Macrolaimus crucis Maupas, 1900

Abolafia, Joaquín & Peña-Santiago, Reyes, 2013, Redescription of Macrolaimus crucis Maupas, 1900 (Nematoda: Rhabditida: Chambersiellidae) from Spain, with scanning electron microscopy study and a compendium of the genus, Journal of Natural History 48 (5 - 6), pp. 257-273 : 258-269

Macrolaimus crucis Maupas, 1900

( Figures 1–3 )

Material examined

Fifteen females and six males, in good state of preservation.

Morphometrics

See Table 1.

Description

Adult. Moderately slender nematodes of small size, 0.65–0.86 mm long. Body cylindrical, tapering towards both extremities, but more so towards the posterior end because the tail is conical. Habitus curved ventrad after fixation, to an open “C” shape. Cuticle c. 1 µm thick, with very fine annuli, hardly perceptible under light microscopy but readily visible under scanning electron microscopy. Lateral field 8–12% of body diameter wide, consisting of two wings (three incisures), starting at level of anterior part of corpus, and ending at level of phasmid. Lip region somewhat truncate, continuous with the adjacent body, with its inner region weakly elevated or protruding. Scanning electron microscope observations: lips mostly fused, but their inner (perioral) region forming six curved, triangular liplets covering the oral aperture; anterior

Locality Salinas de Cabo de Gata

Habitat Glasswort

Character 15 ♀♀ 6 ♂♂

Body length 755.0 ± 62.7 (654−863) 699.4 ± 43.6 (654−767) a 28.1 ± 1.8 (23.4−30.0) 31.8 ± 1.2 (29.7−33.3) b 4.7 ± 0.5 (4.0−5.8) 4.4 ± 0.3 (4.1−4.8)

c 14.2 ± 0.6 (13.1−15.1) 15.5 ± 0.9 (14.6−17.2) c l 3.5 ± 0.3 (3.1−4.0) 2.4 ± 0.2 (2.0−2.6)

V 57.8 ± 1.7 (55−61) −

Lip region width 14.5 ± 1.2 (13−18) 13.0 ± 1.0 (12−14) Stoma length 10.2 ± 1.0 (9−13) 10.3 ± 0.5 (10−11) Stoma width 8.1 ± 1.0 (7−11) 6.7 ± 0.8 (6−8) Pharyngeal corpus 84.5 ± 5.0 (77−93) 78.9 ± 3.3 (72−82) Isthmus 39.6 ± 5.1 (33−50) 46.1 ± 5.5 (37−50) Bulbus 26.8 ± 2.2 (24−30) 23.1 ± 1.9 (20−25) Pharynx length 151.0 ± 11.3 (134−173) 148.1 ± 7.8 (133−156) Nerve ring – anterior end 120.3 ± 14.2 (104−139) 112.7 ± 6.7 (104−124) Excretory pore – anterior end 121.3 ± 9.3 (109−139) 114.1 ± 6.5 (108−126) Deirid – anterior end 129.0 ± 10.4 (116−140) 123.7 ± 4.0 (120−128) Neck length 161.8 ± 14.7 (140−188) 161.3 ± 10.0 (144−171) Annuli 1.4 ± 0.2 (1.2−1.6) 1.0 ± 0.0 (1.0) Cuticle at midbody 1.1 ± 0.1 (1.0−1.4) 1.0 ± 0.0 (1.0)

Body diameter at neck base 24.3 ± 1.4 (22−26) 21.0 ± 0.6 (20−22) Body diameter at midbody 26.6 ± 1.7 (23−29) 22.0 ± 0.8 (21−23) Lateral field width 2.5 ± 0.4 (2.0−3.0) 2.5 ± 0.0 (2.5) Anterior ovary / testis length 289.9 ± 60.7 (213−376) 167.3 ± 17.0 (148−180) Anterior uterus length 132.2 ± 31.2 (96−165) − Postvulval uterine sac 2.3 ± 3.1 (0−6) −

Vagina length 9.6 ± 0.5 (9−10) − Vulva–anterior end 431.4 ± 34.0 (370−497) −

Rectum length 23.1 ± 1.5 (21−26) 6.3 ± 1.5 (5−9)

