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. 2007 Sep;39(3):263–274.

Nematodes of the Order Rhabditida from Andalucía Oriental, Spain. The Genera Protorhabditis (Osche, 1952) Dougherty, 1953 and Diploscapter Cobb, 1913, with Description of P. spiculocrestata sp. n. and a Species Protorhabditis Key

J Abolafia 1, R Peña-Santiago 1
PMCID: PMC2586499  PMID: 19259497

Abstract

A new species of the genus Protorhabditis is described from natural areas in the SE Iberian Peninsula. Protorhabditis spiculocrestata sp. n. is distinguished by its body length 387–707 μm in females and 375–546 μm in males, lip very low and flattened, stoma 14–22 μm long, female tail conical-elongate (48–100 μm, c = 6.4–8.3, c′ = 4.8–7.5), phasmid near anus, male tail conical (20–27 μm, c = 18.3–22.3, c′ = 1.4–1.5), bursa peloderan closed anteriorly and bears eight papillae (1+2+1+1+3), spicules 23–26 μm long, and gubernaculum 10–16 μm long. Diploscapter coronatus is also presented. Description, measurements and illustrations, including SEM photographs, are provided. A key to species of Protorhabditis is also given as well a compendium of their measurements.

Keywords: description, Diploscapter, key, morphology, new species, Protorhabditis, Rhabditids, SE Spain, SEM, taxonomy

Rhabditid nematodes are an interesting zoological taxon. They are very abundant in all types of soil and sediments of freshwater bodies and play important ecological roles mainly as primary consumers—their free-living forms display saprophagous or bacteriophagous feeding habits—but also as animal parasites, in particular enthomopathogenic forms. From a systematic point of view, rhabdits are a difficult nematode group whose classification has been matter of long and strong discussions and whose diversity is far from being well known.

Several years ago, a research project was planned to study the Iberian rhabditid fauna, focused on both its morphological characterization and its taxonomy, since no monographic study on this matter was available.

The genera Protorhabditis (Osche, 1952) Dougherty, 1953 and Diploscapter Cobb, 1913 are two rhabditid taxa characterized by having a long stoma whose stegostom lacks glottoid apparatus. They were classified by Andrássy (1983) in separate families (Rhabditidae Örley, 1880 and Diploscapteridae Micoletzky, 1922, respectively) of the superfamily Rhabditoidea Örley, 1880, mainly due to morphology of lip region: six rounded lips with similar aspect in Protorhabditis; subdorsal and subventral lips hook-like and lateral lips membranous and rounded with dentate margin in Diploscapter. However, more recent evidence based on both morphological and molecular studies demonstrated a close relationship between both genera (Fitch, 2000; Sudhaus and Fitch, 2001).

Three species belonging to these two genera have been recorded from several localities in the Iberian Peninsula (Abolafia and Peña-Santiago, 2001): P. filiformis (Bütschli, 1873) Sudhaus, 1976, P. tristis (Hirschmann, 1952) Dougherty, 1955 and D. coronatus (Cobb, 1893) Cobb, 1913. Nevertheless, no relevant morphological or taxonomical information on them was provided in the corresponding publications. In this contribution, part of the series on rhabditid species from Andalucía Oriental (SE Iberian Peninsula, Spain), D. coronatus and an undescribed species of Protorhabditis are reported.

Materials and Methods

Nematodes were extracted from soil samples by Flegg's (1967) method and a somewhat modified Baermann's (1917) funnel technique. Nematodes obtained were later relaxed and killed by heat, fixed in 4% form-aldehyde, and processed to anhydrous glycerine according to Siddiqi (1964). Measurements were taken using an ocular micrometer, and drawings were made using a drawing tube attached to a Leica microscope; LM pictures were made using a Nikon Eclipse 80i microscope provided with a digital video camera Nikon Digital Sight DS-5M. For SEM studies, fixed specimens were hydrated in distilled water, dehydrated in a graded ethanol and acetone series, critical point dried and coated with gold (Abolafia and Peña-Santiago, 2005), and observed with a JEOL JSM-5800 microscope. The terminology used for morphology of stoma and spicules follows the proposals by De Ley et al. (1995) and Abolafia and Peña-Santiago (2006), respectively.

In addition, the D. coronatus specimens examined were cultured in vitro in petri dishes (2% agar and 1.5% glucose) and maintained under laboratory conditions for several months. This culture is no longer available.

Description

Protorhabditis spiculocrestata sp. n. (Figs. 1–3)

Fig. 1.

