Chordodes combiareolatus Schmidt-Rhaesa & Yadav, 2015, n. sp.
Creators: name: Schmidt-Rhaesa, Andreas
name: Yadav, Arun K.
Publisher: name: Zenodo
Year: 2015
Subjects: Biodiversity
Taxonomy
Animalia
Nematomorpha
Gordioida
Gordioidea
Chordodidae
Chordodes
Chordodes combiareolatus

description: Chordodes combiareolatus n. sp.
(Figures 1, 2)
Holotype. One female from the type locality, deposited in the Zoological Survey of India, North Eastern Regional Centre, Shillong under the accession number IV/NERC-308.
Etymology. The name “ combiareolatus ” refers to a unique type of areoles, in which characteristics of two areoles are combined.
Type locality. Terrace paddy field in Tsupo, Viswema, Kohima, Nagaland, India (25°34’50.59”N / 94°09’56.89”E), elevation: 4175 feet.
Description of female. The specimen is 210 mm long and has a width of 1.9 mm in the midbody region. The anterior end is tapered; the anterior most tip is white. The main body colour is moderately dark brown with darker patches forming the so-called “leopard pattern”. The posterior end is distinctly swollen (Fig. 2 C), the cloacal opening is terminal.
In the midbody region, all 6 types of areoles known from the genus Chordodes are present. Areoles cover the body with moderate density, meaning that regions of non-areolar cuticular surface can be seen between the areoles (Figs. 1 A, 1C). This surface is structured into parallel superficial folds (Fig. 1 A). The most abundant type of areoles is simple areoles (Figs. 1 A, 1C). They are of differing height and smooth except for an apical tiny tuft of bristles. Tubercle areoles are present among simple areoles (Fig. 1 A). They appear as a mixture between simple and tubercle areoles by combining characters of both these areolar types. Tubercle areoles carry a tuft of small bristles on their apical surface and have a finger-like tubercle, which is rarely placed centrally, but more often shifted towards the edge of the areole or even originating from the side of the areole (Figs. 1 A, 1B). There are also tubercle areoles that correspond to the “typical” form (i.e. without bristles and with a more or less central tubercle) (e.g. Fig. 1 C), but the “combined type ” occurs more often. Thorn areoles are present, and the thorns have a broad basis and are slightly curved (Fig. 1 C). Clusters of crowned areoles are present. On the lateral sides of the body, these clusters are composed of two central crowned areoles and 8‒10 surrounding circumcluster areoles (Figs. 1 D, 1E). The circumcluster areoles appear as elongated simple areoles, they also carry a tuft of bristles on top (Fig. 1 E). The crowned areoles have a flat apical surface, from which filaments of moderate length (10‒15 µm) extend laterally (Fig. 1 E). Some of these filaments divide into several branches. We observed in several cases that in one of the two crowned areoles the filaments branch off from the entire surface, while in the second areole the side facing the first areole remains free of filaments (Fig. 1 E). We could not observe a tubercle between the crowned areole, a structure which is present in several other Chordodes species. Along the midline (it was not possible to determine if this was the ventral or the dorsal one) crowned areoles occur on both sides next to the midline and have distinctly longer apical filaments (Fig. 1 D). The length of the filaments is maximally around 150 µm.
We could also observe a number of arrangements of areoles, in which areoles resembling circumcluster areoles surround a central flat region with roughly structures surface (Figs. 1 F, 1G).
In the anterior end, the shape of the areoles changes strongly (Fig. 2 A). The dominating type of areoles has a dense tuft of apical filaments on top (Fig. 2 B). These areoles are not arranged in particular patterns with respect to each other, but cover the cuticle densely. Between these areoles some long tubercles appear, but the origin of these tubercles was unclear, i.e. whether they originated directly from the cuticular surface or from an areole (Fig. 2 B). In the anterior-most tip of the animal the areoles still have a tuft of apical filaments, but not as dense as in the areoles described previously. Additionally, the apical surface is depressed (Fig. 2 A).
