TENTACULARIID TRYPANORHYNCHS FROM THE NHM 



151 



43 



Fig. 42-44 H. yamagutii. Strobila 4-5 cm (42) and 7-8 cm (43) behind 

 scolex, and last proglottids (44). Scale bar=500(jm. 



BMNH 1997.3.24.1, 1997.3.24.2, 1997.3.24.3^, 1997.3.24.5. M. 

 beveridgei was described in detail by Palm et al. (1997). 



17. Mixonybelinia southwelli (Palm & Walter, 1999) 

 comb. nov. 



Material examined. The Natural History Museum London: 

 BMNH 1977.11.4.7, 1 977. 11. 4.8-9. M. southwelli was described in 

 detail by Southwell (1929) and Palm & Walter (1999). 



DISCUSSION 



Of the material deposited at the British Museum Natural History, 17 

 different trypanorhynch species, formerly all belonging to the genus 

 Nybelinia Poche, 1926, were identified. In addition, two new gen- 

 era, Heteronybelinia gen. nov. and Mixonybelinia gen. nov., are 

 erected, and 4 new species, N. sakanariae sp. nov., N. schmidti sp. 

 nov., H. heteromorphi sp. nov., and H. minima sp. nov., are de- 

 scribed. The new genera separate species with a homeoacanthous, 

 homeomorphous (Nybelinia) from those having a homeoacanthous, 

 heteromorphous metabasal armature with heteromorphous basal 

 hooks {Heteronybelinia gen. nov.) and from species with a 

 heteromophous metabasal and homeomorphous basal armature, 

 which are assigned to Mixonybelinia gen. nov. Mixonybelinia is a 

 tentaculariid genus in which two different armature types occur 

 along the tentacle. This has been described earlier for non- 

 tentaculariid trypanorhynchs, such as the mixodigmatid Mixodigma 



leptaleum Dailey & Vogelbein, 1982 and the lacistorhynchid 

 Dasyrhynchus talismani, Dollfus, 1935 (Dailey & Vogelbein, 1982; 

 Beveridge & Campbell, 1993) 



After a first subdivision of the genus by Dollfus ( 1960), Palm et 

 al. (1997) recently subdivided the different Nybelinia species on the 

 basis of the tentacular armature and discussed the erection of 

 subgenera. However, the authors did not split the genus into several 

 genera or subgenera. The material in the Natural History Museum 

 clearly demonstrates that the species of the subgroupings as pro- 

 posed by Palm et al. (1997) can be consistently separated on the 

 basis of their characteristic metabasal and basal tentacular armature. 

 They can clearly be recognised, though there is a higher level of 

 intraspecific variation associated with the scolex as well as hook 

 sizes along the tentacles than previously indicated. 



Following Campbell & Beveridge (1994) and Palm (1995), the 

 erection of different genera on the basis of the tentacular armature is 

 justified. In their most recent classification, Campbell & Beveridge 

 (1994) used the tentacular armature at the superfamily level, and 

 Palm (1995) at the generic level. In other families within the order, 

 several genera can be distinguished mainly on basis of their charac- 

 teristic tentacular armature, such as the genera Callitetrarhynchus, 

 Lacistorhynchus, Mixodigma, Poeciloacanthum and Pseudolacisto- 

 rhynchus (other examples see Campbell & Beveridge, 1994, Palm, 

 1 995). This simplifies further studies of tentaculariid trypanorhynchs 

 of the Nybelinia type. 



The present study again demonstrates a high level of morphologi- 

 cal variation within different species of Nybelinia and Hetero- 

 nybelinia. Nybelinia africana and Heteronybelinia yamagutii have 

 been re-described and do not correspond in every detail with the 

 original descriptions of the type material. Similar morphological 

 variation occurs in other tentaculariid trypanorhynchs, such as 

 Tentacularia coryphaenae, evidenced by the numerous synonymies 

 in the literature (see Dollfus, 1942, Palm, 1995). In comparing the 

 detailed descriptions of 1 6 Nybelinia species recognised by Dollfus 

 (1960), several of them are very similar and can be distinguished 

 only on the basis of minor differences of the hooks, which lie within 

 the limits of intraspecific variation for this character in more re- 

 cently described species (see Palm & Walter, 1999). Additionally, 

 Palm et al. (1997) demonstrated a low host specificity of several 

 Nybelinia species, which leads to the suggestion that some of the 

 material examined by Dollfus, which was mainly obtained from the 

 same region off Dakar but from different host fish species, might 

 belong to the same species. This is especially possible in subgroup 

 IIAa (Heteronybelinia estigmena species complex) and in the 

 Nybelinia aequidentata species complex (see remarks above). It is 

 recommended that until the type material and more material from 

 the Dakar region can be examined, the species described by Dollfus 

 (1960) remain valid. However, several are possible synonyms. 



Adult tentaculariids also can show a low level of host specificity 

 and different shark species can harbour several Nybelinia and 

 Heteronybelinia species. During the present study, Carcharhinus 

 limbatus and C. leucas were found to be infested with 3 species 

 {Nybelinia scoliodoni, Heteronybelinia estigmena, H. robusta) and 

 2 species {Nybelinia africana, Heteronybelinia estigmena) respec- 

 tively. A similar wide host range has been also demonstrated for 

 some other trypanorhynchs (Palm & Overstreet in press, Palm, 

 1997b) as well as other marine parasite species, such as Antarctic 

 parasites infesting the rock cod Notothenia coriiceps from the 

 South Shetland Islands (Palm et al., 1998). This behaviour seems 

 to be characteristic for cosmopolitan marine parasitic helminths, 

 such as the nematodes Contracaecum osculatum and 

 Pseudoterranova decipiens. In conclusion, it is postulated that the 

 currently known tentaculariid genera and most of the species are 



