Chordodes mizoramensis (Nematomorpha, Gordiida), a new species of horsehair worm from Mizoram, North-East India

Abstract Chordodes mizoramensis, a new species of freshwater gordiid horsehair worm, is described from Mizoram, NE India on the basis of scanning electron microscopic and morphometric studies. The new species can be distinguished from its congeners in that the apical filaments of the crowned areoles are branched several times, a pattern that has not been observed in other species. An additional distinguishing character is that it has more bulging areoles, which are distributed among simple areoles alone or in groups, do not form clear patterns.


Introduction
About 350 species of freshwater horsehair worms (Nematomorpha: Gordiida) are currently known. Of these, only 14 species (plus an additional undetermined Gordius sp.) have been reported from India (Schmidt-Rhaesa and Yadav 2004). Considering the size of India and the diversity of habitats, this number appears to be only a fragment of the existing gordiid diversity. We describe here a new species of the genus Chordodes Camerano, 1897. Chordodes includes mainly tropical and subtropical species. All horsehair worms are parasites of arthropods, which leave their host for reproduction (Hanelt et al. 2005). Praying mantids form the main group of fi nal hosts for species of Chordodes (see Schmidt-Rhaesa and Ehrmann 2001). Recently, the terminology for cuticular structures was unifi ed and an overview and key were developed (Schmidt-Rhaesa et al. 2008). Characteristic for Chordodes species is, in comparison with other freshwater genera, the diversity of cuticular structures. Th e cuticle is often structured into polygonal or roundish structures named areoles. While in other genera not more than two diff erent types of areoles can be recognized, species of Chordodes may exhibit up to seven types.

Material and methods
Th e specimens investigated were preserved in 70% ethanol, directly after their emergence from the host, an undetermined praying mantis. Pieces about 1 mm long were cut from the mid-body region of each worm. Th ese and the entire posterior ends were prepared for Scanning Electron Microscopy (SEM). Th e pieces were dehydrated in an increasing ethanol series, critically point dried and coated with gold in a sputter coater. Observation took place using a LEO SEM 1524 under 10 kV. Digital images were taken. Host. Both specimens emerged from one specimen of Hierodula sp. (Mantodea) (Fig. 1A).

Chordodes mizoramensis
Etymology. Th e name refers to the region in which the new species was found, Mizoram in NE India.
Description. Th e holotype is 200 mm long, with a diameter of 1.3 mm in the midbody region. Towards the posterior end, the diameter decreases to about 0.7 mm at the level of the cloacal opening. Th e anterior end is also tapered. Th e paratype is 265 mm long and has a diameter in the mid-body region of 1.5 mm;, at the level of the cloacal opening the diameter is 0.79 mm. Th e frontal tip in both specimens is white, whereas the remaining body is medium brown. A pattern of darker patches (the "leopard pattern") is present in both specimens; in the holotype this is more pronounced than in the paratype.
Th e cuticle contains six types of areoles (areoles are elevated cuticular structures), for which the terminology of Schmidt-Rhaesa et al. (2008) will be applied. Most abun- dant are simple and bulging areoles (Fig. 1B-D). Simple areoles are quite fl at semicircular elevations with a rough surface but no further structure (Fig. 1D). Bulging areoles are more elevated and carry a small tuft of very short bristles on top (Fig. 1C, D). Compared with other species, bulging areoles are quite abundant; they are distributed among simple areoles alone or in groups, without forming clear patterns (Fig. 1C). Tubercle areoles regularly occur among the simple and bulging areoles (Fig. 1C, D), as rarely do thorn areoles (Fig. 1C). Tubercle areoles carry a fi nger-like process on top; thorn areoles have a strong thorn on top of a broader basis.  Characteristic for species of Chordodes are crowned areoles, which carry a crown of apical fi laments on an elevated "stem". Crowned areoles occur in pairs and are surrounded by so-called circumcluster areoles ( Fig. 2A, B). Th is last type resembles the bulging areoles, but is longer (as elevated as the crowned areoles) and more slender ( Fig. 2A, B). It also carries an apical tuft of short bristles, some of which can be slightly branched. Several circumcluster areoles have a more or less central "plug" among the apical bristles ( Fig. 2A-D). Th is "plug" is variable in shape, in some cases appearing as a drop-like structure emerging from the centre of the areole, but in others it is a broader, more voluminous structure. One pair of crowned areoles occurs in the centre, between the circumcluster areoles. Each crowned areole has a fl at, smooth surface, with fi laments emerging from the margin, except for the region where both areoles face each other ( Fig. 2A-C). Th e fi laments spread fl at from the central surface and project between the circumcluster areoles. Th eir length is about 25 μm. Most fi laments divide several times, forming multiple branches ( Fig. 2A-D). Only one type of crowned areoles could be found.
Th e posterior end of the males is rounded, and a small median incision may be present (Fig. 3A, B). An approximately 150 μm broad ventral strip is free of areoles of the types described above, but forms polygonal or interdigitating compartments with a smooth surface (Fig. 3A, B). Th is smooth region extends around the ventral cloacal opening, which is about 200 μm anterior of the posterior margin of the worm. Th e cloacal opening is oval, with a number of long, fi ne bristles, the circumcloacal bristles, present in a ring emerging approximately 10 μm below its surface (Fig. 3C, D). In the region around the cloacal opening are further bristles; these are abundant and variable in length (Fig. 3C, D). Th e areoles described above are replaced at the posterior end, at least on the lateral sides, by elevated, conical areoles with an apical tuft of bristles (Fig. 3F). Th ese areoles may represent bulging areoles, but are distinctly pointed apically and more abundant. In a region anterolateral to the cloacal opening is, in the region with areoles, an oval region with more bristles (Fig. 3A, B, E). Th ese are very dense, appear to be all unbranched and have a lengths of up to about 30 μm.
Th e types of areoles present on the cuticle of Chordodes mizoramensis sp. n. represent the "usual" set of areoles present in other Chordodes species, but there are some notable diff erences. Bulging areoles occur in some, but not all Chordodes species (see Schmidt-Rhaesa et al. 2008). Th ey are distinctly more abundant in C. mizoramensis than in other species. Crowned areoles surrounded by circumcluster areoles is also a common pattern, but there is no species in which a branching of the apical fi laments has been described.
Several Chordodes species have two types of crowned areoles; those with distinctly longer apical fi laments are present along the ventral and sometimes also the dorsal mid-line (see Schmidt-Rhaesa et al. 2008). In C. mizoramensis, only one type of crowned areoles could be found. However, crowned areoles appear to be a sexually dimorphic character, with females showing both types of crowned areoles, whereas in males the diff erences appear to be much less distinct or absent (see, e.g. Schmidt-Rhaesa 2002 for C. queenslandi Schmidt-Rhaesa, 2002or De Villalobos et al. 2004for C. brasiliensis Janda, 1894. Th erefore, it cannot be excluded that the females of C. mizoramensis also exhibit such a dimorphism. Th e male posterior end of the new species corresponds, as far as is known, in general with those of the males of other Chordodes species. However, the shape of the areoles on the posterior end (conical, with tuft of bristles on top) may be peculiar to C. mizoramensis.
In summary, C. mizoramensis exhibits some unique features, which justify its description as a new species.