Adult. Body cylindrical or fusiform, tapering anteriorly in the pharyngeal region and posteriorly in the tail region, straight or curved, either ventrally or dorsally, upon fixation. Cuticle annulated along the entire body, annules equal in width; annulation starts at a level with the cephalic setae bases and extends towards the tail terminus; annules visually smooth or with fine longitudinal striation as seen under the light microscope. When present, longitudinal striation covers annules over the entire body length. Lateral alae present; anterior end of lateral alae may connect with the amphideal fovea in some species; posterior end extends towards tail terminus, ending at a certain distance from the tail tip. Body pores and epidermal glands absent. Somatic sensilla present. Labial region bluntly rounded, lips fused, tip of the anterior end often with much thicker cuticle. There are no cuticularised plates or other refractive structures around the anterior end. Inner labial sensilla invisible if present. Outer labial sensilla on the apical surface of the labial region. Of the outer labial sensilla, only lateral ones are often clearly visible under the light microscipe, located half way between the tip of the lip region and the anterior margin of the amphid. Cephalic sensilla setiform; their bases located at the base of the labial region, at various levels relative to the anterior edge of the amphid. Subcephalic and cervical sensilla, deirid and ocelli absent. Amphids usually similar in shape and size between sexes, sexual dimorphism, if present, is reflected in the relative length of the amphid or its sections: amphidial fovea an inverted U-shape with its ventral limb as long as or longer than the dorsal limb. Space between the amphidial limbs is variable in size (narrow or wide). Two species with the amphid in a shape of a longitudinal slit, assumed to be formed due to the reduction of the dorsal limb (Thanh and Gagarin 2011, Thanh et al. 2012). Amphidial glands often large, located at the level with the posterior part of the pharynx. Secretory-excretory system usually present; renette cell located opposite to the anterior part of intestine. Secretory-excretory ampulla present, located at the level of the intestine in the majority of species (if known). Cuticularised secretory-excretory duct very short, opens to the exterior via a pore, located at the level of the anterior part of intestine, except for C. amphidialis, in which it opens to the outside on the labial region. Nerve ring surrounding pharyngo-intestinal junction, just posterior to the muscular pharynx. Buccal cavity small and undifferentiated: cheilostom broad cylndrical, without rhabdia or sclerotisations; gymnostom and stegostom undifferentiated, closed or funnel-shaped, its slender lining continuous with that of the pharynx. Pharyngeal tubes absent. Pharynx uniformly muscular, cylindrical or fusiform, without visible subdivisions, with evenly distributed myofilaments; pharyngeal lumen uniform in thickness along the entire pharynx length; valves absent. Number and arrangement of pharyngeal glands and their orifices unclear. Cardia elongate, glandular. Tail conoid or subcylindrical, in some species with clavate terminal part. Three caudal glands present, their bodies and nuclei are incaudal; they open via a common spinneret.

Female reproductive system didelphic-amphidelphic with equally developed branches, ovaries outstretched. Spermatheca present in some species. Vulva equatorial, transverse (when described). Vagina straight; pars proximalis vaginae encircled by single sphincter muscle; pars refringens vaginae and epiptygmata absent. Tail most commonly with one pair of ventrosublateral setae located along the middle of the tail and one pair of sublateral setae located subterminally. Rectum short.

Male reproductive system diorchic, testes opposed: anterior testis outstretched and posterior testis reflexed. Spicules paired and symmetrical, arcuate, with weakly defined manubrium and subcylindrical shaft. Gubernaculum plate-like, without strongly developed apophysis. Some species with 2-5 precloacal supplements arranged midventrally; ventrosublateral precloacal and postcloacal sensilla absent. Tail most commonly with two pairs of ventrosublateral setae located along the posterior half of the tail and one pair of sublateral setae located subterminally.

Campylaimus abnormis Nguyen Vu Thanh & Gagarin, 2011 (Thanh and Gagarin 2011)

Campylaimus amphidialis Fadeeva, Mordukhovich & Zograf, 2016 (Fadeeva et al. 2016)

Campylaimus arquatus Villares, Martelli, Lo Russo & Pastor, 2013 (Villares et al. 2013)

Campylaimus bonariensis Villares, Martelli, Lo Russo & Pastor, 2013 (Villares et al. 2013)

Campylaimus cylindricus Gerlach, 1956 (Gerlach 1956)

Campylaimus gerlachi Timm, 1961 (Gerlach 1950, Timm 1961)

Campylaimus gracilis Nguyen Vu Thanh, Nguyen Thanh Hien & Gagarin, 2012 (Thanh et al. 2012)

Campylaimus inaequalis Cobb, 1920 (Cobb 1920)

Campylaimus lefeverei Gerlach, 1956 (Gerlach 1956)

Campylaimus longispiculus sp. n.

