Research Article |
Corresponding author: Andreas Schmidt-Rhaesa ( a.schmidt-rhaesa@leibniz-lib.de ) Academic editor: Hans-Peter Fagerholm
© 2016 Andreas Schmidt-Rhaesa, Renzo Perissinotto.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Schmidt-Rhaesa A, Perissinotto R (2016) Chordodes ferox, a new record of horsehair worms (Nematomorpha, Gordiida) from South Africa. ZooKeys 566: 1-11. https://doi.org/10.3897/zookeys.566.6810
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Three females and one male specimen of a previously unconfirmed species of horsehair worms (Nematomorpha) from South Africa are described using Scanning Electron Microscopy. The females correspond to the description of Chordodes ferox Camerano, 1897, a species previously described from the Democratic Republic of the Congo (Congo-Kinshasa) and an adjacent, not further specified region of the Republic of Congo (Congo-Brazzaville). Characteristic is the presence of enlarged and elevated simple areoles around the base of a thorn areole, in combination with further cuticular characters. This is the latest of a total of six species of horsehair worms reported from South Africa so far. Two species of praying mantids, Polyspilota aeruginosa (Goeze, 1778) and Sphodromantis gastrica Stål, 1858, have been identified as hosts of C. ferox, while its distribution range in the region and the period of adult emergence from the host remain largely unknown.
Nematomorpha , Chordodes ferox , praying mantid hosts, new records, South Africa
A number of horsehair worms (Nematomorpha) are known and have been described from Africa, but most are occasional records, with few results from extensive sampling. Although still far from systematic sampling,
Nematomorpha are long and slender worms, which develop parasitically in terrestrial insects (mainly praying mantids, carabid beetles, crickets and cockroaches) and a few other arthropods. Eventually, they emerge from these hosts into water for reproduction (see e.g.
Gordiids have comparably few diagnostic features. These are the shape of the posterior end and cuticular structures, such as bristles, spines and variously shaped elevations called areoles. Traditionally, cuticular samples were removed from the animals and investigated with the microscope, but now scanning electron microscopical (SEM) investigation has become the standard method, because with this technique characters can be documented at higher magnification and better quality. A number of African species have been reinvestigated using SEM (e.g.
We report here the determination of four specimens of horsehair worms, as Chordodes ferox Camerano, 1897 (at least the females). This species has been reported once before from Pietermaritzburg, KwaZulu-Natal, based on an old and poorly preserved specimen deposited in the Natural History Museum, London (see
A total of four specimens were found in the Baviaanskloof Valley at Kudu Kaya Farm (river at campsite, 33°39'12.4"S, 24°34'59.7"E) in the Eastern Cape Province of South Africa, on 22 March 2015, while undertaking preliminary observations in the area. Two specimens emerged from the abdomen of a praying mantid, identified as Polyspilota aeruginosa (Figure
Specimens are deposited in the Zoological Museum in the Centrum für Naturkunde of the University Hamburg under the numbers ZMH13363-ZMH13366.
For Scanning Electron Microscopy (SEM), both anterior and posterior ends of the body as well as a 2-3 mm long section from the middle region of the body were cut and dehydrated in an increasing ethanol:water gradient, then critically point dried, and coated with gold in a sputter coater. Observations were made using JSM-6360 (JEOL) SEM operating at 15 kV. Digital images were taken. Specimens comprise three females and one male, which are described separately here. All females are similar in their diagnostic characters, while the male differs slightly from the females in some characters. Figures used here come from the male (ZMH13363) and two females (ZMH13364 and ZMH13367), because in the third female (ZMH13366) the cuticle was dirty and less well preserved. For the description of cuticular structures (areoles) the terminology of
The posterior end of the females appears slightly swollen because the diameter of the body decreases slightly about 1 mm from the posterior tip (Figure
Chordodes ferox: a posterior end of female with terminal cloacal opening (co) b ventral view of posterior end of male with ventral cloacal opening (co) and precloacal bristlefields (pbf)c enlargement of bristles in the precloacal bristlefields d clusters of crowned areoles with long apical filaments (encircled) along both sides of the ventral midline (vml) in a female e overview of the ventral side of a female showing the distribution of clusters of crowned areoles with long (oval with unbroken line) and short (circle with broken line) apical filaments f clusters of crowned areoles in center and surrounding circum-cluster areoles (entire cluster encircled). SEM images: Andreas Schmidt-Rhaesa a, f from ZMH13366 b, c from ZMH13363 d, e from ZMH13364.
Five different types of areoles were observed on the cuticle of the median piece. Simple areoles are roundish and have an almost smooth surface (Figures
Chordodes ferox, higher magnification of cuticular characters: a cluster composed of two central crowned areoles (car) and surrounding circumcluster areoles (ccar)b cluster with fewer circumcluster areoles (Note transition between circumcluster areoles and simple areoles,sar) c cluster of crowned areoles with long apical filaments (encircled is a thorn areoles) d, f thorn areoles e isolated tubercle next to simple areoles. SEM images: Andreas Schmidt-Rhaesa a from ZMH13363 b, d, e from ZMH13364 c, f from ZMH13366.
The posterior end exhibits the typical characteristics of the genus Chordodes (Figure
Simple areoles are roundish and their apical surface has small “knobs” (Figure
Simple areoles, tubercle areoles, thorn areoles, crowned areoles in clusters surrounded by circum-cluster areoles and the presence of crowned areoles with conspicuously long apical filaments are typical characters found in Chordodes species (
The characters of the female specimens investigated here correspond well with those reported in the description of Chordodes ferox Camerano, 1893. The species has been described based on one female specimen from the Republic of Congo (“French Congo”) found in an unidentified mantid species (
The holotype of this species as well as further specimens have been investigated using SEM by
In addition, one potential further character of the specimens reported here is that the thorn areoles appear to be surrounded by a few large simple areoles. In most other species, thorn areoles are composed of a base, which resembles a “usual” areole and the thorn itself (compare, e.g. with figure 2C in
The single male specimen available differs in its cuticular characters from the female specimens. The most conspicuous difference is the lack of crowned areoles with long apical filaments, which is a well-known sexually dimorphic character in the genus Chordodes (e.g.
Praying mantids are the dominant host insects of horsehair worms of the genus Chordodes (
Although direct evidence of worm emergence was only observed from the abdomen of P. aeruginosa, the second mantid species, S. gastrica, was found floating on the water in close proximity to one of the free-living worms, still alive but poorly active. There is little doubt, therefore, that it was involved in the release of the worm. Regarding timing and locality of the finding of the C. ferox specimens, it is not known yet whether the period of emergence from the host is restricted to the austral autumn, as all specimens were collected towards the end of March. Searches during other seasons of the year are currently in progress but have so far yielded no further specimens. Regarding locality, all specimens were found in a relatively small riverine area within the Baviaanskloof valley. Although in a privately owned farm, the area is completely surrounded by the Baviaanskloof Wilderness Area, which is part of the Cape Floral Kingdom World Heritage Site. It is virtually certain that C. ferox occurs through much of this area, particularly in the smaller water courses that act as tributaries to the main river.
Lynette Clennell is thanked for providing photos of live specimens and assisting with field observations. We are grateful for the Eastern Cape Department of Economic Affairs, Environmental Affairs and Tourism for granting permit No. CRO112/14CR to collect aquatic invertebrates throughout the province. We also thank Liza Rishworth for her help in formatting the manuscript.