth. Cheilostome is narrow and indistinct. Pharyngostome consists of two chambers. Anterior chamber is cup-shaped. Its walls are strengthened by three sclerotized rhabdions terminating posteriorly, with a group or five small cusps or denticles projected freely into the buccal cavity. The anterior rhabdions spread widely, thus making the anterior chamber bowl-shaped. In each group, the median tooth is tridentate, while teeth of two lateral pairs are bidentate. Posterior chamber cylindrical and narrow; its walls are strengthened by three sclerotized rhabdions. Pharynx cylindrical and evenly strongly muscular along its entire length.

Reproductive system is diorchic. Anterior outstretched testis situated ventrally to the intestine; posterior reflexed testis situated to the right of the vas deferens and intestine. Spicules paired, arcuate, distally pointed, and proximally very slightly cephalated. Gubernaculum as paired, nearly straight bars directed dorsally. Midventral supplementary organs, ten to thirteen in number, shaped as a nail-head 5–6 μm in diameter; the posteriormost organ situated at a distance 39 μm from the cloacal opening. A short conical midventral precloacal seta is present.

Tail very short; its conical tip turned left in all the specimens.


**Table 3.** Morphometrics of males *Gammanema okhlopkovi* sp. n. (holotype and paratypes).

#### 3.2.4. Diagnosis

*Gammanema* with short and stout body (L 961–1150 μm, a 25–31). Twelve prominent peg-like projections protruded outward from inner side of the circumoral membranous fringe. Set of anterior sensilla composed of six inner labial setae 4–5 μm, six outer labial setae 5–7 μm, and cephalic setae 9–19 μm long. Amphideal fovea spirally coiled in three turns, 32–48 μm wide. Rhabdion of anterior pharyngostome chamber 13–17 μm, rhabdion of posterior pharyngostome chamber 11–16 μm long. Spicules 32–39 μm long. Midventral preanal row of supplementary organs consists of precloacal seta and 10–13 nail-head organs. Tail short and conical, c' 1–1.6.

#### 3.2.5. Differential Diagnosis

*G. okhlopkovi* sp. n. is closest to *G. anthostoma*, sharing similar body length and body proportions a, b, and c, and similar size of amphids and spicules. The most obvious differences between the two species are longer cephalic setae (8.5–19 μm in *G. okhlopkovi* versus 6–7.5 μm in *G. anthostoma*), as well as a lack of precloacal supplementary organs in *G. anthostoma* (present in *G. okhlopkovi*).

#### *3.3. Description of New Species of* Latronema

## Genus *Latronema* (Wieser 1954)

Diagnosis of the genus has been recently updated by Leduc and Zhao [30]. A detailed review of the taxon is intended in forthcoming work on a peculiar diversity of *Latronema* species on an Atlantic seamount.

*Latronema obscuramphis* sp. n.

http://zoobank.org/urn:lsid:zoobank.org:act:5E195F44-8FDA-48D4-9E71-00855406670D Figures 8 and 9, Table 4.

#### 3.3.1. Etymology

The species name reflects the indistinctness of the amphids (from Latin "obscurus", inconspicuous).

## 3.3.2. Material Examined

One holotype male, two paratype females, and four juveniles were deposited in National Institute of Biological Resources (South Korea). Inventory numbers of the holotype and paratypes are NIBRIV0000861678 and NIBRIV0000861679–NIBRIV0000861680, respectively.

### 3.3.3. Description

Body stout cylindrical, with truncate anterior end and short conical tail. Body cuticle finely cross-striated (16 annules in 20 μm in light microscope, 12 annules in 10 μm, from scanning electron micrographs) in the midbody laterally. The cuticle is not punctated under light microscope but marked with longitudinal wings. The wings number approximately five, visible on the lateral body side. Anteriorly, short and weak extra wings are added between the main wings, close to the head.

Labial region is presented by circular labial membrane with fine longitudinal ribbing (about ten ribs in between two adjacent setae of cephalic crown counted under light microscope, or seven to ten in SEM). Since the edges of the labial membrane are rolled inward, it is impossible to discern whether the membrane is divided into labial lobes. Labial region is encircled by a light cuticular ridge (collar).