In the posterior end the terminal cloacal opening is surrounded by a region with smooth cuticle with a radius of approximately 200 µm (Figs. 2 C, 2D). In the margin of this smooth circular region of the cuticle some bristles are present as the cuticle transitions into the typical areolar pattern (Fig. 2 E). Areoles transform from simple elevations of different shape to the areolar pattern described above. Crowned areole clusters start about 600 µm from the margin between smooth and areolated cuticle. The circular appearance of the posterior end is only interrupted by one slight groove that runs to the margin of the terminal smooth region (Fig. 2 D). In this part, areoles are present a bit further inside the smooth region than in other places.
Taxonomic comments. The specimen described above shows several characters well distributed among species of the genus Chordodes. Simple areoles are the most abundant type of areole, and tubercle and thorn areoles are also widely distributed types. Crowned areoles are characteristic for the genus Chordodes and in many species they occur along the ventral and sometimes also along the dorsal midline with very long bristles. The character that separates the new species from the previous descriptions is that the tubercle areoles include the tuft of bristles present in simple areoles. Usually, tubercle areoles have a smooth surface and the tubercle is positioned apically. Some exceptions are known. In the African species C. digitatus Von Linstow, 1901 the basal areolar part is horseshoe-shaped and surrounds the tubercle (Fig. 5 A, 5B in De Villalobos et al. 2007). In the African species C. tuberculatus Von Linstow, 1901 tubercles appear to be displaced from areoles or attach laterally on areoles (see De Villalobos et al. 2007). In the Japanese species C. japonensis Inoue, 1951, tubercle areoles are usually of the “standard pattern”, but one broad tubercle areole is documented, which carries a tubercle and a small tuft of bristles (Fig. 2 C in Schmidt-Rhaesa 2004). None of these cases looks exactly like in the new species, but this shows that too little attention has been paid to the exact shape of certain areolar types.
The crowned areoles of the new species show (at least in several clusters) an asymmetrical pair of crowned areoles, where apical filaments originate from all sides in one areole, but not from all sides in the other areole. Such a pattern has not been described yet and may be another diagnostic character of the new species.
The regions, in which some longer areoles surround a circular region of flat surface are interpreted by us as crowned areole clusters (circumcluster areoles), where the central crowned areoles are broken off. The reasons for this interpretation are that the regions with an “empty center” are distributed in the same pattern as otherwise the crowned areole clusters. The circular ring of elevated areoles resembles circumcluster areoles and the rough surface in the centre does not appear to be the regular, undamaged cuticular surface. Crowned areoles are prominent elevated structures that might be prone to mechanical damage and abrasion under some circumstances.
The anterior end of the specimen described above shows a dramatic change in areoles and the areolar pattern in the anterior end differs completely from the one in midbody. This shows the importance of comparing cuticular sections from comparable body regions. The cuticular structure is rarely described in detail. Areoles with a dense tuft of bristles are described also from C. moutoni (see below) and from C. fomosanus Chiu, Huang, Wu & Shiao, 2011 (Chiu et al. 2011). Therefore the change of the areolar pattern may be further distributed than currently documented and we hesitate to include this character as species specific for C. combiareolatus.
The posterior end in general corresponds to the female posterior ends that have been described for the genus Chordodes. It is usually swollen, in contrast to the posterior ends in other genera (see Schmidt-Rhaesa 2012) and the terminal cloacal opening is in the center of a flat or even concave terminal disc.
description: Published as part of Schmidt-Rhaesa, Andreas & Yadav, Arun K., 2015, Chordodes combiareolatus, a new species of horsehair worms (Nematomorpha) from Nagaland, India, with further comments on Chordodes moutoni, pp. 202-210 in Zootaxa 3925 (2) on pages 203-206, DOI: 10.11646/zootaxa.3925.2.3, http://zenodo.org/record/237357