Nematology, 2007, Vol. 9(1), 43-47

Nematodes of the order Rhabditida from India. Description ofSclerorhabditis tridentatus gen. n., sp. n. (Nematoda: Rhabditidae)

Irfan AHMAD ∗, Ali Asghar SHAH and Mohammad MAHAMOOD

Section of Nematology, Department of Zoology, Aligarh Muslim University, Aligarh 202002, India

Received: 4 May 2005; revised: 16 October 2006Accepted for publication: 16 October 2006

Summary – A new rhabditid nematode, Sclerorhabditis tridentatus gen. n., sp. n. is described and illustrated. The body is small,less than 0.5 mm, and has an unusual labial and cephalic organisation. The dorsal and ventral lips have strongly sclerotised tridentatestructures with the free ends of the forks directed towards the stoma, and the anterior margins of the lateral lips are sclerotised. Anunusual feature of this species is the contour of the cephalic border that has axillae-like structures on the lateral sides. The stomais wide and lacks a glottoid apparatus. The females are amphidelphic with reflexed ovaries and elongate conoid tails. Males werenot found. The new genus resembles Diploscapter and the related genus Carinoscapter in having membranous lateral lips, absence ofglottoid apparatus and amphidelphic reproductive system, but is clearly distinguishable by the shape and orientation of the sclerotisationof the dorsal and ventral lips and by the presence of a cephalic border.

Keywords – morphology, morphometrics, new genus, new species, Rhabditina, taxonomy.

During a survey for rhabditid nematodes, a very inter-esting species with an unusual labial sclerotisation wascollected from inside a hollow cavity in the trunk ofan avenue palm (Oreodoxa regia L.). Although resem-bling Diploscapter Cobb, 1913 and Carinoscapter Sid-diqi, 1998, detailed observations revealed it to be a specieswhich could not be assigned to any of the known genera ofRhabditina. We, therefore, propose the genus Sclerorhab-ditis gen. n. to accommodate this species.

The nematodes were isolated by modified sieving anddecanting and the Baermann funnel technique. They werekilled and fixed in hot 4% formaldehyde and left for 24h, after which they were transferred to glycerin-alcohol(5 parts glycerin, 95 parts 30% alcohol), dehydrated ina desiccator and mounted in anhydrous glycerin. Allmorphological observations, measurements and drawingswere made on an Olympus BX 50 DIC microscope.

Sclerorhabditis** gen. n.

DIAGNOSIS

Rhabditidae. Body small, less than 0.5 mm long. Cuti-cle finely annulated. Lip region offset, symmetrical, dor-

∗ Corresponding author; e-mail: ahmadirfi@yahoo.co.in** The genus name is derived from the unique sclerotisation ofthe lip region and is feminine in gender.

sal and ventral lips with fork-like sclerotisations. Freetips of forks directed towards stoma. Lateral lips some-what pyramidal in shape with flat sclerotised apical mar-gins. Anterior body margin forming a cephalic collar withdeep clefts on lateral sides. Amphidial apertures indis-tinct. Stoma long, tubular, sometimes widening anteriorly.Cheilostom not sclerotised; gymnostom broad, evenly cu-ticularised. Stegostom longer than gymnostom; glottoidapparatus absent. Pharyngeal corpus broad, swollen atbase. Female reproductive system amphidelphic; vulvaslightly post-median. Tail elongate conoid. Males notfound.

TYPE AND ONLY SPECIES

Sclerorhabditis tridentatus gen. n., sp. n.

RELATIONSHIPS

The new genus is related to Diploscapter and Carinos-capter in body size, the modified dorsal and ventral lips,lack of glottoid apparatus, similar pharynx, reproductivesystem and tail. However, the new genus can be eas-ily distinguished by the inwardly directed fork-shaped

© Koninklijke Brill NV, Leiden, 2007 43Also available online - www.brill.nl/nemy

I. Ahmad et al.

sclerotisations of the dorsal and ventral lips and the un-usual cephalic border with axillae-like structures later-ally (dorsal and ventral lips hook-shaped, points bifidand outwardly directed and cephalic border absent inDiploscapter and Carinoscapter).

Sclerorhabditis tridentatus* gen. n., sp. n.(Fig. 1)

MEASUREMENTS

See Table 1.

