Description of a new species of insect parasitic nematode , Leidynema ( Schwenck , in Travassos 1929 ) ( Thelastomatidae ) from host Periplaneta americana of Meerut region-India

Three different types of insect parasitic nematodes namely Leidynema, Thelastoma and Hammerschmidtiella, were collected from hind gut of host Periplaneta americana. The new species Leidynema meerutensis sp. nov., is characterized with its females having a typical corpus broader at posterior and an enlarged blind intestinal diverticulum, females with unequally disposed lateral alae with posteriorly directed terminal spine, much enlarged excretory sac/bulb and a short attenuated tail. The male Leidynema meerutensis sp. nov. have four pairs of caudal papillae and a truncated tail with a short spine projection.


INTRODUCTION
The animal parasitic nematodes belonging to Order -Oxyurida, constitute two super-families -Oxyuroidea (nematode parasites of vertebrates) and Thelastomatoidea (the nematode parasites of invertebrates essentially arthropods) of order oxyurida.The thelastomatides are essentially the parasites thriving in invertebrate hosts, mostly the arthropods.They are parasitic (or commensal) in the gut of most saprophytic insect and other arthropod hosts.They feed upon host's gut contents like its micro-flora and body fluid (Jex et al., 2005).The super-family Thelastomatidae has been organized into five different families (Adamson and Van Waerebeke, 1992) -Thelastomatidae, Protrelloididae, Hystrignathidae, Travassosinematidae and Pseudonymidae.Family Thelastomatidae is the largest family and have more than 35 genera.

MATERIALS AND METHODS
Different household insects including house hold cockroaches (P.americana) were collected from different regions of district Meerut.The collected host insects were anaesthetized and dissected and nematodes were recovered from their hindgut.The collected nematodes were heat killed and fixed in Triethanolamine formalin (TAF) fixative.Nematodes were then dehydrated by slow dehydration method in alcohol glycerin mixture.The fixed nematodes were put into alcoholglycerin mixture and kept in glass dessicator with anhydrous CaCl2 for 3-5 days to allow slow dehydration.The dehydrated nematodes were mounted on glass slides in anhydrous glycerin with glass wool and sealed.Outline structures were drawn with the help of camera Lucida and photographs were taken using Motic image 2000 DMB 1 microscope.Morphometric measurements were recorded using stage and ocular micrometers.Comparative studies of morphology and morphometric measurements of different specimens of collected of nematode parasites were done using De Mann's formulae and parameters (De Man, 1884).The measurements and parameters are expressed in mean, range and standard deviation from the mean.
For scanning electron microscopy -the heat killed nematodes were transferred in primary fixative -Karnovasky's fixative for overnight and then transferred in 2.5% gluteraldehyde.The fixed nematodes were washed with 0.1 M phosphate buffer (pH -7.2) at 4°C and gradually dehydrated in different grades of acetone.The dehydrated specimens were dried by critical point drying method using liquid CO2.Dried specimens were mounted on aluminum stubs and gold coated.Scanning photography was done using LEO435 VP scanning electron microscope and measurements were recorded with LEO-32 annotation programme Tables 1 and 2.

Female
Mouth surrounded with eight large sub-median labiopapillae and a pair of small amphids.Cephalic extremity formed by two annules.Oesophageal corpus divided into anterior narrow and relatively broader posterior portions of nearly equal length, a short distinct isthmus and a valvular spherical end bulb.Intestine have a large blind intestinal diverticulum called cardium.Lateral alae are present and terminate into terminal spine.Excretory pore is present at the posterior to base of oesophagus.Vulva is present at or near mid-body.Vagina anteriorly directed and opens into a common uterus.Ovaries are two in number and directed opposite -didelphic and amphidelphic.Eggs are large, elongate, ellipsoidal, crescent shaped and triangular in cross-section.Tail attenuated to long filliform.

Male
Cephalic extremity is formed by a single expanded annulus.Lateral alae may be present or absent.Oesophagus is simple and without any posterior swellings.Intestine is simple and without diverticulum.Caudal extremity abruptly truncated, with or without short terminal spine (spine like process on its ventral side) or provided with several protrubences.Caudal papillae 3-5 pairs, consisting of one pair of large sub-ventral pre-anal, one to three pairs tiny sub-ventral and one pair sub-lateral post-anal papillae.Spicule is present.

