Erection of Euterranova n. gen. and Neoterranova n. gen. (Nematoda, Anisakidae), with the description of E. dentiduplicata n. sp. and new records of two other anisakid nematodes from sharks off New Caledonia

Helminthological examinations of three species of sharks, Galeocerdo cuvier, Triaenodon obesus (both Carcharhinidae, Carcharhiniformes) and Stegostoma fasciatum (Stegostomatidae, Orectolobiformes) from New Caledonian waters, carried out during 2003–2005, revealed the presence of three species of adult anisakid nematodes referable to Terranova Leiper et Atkinson, 1914. However, this genus can no longer be considered valid, because its type species has been designated a species inquirenda. Therefore, the present nematodes are assigned to two newly established genera, Euterranova n. gen. [type species E. dentiduplicata n. sp.] and Neoterranova n. gen. [type species N. scoliodontis (Baylis, 1931) n. comb.], based mainly on different labial structures. Euterranova dentiduplicata n. sp. from the stomach of S. fasciatum is mainly characterized by the presence of lips with two rows of denticles. Innominate specimens of Euterranova (a female and a third-stage larva) were collected from the digestive tract of T. obesus. Specimens of N. scoliodontis were recorded from G. cuvier. The two named species are described based on light and scanning electron microscopical examinations. Neoterranova scoliodontis has previously been recorded in New Caledonian waters from the same host species. Species previously attributed to Terranova are transferred to Euterranova (5 species), Neoterranova (4 species) or considered species inquirendae (10 species). Since Pseudoterranova Mozgovoy, 1950 was found to be a nomen nudum according to the International Code of Zoological Nomenclature (ICZN), the available name of this genus is Pseudoterranova Mozgovoy, 1953. A key to Porrocaecum-like nematode genera (Porrocaecum, Pseudoterranova, Pulchrascaris, Euterranova, and Neoterranova) is provided.


Introduction
As stated by Moravec and Justine [29], the taxonomy of anisakid nematodes parasitizing elasmobranchs remains rather confused, mainly because of the inadequate descriptions of many species, and this unsatisfactory situation still exists. This mainly concerns representatives of the controversial genus Terranova Leiper et Atkinson, 1914, which contains many species parasitic in elasmobranchs, teleosts, crocodilians, colubrid snakes and, previously, marine mammals (e.g. [1,14,32,35,41,43]). Currently, with some original descriptions being either incomplete or inaccurate and some type material either lost or unknown, there is no general consensus on the specific composition of this genus [42]. In addition, the taxonomic status of Terranova is questionable and, as indicated by Gibson [14], Deardorff [11] and Bruce and Cannon [10], important interspecific morphological features, such as lip characters, spicule differences or the presence or absence of plectanes, indicate the need for a new generic conception for these species.
The recent examination of nematodes collected by J.-L. Justine and his students from the sharks Galeocerdo cuvier, Triaenodon obesus (Rüppel) (both Carcharhinidae, Carcharhiniformes) and Stegostoma fasciatum (Hermann) (Stegostomatidae, Orectolobiformes) off New Caledonia during 2003-2005 revealed the presence of three different representatives of Terranova (sensu lato), one new and one known species, plus one unidentifiable at the species level; these are dealt with below. Since Terranova was found to be a genus inquirendum, two new genera are proposed to accommodate these species.

Materials and methods Ethics
Big sharks are top predators and thus important for ecology; the sharks used in this study were generally by-catches from other studies or caught by private fishermen and then used for our parasitological survey. All work was conducted in accordance with the laws of the Southern Province of New Caledonia.

Methods
Sharks were either speared or caught by line. The nematodes were fixed in hot 70% ethanol and preserved in the same liquid. For light microscopical (LM) examination, they were cleared with glycerine. Drawings were made with the aid of a Zeiss microscope drawing attachment. Specimens used for scanning electron microscopical (SEM) examination were postfixed in 1% osmium tetroxide (in phosphate buffer), dehydrated through a graded acetone series, critical-point-dried and sputtercoated with gold; they were examined using a JEOL JSM-7401F scanning electron microscope at an accelerating voltage of 4 kV (GB low mode). All measurements are in micrometres unless otherwise indicated. The fish nomenclature follows Fish-Base [12].

