Fotolaimus cavus, Shimada & Kakui & Fujita, 2023

Shimada, Daisuke, Kakui, Keiichi & Fujita, Yoshihisa, 2023, A new species of free-living marine nematode, Fotolaimus cavus sp. nov. (Nematoda, Oncholaimida, Oncholaimidae), isolated from a submarine anchialine cave in the Ryukyu Islands, southwestern Japan, Zoosystematics and Evolution 99 (2), pp. 519-533 : 519

publication ID	https://dx.doi.org/10.3897/zse.99.109097
publication LSID	lsid:zoobank.org:pub:75589A9A-94C3-4F20-BBEC-A4C7D3799836
DOI	https://doi.org/10.5281/zenodo.10170830
persistent identifier	https://treatment.plazi.org/id/A0509360-77DD-4387-9FAD-92B14758952F
taxon LSID	lsid:zoobank.org:act:A0509360-77DD-4387-9FAD-92B14758952F
treatment provided by	Zoosystematics and Evolution by Pensoft
scientific name	Fotolaimus cavus
status	sp. nov.

Treatment

Fotolaimus cavus sp. nov.

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3 , 4 View Figure 4

Material examined.

Holotype. Japan • male (permanent whole mount in glycerin); Ryukyu Islands , Miyako Island Group , Shimoji Island, a submarine cave called Akuma-no-yakata; 24°49'22.5"N, 125°08'07.8"E; 26 Oct. 2018; anchialine zone, depth 7 m, collected by Yoshihisa Fujita; ICHUM 8474. GoogleMaps

Paratypes. Japan • two males (permanent whole mounts in glycerin); same collection data as for holotype; 26 Oct. 2018; anchialine zone, depth 20 m, collected by Yoshihisa Fujita; ICHUM 8475 and 8476 GoogleMaps • four females (permanent whole mounts in glycerin); same collection data as for preceding; ICHUM 8477-8480 GoogleMaps .

Other material.

Japan • one male (SEM specimen); same collection data as for paratypes ; • one female (SEM specimen); same collection data as for preceding .

Etymology.

The specific name cavus (cave) is a Latin noun in apposition derived from the type locality.

Description.

Body (Fig. 1A, B View Figure 1 ) elongated, almost cylindrical but gradually tapering toward both extremities. Cuticle smooth throughout body besides oblique striations (Fig. 2A View Figure 2 ; cf. Leduc 2013) crossing at angle of ca. 120° between amphids and anteriormost cervical setae visualized using SEM. Somatic sensilla arranged in eight longitudinal rows: setiform in anterior half of cervical (Figs 1C View Figure 1 , 2B View Figure 2 ) and caudal (Fig. 2C View Figure 2 ) regions; papilliform or very short setiform in rest of body (Fig. 2D View Figure 2 ), difficult to observe without SEM. Cephalic region (Figs 1D-F View Figure 1 , 2E-G View Figure 2 , 3A-D View Figure 3 ) rounded at anterior end, with six lips, slightly constricted posterior to amphids, as wide as 0.3-0.4 maximum body diameters at cephalic sensilla level. Six inner labial sensilla papilliform. Six outer labial and four cephalic sensilla setiform, arranged in single circle, 5-8 μm or 0.20-0.30 corresponding body diameters long in males and 6-9 μm or 0.25-0.35 corresponding body diameters long in females. Amphids (Figs 1D, E View Figure 1 , 2E View Figure 2 , 3B View Figure 3 ) pocket-like, with elliptical aperture and cup-shaped fovea, 0.40-0.45 corresponding body diameters wide in males and 0.35-0.40 corresponding body diameters wide in females, anterior margin located at 0.4-0.5 buccal cavity lengths from anterior body end. Buccal cavity (Figs 1D-F View Figure 1 , 3C, D View Figure 3 ) barrel-shaped, length/width = 2.5-3.0, surrounded by pharyngeal tissue in posterior 15%-25%. Three well-developed teeth: left ventrosublateral tooth largest, 4-6 μm longer than right and dorsal teeth. Tip of left ventrosublateral tooth at 0.2 buccal cavity lengths from anterior body end (i.e., level of cephalic sensilla). Pharynx (Figs 1C View Figure 1 , 3E View Figure 3 ) cylindrical, evenly muscular, gradually widened toward posterior end. Cardia surrounded by intestine. Rectum (Fig. 4A, B View Figure 4 ) slightly longer than cloacal body diameter. Pore of secretory-excretory system (Figs 1C View Figure 1 , 2H View Figure 2 ; SE-pore) with ampulla, at 2.0-2.2 buccal cavity lengths or 0.2 pharyngeal lengths from anterior body end. Renette cell not observed. Nerve ring (Fig. 1C View Figure 1 ) located at 0.45-0.50 pharyngeal lengths from anterior body end. Tail sexually dimorphic: male tail (Figs 2I, J View Figure 2 , 3F View Figure 3 , 4A View Figure 4 ) strongly tapering in anterior 1/5, gradually tapering in next 2/5, and almost cylindrical in posterior 2/5, as long as 3.9-5.7 cloacal body diameters; female tail (Figs 3G View Figure 3 , 4B View Figure 4 ) more gradually tapering throughout its length, as long as 5.5-6.1 anal body diameters. Tail tip slightly expanded, with spinneret and one pair of subterminal setae in both sexes. Body diameter at level of cloacal opening or anus equal to 0.5 maximum body diameters, at cylindrical portion of tail equal to 0.20-0.25 cloacal body diameters. Caudal glands inconspicuous. Caudal setae arranged in longitudinal rows, number and location varying from individuals.

