Acrobeles bushmanicus Heyns, 1969

Abolafia, Joaquín & Peña-Santiago, Reyes, 2015, Some rare species of cephalobs (Nematoda: Rhabditida: Cephalobidae) from Southern Iberian Peninsula, Journal of Natural History 50, pp. 557-581 : 575-580

Acrobeles bushmanicus Heyns, 1969

( Figures 8 – 10 )

Material examined

Six females and six males from one locality.

Morphometrics

See Table 1.

Description

Adult. Stout to moderately slender nematodes, body length 0.43 – 0.57 mm. Habitus somewhat curved ventrad after fixation. Cuticle deeply annulated. Lateral field with three longitudinal incisures or two areolated wings, occupying 17 – 23% of midbody diameter, extending to tail tip. Lip region continuous with the adjacent body, bearing three pairs of asymmetrical lips, one dorsal and two ventrolateral, and six labial and four cephalic sensillae; primary axils deep, U-shaped, bearing two elongate, triangular, guarding processes originating from the incomplete first annulus; secondary axils with two triangular guarding processes, each one originating from each lip; lips asymmetrical, triangular, with dentate margin, five tines at primary axil (all rounded), six tines at secondary axil (rounded except the fifth acute) and a long acute apical tine; oral opening surrounded by three labial probolae, connected at bases by tangential ridges; each labial probola with a very short basal part and a longer and bifurcated distal part with prongs very long and divergent, straight, bearing lateral tines (eight rounded plus one apical acute at outer margin and eight or nine at inner margin plus one apical acute); the base of bifurcation is slightly expanded toward the secondary axil; two tubular projections and one adoral pedestal at base of each labial probola. Amphids clearly visible, large and rounded. Stoma cephaloboid: cheilostom with well-developed oval rhabdia, gymnostom very short, and stegostom with minute discernible rhabdia. Pharynx also cephaloboid: pharyngeal corpus subcylindrical, 3.0 – 4.3 times isthmus length; isthmus robust; basal bulb ovoid, with valvular apparatus. Cardia conoid, surrounded by intestinal tissue. Nerve ring at 65 – 76% of neck length, at level of isthmus. Excretory pore at 71 – 90% of neck length, at level of isthmus, 35 annuli from anterior end. Deirids at 84 – 92% of neck length, at level of bulb, 38 – 39 annuli from anterior end. Intestine without distinct specializations.

Female. Reproductive system monodelphic-prodelphic, in dextral position to intestine. Ovary long, lacking flexures. Oviduct very short. Spermatheca well developed, slightly longer than the corresponding body diameter, sometimes with sperm. Uterus 2.2 – 3.4 times as long as the corresponding body diameter, tubular at distal part and swollen at proximal part. Postuterine sac short, 0.6 – 0.8 times body diameter long, swollen. Vagina short, extending inward 22 – 39% of body diameter. Vulva with protruding lips. Rectum 0.9 – 1.2 times anal body diameter; three large gland-like cells are distinguishable around the intestine – rectum junction. Tail conical with acute terminus. Phasmids located at 14 – 22% of tail length.

Male. General morphology similar to female. Reproductive system monorchic, dextral in position, with testis reflexed ventrad anteriorly. Spicules paired and symmetrical: more or less rounded manubrium, conoid calamus and ventrad curved lamina with acute tip. Gubernaculum well developed, curved, about one half of the spicules length, with cornua crurum well developed. Three small gland-like cells are distinguishable around the beginning of the cloaca. Genital papillae as follows: two pairs precloacal, one adcloacal and five pairs caudal (two at the middle part, one ventral pair and one lateral pair, and three pairs near tail terminus, one dorsal and two subventral). Tail conical and curved ventrad, ending in an acute mucro. Phasmids located at 38 – 49% of tail length.

Distribution

Province of Almería, Salinas de Cabo de Gata, Cabo de Gata-Níjar Natural Park, near a salt mine, in volcanic sandy soil, associated with Sarcocornia fruticosa (L.) Scott., Urginea maritima (L.) Baker and Lygeum spartum L.

Remarks

This Iberian population is very similar to those described from South Africa and Namibia by Heyns (1969) but, as usual, some minor morphometric differences exist (see Table 4): more posterior position of nerve ring (82 – 100 vs 74 μm from the anterior end) and excretory pore (98 – 114 vs 89 μm from the anterior end), shorter postvulval sac (0.6 – 0.8 vs 1.0 – 1.5 times the corresponding body diameter long) and slightly longer rectum in females (17 – 22 vs 14 μm long).

This species is reported for the first time from the Iberian Peninsula and Europe.

Figures

Figure 8. Acrobeles bushmanicus Heyns, 1969: (A) neck; (B) female genital system; (C) lip region; (D, E) female tail; (F) entire female; (G) entire male; (H) male posterior end; (I) lateral field.

Figure 9. Acrobeles bushmanicus Heyns, 1969 (LM): (A) neck (arrow points at excretory pore); (B, C) lip region in dorsal and lateral views, respectively (I: primary axil, II: secondary axil; arrow points at amphid); (D) lateral field at deirid level (arrow); (E) male genital system; (F, G) female posterior end (arrow points at phasmid); (H) male posterior end (ph = phasmid, p1–p5 = genital papillae).

Figure 10. Acrobeles bushmanicus Heyns, 1969 (SEM): (A) anterior end showing the beginning of the lateral field; (B–E) lip region in left subventral, left sublateral, frontal and ventral views, respectively (I = primary axil, II = secondary axil; arrow points at amphid); (F) oral opening (ap = adoral pedestal, tp = tubular projection); (G) lip (ls = labial sensilla, cs = cephalic sensilla); (I, J) female tail (lateral and ventral views, respectively).