Observations on the Subfamily Aetholaiminae Jairajpuri , 1965 ( Nygolaimidae : Nematoda )

Mylocliscus nanus Thorne, 1939 is redescribed from specimens collected in the State of Bahia, Brazil. It has an axial odontostyle and therefore does not belong with Aetholaimus Williams, 1962 to the Nygolaimidae, subfamily Aetholaiminae. The abrupt esophageal expansion, location of dorsal esophageal gland orifice, and presence of oval organs in the lateral chord indicate that it belongs to Discolaimidae. Donjlaimus rotundicauda de Man, 1880, currently placed under Carcharolaimus Thorne, 1939, is redescribed from specimens collected in the Netherlands and Switzerland. The presence of a mural tooth and of three "cardiac glands" show that it belongs to the Nygolaimidae; it is transferred to Aetholaimus. The latter genus now contains four species and is briefly reviewed. In 1939 Thorne described a new genus and species Mylocliscus nanus from a single female collected on the Island of Sumatra, Indonesia. He placed this genus in the subfamily Actinolaiminae of the family Dorylaimidae because of the presence of sclerotization in the stomatal region. He could not decide whether it had an axial stylet or a mural tooth. In 1962 Williams described a new genus and species Aetholaimus bucculentus from the Island of Mauritius, which he placed in the family Nygolaimidae because it possessed a mural tooth instead of an axial odontostyle. He noted, however, that this species also possessed a character reminiscent of the Actinolaiminae, viz. sclerotization in the stomatal region; and he noted certain resemblances between Aetholaimus and Mylocliscus. In 1965 Jairajpuri united these two genera into the new subfamily Aetholaiminae—recently raised to family rank by Andrassy (1976); again he noted that the position of Mijlodiscus required further clarification. During a survey of plant parasitic nematodes in the State of Bahia, Brazil, carried out in cooperation with Dr. R. D. Sharma, the second author collected several females and juveniles of Mijlodiscus, so that redescription is possible and its taxonomic position can be clarified. Paratypes of Aetholaimus bucculentus were kindly put at our disposal by Mr. D. J. Hooper, Rothamsted, England, and Dr. M. S. Jairajpuri lent a specimen from India, identified by him as Ae. indicus. Copyright © 2011, The Helminthological Society of Washington OF WASHINGTON, VOLUME 45, NUMBER 1, JANUARY 1978 83 Before dealing with these species, however, we want to discuss the taxonomic value of stomatal sclerotization in the Dorylaimoidea. In our opinion this value has been strongly overrated. Thorne (1939) united all dorylaims which possess such sclerotization, viz. the genera Actinolaimus Cobb, 1913 (in its old wide sense), Antholaimus Cobb, 1913, Carcha.rolaimus Thorne, 1939, Mylodiscus Thorne, 1939 and Trachypleura Thorne, 1939, to a subfamily Actinolaiminae of the Dorylaimidae. Meyl (1957) raised the group to family rank; Thorne (1967) made it a superfamily Actinolaimoidea with six families: Actinolaimidae, Neoactinolaimidae, Paractinolaimidae, Trachypleurosidae, Carcharolaimidae and Mylodiscidae. Leaving aside the Trachypleurosidae— based upon two insufficiently known species —we can say that the first three families contain species with long-tailed females and shorttailed males (Brittonema Thorne, 1967 was defined as having long-tailed males, but Thome's drawing suggests that the long male tail of B. sulcatwn is an artifact, and males are unknown in all other species; the genus may be identical with Actinca Andrassy, 1964. Thorne also reported a long-tailed male of the genus Practinocephalus Andrassy, 1973 [ = Actinocephalus Thorne, 1967 nee Stein, 1848] but did not describe or illustrate it), whereas the Carcharolaimidae and Mylodiscidae have short tails, generally rounded (except in a few species of Carcharolaimus), and no sexual dimorphism. The first three families stand, in general morphology, close to certain genera of the Dorylaimidae sensu stricto