DESCRIPTION

Female

Body small, almost straight when relaxed, taperingslightly anteriorly but more posteriorly. Greatest body dia-meter at vulval region. Cuticle finely transversely annu-lated, annules more pronounced in anterior and poste-rior region. Lateral fields wide, with two lines, beginningat base of stoma. Labial region dome-shaped, set off byconstriction, symmetrical, 7-9 µm diam. Lips unusuallymodified, dimorphic; dorsal and ventral with sclerotisedfork-like structures with points directed towards stoma.Lateral lips membranous, somewhat pyramidal in shapewith flat sclerotised apical margins. Amphidial aperturesindistinct. Cephalic margin of body wall well defined, di-vided into dorsal and ventral sectors by deep lateral cleftsresembling primary axils of cephalobids. Stoma tubular,1.7-2.4 lip region diam. long. Cheilostom not sclerotised.Gymnostom short, wide, walls parallel or slightly diver-gent anteriorly. Stegostom without glottoid apparatus anddenticles, 2.5-3.0 times gymnostom length. Corpus mus-cular, 59-61% of pharyngeal length. Metacorpus swollen,bulb-like, 1.0-1.7 lip region diam. in diam. Isthmus rel-atively broad, encircled by nerve ring in posterior half,57-74 µm from anterior end. Excretory pore located at75-96% of pharyngeal length. Terminal bulb ovoid, mus-cular, 1.5-2.4 times lip region diam. wide. Anterior pha-rynx (measured from anterior end to base of corpus) 1.4-1.6 times longer than posterior pharynx (from isthmus toend of basal bulb). Cardia prominent, 1.5-3.0 µm long.Intestine granular with well-defined lumen. Rectum nar-row with closed lumen, or wide with dilated lumen. Re-productive system amphidelphic; both genital branches

* The specific name is derived from the three-pronged lipsclerotisation.

Table 1. Morphometrics of female Sclerorhabditis tridentatusgen. n., sp. n. Measurements are in µm and in the form: mean ±SD (range).

Character Holotype Paratypes

n – 10L 399 400 ± 28 (356-461)a 20.5 16.5 ± 2.1 (14.1-21.0)b 4.2 4.2 ± 0.2 (3.6-4.5)c 6.6 7.6 ± 0.7 (6.6-8.6)c′ 6.9 5.4 ± 1.1 (3.8-6.5)V 53.0 54.4 ± 2.1 (52.0-59.5)Maximum body diam. 19 23.3 ± 1.8 (20-32)Lip diam. 11 9.5 ± 1.1 (8-11)Length of stoma 18 17 ± 1 (16-19)Anterior pharynx 52 55.2 ± 4.3 (49-63)Posterior pharynx 42 40.1 ± 6.7 (32-56)Pharynx 94 95.3 ± 10.4 (83-116)Excretory pore from 80 75 ± 5.1 (69-84)

anterior endNerve ring 65 65.8 ± 4.1 (60-73)

from anterior endMedian bulb diam. 10 11.2 ± 2 (10-16)Basal bulb diam. 15 16.6 ± 1.8 (15-21)Anterior gonad 80 73.1 ± 10 (55-87)Posterior gonad 65 69 ± 7.6 (60-85)Vulval body diam. 18 23 ± 3.8 (20-26)Vulva to anus distance 127 132.5 ± 11.3 (117-158)Rectum 14 14.3 ± 1 (12-16)Phasmids to anus 8 8.5 ± 0.7 (8-10)Tail 60 53 ± 6 (45-63)Anal body diam. 9 10 ± 1 (9-12)

equally developed, anterior on right and posterior on leftside of intestine. Ovaries reflexed; flexure small, dor-sal to gonoduct or occasionally absent. Oocytes usuallyarranged in two or more rows with large, prominent, nu-clei. Oviduct short, usually not clearly distinguishable be-cause of developing oocytes. Uterus not distinctly demar-cated into glandular and muscular parts, distally slightlydilated and containing sperms. Uterine eggs measuring25-32 × 13-17 µm. Vagina muscular, less than half cor-responding body diam. long. Developing uterine eggs inproximal part of uterus may cause vagina to be slightly an-teriorly or posteriorly directed. Single pair of vaginal mus-cles present. Vulva a transverse slit with slightly raisedlips. Tail conoid to elongate conoid, 40-50% vulva-anusdistance long, tip finely rounded. Phasmids small, located0.8-1.2 anal body diam. posterior to anus.

Male

Not found.

44 Nematology

Sclerorhabditis tridentatus gen. n., sp. n. from India

Fig. 1. Sclerorhabditis tridentatus gen. n., sp. n. A: Entire female; B: Pharyngeal region; C: Base of pharynx showing excretory pore,lateral field and deirid; D: Labial sclerotisation in face view; E: Labial region, lateral; F-H: Stoma; I, J: Anterior genital branches;K: Vaginal area showing muscles; L: Lateral field at midbody; M-P: Tails.

Vol. 9(1), 2007 45

I. Ahmad et al.

TYPE HABITAT AND LOCALITY

Collected from inside a hollow in an avenue palm(Oreodoxa regia L.) trunk containing decaying wood andbat and bird droppings, Department of Zoology, AligarhMuslim University, Aligarh, India.

