Enoplolaimus variispiculum, Pastor & Russo, 2021

Pastor, Catalina & Russo, Virginia Lo, 2021, Two new species of Enoplolaiminae (Enoplida: Thoracostomopsidae) from Río Negro and Chubut, Argentina, Zootaxa 5020 (2), pp. 337-351 : 341-346

Enoplolaimus variispiculum sp. n.

( Figure 1B , 2 , 3 ; Table 1, 2)

Measurements. See Table 1.

Description. Males: Body cylindrical, slender, anteriorly narrow, weakly tapering posteriorly. Cuticle finely striated. Head rectangular and set off, with three lips (one dorsal and two ventrosublateral), without striations and separated by clefts, 8 µm high. Each lip bearing two inner labial sensilla, 0.2 corresponding body diameters in length. Cephalic glandular organ was observed on ventrosublateral lips. It is straight in males and arched in females. Six outer labial sensilla, 2.1 corresponding body diameters in length, inserted at level of posterior margin of cephalic capsule. A second crown of four cephalic setae 1.8 corresponding body diameters in length. A third crown of six subcephalic setae 1.4 corresponding body diameters in length. Three crowns of cervical setae in dorsosublateral, lateral and ventrosublateral position. First crown with 6 setae, 0.6 corresponding body diameters in length, second crown with 6 setae, 0.5 corresponding body diameters in length, third crown with 4 setae, 0.5 corresponding body diameters in length. Body with dispersed somatic setae, 8–10 µm long.

Cephalic capsule well developed. Posterior margin of cephalic capsule with deep incisions accommodating the first crown of outer labial setae, cephalic setae and subcephalic setae. Three broad, arched, mandibular plates with pointed tips projecting into stoma. Mandibular plates slightly curved and thin and with two small projections located laterally, at level of mandibular ring, 1 µm long. Three onchia, one dorsal and two ventrosublateral, equal in size, at the base of each mandible. Amphids and excretory pore not observed. Metanemes not observed. Pharynx cylindrical, slightly englobed anteriorly and with outer wall crenated posteriorly.

Reproductive system diorchic, anterior testis outstretched, posterior one reflexed. Spicules paired, asymmetrical, longest spicule (left) arcuate, cephalated (1.7 cloacal body diameters in length), with pointed distal end. The other spicule (right) short and straight, slightly cephalated with sharp distal end, 0.8 cloacal body diameters in length. Gubernaculum present, plate-like, triangular, without any structures, 0.5 cloacal body diameters in length. One preanal supplement present. One setae observed before cloaca. Tail 4.2 cloacal body diameter long. Three caudal glands and spinneret were observed.

Females: Similar to male in general body shape, but usually larger. It differs in head shape and outer labial and cervical setae number. Six labial sensilla 0.2 corresponding body diameters in length, six long outer labial sensilla 2.1 corresponding body diameters in length and four short cephalic setae 1 corresponding body diameter in length, inserted at posterior margin of cephalic capsule. One crown of four cervical setae 0.4 corresponding body diameters long. Lateral mandibles and onchia slightly smaller than in males. Three arched, mandibular plates with pointed tips projecting into stoma. Mandibular plates slightly curved and thin. Three onchia, one dorsal and two ventrosublateral, equal size, at the base of each mandible. Reproductive system didelphic, amphidelphic, ovaries reflexed. Vagina with thick walls and well developed sphincter muscles. Tail 4 anal body diameters in length, without setae.

Material examined. Holotype Male, CNP-NEM N° 27798, collected on 1/4/2006 at “El Límite” beach (lat. 45º59’38”S, long. 67º35’31”W), during mid tide. Collector: Catalina Pastor. Paratypes two males and one female, same data as holotype, mounted on slide numbers CNP-NEM N° 27849, 27888, 27601 .

Type locality and habitat. “El Límite” beach, 1/4/2006, mid tide 30 cm deep in sediment; salinity = 38 psu; temp. = 13.2–14.5 ºC. Characteristics of surface sediment layer: mean particle size Q2 (50%) = 0.2; FF (%) = 0.8–1.2; SO index = 0.7–0.8; SK index = 1.0–1.2. Organic matter content/ 100g sediment = 1.2–1.5 mg.