Campylaimus minor Timm, 1961 (Timm 1961)

Campylaimus minutus Fadeeva, Mordukhovich & Zograf, 2016 (Fadeeva et al. 2016)

Campylaimus mirus Gerlach, 1950 (Gerlach 1956)

Campylaimus orientalis Fadeeva, Mordukhovich & Zograf, 2016 (Fadeeva et al. 2016)

Campylaimus patagonicus Villares, Martelli, Lo Russo & Pastor, 2013 (Villares et al. 2013)

Campylaimus ponticus Sergeeva, 1981 (Sergeeva 1981)

Campylaimus pulcher Fadeeva, Mordukhovich & Zograf, 2016 (Fadeeva et al. 2016)

Campylaimus rimatus Vitiello, 1974 (Vitiello 1974)

Campylaimus siwaschensis Sergeeva, 1981 (Sergeeva 1981)

Campylaimus striatus Boucher & Helléouët, 1977 (Boucher and Helléouët 1977)

Campylaimus tkatchevi Tchesunov, 1978 (Tchesunov 1978)

Campylaimus triclados sp. n.

Campylaimus abditus Bussau, 1993 (Bussau 1993)

Measurements. Table 1. Adult. Figs 1, 2, 3. Cuticle without longitudinal striation. Space between dorsal and ventral limbs of amphid not developed (Fig. 2a). Lateral alae narrow, appearing externally as two straight lines encompassing entire length of amphid. It originates at level with anterior edge of amphid, extends posteriorly as two lines parallel and very close to ventral limb of the amphid (Fig. 2b) and ends at level of posterior fifth of tail by merging with posterior end of ventral limb of amphid (Fig. 3c, d). Secretory-excretory pore opens posterior to cardia, at level with anterior part of intestine (Fig. 2d). Tail with clavate terminal part. Male. Anteriormost edge of amphid positioned just posterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 2.2–2.7 labial region diameters in length. Ventral limb of amphid extends along entire body to posterior fifth of tail. Ventral limb of amphid is 1.0–1.5 wider than dorsal limb. Spicules with rounded manubrium and subcylindrical, arcuate shaft (Fig. 3a). Gubernaculum with dorsal apophysis (Fig. 3b). Precloacal supplements/sensilla invisible in current specimens. Two pairs of ventrosublateral setae located along posterior half of tail and one pair of sublateral setae located subterminally. Female. Anteriormost edge of amphid positioned just posterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 2.1–2.3 labial region diameters in length. Ventral limb of amphid extends along entire body to posterior fifth of tail. Ventral limb of amphid is 1.5 wider than dorsal limb. Vagina straight (Fig. 2e, f). One pair of ventrosublateral setae located along middle of tail and one pair of sublateral setae located subterminally.

Body 0.34–0.52 mm long; cuticle without longitudinal striation; anteriormost edge of amphid just posterior to oral opening; dorsal limb of amphid equal to 2.2–2.7 labial region diameters in male, 2.1–2.3 labial region diameters in female; ventral limb of amphid extends towards posterior fifth of tail in both female and male; ventral limb of amphid is 1.0–1.5 wider than dorsal limb; interamphideal space absent; secretory-excretory pore opens posterior to cardia; spicules 14–22 µm long; precloacal supplements indistinct; tail equal to 4.7–8.9 anal body diameters in length, with clavate terminal part.

Originally described as C. inaequalis by Gerlach (1950) and subsequently renamed into C. gerlachi by Timm (1961), the species was described from the Kiel Bay (Gerlach 1950), the Bay of Bengal (Timm 1961) and from the Yellow Sea (Huang and Zhang 2006), not accounting for published records from other parts of the world which were not accompanied by the proper species descriptions. Recent specimens and populations described by Gerlach (1950), Huang and Zhang (2006), Timm (1961) are united by a combination of the following characters: body less than 0.7 mm long, dorsal limb of the amphid equal to 2–3 labial region diameters in length, ventral limb of the amphid extends towards the posterior part of the tail, but does not reach the tail tip, both limbs of roughly equal width and the tail terminus clavate in shape. Villares et al. (2013) found a single male from Argentina with two precloacal supplements, which they also described under the name C. gerlachi. Unfortunately, since the description of this specimen does not cover all diagnostic features, it is impossible to verify the taxonomic position of the specimen and compare it to the population of C. gerlachi found in Sweden.

