Seleneella Rahm, 1932

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 : 269-272

Syn. Seleneella Rahm, 1932 [syn. by Andrássy (1978)]

Diagnosis (emended)

Chambersiellidae , Macrolaiminae . Small nematodes, 0.65–1.30 mm long. Cuticle very finely annulated. Lateral field with two to five incisures. Lip region rounded, continuous with adjacent body. Lips more or less fused, having anterior sensilla arranged in two circles: six conical labial setae directed forward and four (two subdorsal and two subventral) papillae. Oral opening surrounded by six curved triangular liplets. Amphid aperture a transverse oval slit located at the base of lateral lips. Stoma subdivided into cheilostome and gymnostome with strongly sclerotized rhabdia, and stegostome enveloped by muscular pharyngeal tissue and lacking visible rhabdia. Pharynx cephaloboid, with pharyngeal corpus cylindrical and metacorpus slightly swollen. Cardia conoid and short. Female reproductive system monodelphic– prodelphic. Postvulval uterine sac very short or absent. Male reproductive system monorchic. Spicules curved ventrad, with more or less rounded to slightly hooked manubrium. Gubernaculum oval or more or less triangular. Tail of both sexes conical, ending in an acute tip or a short mucro, straight or slightly dorsad curved.

List of species

Type species:

M. crucis Maupas, 1900

Other valid species:

M. arboreus Truskova and Eroshenko, 1977

M. canadensis Sanwal, 1960

= Macrolaimus crucis apud Fuchs (1938) nec Maupas (1900) [syn. by Sanwal (1960)] M. hamatus Thorne, 1937

M. natator Timm, 1960

M. richteri Swart and Heyns, 1992

M. ruehmi Andrássy, 1966

= Macrolaimus crucis apud Rühm (1950, 1956 ) nec Maupas (1900)

= Macrolaimus crucis apud Meyl (1960) nec Maupas (1900) syn. nov. M. somniorum Andrássy, 1984

M. taurus Thorne, 1937

Species inquirendae

M. citri Rahm, 1928 [by Andrássy (1984)]

M. crucis var. gracilis Rahm, 1929 [by Andrássy (1984)]

= Seleneella gracilis ( Rahm, 1929) Rahm, 1932

M. crucis var. tenuis Rahm, 1928 [by Andrássy (1984)]

M. maipoensis ( Rahm, 1932) Andrássy, 1978 [by Andrássy (1984)]

= Seleneella maipoensis Rahm, 1932

Notes on some species

Macrolaimus citri: The original description of this species by Rahm (1928) is of very poor quality and lacks relevant morphological details. It was said to be similar to M. crucis but bearing a tooth-like or stylet structure at the base of stoma, a feature that raises serious doubts as to the true identity of this taxon. Actually, Rahm (1929) reported the species again and considered that it might not belong to Macrolaimus . Andrássy (1984) regarded it as species inquirenda, an action that seems to be well justified.

Macrolaimus maipoensis: Rahm (1932) originally described this species under the new genus Seleneella , which was separated from Macrolaimus in having poorly developed labial papillae, and stoma with half-moon-shaped rhabdia between cheilostome and gymnostome. Information about this taxon lacks relevant details for its characterization, but available illustrations suggest that it is very similar, if not identical, to M. crucis var. gracilis by Rahm (1929); Andrássy (1984) also regarded it as species inquirenda, an opinion that is herein followed.

Macrolaimus somniorum: The original description of this species appears in Andrássy’s book ( Andrassy 1984) where illustrations of new species are not provided. According to this, its description is very similar to that of M. arboreus but distinguished from it by having spicules with manubrium bent ventrad as a hook.

Macrolaimus taurus: The original description of this species by Thorne (1937; see also Massey 1974) is very simple but it includes good illustrations of the anterior body region and male tail. Andrássy (1966, 1984) suggested that M. taurus might be identical to M. crucis , but it differs in the morphology of stoma (longer than wide versus as long as wide) and the presence (versus absence) of postvulval uterine sac.

Macrolaimus sp. : Holovachov et al. (2003) described a female from Costa Rica that resembles M. taurus in having longer than wide stoma and the presence of postvulval uterine sac. However, its stoma is distinctly larger (15 × 23 versus 6.5 × 11 µm long) and the postvulval uterine sac is longer (1.6 versus 1.0 times the corresponding body diameter long).

Key to identification of valid species

1. Cheilostome less than two times longer than gymnostom................. 2 Cheilostome two to four times longer than gymnostome.................. 5

2. Buccal cavity almost as long as wide (1.2–1.5 times)...................... 3 Buccal cavity longer than wide (1.7–2.2 times)............................ 4

3. Lateral field with three longitudinal incisures........................ crucis Lateral field with five longitudinal incisures......................... richteri

4. Postvulval uterine sac less than the corresponding body diameter long.......................................................................... ruehmi Postvulval uterine sac slightly longer than the corresponding body diameter................................................................... taurus

5. Labial setae thinner, hair-like, one-third of lip region width.......... natator Labial setae thicker, one-quarter or one-fifth of lip region width........... 6

6. Gymnostom about half as long as cheilostome.................... arboreus Gymnostom about one-third as long as cheilostome...................... 7

7. Spicules with hook-shaped manubrium......................... somniorum Spicules with rounded, not arcuated manubrium......................... 8

8. Gubernaculum more or less triangular (2.6–3.1 times longer than wide).................................................................... canadensis Gubernaculum fusiform (5.3 times longer than wide).............. hamatus

Table 2 provides a compendium of morphometrics and diagnostic features of Macrolaimus species.