Anal body diameter 15.5 ± 1.3 (13−18) 19.0 ± 0.8 (18−20) Tail length 53.3 ± 3.7 (46−61) 45.1 ± 3.6 (38−48) Phasmid – anus distance 33.8 ± 3.6 (29−38) 16.0 ± 1.4 (15−18) Spicules length − 30.0 ± 3.8 (26−38) Gubernaculum − 11.6 ± 1.3 (10−13)

sensilla arranged in two circles, with six labial setae c.2.5 µm long projecting forwards and located at the margin of the oral field, and four (two subdorsal and two subventral) cephalic papillae situated just behind the level of labial setae. Amphid aperture small, oval, located at base of lateral lips. Stoma 0.7–1.4 times as long as lip region diameter, heavily sclerotized, subdivided into cheilo-, gymno- and stegostoma. Cheilostome 5.0–5.5 µm long and 6–11 µm wide, its cheilorhabdia strongly sclerotized, but convergent (curved) and thinner anteriorly. Gymnostome 3.0–5.0 µm long, as wide as cheilostome, with arched gymnorhabdia. Buccal cavity (= cheilo-gymnostome) 1.1–1.4 times longer than wide. Stegostome 1–3 µm long, funnel-shaped, enveloped by the anterior end of pharynx, lacking visible rhabdia. Dorsal pharyngeal gland opening at base of stegostome. Pharynx cephaloboid: pharyngeal corpus cylindrical, 1.6–2.4 times longer than isthmus and with slightly swollen metacorpus; isthmus narrower than, and clearly delimited from corpus; basal bulb nearly pyriform, with strongly developed valvular apparatus located at its posterior half; pharyngeal gland nuclei obscure. Cardia short and conoid. Nerve ring at 66–77% of neck length, encircling pharynx at level of middle or posterior half of isthmus. Secretory–excretory gland cell located left subventrally to basal bulb, its excretory pore opening posterior to nerve ring, at 65–86% of neck length. Deirid located posterior to nerve ring, inside the lateral field, at 73–92% of neck length.

Female. Reproductive system monodelphic–prodelphic. Ovary reflexed near to oviduct junction, very long, surpassing the level of the vulva and nearly overlapping the posterior third of intestine; oocytes first in two or more rows, then in only one row. Oviduct narrow and short; no distinct narrowing is observed at ovary–oviduct junction. Uterus located on right-hand side of intestine, with two sections separated by a weak narrowing: the distal part is long, tubular, with thick walls and four to six times the corresponding body diameter long, whereas the proximal one is short and swollen (ovijector), and with thin walls. Uterine egg 82 × 22 µm. Postvulval uterine sac absent. Vagina occupying one-third to two-fifths (33–40%) of body diameter, perceptibly bent forward. Vulva a transverse slit, with distinctly protruded lips that forms a vulval cone; advulval cuticle lacking differentiations. Rectum 1.4–1.8 times longer than anal body diameter, its anterior part surrounded by three gland-like cells; anal lips slightly prominent, especially the posterior one. Tail conical, straight, tapering very gradually and ending in an acute tip somewhat dorsad curved. Phasmids very posterior, at 60–70% of tail length from anus.

Male. Reproductive system monorchic, with testis reflexed dorsad, on right-hand side of intestine. Spicules paired and symmetrical, curved ventrad with more or less rounded to slightly hooked manubrium, conoid calamus, ventrad curved lamina, poorly developed proximal dorsal hump, and a thin velum at ventral side. Gubernaculum oval, weakly curved ventrad. Three large gland-like cells are distinguishable around the beginning of the cloaca. Genital papillae two subventral precloacal pairs and five postcloacal pairs arranged as follows: one sublateral pair a short distance behind the level of cloacal aperture, two ventral pairs, one of them at the anterior third and another at the posterior third to tail length, and two dorsal pairs at the posterior half of tail; a mid-ventral papilla is located in front of the anterior lip of cloacal aperture. Tail similar to that of female but tapering less gradually and curved ventrad. Phasmids located at anterior half of tail.

Diagnosis (based on Iberian material)

The Iberian material of M. crucis is characterized by its body 0.65–0.86 mm long in females and 0.65–0.77 mm in males, lip region 12–18 µm broad and bearing six setae c.2.5 µm long, stoma 9–13 × 6–11 µm, neck 140–188 µm long, pharyngeal corpus 1.6–2.4 times isthmus length, excretory pore located at isthmus level, female reproductive system monodelphic–prodelphic, postvulval uterine sac absent, female tail conical (46–61 µm, c = 13.1–15.1, c l = 3.1–4.0) with acute tip bent dorsad, phasmids located at 60–70% of tail length from anus, male tail conical and curved ventrad (38–48 µm, c = 14.6–17.2, c l = 2.0–2.6), spicules 26–38 µm long, and gubernaculum 10–13 µm long.