Measurements. Table 1. Adult. Figs 4, 5. Cuticle without longitudinal striation. Space between dorsal and ventral limbs of amphid not developed. Lateral alae narrow, appearing externally as two straight lines encompassing entire length of amphid. It originates at level with anterior edge of amphid, extends posteriorly as two lines parallel and very close to ventral limb of amphid and ends close to tail tip by merging with posterior end of ventral limb of amphid (Fig. 5d). Secretory-excretory pore opens posterior to cardia, at level with anterior part of intestine. Tail with conoid terminal part. Male. Anteriormost edge of amphid positioned at level with oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 2.2 labial region diameters in length. Ventral limb of amphid extends along entire body to terminal part of tail. Ventral limb of the amphid is 1.0-1.5 wider than dorsal limb. Spicules with rounded manubrium and subcylindrical, arcuate shaft. Gubernaculum platelike, without apophysis. Precloacal supplements indistinct/absent. Female. Anteriormost edge of amphid positioned just posterior to or at level with oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.6-2.6 labial region diameters in length. Ventral limb of amphid extends along entire body to terminal part of tail. Ventral limb of amphid is 1.5-2.0 wider than dorsal limb. Vagina straight (Fig. 5c). One pair of ventrosublateral setae located along the middle of tail and one pair of sublateral setae located subterminally.

Body 0.36–0.56 mm long; cuticle without longitudinal striation; anteriormost edge of amphid at level with oral opening; dorsal limb of amphid equal to 2.2 labial region diameters in male, 1.6–2.6 labial region diameters in female; ventral limb of amphid extends towards terminal part of tail in both female and male; ventral limb of amphid is 1.0–2.0 times wider than dorsal limb; interamphideal space absent; secretory-excretory pore opens posterior to cardia; spicules 16 µm long; precloacal supplements indistinct; tail equal to 4.1–6.0 anal body diameters in length, with conoid terminal part.

Recent specimens are nearly identical with the type populaiton of C. minutus from the Sea of Japan (Fadeeva et al. 2016) in qualitative and quantitative characters. C. minutus was originally distinguished from C. gerlachi in having relatively shorter cephalic setae (equal to 20% vs. 50% of the labial region width in length) and relatively shorter tail (<5 vs. >5 anal body diameters in length). As pointed below in the discussion, length of cephalic setae is often impossible to measure correctly, while the relative length of the tail in the C. gerlachi from Kiel Bay is exactly 5 (Gerlach 1950). Two species can however be distinguished from each other by the shape of the tail (clavate in C. gerlachi vs. conoid in C. minutus, see also Figure 5B in Fadeeva et al. (2016)) and in the position of the posterior end of the amphid (at a distance from the tail terminus in C. gerlachi vs. close to the tail terminus in C. minutus). Female specimen depicted on the Figures 5F-G in Fadeeva et al. (2016) could belong to C. gerlachi instead.

Measurements. Table 2. Adult. Figs 6, 7. Cuticle without longitudinal striation. Space between dorsal and ventral limbs of amphid not developed. Lateral alae broad, appearing externally as two crenate lines encompassing entire length of amphid. It originates at level with anterior edge of amphid, extends posteriorly as two lines parallel to and widely spaced from ventral limb of the amphid (Fig. 7c, d) and ends at level of posterior fourth of tail by merging with posterior end of ventral limb of amphid. Secretory-excretory pore opens posterior to cardia, at level with anterior part of intestine (Fig. 7f). Tail with clavate terminal part. Male. Anteriormost edge of amphid positioned at level with oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 2.1–2.6 labial region diameters in length. Ventral limb of amphid extends along entire body to terminal part of tail. Ventral limb of amphid is 1.7–2.0 times wider than dorsal limb. Spicules with rounded manubrium and conoid, arcuate shaft. Gubernaculum platelike, without apophysis. Precloacal supplements absent/indistinct. Two pairs of ventrosublateral setae located along posterior half of tail and one pair of sublateral setae located between posterior end of lateral alae and tail terminus. Female. Anteriormost edge of amphid positioned at level with oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.8–2.4 labial region diameters in length. Ventral limb of amphid extends along entire body to terminal part of tail. Ventral limb of amphid is 1.7–2.5 times wider than dorsal limb. Vagina straight (Fig. 7e). One pair of ventrosublateral setae located along middle of tail and one pair of sublateral setae located close to posterior end of lateral alae.