Female
Body cylindrical, tapering at both ends, 2.5 -3.15 mm in length and with maximum body width of 0.28 -0.35 mm; head with 2 nd annulus much wider and with close-set of 5-6 annuli and then annuli expand abruptly in both, its length and width.First annule with 8 pairs of labial papillae have surrounding mouth.Cuticle is closely annulated throughout the body length.Lateral alae are prominent and each alae terminate into a spine-like projection at the posterior.These lateral alae and its spinelike projections are equally disposed in all species of Leidynema described so far (namely: Leidynema appendiculatum; however, in the present species -L.meerutensis sp.nov., it is much unequally disposed).Oesophagus is 0.37-0.45mm long (1/7 th ) occupying anterior 14-15% of the body length and consists of a 0.29 -0.31 mm long corpus, 0.020-0.025mm long distinct isthmus and an end bulb of 0.11 × 0.10 mm dimension.Corpus is demarcated into two distinct regions, the anterior half is narrow and its posterior part is cylindrical and broader.Intestine prominently enlarged at the anterior end and is provided with a posteriorly directed much enlarged characteristic oblong, blind intestinal diverticulum.Nerve ring is at the anterior 1/20 th of the body and is located at 0.135 -0.150 mm from anterior end (NR% -5.04%).Excretory pore at 0.55 -0.65 mm from the anterior end occupying anterior 1/5 th of the body length (Ex% -20.74%).The excretory bulb/sac is much enlarged and of the size approximately similar to the oesophageal end-bulb.Ovaries are paired and two in number and are divergent to each other -didelphic, amphidelphic.Vulva is transverse in orientation and slightly anterior to middle of the body at 1.27 -1.56 mm from anterior end (V% = 48%).Vagina is sclerotized, muscular and anteriorly directed opening into a common uterus.Eggs are elliptical in shape with dimension of 0.125 × 0.050 mm and are laid singly.Tail attenuated and relatively much shorter comprising 1/6 th of body length.A pair of phasmid is visible at the anterior of the tail (visible in SEM photomicrograph).

Male
Small body with length 0.80 -1.15 mm and width 0.06-0.09mm, curved at the posterior end upon fixation.Cuticle is annulated throughout the body length.Lateral alae present and continue to the tail.Oesophagus 0.18 -0.20 mm long occupying anterior 1/5 th of the body and having a corpus of uniform diameter with length 0.11 -0.13 mm, a short isthmus 0.02 mm and an end-bulb with dimension 0.03 -0.04 mm × 0.03 -0.04 mm.Nerve ring situated at anterior 1/10 th at 0.08 -0.10 mm from the anterior end (NR -9.53%) and excretory pore occupy anterior 1/3 rd of body at 0.27 -0.35 mm from anterior end (Ex% -33.12%).Testis is single and reflexed at the tip.Spicule is prominent with its length of 0.033 mm.Caudal extremity in male is abruptly truncated with a short terminal spine like structure, tail 0.015 -0.017 mm in length from the anus.Caudal papillae four (four pairs) pairs in number and are symmetrically disposed -one pair sub-ventral pre-anal, two pairs ventral post-anal and one pair small sub-dorsal post-anal papillae.

Habitat/site of collection
Hind gut of the host.

Etymology
The present species name, Leidynema meerutensis is based on type locality of host collection.

Species diagnosis
The new species is characterized by the unequal distribution of lateral alae and terminal spine and short tail in females and 4 pair anal papillae in males.Also, the females have unusually large excretory sac/bulb opening in to excretory pore (not been reported so far).These three features make the species unique and distinct from all other eight species described so far.Leidynema Schwenck, (in Travassos, 1929) with the type species L. appendiculatum Leidy 1850 (Chitwood 1932), is characterized by its gut diverticulum.Leidynema meerutensis sp.nov. shares the similarities in generic characters with

Table 1 .
Comparative morphometric measurements of different species of Leidynema (Female).