Comparison of Iberian material with previous records of the species

The Iberian material of M. crucis is very similar to the only female specimen described by Maupas (1900) in relevant morphological features: stoma morphology (cheilostome as long as gymnostome, and buccal cavity 1.3–1.5 times longer than wide), absence of postvulval uterine sac, and tail length. Some differences have also been noted: slightly smaller general size (body 0.65–0.86 versus 0.96 mm long), shorter isthmus (pharyngeal corpus 1.9–2.4 versus 1.7 times isthmus length, although isthmus is clearly contracted in the Iberian material), and tip tail curved dorsad (versus almost straight); nevertheless, these differences are regarded as geographical variations or simply due to the low number of known specimens.

In spite of their poor descriptions, the populations studied by Micoletzky (1922), Goffart (1933) and Andrássy (1958) might belong to M. crucis because their morphometrics (see Table 2) do not differ significantly from those provided in the original description and those given herein.

Serious doubts persist on the true identity of the material identified as M. crucis by several authors because there are relevant differences in their morphology and / or morphometrics when compared with the above characterization.

Rahm (1928, 1929) described two varieties of M. crucis from Brazil, named var. tenuis and var. gracilis , respectively, but provided poor descriptions of them and illustrated only the second. Both varieties were morphometrically similar and differed from other M. crucis populations in their larger general size (female body 1.26 mm long) and shorter gymnostome (distinctly smaller than cheilostome versus cheilostome and gymnostome with similar length in M. crucis ). This material resembles Macrolaimus canadensis Sanwal, 1960 , but the spicules are visibly larger (45 versus 37 µm).

Fuchs (1938) studied both females and males from Germany, which differ from type material in their shorter gymnostome and presence of a postvulval uterine sac, and from Iberian specimens herein studied in having triangular (versus fusiform) gubernaculum, and male tail with tip strongly bent dorsad. This German material might also belong to M. canadensis .

Rühm (1950, 1956; see also Meyl 1960) also examined females and males from Germany, which are distinguishable from the type of M. crucis in their longer than wide (versus as long as wide) buccal cavity, and female tail relatively shorter (c l = 2.6 versus c l = 3.5) and ending in a short mucro (versus no mucro). Compared with Iberian M. crucis , Rühm’s material differs in the morphology of spicules (rounded manubrium, calamus very thick and lamina arquate at middle length versus slightly bent manubrium, calamus thinner and lamina arcuate distally) and gubernaculum (more or less triangular versus fusiform). Andrássy (1966) was aware of these differences and regarded this German population as a separate species Macrolaimus ruehmi , an action that seems to be well supported.

Macrolaimus 1 ♀ 0.80 31.0 4.0 13.7? 2.0 d (2.8 d)?? 58 e (hooked) 55? Georgia Thorne, 1937 hamatus ( USA)

1 ♂ 0.70 32.0 4.0 14.5 2.0 d =?? 48 e (hooked) 29 e 14 e (5.3 d)

Macrolaimus 1 ♂ 0.81 37.0 5.4 17 3.2 d 1.6 d (4.2 d)? 3 47 d (dorsad 28 11 (8.1 d) Bangladesh Timm, 1960 natator bent)

Macrolaimus 28 ♀♀ 0.74–0.90 27.2–32.2 4.2–4.8 11.9–13.8 3.5–4.8 1.2–1.4 d 1.9 d 5 57–69 57–60 absent South Africa Swart and richteri (1.6–1.7 d) (slightly Heyns, 1992

dorsally

bent)

Macrolaimus ? ♀♀ ???? 2.6 d 1.7–1.9 d 2.7 d 3 60 d (short?? (short) Germany Rühm, 1950, ruehmi as M. (1.8 d) mucronated) 1956

crucis

? ♂♂ ???? 2.2 d = = 3 62 d (dorsad 31 d 16 d (2.3 d)

bent)

as M. crucis ? ♀♀ 0.80–1.00 22.0–36.9 4.0–5.7 13.7–15.0 2.6 d 1.7 d (1.8 d)??? (dorsad 55–58? Germany Meyl, 1960 c

bent)

? ♂♂ 0.70 32.0–35.7 4.0–4.3 14.5–20.4 2.2 d ???? (dorsad 30 15 (2.3 d)

bent)

Macrolaimus 1 ♀ 0.96 26.0 5.0 15.0 4.0 1.6– 1.7 e ???? 56? Italy Andrássy , somniorum 1984

1 ♂ 1.00 40.0 5.0 18.0 3.0 =??? 32 18 (?)