Body 0.56–0.73 mm long; cuticle without longitudinal striation; anteriormost edge of amphid at level with oral opening; dorsal limb of amphid equal to 2.1–2.6 labial region diameters in male, 1.8–2.4 labial region diameters in female; ventral limb of amphid extends towards posterior fourth of tail in both female and male; ventral limb of amphid is 1.7–2.5 wider than dorsal limb; interamphideal space absent; secretory-excretory pore opens posterior to cardia; spicules 27–30 µm long; precloacal supplements indistinct; tail equal to 4.8–5.9 anal body diameters in length, with clavate terminal part.

In having relatively long dorsal branch of the amphid, broad ventral branch of the amphid and clavate tail, recent specimens are most similar to C. tkatchevi described from the Caspian Sea (Tchesunov 1978), differing only in somewhat longer body (0.56–0.73 mm vs. 0.45–0.61 mm in the type population) and spicules (27–30 µm vs. 23 µm in the type population).

Measurements. Table 2. Adult. Figs 8, 9. Cuticle without longitudinal striation. Space between dorsal and ventral limbs of amphid not developed. Lateral alae narrow, appearing externally as two straight lines encompassing entire length of amphid. It originates at level with anterior edge of amphid, extends posteriorly as two lines parallel and very close to ventral limb of amphid and ends at level of posterior fifth of tail (Fig. 9c) by merging with posterior end of ventral limb of amphid. Secretory-excretory pore opens posterior to cardia, at level with anterior part of intestine. Tail with clavate terminal part. Male. Not found. Female. Anteriormost edge of amphid positioned just posterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.2 labial region diameters in length. Ventral limb of amphid extends along entire body to terminal part of tail. Ventral limb of amphid is 1.3 times wider than dorsal limb. Vagina straight. One pair of ventrosublateral setae located along middle of tail and one pair of dorsosublateral setae located half way between posterior end of lateral alae and tal terminus.

Body 0.6 mm long; cuticle without longitudinal striation; anteriormost edge of amphid posterior to oral opening; dorsal limb of amphid equal to 1.2 labial region diameters in female; ventral limb of amphid extends towards posterior fifth of tail; ventral limb of amphid is 1.3 wider than dorsal limb; interamphideal space absent; secretory-excretory pore opens posterior to cardia; tail equal to 5.8 anal body diameters in length, with clavate terminal part.

This species was originally described from the Lake Syvash, based on a single female (Sergeeva 1981). The original description has crucial disagreements between the text and the illustration of the species regarding the size of the dorsal amphideal limb: the text states that the dorsal limb of the amphid is 23.3 µm long, but the illustration shows it to be only around 12–13 µm long. Recent specimen collected in the Baltic is similar to the holotype female in most body measurements and specifically in relatively short dorsal amphideal limb (12–13 µm vs. 14 µm in recent specimen), if the illustration of the holotype is to be trusted.

Measurements. Table 2. Adult. Figs 8, 10. Cuticle without longitudinal striation. Space between dorsal and ventral limbs of amphid not developed. Lateral alae broad, appearing externally as two crenate lines encompassing entire length of the amphid. It originates at level with anterior edge of amphid, extends posteriorly as two lines parallel to and widely spaced from ventral limb of amphid (Fig. 10f) and ends at level of posterior fourth of tail by merging with posterior end of ventral limb of amphid. Interamphideal space absent. Cardia extremely long, more than corresponding body diameter in length. Secretory-excretory pore opens posterior to cardia, at level with anterior part of intestine (Fig. 10d). Tail with clavate terminal part. Male. Not found. Female. Anteriormost edge of amphid posterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.6 labial region diameters in length. Ventral limb of amphid extends along entire body to posterior fourth of tail. Ventral limb of amphid is 3 times wider than dorsal limb. Vagina straight (Fig. 10e). Spermatheca absent, spermathozoa in uterus. One pair of ventrosublateral setae located along middle of tail and one pair of dorsosublateral setae located just behind posterior end of the lateral alae.

Body 0.96 mm long; cuticle without longitudinal striation; anteriormost edge of amphid posterior to oral opening; dorsal limb of amphid equal to 1.6 labial region diameters in female; ventral limb of amphid extends towards posterior fourth of tail; ventral limb of amphid is 3 times wider than dorsal limb; interamphideal space absent; secretory-excretory pore opens posterior to cardia; tail equal to 14.5 anal body diameters in length, with clavate terminal part.