Fig. 1

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Protorhabditis spiculocrestata sp. n. A: Neck. B: Anterior end. C: Female reproductive system. D: Entire male. E: Female posterior end. F: Entire female. G, H: Male posterior end (lateral side). J: Idem (ventral side). I: Spicule.

Fig. 3.

Fig. 3

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Protorhabditis spiculocrestata sp. n. (SEM). A: Lip region (arrow indicates amphid opening). B: Lateral field at middle body. C: idem at posterior end. D: idem near to anus. E: Phasmid. F, G: Male posterior end.

Fig. 2.

Fig. 2

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Protorhabditis spiculocrestata sp. n. (LM). A: Neck. B: Female reproductive system (anterior branch). C: Female tail. D. Male posterior end (bursa view). E. Male posterior end (spicule view).

The specific epithet refers to the presence of a subdorsal crest in the spicules, a remarkable morphological feature of this species.

Measurements: Listed in micrometers in Table 1.

Table 1.

Measurements (in μm) of females (n = 17) and males (n = 11) of Protorhabditis spiculocrestata sp. n. presented as mean ± s.d. and (range).

graphic file with name 263tbl1.jpg

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Type population collected near road from Fuente de Piedra to Alameda, province of Málaga

Female (n = 7): Small nematodes, 441–561 μm long. Body cylindrical, tapering towards both ends, more so posteriad. Habitus rather sigmoid after fixation. Cuticle with distinct transverse striations or annuli, about 1 μm wide at midbody. Lateral field with five incisures or four ridged wings at midbody, two at posterior region which fade out near anus. Lip region with six small lips, more or less rounded; papillae visible. Stoma rhabditoid, lacking glottoid apparatus. Cheilostom with weakly refractive walls. Buccal ring (membrane wedge ring) lower in longitudinal section. Buccal prism with straight walls, very long and narrow. Pharyngeal collar very short. Procorpus cylindrical. Metacorpus swollen, almost ovoid, with its inner walls more refractive. Isthmus almost as long as procorpus. Basal bulb small, ovoid or pyriform. Cardia conoid to hemispherical, surrounded by intestinal tissue. Intestine lacking distinct specializations, but a cardiac portion is sometimes differentiated at its anterior part. Nerve ring at 71–80% of neck length, surrounding the isthmus. Excretory pore at 82–92% of neck length, at level of isthmus base or basal bulb, behind the hemizonid. Deirid at basal bulb level, at 90–97% of neck length. Reproductive system didelphic-amphidelphic, with anterior branch dextral and posterior branch sinistral. Ovaries having a flexure. Uterus two times the corresponding body diameter long, having thicker walls at proximal portion and distinct lumen at distal one. Eggs 15–23 × 37–39 μm. Vagina extending inwards to one-third of body diameter, with thicker walls at proximal portion. Rectum 1.1–1.3 times as long as anal body diameter. Tail conicalelongate, and terminus with acute mucro. Phasmid near anus.

Male (n = 3): Similar to female in general morphology. Habitus ventrad curved after fixation. Reproductive system monorchic. Testis reflexed ventrally anteriorly. Tail conical. Bursa pelodera, closed anteriorly, and with eight papillae (1+2+1+1+3). Spicules free: manubrium rounded; lamina bent at its middle, with well developed dorsal hump and ventral wing at its middle; terminus ventrad curved, with acute tip and a subdorsal crest. Gubernaculum sigmoid.

Other material examined (see Table 1)

Very similar to type population, but showing variations in body length, shorter in the population from Almijara Mountain (387 μm in females and 395–405 μm in males), and longer in the populations from Almargen and Sierra de las Nieves (634 μm and 644–707 μm in females, respectively).

Diagnosis

Protorhabditis spiculocrestata sp. n. is distinguished by its body length 387–707 μm in females and 375–546 μm in males, lips very low and flattened, stoma 14–22 μm, female tail conical-elongate (48–100 μm, c = 6.4–8.3, c′ = 4.8–7.5), phasmid near to anus, male tail conical (20–27 μm, c = 18.3–22.3, c′ = 1.4–1.5), bursa peloderan closed anteriorly and bears eight papillae (1+2+1+1+3), spicules 23–26 μm long, and gubernaculum 10–16 μm long.

Relationships

The new species resembles Protorhabditis oxyuroides Sudhaus, 1974, although it can be distinguished from it by its having lips lower and reduced (vs. more prominent), stoma shorter (14–22 μm vs. 21–27 μm), and spicules with different morphology (vs. terminus lacking subdorsal crest).

