INTRODUCTION

Herein we describe a new cestode from the white-throated monitor Varanus albigularis (Daudin, 1802), collected south of Lake Turkana in the Rift Valley Province of Kenya. Species of Oochoristica Lühe, 1898 are commonly encountered in reptiles worldwide and about 100 species are presently known (McAllister & Bursey, 2017). Only a very few have, however, been reported from monitor lizards.

MATERIAL AND METHODS

This material was given to us by Dr M. Jirků (České Budějovice, Czech Republic) who collected it during fieldwork in the Lake Turkana area in 2006. A single V. albigularis, killed by a cobra, was examined. After dissection, the worms were relaxed in physiological saline, then fixed in hot 4% formaldehyde, and finally transferred to 70% ethanol. They were stained in Mayer's hydrochloric carmine, dehydrated in an ethanol series, cleared in eugenol and mounted in Canada balsam. The slides were examined with a Nikon Eclipse-80i microscope equipped with Nomarski interference contrast optics. Drawings were made with a drawing tube. Photographs were taken on the same microscope with a Jenoptik camera and treated with Progres Gryphax 1.1.8 software^©. All measurements are expressed in micrometers unless otherwise indicated. Metric and meristic values are presented as the range followed by their mean and the number of measurements made in parentheses.

Abbreviations. MHNG-PLAT: Natural History Museum of Geneva, Platyhelminthes collections. BMNH: British Museum (Natural History), London.

TAXONOMIC PART

Fig. 1.

Oochoristica varanicola sp. nov. Scolex. Scale bar: 250 µm.

REMARKS

Our material belongs to the genus Oochoristica Lühe, 1898, a taxon with a complex history as summarized e.g. in Hughes (1940); Spasskii (1951); Della Santa (1956); Beveridge (1994, 2008); or Masová et al. (2012). The most recent generic diagnosis (Beveridge, 1994) has been subsequently emended by Masová et al. (2012) for a number of minor details as well as removing the acraspedote nature of proglottides as a generic character. This latter character however would imply the synonymy of Mathevotaenia Akhumyan, 1946, whose members are primarily parasites of mammals, with Oochoristica, found essentially in reptiles (although exceptions do exist) (Beveridge, 1994). Although certainly needing investigation, this character is the single feature allowing separation of both genera. We thus consider here the genus Oochoristica sensu Beveridge, 1994, and accept only part of the emendation of Masová et al. (2012) in recognizing that testes can also be lateral to the vitellarium in some species.

Fig. 2.

Oochoristica varanicola sp. nov. Mature proglottis. Ventral view. Note the multilobed vitellarium (arrows). Scale bar: 500 µm.

A recent list, including almost 100 valid species of Oochoristica, was provided by McAllister & Bursey (2017), who also listed selected major discriminating characters for these species. In their table, these authors list eight species from the Afrotropical region. To our knowledge no other species in this genus has been described more recently.

Although the genus is widely diversified in the Squamata, especially in the Lacertilia, only two species of Oochoristica have been reported from Varanidae. Oochoristica varani Nama & Khichi, 1972 was found in Jodhpur (Rajasthan) in “Varanus monitor”, a taxon which does not exist: the authors most likely referring to V. bengalensis (Daudin, 1802) the common local monitor, or, possibly, to V. flavescens (Hardwicke & Gray, 1827) although this species is morphologically quite distinct and would probably have been correctly identified. Oochoristica varani can easily be distinguished from our material by its smaller scolex (270-412 µm) and suckers (150-200 × 140-170 µm), shorter cirrus-sac (140-210 µm) and lower number of testes (40-55) (Nama & Khichi, 1972).

Oochoristica tuberculata (Rudolphi, 1819) has been reported from a number of lizards, mostly Lacertidae, Scincidae and Agamidae (Della Santa, 1956), but also from V. griseus (Daudin, 1803), in Tunisia (Joyeux, 1923) and in Iran (Dollfus, 1965). Those reports should however be considered with caution as the Tunisian material is composed of a few young specimens that were only tentatively attributed to O. truncata, and the Iranian material is composed of “quelques débris en mauvais état” (several fragments in a poor state (of preservation) that “il est possible que l'on puisse rapporter les débris... à… O. tuberculata” (may possibly be attributed to O. truncata). The presence of this species in Varanus is thus highly questionable. In any case, O. tuberculata clearly differs from our material by its smaller scolex (160-230 µm), smaller suckers (110-140 µm), lower number of testes (20-50), and smaller number of ovarian lobules (4-6) (McAllister & Bursey, 2017).

Fig. 3.

Oochoristica varanicola sp. nov. Copulatory organs.

Fig. 4.

Oochoristica varanicola sp. nov. Eggs in gravid proglottis.

Fig. 5.

Oochoristica varanicola sp. nov. Eggs.