Original description of this species is based on two specimens, a male and a female (Gerlach 1956) while the recent specimen is a female. Both populations are similar in the morphology of the anterior end: position of the oral opening anterior to the anteriormost edge of the amphid and in the shape of the amphid without interamphideal space, with ventral limb of the amphid extending towards tail tip and the dorsal limb of the amphid 1.6–1.7 times the labial region diameter in length. Observed differences between the two populations include much smaller body of the recently collected female (959 µm vs. 1553–1555 µm in the original description) and thus smaller measurements of a number of characters (length of cephalic setae, length of dorsal limb of the amphid etc.). Since inter- and intraspecific variability in species of the genus Campylaimus are currently poorly understood and since no qualitative differences can be found between these two populations, they are considered here to belong to the same species.

Measurements. Table 3. Adult. Figs 11, 12, 13, 14. Cuticle without longitudinal striation. Lateral pair of outer labial sensilla distinct in some specimens, located half way between tip of lip region and anterior margin of amphid (Fig. 12a). Space between dorsal and ventral limbs of amphid developed. Lateral alae narrow, appearing externally as smooth uniform band with straight margins (Fig. 13e), but with distinct subcuticular channel and crenate margins when focused midway (Fig. 13f). It originates at posterior end of dorsal limb of amphid and ends in a small expansion at basis of clavate part of tail. Secretory-excretory pore opens posterior to cardia, at level with anterior part of intestine (Fig. 13c, d). Tail with clavate terminal part. Male. Anteriormost edge of amphid positioned anterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 2.2–2.6 labial region diameters in length. Ventral limb of amphid extends along pharyngeal region to level of midpharynx; 1.9–2.4 times the length of dorsal limb. Ventral limb of amphid is as wide as dorsal limb. Interamphideal space extends along pharyngeal region to same level as ventral limb. Spicules with rounded manubrium and conoid, arcuate shaft; distinct velum. Gubernaculum with weak caudal apophysis, often hard to discern. One small precloacal papilliform sensillum located on 5th–6th annule anterior to cloacal opening (Fig. 14a, b). Second precloacal pore-like sensillum located on 11th annule anterior to cloacal opening (Fig. 14a, b). Two pairs of ventrosublateral setae located along posterior half of tail and one pair of dorsosublateral setae located subterminally. Female. Anteriormost edge of amphid positioned anterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.9–2.2 labial region diameters in length. Ventral limb of amphid extends along pharyngeal region to level of midpharynx; 1.6–1.9 times the length of dorsal limb. Ventral limb of amphid is as wide as dorsal limb. Interamphideal space extends along pharyngeal region to same level as ventral limb. Vagina straight. One pair of ventrosublateral setae located along posterior third of tail and one pair of dorsosublateral setae located subterminally.

Body 0.63–0.73 mm long; cuticle without longitudinal striation; anteriormost edge of amphid anterior to oral opening; dorsal limb of amphid equal to 2.2–2.6 labial region diameters in male, 1.9–2.6 labial region diameters in female; ventral limb of amphid extends towards midpharynx in both sexes, 1.9-2.4 times the length of dorsal limb in male and 1.6-1.9 times the length of dorsal limb in female; ventral limb of amphid is as wide as dorsal limb; interamphideal space extends to same level as ventral limb; secretory-excretory pore opens posterior to cardia; spicules 23–26 µm long; two precloacal supplements; tail equal to 4.1–5.3 anal body diameters in length, with clavate terminal part.

Original description of this species is based on one male and two females (Vitiello 1974), while recent material includes 11 specimens. Both populations are similar in most body measurements and in the morphology of the anterior end: position of the oral opening posterior to the anteriormost edge of the amphid and in the shape of the amphid with developed interamphideal space, ventral limb of the amphid two times the length of the dorsal limb and extending to the level of the middle of the pharynx. Observed differences between two populations are limited to spicule length (31 µm in the holotype male and 23-26 µm in recent specimens).