Macrolaimus 1 ♀ 1.30 30.0 5.9 18.0? 2.2 d (1.3 d)? 3 72 e (almost 60? Utah ( USA) Thorne, 1937 taurus straight)

1 ♂ 1.10 31.0 5.8 21.0 2.2 d =? 3 52 e (almost 29 e 15 e (2.8 d)

straight)

? ♀♀ 1.30 30.0 5.9 18 4.1 d 1.8 d (1.2 d) 2.1 2 78 d (almost 60 1.0 North Massey, 1974

straight) Dakota

( USA)

? ♂♂ 1.10 30.0 5.8 21 2.3 d = = 2 58 d (almost 29 d 16 d (4.0 d)

straight)

Other material

Macrolaimus 1 ♀ 1.26 28.0–37.0 4.0 14.0? 1.9 d (1.8 d) 1.6 d? 90 e 59? Brazil Rahm, 1929 crucis var .

gracilis

1♂ 1.17 35.5 4.0 14.5 2.6 d = =? 81 e (dorsad 45? (3.6 d)

bent)

Macrolaimus 1♂ 1.17 38.5 4.0 14.5???? 81 e 45? Brazil Rahm, 1928 crucis var .

tenuis

(Continued)

Brzeski (1961) studied one female and one male from Poland, providing descriptions and morphometrics but no illustration. This material has large general size (body length 1.10 mm in female and 1.22 mm in male), stoma slightly longer than wide, tail of both sexes ending in a dorsad curved mucro, spicules thin and little longer than cloacal body diameter, and triangular gubernaculum. These Polish specimens might also belong to M. canadensis .

Relationships

Macrolaimus crucis resembles Macrolaimus richteri , M. ruehmi and Macrolaimus taurus . It differs from M. richteri by its lateral field with three (versus five) longitudinal incisures. From M. ruehmi by having female tail comparatively longer (c l = 3.1–4.0 versus c l = 2.6) and tip slightly bent dorsad (versus tip rounded and ending in a short mucro), and the morphology of spicules (slightly bent manubrium, calamus thinner and lamina arquate distally versus rounded manubrium, calamus very thick and lamina arquate at middle length) and gubernaculum (fusiform versus more or less triangular). In addition, it differs from M. taurus in its smaller general size (versus body 1.30 mm long in females and 1.10 mm long in males), buccal cavity scarcely longer than wide (1.1–1.3 versus 1.7 times longer than wide), postvulval sac absent (versus present), spicules with distally arcuate lamina (versus proximally arcuate), and gubernaculum fusiform (versus more or less triangular).

Distribution in the Iberian Peninsula

Macrolaimus crucis is known to occur in three localities on the southeastern Iberian Peninsula: (i) Almería province, Cabo de Gata Natural Park, Salinas de Cabo de Gata, near the salt mine, where it was collected in volcanic sandy soil, associated with Sarcocornia fruticosa (L.) Scott, Urginea maritima (L.) Baker and Lygeum spartum L.; (ii) Almería province, Tabernas Desert, near the crossroad of Rioja and Tabernas, in a seasonally dry brook; and (iii) Jaén province, Sierra de Segura, Camino de las Acebeas, in the rhizosphere of Corylus avellana L. and Quercus faginea Lam.

Figures

Figure 1. Macrolaimus crucis Maupas, 1900. (A) Neck; (B) female reproductive system; (C) male posterior end; (D) female posterior end; (E) lip region; (F) entire male; (G) entire female.

Figure 2. Macrolaimus crucis Maupas, 1900 (light micrographs). (A) Neck; (B) anterior end (C) vagina region (D); female posterior end; (E) male posterior end.

Figure 3. Macrolaimus crucis Maupas, 1900 (female, scanning electron micrographs). (A, B, C) Lip region in subventral (A, B) and frontal (C) view; (D) lateral field at deirid level (arrow points excretory pore); (E) lateral field at midbody (F, G) female tail in lateral and subventral view, respectively.