Type locality and habitat

Los Carvajales, near the road from Alameda to Fuente de Piedra, province of Málaga, Spain; GPS coordinates: N 37°8.0′, E 4°43.0′. Soil in a Mediterranean plant community whose dominant species are Olea europaea L. var. sylvestris Brot., Daphne gnidium L., Rosmarinus officinalis L., Cistus monspeliensis L., Retama sphaerocarpa (L.) Boiss., Phlomis purpurea L., Thymus sp., Quercus coccifera L., and Ulex parviflorus Pourret. Collected on 19 October 1991.

Other localities and habitats

The species has also been collected from several localities in the SE Iberian Peninsula: Sierra de Guillimona (province of Granada); Sierras de Cazorla, Segura and Las Villas Natural Park (province of Jaén); road to Canillas de Aceituno, Periana, road from Archidona to Villanueva del Trabuco, Sierra de Mijas, and Sierra de las Nieves Natural Park (province of Málaga). It has been found associated with the rhizosphere of several wild plant communities whose dominant species were Pinus nigra Arn. var. salzmannii (Dunal) Franco, Pinus pinaster Aiton, Quercus rotundifolia Lam., Q. coccifera L., Juglans regia L., Retama sphaerocarpa (L.) Boiss., Juniperus oxycedrus L., Ulex sp., Cistus sp., Nerium oleander L. and Eucalyptus sp.

Type material

Six females (holotype and paratypes) and three males (paratypes) deposited in Departamento de Biología Animal, Biología Vegetal y Ecología, Universidad de Jaén, Spain; and one female (paratype) deposited in the nematode collection of the Swedish Museum of Natural History, Stockholm (Sweden).

Diploscapter coronatus (Cobb, 1893) Cobb, 1913 syn. Rhabditis coronata Cobb, 1893; Rhabditis bicornis Zimmermann, 1898; Diploscapter bicornis (Zimmermann, 1898) Goodey, 1963; Rhabditis cephaloides Stefański, 1922; Acrobeles armatus Kreis, 1929. (Figs. 4–6)

Fig. 4.

Fig. 4

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Diploscapter coronatus (Cobb, 1893) Cobb, 1913 (female). A: Neck. B: Anterior end. C: Entire female. D: Reproductive system. E: Posterior end.

Fig. 6.

Fig. 6

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Diploscapter coronatus (Cobb, 1893) Cobb, 1913 (SEM). A–C: Lip region (A: lateral view. B: frontal view. C: ventral view). D: Lateral field. E–F: Female tail (E: lateral view. F: ventral view).

Fig. 5.

Fig. 5

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Diploscapter coronatus (Cobb, 1893) Cobb, 1913 (LM). A: Neck. B: Female reproductive system. C: Lip region (lacinia level). D: Female tail. E. Lateral field.

Measurements: Listed in micrometers in Table 2.

Table 2.

Measurements (in μm) of females (n = 21) of Diploscapter coronatus (Cobb, 1893) Cobb, 1913 presented as mean ± s.d. and (range).

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Population from agar culture comes from specimens collected in Carchuna, province of Granada

Female (n = 20): Small nematodes, 358–504 μm long. Habitus ventrad curved after fixation. Cuticle annulated; annuli 1–2 μm wide at midbody. Lateral field occupying 14–22% of the midbody diameter, with four incisures under LM and two separated wings under SEM which fade out before to anus level. Lip region with six lips: the subdorsal and the subventral are very refractive and hook-like (4–5 μm high); the lateral lips are membranous (termed laciniae), high and with dentate margin, not easily observed under LM since only the central triangular part is more refractive. Stoma rhabditoid. Buccal prism with straight walls, very long and narrow. Stegostom lacking glottoid apparatus. Pharyngeal corpus well demarcated, slightly longer than isthmus and basal bulb together; procorpus cylindrical and metacorpus swollen, almost as long as wide. Basal bulb spheroid, with well developed valves at its middle. Cardia hemispherical, surrounded by intestinal tissue. Intestine lacking any peculiar differentiation. Nerve ring at isthmus level, at 70–77% of neck length. Excretory pore at 77–92% of neck length, at level of posterior portion of isthmus or basal bulb. Deirid at basal bulb level, at 81–97% of neck length. Reproductive system didelphic-amphidelphic. Anterior genital branch dextral (on the right side of intestine) and posterior branch sinistral (on the left). Ovaries with a flexure, rarely straight. Uterus short, less than the corresponding body diameter long. Vagina with thin walls, extending inwards one-third of body diameter. Rectum 0.8–2.0 times anal body diameter long. Tail conicalelongate to filiform, ending in acute tip. Phasmid at 11–12% of tail length.