Measurements. Table 3. Adult. Figs 15, 16, 17. Cuticle without longitudinal striation. Lateral pair of outer labial sensilla distinct in some specimens, located half way between tip of lip region and anterior margin of amphid. Space between dorsal and ventral limbs of amphid developed. Lateral alae narrow, appearing externally as smooth uniform band with straight margins. It originates at posterior end of dorsal limb of amphid and ends in a small expansion at basis of tail tip (Fig. 17f). Secretory-excretory pore opens posterior to cardia, at level with anterior part of intestine. Tail with conoid, gradually narrowing terminal part. Male. Anteriormost edge of amphid positioned anterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.9–2.3 labial region diameters in length. Ventral limb of amphid extends along pharyngeal region to level of anterior third of pharynx; 1.2–1.4 times the length of dorsal limb. Ventral limb of amphid is as wide as dorsal limb. Interamphideal space extends along pharyngeal region to same level as ventral limb. Spicules with rounded manubrium and conoid, arcuate shaft. Gubernaculum plate-like, without apophysis. One small precloacal papilliform sensillum located on 6th annule anterior to cloacal opening (Fig. 17c, d). Second precloacal pore-like sensillum located on 10th–11th annule anterior to cloacal opening (Fig. 17c, d). Two pairs of ventrosublateral setae located along posterior half of tail and one pair of dorsosublateral setae located subterminally. Female. Anteriormost edge of amphid positioned anterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.6–2.3 labial region diameters in length. Ventral limb of amphid extends along pharyngeal region to level of anterior third of pharynx; 1.2–1.4 times the length of dorsal limb. Ventral limb of amphid is as wide as dorsal limb. Interamphideal space extends along pharyngeal region to same level as ventral limb. Vagina straight. Vulva a transverse slit. One pair of ventrosublateral setae located along posterior third of tail and one pair of dorsosublateral setae located subterminally.

Body 0.58–0.65 mm long; cuticle without longitudinal striation; anteriormost edge of amphid anterior to oral opening; dorsal limb of amphid equal to 1.9–2.3 labial region diameters in male, 1.6–2.3 labial region diameters in female; ventral limb of amphid extends towards anterior third of pharynx in both sexes, 1.2–1.4 times the length of dorsal limb in both sexes; ventral limb of amphid is as wide as dorsal limb; interamphideal space extends to same level as ventral limb; secretory-excretory pore opens posterior to cardia; spicules 23–27 µm long; two precloacal supplements; tail equal to 3.9–5.3 anal body diameters in length, with conoid terminal part.

The main distinguishing feature of C. orientalis is the shape of the amphid, where the ventral limb is only slightly longer than the dorsal limb and the inter-amphideal space is equal in width to either of the limbs of the amphid (Fadeeva et al. 2016). This feature unites both type population from the Sea of Japan and recently collected specimens from the Skagerrak, with recent specimens only being somewhat smaller in size (0.58–0.65 mm vs. 0.61–0.85 mm in type specimens), which also proportionally affects a number of other characters.

Measurements. Table 4. Adult. Figs 18, 19, 20, 21. Cuticle without longitudinal striation. Space between dorsal and ventral limbs of amphid developed. Lateral alae narrow, appearing externally as smooth uniform band with straight margins, but with crenate margins when focused midway. It originates at posterior end of dorsal limb of amphid and gradually disappears at a short distance from the tail tip. Secretory-excretory pore opens posterior to cardia, at level with anterior part of intestine (Fig. 20c, d). Tail with conoid terminal part. Male. Anteriormost edge of amphid positioned anterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.6–2.5 labial region diameters in length. Ventral limb of amphid extends along pharyngeal region to level of anterior part of intestine; 4.3–5.5 times the length of dorsal limb. Ventral limb of amphid is as wide as dorsal limb. Interamphideal space extends along pharyngeal region further than posterior end of dorsal limb but not reaching posterior end of ventral limb. Spicules with rounded manubrium and conoid, arcuate shaft; distinct velum. Gubernaculum platelike, without apophysis. One small precloacal papilliform sensillum located on 5th-6th annule anterior to cloacal opening (Fig. 21a). Second precloacal pore-like sensillum located on 9th annule anterior to cloacal opening (Fig. 21a). Two pairs of ventrosublateral setae located along posterior half of tail and one pair of dorsosublateral setae located subterminally. Female. Anteriormost edge of amphid positioned anterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.9 labial region diameters in length. Ventral limb of amphid extends along pharyngeal region to level of midpharynx; 2.2–2.8 times the length of dorsal limb. Ventral limb of amphid is as wide as dorsal limb. Interamphideal space extends along pharyngeal region further than posterior end of the dorsal limb but not reaching posterior end of ventral limb. Vagina straight. One pair of ventrosublateral setae located along posterior third of tail and one pair of dorsosublateral setae located subterminally.