Etymology. “ variispiculum ” from Latin word “variis” = various and “spicules” referring to the different size and shape of spicules.

Differential diagnosis. E. variispiculum sp. n. is characterized by having asymmetric spicules, different in size, shape and distal tips. It is the only species with this characteristic in the whole genus. It also has the shortest inner labial sensilla than all the species without an apophysis on the gubernaculum and with short tail (group 6, Fadeeva & Zograf, 2010) plus the species added in this paper, nine species in total. In Table 2 we show the comparison of the diagnostic morphological characters of those nine species.

E. variispiculum sp. n. is related to E. enatus Hopper, 1962 , E. lenunculus Wieser, 1959 , E. mus Inglis, 1964 and E. paralitoralis Wieser, 1959 .

E. enatus has similar outer labial sensilla length, onchia and gubernaculum length in cloacal body diameter, and de Man’s ratio “b”. But it differs in length of inner labial sensilla (5 µm vs 10–11 µm), cephalic setae length (35.7 µm vs 19–20 µm), cephalic capsule height/width (0.3 vs 2.4), mandible height/width (2.5 vs 1.2), spicule length in cloacal body diameter (two different 1.7 and 0.8 vs 1.3) and tail length in cloacal body diameter (3.9 vs 5.0–6.0).

E. lenunculus has similar general size, outer labial sensilla, de Man’s ratio “a, b, c” and tail length. But it differs in length of inner labial sensilla (5 µm vs. 12-15 µm), length of cephalic sensilla (35.7 µm vs 22.0 µm), mandible height/width (2.5 vs 1.2), and spicule length in cloacal body diameter (two different 1.7 and 0.8 vs 1.3).

E. mus has similar “b” and “c” de Man’s ratios, gubernaculum and tail length in cloacal body diameter. But it differs in total body length (4700 vs 2540), inner labial, outer labial and cephalic sensilla length (17 vs 5 µm; 105 vs 50 µm; 55 vs 35.7 µm), mandible H/W (1.2 vs 2.5), and onchia length (27 vs 8 µm).

E. paralitoralis has similar “b” and “c” de Man’s ratios, cephalic sensilla and tail length. But it differs in total length (1670 vs 2540 um), in inner labial and outer labial sensilla length (10–12 vs 5 µm; 62–66 vs 50.7), in cephalic capsule H/W (0.7 vs 0.3), and in mandible H/W (5.8 vs 2.5).

Figures

FIGURE 1. Map showing the study sites. Map of sampling areas:A. “San Antonio Oeste river estuary” beach, Río Negro Province; B. “El Límite” beach, Chubut Province.

FIGURE 2. E. variispiculum n. sp. Line drawings. A. Cephalic sense organs on anterior end of male holotype; B. Cephalic sense organs on female paratype; C. Buccal cavity and mandibles of male holotype; D. Copulatory apparatus, spicules and gubernaculum of male holotype; E. Buccal cavity and mandibles of female paratype; F. Entire female paratype showing vulva and gonadal apparatus; G. Posterior end of male holotype; H. Posterior end of female paratype. Scale bar: 1 = 20 μm; 2 and 3 = 100 μm.

FIGURE 3. E. variispiculum n. sp. Micrographs of slide mounted specimens.A. Buccal cavity and mandibles of male holotype; B. Cephalic sense organs on anterior end of male holotype; C. Vulva opening in subventral view of female paratype; D. Onchia in female paratype; E. Onchia in male paratype; F. Posterior end of female paratype; G. Cephalic sense organs on female paratype; H. Cardia and muscular esophagus in male holotype; I. Subventral view of copulatory apparatus, spicule and gubernaculum of male paratype; J. Lateral view of left spicule, gubernaculum and tail of male holotype; K. Lateral view of right spicule, gubernaculum and tail of male holotype. Abbrev: Ca = Cardia; Mb = Mandible; O = Onchia; V = Vulva. Scale bar: 1 = 20 μm.