Among the other taxa listed by McAllister & Bursey (2017) from Africa, none presents characters close to those observed in our material. The most similar species are O. koubeki Mašová, Tenora & Baruš, 2012, and O. zonuri Baylis, 1919 which possess a cirrus-sac of similar length but far fewer testes and different scolex dimensions. Our observations of the type material of O. zonuri also confirm that the testes extend to the anterior margin of the segment as shown in the original description (Baylis, 1919: fig. 2), which thus excludes this species from Oochoristica sensu Beveridge (1994).

Our material further differs from most other known species in various hosts and localities because of its rare combination of a long cirrus-sac and high number of testes. The only species showing similar values for both traits are O. bivitellobata Loewen, 1940, O. gracewileyae Loewen, 1940, O. leonregagnonae Arizmendi-Espinosa, Garcia-Prieto & Guillen-Hernandez, 2005 and O. rostellata Zschokke, 1905. Oochoristica bivitellobata was reported from a member of the Teiidae in Kansas, USA. It is a very short worm consisting of only a small number of proglottides, small scolex (396 µm) and suckers (140 µm) and although both its cirrus sac length and testis number ranges overlap that of our material, they remain shorter (165 µm) and fewer (76) on average. The testes are also distinctly posterior, not reaching the lateral sides of the female organs (Loewen, 1940). Oochoristica gracewileyae was found in a rattlesnake in Texas. It also possesses a smaller scolex and suckers (426 µm and 145 × 152 µm respectively). Its cirrus-sac has a distinctive globular proximal extremity and does not extend beyond the excretory canals, and its testes are entirely posterior to the female genital complex (Loewen, 1940). Oochoristica leonregagnonae was reported from an Iguanidae in Mexico. Although similar, its average number of testes (95) is lower, and its cirrus-sac length (180-230 µm) only marginally overlaps that of our material (Arizmendi-Espinosa et al., 2005). Finally, O. rostellata was found in a colubrid snake in Italy (Zschokke, 1905). In its original description, Zschokke (1905) mentioned “2 to 3 rows of testes… each with 16 to 20 testes”, although his figure 3 shows 78 testes. Other metric data are lacking from this description and more recent reports (Baer, 1927; Della Santa, 1956; McAllister & Bursey, 2017) confuse various sources including data from O. cryptobothrium (von Linstow, 1906) that has been synonymized with it by some authors (Baer, 1927). Apparently Zschokke's species was subsequently found in North African snakes by Joyeux (1927), who described a much shorter cirrus-sac than that in our material. Our own observations of this material also confirm a lower number of testes 51-70 (60, n=5).

Oochoristica cryptobothrium was recognized as a valid species by Spasskii (1951) and McAllister & Bursey (2017) and its suggested synonymy with O. rostellata by Hughes (1940) or Della Santa (1956) have contributed to the great variation in the morphological features reported for this species. Von Linstow's (1906) original description, from a colubrid snake in Sri Lanka, is not sufficient to unambiguously characterize O. cryptobothrium and doubts remain about the validity of this taxon. Characteristics of this species, as summarized in McAllister & Bursey (2017) are based on a redescription of the original specimens provided by Fuhrmann (1927). We studied this material in the Geneva collections and note that although some of Fuhrmann's measurements are correct, major discrepancies, especially the length of the cirrus-sac (we measured 225 to 305 µm) and, to a lesser extent, the number of testes (about 50 to 60) exist. Our observations are approximate as the available material is not well preserved, but they nevertheless allow the separation of O. cryptobothrium from our material on the basis of a significantly lower number of testes. Additional specimens identified as O. cryptobothrium from a lizard from Accra (BMNH 1977.11.3.15-16) and re-examined appear to be O. rostellata. A detailed revision of all of the material currently attributed to O. cryptobothrium and O. rostellata is therefore needed.

In summary, our morphological observations, together with its geographical origin and host, allow us to conclude that our material from Varanus albigularis in Kenya represents a new species Oochoristica varanicola sp. nov.

Oochoristica varanicola is only the third (or possibly the second) species of the genus reported from monitor lizards, indicating that they are probably not ideal hosts for these anoplocephalids. Brooks et al. (1999) suggested that species of Oochoristica are highly specific and that their geographical distribution is restricted. Although our results seem to corroborate this assumption, it is difficult to confirm its generality given the limited availability of comparative material.

We should finally note that, for Oochoristica, like many groups of cestodes lacking rostellar hooks, specific identification relies heavily on a small number of strobilar characters. In the case of Oochoristica, some of them, e.g. testis numbers, are particularly difficult to observe and may often be inaccurate. As records for most species in the genus are scarce, independent verification of this character is problematic. Molecular data are essentially lacking in the group but will undoubtedly help clarify its structure and composition in the future.