Body 0.59–0.69 mm long; cuticle without longitudinal striation; anteriormost edge of amphid anterior to oral opening; dorsal limb of amphid equal to 1.6–2.5 labial region diameters in male, 1.9 labial region diameters in female; ventral limb of amphid extends towards anterior part of intestine in male and midpharynx in female, 4.3–5.5 times the length of dorsal limb in male and 2.2–2.8 times the length of dorsal limb in female; ventral limb of amphid is as wide as the dorsal limb; interamphideal space extends further than posterior end of dorsal limb but not reaching posterior end of ventral limb; secretory-excretory pore opens posterior to cardia; spicules 19–24 µm long; two precloacal supplements; tail equal to 4.3–5.6 anal body diameters in length, with conoid terminal part.

The specific epithet refers to the three-partite shape of the amphid, with three "branches": strongly developed dorsal and ventral limbs and prominent interamphideal space.

This new species can be easily differentiated from all currently known species of the genus Campylaimus by the shape of the amphid, with interamphideal space being longer than the dorsal limb of the amphid, but shorter than the ventral limb of the amphid. In all other known species with developed interamphideal space (C. rimatus, C. mirus and C. orientalis), it is usually as long as the ventral limb of the amphid.

Measurements. Table 4. Adult. Figs 22, 23. Cuticle without longitudinal striation. Space between dorsal and ventral limbs of amphid developed. Lateral alae narrow, with crenate margins. It originates at posterior end of ventral limb of amphid and ends in a long expansion along posterior third of tail. Secretory-excretory pore opens posterior to cardia, at level with anterior part of intestine. Tail with clavate terminal part. Male. Not found. Female. Anteriormost edge of amphid positioned anterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.7 labial region diameters in length. Ventral limb of amphid extends along pharyngeal region to level of anterior third of the pharynx; 1.4 times the length of dorsal limb. Ventral limb of amphid 1.3 wider than dorsal limb. Interamphideal space very broad, extends along pharyngeal region to same level as ventral limb. Vagina straight. Spermatheca absent, spermathozoa in uterus. One pair of ventrosublateral setae located along middle of tail and one pair of dorsosublateral setae located half way between posterior end of lateral alae and tal terminus.

Body 0.93 mm long; cuticle without longitudinal striation; anteriormost edge of amphid anterior to oral opening; dorsal limb of amphid equal to 1.7 labial region diameters in female; ventral limb of amphid extends towards anterior part of pharynx, 1.4 times the length of dorsal limb in female; ventral limb of amphid is 1.3 wider than dorsal limb; interamphideal space extends to same level as ventral limb; secretory-excretory pore opens posterior to cardia; tail equal to 7.3 anal body diameters in length, with clavate terminal part.

Original description of this species is based on a single male specimen (Gerlach 1950), while the recent specimen is a female. Both specimens are similar in most body measurements and in the morphology of the anterior end: position of the oral opening posterior to the anteriormost edge of the amphid and in the shape of the amphid with developed interamphideal space, ventral limb of the amphid 1.4 times the length of the dorsal limb and extending to the level of the anterior third of the pharynx. Observed differences between the two specimens include slender body (a = 42) shorter amphid (36 µm) and broader annules (5 µm) in the male (vs. a = 28, 46 µm and 2 µm, respectively, in the female).

Measurements. Table 5. Adult. Figs 24, 25. Cuticle without longitudinal striation. Space between dorsal and ventral limbs of amphid not developed. Lateral alae narrow, with straight margins. It originates at posterior end of ventral limb of amphid and ends along posterior third of the tail. Secretory-excretory pore opens posterior to cardia, at level with anterior part of intestine. Tail with clavate terminal part. Male. Anteriormost edge of amphid positioned anterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 2.3 labial region diameters in length. Ventral limb of amphid extends along pharyngeal region to level of mid-pharynx; 1.7 times the length of dorsal limb. Ventral limb of amphid two times wider than dorsal limb. Spicules with rounded manubrium and conoid, arcuate shaft. Gubernaculum platelike, without apophysis. One small precloacal papilliform sensillum located on 5th annule anterior to cloacal opening. Second precloacal pore-like sensillum located on 8th annule anterior to cloacal opening. Two pairs of ventrosublateral setae located along posterior half of tail and one pair of sublateral setae located subterminally. Female. Anteriormost edge of amphid positioned anterior to oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.9–2.0 labial region diameters in length. Ventral limb of amphid extends along pharyngeal region to level of midpharynx; 2.0–2.3 times the length of dorsal limb. Ventral limb of amphid two times wider than dorsal limb. Vagina straight. One pair of ventrosublateral setae located along middle of tail and one pair of dorsosublateral setae located subterminally.