Male: Not found.

Other material examined (see Table 2)

Very similar to population from Carchuna, although having smaller body (273 μm long) and pharyngeal corpus shorter than isthmus-basal bulb.

Distribution

The species has been collected in six localities: (i) Vélez-Málaga, province of Málaga, in association with Persea americana Miller; (ii) La Vidriera, Guillimona Mountain, province of Granada, in association with Quercus rotundifolia Lam. and Pinus sp.; (iii) Santa Fé, province of Granada, in association with Populus alba L.; (iv) Desfiladero de los Gaitanes, province of Málaga, in association with Citrus limon (L.) Burm. fil.; (v) Carchuna, province of Granada, in association with Lycopersicum esculentum Miller.; and (vi) La Caldera pool, Sierra Nevada National Park (3,000 m height), province of Granada.

Remarks

The material examined agrees well with the redescription by Eyualem et al. (1998) and previous descriptions by Paetzold (1958), Loof (1964), Andrássy (1968) and Bongers (1988), although the specimen collected in Sierra de Guillimona is smaller (273 vs. 317–480 μm). Our material is also very similar to populations studied by Tahseen et al. (2002), although having greater body length range (273–504 vs. 300–491 μm), greater tail width range, c value, and c′ value (54–80 μm, c = 5.1–7.4, c′ = 4.4–6.8 vs. 42–65 μm, c = 5–8, c′ = 5–8, respectively).

Comments on the genus Protorhabditis (Osche, 1952) Dougherty, 1953 syn. Rhabditis (Protorhabditis) Osche, 1952

Paradoxorhabditis Khera, 1971 op. Andrássy (2005)

Andrássy (2005) has provided an emended diagnosis of Protorhabditis as well a list of its species. Sudhaus (1991) transferred the type and only species of the genus Paradoxorhabditis Khera 1971, P. paradoxa Khera, 1971, to Rhabditis, but did not formally propose the synonymy of both genera, although very recently, Andrássy (2005) proposed its synonymy with Protorhabditis. Paradoxorhabditis is characterized by, among other features, the absence of glottoid apparatus and fits well the diagnosis of Protorhabditis, a fact that justifies the proposed synonymy by Andrássy. The presence of pseudo-peloderan bursa in P. paradoxa is a peculiar feature of this species, which is herein regarded as intrageneric variability, but that should be incorporated in the diagnosis of Protorhabditis.

The genus includes hitherto 13 species plus two species inquirendae or incertae sedis (see Table 3):

Table 3.

Morphometrics of Protorhabditis species.

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Type species:

Protorhabditis xylocola (Körner in Osche, 1952) Dougherty, 1953 syn. Rhabditis (Protorhabditis) xylocola Körner in Osche, 1952

Other species:

P. cervi (Andrássy, 1985) Sudhaus, 1991 syn. Caenorhabditis cervi Andrássy, 1985

P. elaphri (Hirschmann, 1952) Dougherty, 1955 syn. Rhabditis (Protorhabditis) elaphri Hirschmann, 1952

P. filiformis (Bütschli, 1873) Sudhaus, 1976 syn. Rhabditis filiformis Bütschli, 1873 Rhabditis (Choriorhabditis) filiformis (Bütschli, 1873) Osche, 1952 Rhabditis agilis von Linstow, 1876 Protorhabditis lengerkeni Paezotld, 1958

P. macrovelata Sudhaus, 1974

P. oxyuroides Sudhaus, 1974 syn. Rhabditis oxyuris apud Bütschli, 1873, nec Claus, 1862

P. paradoxa (Khera, 1971) Andrássy, 2005 syn. Paradoxorhabditis paradoxa Khera, 1971 Rhabditis (Rhabditis) paradoxa (Khera, 1971) Sudhaus, 1991

P. parvovelata (Körner in Osche, 1952) Dougherty, 1955 syn. Rhabditis (Protorhabditis) parvovelata Körner in Osche, 1952

P. postneri (Körner in Osche, 1952) Dougherty, 1955 syn. Rhabditis (Protorhabditis) postneri Körner in Osche, 1952

P. ruehmi (Körner in Osche, 1952) Dougherty, 1955 syn. Rhabditis (Protorhabditis) ruehmi Körner in Osche, 1952

P. spiculocrestata sp. n.

P. tristis (Hirschmann, 1952) Dougherty, 1955 syn. Rhabditis (Protorhabditis) tristis Hirschmann, 1952

P. virgo (Körner in Osche, 1952) Dougherty, 1955 syn. Rhabditis (Protorhabditis) virgo Körner in Osche, 1952

Species inquirendae and/or incertae sedis:

P. lepida (Kreis, 1930) Sudhaus, 1976 syn. Rhabditis lepida Kreis, 1930 Rhabditis (Choriorhabditis) lepida Kreis, 1930 (Osche, 1952) Rhabditis elegans apud Kreis, 1929, nec Maupas, 1899

P. minuta (Cobb, 1893) Dougherty, 1955 syn. Rhabditis minuta Cobb, 1893

Notes on some species

The material identified and described as Rhabditis filiformis by Cobb (1893) certainly does not belong to this species because of its rounded lips with acute setae, monodelphic-prodelphic female reproductive system and vulva very posterior close to anus. It better fits the diagnosis of Mesorhabditis (Osche, 1952) Dougherty, 1953, but further studies are needed to clarify its identity.

Some doubts persist on the true identity of Rhabditis agilis von Linstow, 1876. It was considered (Sudhaus, 1976; Andrássy, 1983) to be a junior synonym of P. filiformis (Bütschli, 1873) Sudhaus, 1976. However, there are some remarkable differences between both taxa, among others, shorter female tail (c = 5.5–6.0 vs. c = 3.2–4.0) and spicules (26 vs. 10 μm long), and they might not be identical.

P. lepida (Kreis, 1930) Sudhaus, 1976 (= Rhabditis elegans apud Kreis, 1929) is herein regarded as species inquirendae (cf. Andrássy, 1983), since the original description lacks many morphological details. Very recently, Andrássy (2005) considered it to be a valid species, but it is better to maintain it as species inquirendae.

The original description of Rhabditis minuta Cobb, 1893 is very poor in diagnostic features, and its true identity might not be established with accuracy. Thus, it should be maintained as species incertae sedis (cf. Andrássy, 1983).

Key to Protorhabditis species identification:

  1. Female tail longer (c′ = 10–20)----------------------- 2 Female tail shorter (c′ less than 8)------------------ 5

  2. Pharyngeal collar very long, occupying most of the length of the stoma; pharyngeal corpus cylindrical (metacorpus not swollen) ------------ elaphri Pharyngeal collar short or absent (shorter than stoma width); pharyngeal corpus with metacorpus swollen ----------------------------------------------------- 3

  3. Bursa bearing 9 pairs of papillae ----------------- tristis Bursa bearing 7–8 pairs of papillae ------------------- 4

  4. Cuticle lacking longitudinal striae; female tail shorter (c′ = 10–12); bursa anteriorly closed, pelodera ------------------------------------------------ filiformis Cuticle longitudinally striated; female tail longer (c′ = 15–20); bursa anteriorly open, pseudopelodera, with a short and fine terminal filament ------------------------------------------------ paradoxa

  5. Bursa anteriorly open------------------------------------- 6 Bursa anteriorly closed ----------------------------------- 11

  6. Body length less than 500 μm --------------------- virgo Body length more than 500 μm ------------------------ 7

  7. Bursa with scarcely developed velum, in lateral view not exceeding the ventral margin of body ---------------------------------------------------------- parvovelata Bursa with well developed velum, in lateral view exceeding the ventral margin of body --------------- 8

  8. Lips having acute tines ----------------------------- ruehmi Lips lacking acute tines ------------------------------------ 9

  9. Spicule length 16–21 μm -------------------- macrovelata Spicule length 21–34 μm -------------------------------- 10

  10. Inner (perioral) region of lips peculiarly elevated; cheilorhabdia divergent anteriorly --------------------------------------------------------------- postneri Inner (perioral) region of lips as usual, not peculiarly elevated; cheilorhabdia not divergent anteriorly ------------------------------------------------ xylocola

  11. Pharyngeal collar well developed, occupying more than half of the stoma length -------------- cervi Pharyngeal collar very short or absent (shorter than stoma width)

  12. Lip region narrower than adjacent part of neck; stoma 14–22 μm long; spicules bearing subdor sal crest ------------------------------------------ spiculocrestata Lip region wider than adjacent part of neck; stoma 21–27 μm long; spicules lacking subdor sal crest ----------------------------------------------- oxyuroides

Footnotes

The authors thank Dr. W. Sudhaus for his examination of type material of Protorhabditis spiculocrestata, Research Technical Services of University of Jaén (Spain) for the assistance in SEM study of the material, and the financial support received from the project entitled “Fauna Ibérica VIII” (CGL2004–04680-C10–09 / BOS).

This paper was edited by Zafar Handoo.

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