Spicules (Figs 3H, I View Figure 3 , 4A, C View Figure 4 ) paired, arcuate, distally acute with subterminal opening, proximally with capitulum, as long as 1.3-1.5 cloacal body diameters or 0.25-0.35 tail lengths. Gubernaculum (Figs 3H, I View Figure 3 , 4A, C View Figure 4 ) plate-like, distally associated with spicules, proximally curved, shape similar to that of gubernaculum from Admirandus belogurovi Tchesunov, Mokievsky & Nguyen, 2010 ( Tchesunov et al. 2010), as long as 0.5-0.7 cloacal body diameters or 0.3-0.5 spicule lengths. No precloacal supplement. Circumcloacal setae (Fig. 2C, K View Figure 2 ) arranged in single circle, 9-12 setae in each body side. Three ventral papillae (Fig. 2L View Figure 2 ) present just anterior to cloacal opening, arranged in single longitudinal row, observed only with SEM. Male reproductive system (Fig. 4D View Figure 4 ) diorchic. Two opposed and outstretched telogonic testes, both situated on right side of intestine: germinal zone filled with small cells not arranged in rows; growth zone with larger cells arranged in single row. Blind end of anterior testis at 30%-40% of body length from anterior end; blind end of posterior testis at 70% of body length from anterior end. Seminal vesicle including two (dorsal and ventral) rows of sperms (Fig. 3J View Figure 3 ). Vas deference located on ventral side of intestine, anteriorly filled by single row of sperms.

Female reproductive system (Fig. 4E View Figure 4 ) monodelphic-prodelphic. Telogonic ovary antidromously reflexed, situated on right side of intestine, as long as 6%-10% of body length; anterior end connecting with oviduct at 50%-55% of body length from anterior end; blind end located at 60%-65% of body length from anterior end; germinal zone with small cells not arranged in rows; growth zone with gradually growing cells arranged in two (right and left) rows; ripening zone with grown oocytes arranged in single row. Oviduct situated on left side of ovary (between intestine and ovary). Uterus well developed in two specimens (ICHUM 8477 and 8478), ca. 200 μm in length, each containing one egg (131-141 μm long and 48-62 μm wide). In other two individuals, uterus very short without egg and blind end of ovary located just anterior to vulva. However, the size and degree of maturity of the ovaries similar to those of egg-bearing specimens. Vulva (Figs 2M View Figure 2 , 4E View Figure 4 ) transverse slit with thick cuticular walls, located at 2/3 from anterior body end. Vagina weakly sclerotized. Demanian system (Figs 3K View Figure 3 , 4F, G View Figure 4 ) oncholaimoid type variant D (cf. Belogurov and Belogurova 1988). Ductus uterinus anteriorly inconspicuous. Uvette well-developed, spherical with thick sclerotized wall, situated on right side of intestine at 80%-85% of body lengths, connected to main duct with posterior tip. Main duct on dorsal side of intestine, anteriorly forming one short sac with thick sclerotized wall and filled with sperms, posteriorly forming two sacs on both sides. Ductus entericus very short, situated subterminally on the left side of anterior sac of main duct. Osmosium inconspicuous, may be simple pore. Terminal ducts branching off from posterior sacs of main duct, five or more in number on both sides. Terminal pores (Figs 2N, O View Figure 2 , 3L View Figure 3 , 4F, G View Figure 4 ) arranged in single circle surrounding body, 3-4 anal body diameters anterior to anus.

Diagnosis.

Fotolaimus cavus sp. nov. is characterized by small body size (2.1-3.0 mm), wide amphids (0.35-0.45 corresponding body diameters), a long buccal cavity (length/width = 2.5-3.0), a long (c = 12-15, c’ = 3.9-6.1) conico-cylindrical tail, and a proximally curved gubernaculum.

Remarks.

Fotolaimus cavus sp. nov. differs from the other two species of the genus, i.e., F. marinus and F. apostematus , by the curved shape of the gubernaculum (not curved and smaller in F. marinus and F. apostematus ). Fotolaimus cavus sp. nov. is also different from F. marinus by its shorter body (2.1-3.0 mm in F. cavus sp. nov. vs 5.8-6.2 mm in F. marinus ) and longer tail (c = 12-15, c’ = 3.9-6.1 in F. cavus sp. nov. vs c = 39-51, c’ = 2.3-3.8 in F. marinus ) with conico-cylindrical shape (vs clavate in F. marinus ) (cf. Wieser 1959; Belogurova and Belogurov 1974).