Body 0.53–0.64 mm long; cuticle without longitudinal striation; anteriormost edge of amphid anterior to oral opening; dorsal limb of amphid equal to 2.3 labial region diameters in male, 1.9–2.0 labial region diameters in female; ventral limb of amphid extends towards mid-pharynx in both sexes, 1.7 times the length of dorsal limb in male and 2.0–2.3 times the length of dorsal limb in female; ventral limb of amphid is twice as wide as dorsal limb; interamphideal space absent; secretory-excretory pore opens posterior to cardia; spicules 24 µm long; precloacal supplements indistinct; tail equal to 4.5–5.8 anal body diameters in length, with clavate terminal part.

The original description of C. inaequalis is detailed and well illustrated (Cobb 1920), although without most of the morphometric characters which are currently considered important. The identification of recent specimens is based on the combination of the following two morphological features: ventral limb of the amphid is roughtly twice (1.7–2.3) as long as the dorsal limb and clavate terminal part of the tail. Specimens described by Vitiello (1970) under the name Campylaimus cf. inaequalis cannot be identified to any known species because of the unclear description of the amphid given in the text of an article, in particular the length of the ventral amphideal limb cannot be deduced from either the drawings or the text.

Measurements. Table 5. Adult. Figs 26, 27, 28. Cuticle with distinct longitudinal striation. Space between dorsal and ventral limbs of amphid not developed. Lateral alae narrow, appearing externally as smooth uniform band with straight margins. It originates at posterior end of ventral limb of amphid and ends along posterior fifth of tail. Secretory-excretory pore opens posterior to cardia, at level with anterior part of intestine. Tail with digitate terminal part. Male. Anteriormost edge of amphid positioned at level with oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.9-2.0 labial region diameters in length. Ventral limb of amphid extends along pharyngeal region to level of anterior part of intestine; 8.3-9.5 times the length of dorsal limb. Ventral limb of amphid 1.7-2.5 wider than dorsal limb. Spicules with rounded manubrium and conoid, arcuate shaft. Gubernaculum platelike, without developed apophysis, but with proximal part bent caudally. Precloacal supplements indistinct/absent. Two pairs of ventrosublateral setae located along posterior half of tail and one pair of dorsosublateral setae located just posterior end of the lateral alae. Female. Anteriormost edge of amphid positioned at level with oral opening. Dorsal limb of amphid extends for a short distance posteriorly, equal to 1.8-2.6 labial region diameters in length. Ventral limb of amphid extends along pharyngeal region just anterior or just posterior to pharyngo-intestinal junction; 3.4-5.7 times the length of dorsal limb. Ventral limb of amphid 1–2 times wider than dorsal limb. Vagina straight. One pair of ventrosublateral setae located along middle of tail and one pair of sublateral setae located just posterior to end of lateral alae.

Body 0.52–0.73 mm long; cuticle with longitudinal striation; anteriormost edge of amphid at level with oral opening; dorsal limb of amphid equal to 1.9–2.0 labial region diameters in male, 1.8–2.6 labial region diameters in female; ventral limb of amphid extends towards anterior part of intestine in male and towards pharyngo-intestinal junction in female, 8.3–9.5 times the length of dorsal limb in male and 3.4–5.7 times the length of dorsal limb in female; ventral limb of amphid is 1–2 wider than dorsal limb; interamphideal space absent; secretory-excretory pore opens posterior to cardia; spicules 26–27 µm long; precloacal supplements indistinct; tail equal to 4.6–5.7 anal body diameters in length, with digitate terminal part.

C. striatus is so far the only known species of the genus with distinctly striated cuticular annulation. Original description of this species is based on three males and two females (although only two males and one female were measured, Boucher and Helléouët (1977)) while recent population includes two males and four females. Both populations are similar in the morphology of the cuticle (presence of longitudinal striations), in the size and proportions of the amphid and presence of sexual dimorphism in amphid size (ventral limb of the amphid extends towards anterior part of the intestine in male and towards the pharyngo-intestinal junction in female). Type specimens are relatively larger (L = 0.83-0.89 mm vs. 0.52–0.73 mm), with longer cephalic setae (6–7 µm vs. 1–3 µm) and longer tail (144–154 µm, c' = 6.3–9.6 vs. 82–112 µm, c' = 4.6–5.7). Since no qualitative differences between the two populations can be found and since differences in morphometrics can be explained by georgaphical variability or difficulty in measuring (cephalic sensilla), both populations are herefore considered to be conspecific.