**Figure 8.** *Latronema obscuramphis* sp. n., entire body of the holotype male and surface cuticular structure: (**A**) holotype male, entire view; (**B**) entire view of a female, scanning electron micrograph; (**C**) head of a female laterally, scanning electron micrograph; (**D**) amphideal fovea of a female, scanning electron micrograph; (**E**) body cuticle rings and alae laterally, scanning electron micrograph. Scale bars: (**A**) 50 μm, (**B**) 30 μm, (**C**,**E**) 10 μm, (**D**) 3 μm.

Six slender inner labial setae are situated at the edge of the circular labial membrane. Ten equal setae located at the edge of the collar; they are about equal in length to one another and equal to inner labial setae, but wider basally; all the setae of the anterior circle look delicate and nearly transparent, and hence may be hardly visible against the labial cuticle. Fine ribs (striae) on the circumoral membrane may be arranged in fan-like bundles at sites opposite to cheilostomatal lobes. Quite possible the circle of ten equal setae comprises six outer labial and four cephalic setae, but all the setae are located at the same distance between them and do not make close pairs. Somatic setae comparable in length with anterior setae are distributed along the body in irregular longitudinal sublateral rows. Amphids in males are scarcely discernible under light microscope but detected in SEM as a small pit with simplified spiral structure. Amphids in females are not discernible at all under light microscope.

**Figure 9.** *Latronema obscuramphis* sp. n., male holotype structures: (**A**) surface view of the head; (**B**) sagittal optical section of the head; (**C**) posterior body. Scale bars: 20 μm.

Buccal cavity consists of comparatively narrow cheilostome surrounded by labial membrane and voluminous pharyngostome composed of two compartments, with the anterior being cup-shaped and the posterior cylindrical. Cheilostome walls are differentiated interiorly into twelve rounded lobes that do not continue into anterior free projections, unlike that of *Gammanema*. Walls of the anterior pharyngostome are strengthened by three rhabdions—one dorsal and two lateroventral. The rhabdions terminate posteriorly with about seven acute denticles (one median denticle and two sets of three lateral denticles on both sides of it). Anterior pharyngostome is opened widely, and its rhabdions move apart at obtuse angle. Posterior pharyngostome short and wide, its rhabdions slightly sclerotized, while intermediate cuticle between them thin and soft.



Pharynx cylindrical and strongly muscular. Nerve ring hardly discernible. Intestine is composed of convex enterocytes bulging in the gut lumen. Gut content in the holotype male is a long, fine-granular body, possibly a digested prey nematode in the posterior half of the intestine.

Female reproductive system is didelphic, both ovaries short and small, antidromously reflexed; in one female, anterior ovary to the right and posterior ovary to the left of the intestine, in other female anterior ovary to the left and posterior to the right of the intestine. Both spermathecas and uteri branch are filled with spermatozoa. Posterior ovary contains large oocyte with coarsely granulated cytoplasm and large nucleolated nucleus in the center. Somatic cuticle around vulva is thickened and distinctly set off as a vulvar plate.

Male reproductive system is diorchic. Both anterior outstretched and posterior reflexed testes situated ventrally and to the right of the intestine. Spicules equal, slightly arcuate, distally narrowed, proximally located, with very weakly developed knobs. Gubernaculum as a pair of short bars parallel to posterodistal edge of spicules. Preanal set of midventral supplementary organs composed of a midventral preanal seta and a row of about eight nail-head-shaped organs. The latter are not quite distinctly observed because of their position on the concave body side and covering by foreign particles.

Tail short and conical; its terminal cone covered with smooth cuticle and curved to the left.

#### 3.3.4. Diagnosis

*Latronema* with small and stout body (L 591–718 μm, a 13.9–19). All the anterior setae (i.e., inner labial setae, outer labial setae, and cephalic setae) are similar in length, ca 9-12 μm in males, 6–6.5 μm in females. Amphideal fovea small and obscure. Anterior pharyngostome rhabdion 12–12.5 μm long, posterior rhabdions 7.5–11 μm. Spicules arcuate, 38 μm long, gubernaculum 12 μm. Preanal midventral row of supplementary organs made up of preanal conical seta and twelve sucker-like organs. Tail very short (c 14.4, c' 1.6), with terminal cone ca 16 μm long usually turned left.