TYPE MATERIAL

Holotype female and nine paratype females on slidesSclerorhabditis tridentatus gen. n., sp. n., deposited in theDepartment of Zoology, Aligarh Muslim University, Ali-garh. One paratype female at the Instituut voor Dierkunde,Rijksuniversiteit, Gent, Belgium.

REMARKS

Sclerorhabditis gen. n. is clearly distinguishable fromthe related genera Diploscapter and Carinoscapter bythe three-pronged sclerotisation in the dorsal and ventrallips, the shape of the lateral lips and the cephalic borderwith axillae-like structures. In addition, a long pharyngealcollar and hence a long stegostom, is characteristic of thenew genus. The stegostom to gymnostom ratio varies from2.5 to 3.0. This character could also provide an importantdistinguishing feature but the ratio has generally not been

provided by other authors. However, calculating thesevalues from figures it is 0.3-0.4 for Diploscapter species(D. striatus Siddiqi, 1998; D. angolaensis Siddiqi, 1998;D. coronatus Cobb, 1913; D. lycostoma Volk, 1950) and0.6-1.0 in Carinoscapter (C. cornutus Siddiqi, 1998). Thenew genus is clearly distinguished from Diploscapter andCarinoscapter on this basis but the latter two genera arenot so clearly demarcated. However, unless complete andmore precise information is available for all species thischaracter must be used with caution.

We believe that these three genera are very closely re-lated and that the stem species of the clade was amphidel-phic, lacked a glottoid apparatus and had membranouslateral lips (Fig. 2). The lip sclerotisation, with two out-wardly directed prongs in Diploscapter and Carinoscapterand three inwardly directed prongs in Sclerorhabditis,represents a unique feature in Rhabditidae. From the evo-lutionary point of view, it is difficult to say which of thesetwo types represents the plesiomorphic state as there areno known outgroup taxa with such lip sclerotisation. It ispossible, and we presume it here, that each of the typesrepresents an apomorphic state. The deep clefts resem-bling the primary axils of the cephalobids are a uniquefeature in Rhabditina. Homologisation of these structureswith the primary axils of Cephalobina does not seem to

Fig. 2. Cladogram showing the phylogenetic relationship of the three genera, Diploscapter, Carinoscapter and Sclerorhabditis gen. n.Apomorphies are designated by black squares and plesiomorphies by white squares.

46 Nematology

Sclerorhabditis tridentatus gen. n., sp. n. from India

be possible because of their differing numbers and posi-tions (two lateral vs three, one ventral and two subdorsalin cephalobids). Hence the cephalic margin is divided intotwo sectors, dorsal and ventral, while in the cephalobidsthere are three sectors, one dorsal and two ventrosublat-eral.

Sclerorhabditis tridentatus gen. n., sp. n. males werenot found, although the distal part of the uterus gener-ally contained few to many spermatozoa (Fig. 1I, J), andsometimes so many that this part became dilated. A sper-matheca was never present, the uterus serving the samepurpose. As many of the females were impregnated witha varying number of sperms, the presence of males be-comes a strong possibility, yet none was found. WhetherS. tridentatus gen. n., sp. n. is hermaphroditic or gono-choristic may only be ascertained when more specimensbecome available and the details of its biology are elab-orated. At the moment it is not possible to put forwardany convincing argument for or against either of the tworeproductive states.

The locality of this new species is interesting in thatit was collected from a hollow cavity in the trunk of apalm tree at a height of ca 3.8 m from ground level. Withseveral phoretic associations possible it seems improbablethat the nematodes moved up the trunk. The hollowserved as roosting site for small bats and also the littleowlet. In addition, the decaying matter collected frominside contained several types of small insect. Whileit may be speculative to suggest that the nematodescould be transported on the beaks or claws or body

parts of the owlet or bats, it may be more realistic topresume that the actual phoretic carriers were the insects,a phenomenon that is well documented in the literature(Massey, 1974). The species is probably bacteriophagous,living in decaying wood with bird and bat droppings.

Acknowledgement

The financial assistance provided by the Ministry ofEnvironment and Forests, New Delhi, through the AllIndia Coordinated Project on Taxonomy, is gratefullyacknowledged.

References

COBB, N.A. (1913). New nematode genera found inhabitingfresh water and non-brackish soils. Journal of the WashingtonAcademy of Science 3, 432-444.

MASSEY, C.L. (1974). Biology and taxonomy of nematodeparasites and associates of the bark beetles in the UnitedStates. Agriculture Handbook No. 446. Washington, DC,Forest Service, USDA, 233 pp.

SIDDIQI, M.R. (1998). Carinoscapter cornutus gen. n., sp.n., Diploscapter striatus sp. n. and D. angolaensis sp.n. (Rhabditida: Diploscapteridae). International Journal ofNematology 8, 61-67.

VÖLK, J. (1950). Die Nematoden der Regenwürmer und aas-besuchenden Käfer. Zoologische Jahrbücher (Systematik) 79,1-70.

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