such as Dorylaimus, Laimijdorus and Ischiodorylaimus: the cuticle may possess longitudinal ridges; the esophagus widens more or less gradually, and the orifice of the dorsal gland lies in the expansion region; in some groups the supplements are concentrated into a few clusters; the lip region is usually almost continuous. The Carcharolaimidae, on the other hand, have the lip region strongly offset by constriction; the lateral chord contains a series of large, conspicuous oval organs, each connected with the body surface by a large pore; the esophagus widens very abruptly and the orifice of the dorsal gland lies well behind the expansion zone. In all these characters the Carcharolaimidae agree with Discolaimus. Following a suggestion of Loof and Coomans (1970), Krnjaic and Loof (1976) placed Carcharolaimus in the family Discolaimidae. It thus appears that the superfamily Actinolaimoidea as conceived by Thorne is an artificial taxon. The families Actinolaimidae, Neoactinolaimidae and Paractinolaimidae have such close connections with Dorylaimidae that we think it best to place them as a single family beside the Dorylaimidae (see Baqri et al., 1975). Stomatal sclerotization may evidently develop independently in several groups of dorylaims, and the presence of such sclerotization in Aetholaimus should not a priori be interpreted as evidence of actinolaimid relationship. Mylodiscus nanus Thorne, 1939 (Fig. 1; Diagram 1) DIMENSIONS (based on 13 females): L = 1.09-1.78 mm; width = 36-53 /xm; a = 2438; b = 3.1-4.1; c = 56-72; V = °-1756599-18. odontostyle = 10-12 /xm; odontophore = 23-26 /-on; T/ABW = 0.7-0.9. Body ventrally curved after fixation; cylindrical throughout the greater part of its length but markedly narrowing near the anterior end. Cuticle 2-3 /am thick in midbody, increasing to 6-9 /xm on tail; with fine but distinct transverse striae. Lateral chord 3-6 /xm wide or %— Vi2 of body width at midbody. Lateral body pores in single line along the dorsal side of the chords; in one specimen there were 35: 11 in the neck region, 23 between esophagus base and tail, and one on the tail. Lip region 12-15 /xm wide or two fifths to one third as wide as the base of the neck; disclike with inner bowl-shaped sclerotized lining, the bottom of which is thickened and has radiating ridges. Lips clearly demarcated, with the usual set of six inner and ten outer papillae. Amphids with triangular pouch, 58 ^m wide or about three fifths the width of the base of the lip region. Seiisillae situated opposite the base of the odontophore, 34—40 /xm behind head end. Oral opening a dorsoventral slit. Odontostyle slender and conical, about 0.80X as long as lip region width; with thickened tip and small aperture. Odontophore linear, 23—26 /xm long. Guiding ring "double," fixed ring 8.5-12 /xm or slightly less than one lip region width from head end. The esophagus measures 326-395 /xm; anCopyright © 2011, The Helminthological Society of Washington 84 PROCEEDINGS OF THE HELMINTHOLOGICAL SOCIETY Copyright © 2011, The Helminthological Society of Washington OF WASHINGTON, VOLUME 45, NUMBER 1, JANUARY 1978 85 terior part a narrow tube except for the odontophore region, which is wider and spindleshaped. At 53-58% of the neck length the esophagus expands suddenly, forming the heavily muscular posterior part. Dorsal gland outlet 26—35 /xm behind the expansion or 8— 9% of neck length. Dorsal esophageal gland nucleus oval, measuring 6-8 X 4-5 fun, with rounded nucleolus 3 /xm in diameter; located 11-19 /xm behind the outlet of the gland. First pair of ventrosublateral gland nuclei about 15 tirn apart; the nuclei are rather small (3.0—3.5 /xm, nucleolus 1.5 /mi), oval to rounded to somewhat triangular. Second pair of ventrosublateral gland nuclei at about the same level; measuring 3.5—5.5 /am, nucleolus 2-2.5 /x.m; rounded. LOCATIONS: (gland nuclei and orifices of 5 females): DO 63-67%; DN 68-71%; DODN 3.3-5.8%; S^ 77-80%; S^ 81-83%; dist. 2.8-4.6%; S2N 87-88%; S->O 89-90%; K = 65-77; K' = 73-81.