Family Anisakidae Railliet et Henry, 1912
Genus Euterranova n. gen. urn:lsid:zoobank.org:act:D7135A79-71FD-4A2C-8646-CF42C47D8DEC Diagnosis Ascaridoidea, Anisakidae. Rather large nematodes, widest in midbody. Cuticle slightly transversely striated. Dorsal lip with two double papillae; each subventral lip with one double papilla and lateral amphid. Each lip provided with small, bilobed median elevation armed with two prominent lateral teeth and one row of several median denticles between them; additional row of median denticles may be present somewhat posterior to anterior row. Interlabia absent. Narrow lateral alae present. Deirids well developed, near level of nerve ring. Oesophagus long and narrow. Ventriculus elongate, without ventricular appendix. Intestinal caecum present. Excretory pore between base of subventral lips. Spicules similar, approximately equal in length. Gubernaculum present or absent. Genital papillae numerous. Ventral postcloacal plectane consisting of several transverse plates present. Vulva anterior to midbody. Tail conical; tip without ornamentation. Parasites of elasmobranchs.

Remarks
At present, adult anisakid nematodes possessing a cylindrical ventriculus and an intestinal caecum and parasitizing poikilothermic hosts have been assigned to the genera Terranova and Pulchrascaris Vicente et dos Santos, 1972 [1,11,13]. However, the type species of the former genus is a species inquirenda and, consequently, Terranova should be considered a genus inquirendum (see Discussion). Species of the new genus Euterranova n. gen. differ from those of Pulchrascaris in having well-developed lips, each with an internal median lobe armed with a comb-like dentigerous ridge formed by two prominent lateral teeth and several medial denticles between them (vs. lips reduced, without a median lobe; dorsal lip with two large teeth and both subventral lips each with one large tooth) (see also the key at the end the Discussion).
Cephalic structures are generally considered to be very important taxonomic features in the nematode parasites of vertebrates [1,13] and, in some groups, e.g. in the Cystidicolidae, some genera are based solely on details of the mouth visible only with the use of SEM [27].
Euterranova dentiduplicata n. sp. Figs Etymology: The specific name of this nematode dentiduplicata (= double-indented) is a Latin adjective relating to the characteristic feature of this species, i.e. the presence of two rows of denticles on each lip.

Description
General: Large, whitish nematodes with thick, transversely striated cuticle (Figs. 2B, 2E, 3A and 3B). Maximum width near middle of body. Lips almost equal in size; inner margins of lips rounded; each lip provided with small, bilobed median elevation armed with 2 prominent lateral teeth and row of 6-10 median denticles between them; additional row of 8-10 median denticles present, being located somewhat posterior to anterior row ( Female (

Remarks
This new species is easily distinguishable from other congeners in possessing two (instead of one) transverse rows of denticles on the anterior margin of lips, which is a unique feature within all anisakid nematodes. Of the specimens examined, the second (lower) row of denticles was not clearly visible only in the smallest male.

Remarks
The morphology of the only available adult specimen (female) shows that it belongs to Euterranova n. gen. Nevertheless, the structure of lips is different from that in E. dentiduplicata n. sp. (labial lobes are more prominent and each lip possesses only one transverse row of denticles) and also seems to differ somewhat from E. galeocerdonis and E. pectinolabiata, as is apparent from SEM micrographs of these species provided by Tanzola and Sardella [42] and Shamsi et al. [35], respectively. However, in the absence of a male, the specific identification of the available material is impossible.
Genus Neoterranova n. gen. Etymology: The name Neoterranova is composed of Terranova (the name of a nematode genus) and the prefix Neo-(= new). Gender: feminine.

Remarks
Species of Neoterranova n. gen. differ from those of Pulchrascaris in having moderately-developed lips, each with a continuous row of even-sized denticles extending along entire, sometimes lobular inner anterior margin (vs. lips reduced, without rows of denticles; dorsal lip with two large teeth and both subventral lips each with one large tooth). From those of Euterranova n. gen., they differ in having the lips without an inner median lobe armed with a comb-like dentigerous ridge but, instead, with a continuous row of even-sized denticles on each lip (see also the key at the end of the Discussion).
The three above-mentioned species from reptiles, i.e. N. caballeroi, N. crocodili and N. lanceolata, are assigned to this genus tentatively based on the nature of denticles on lips. However, the structure of lips in these species appears to be considerably different from that of the type species (the anterior lobes are moderately developed or rather indistinct) and these species also appear to differ in the structure of postcloacal plectanes, the number and arrangement of male caudal papillae and the presence of a gubernaculum in two of them [41]. Therefore, subsequent detailed studies of these nematodes may indicate the need for a separate genus to accommodate these species.

Remarks
A detailed redescription of E. scoliodontis (as Terranova), based on specimens collected from the same host species (G. cuvier) from off New Caledonia, has already been provided by Moravec and Justine [29]. Since the morphology of the present specimens (two males and three females) is in full agreement with this redescription, we refrain from describing these nematodes once again. The only difference is that Moravec and Justine [29] reported the presence of a poorly developed median preanal papilla in this species, but this was neither observed in the present study (see Figs. 6C-6D) nor previously by Bruce and Cannon [10].
Originally this species was described by Baylis [3] from the carcharhinid shark Scoliodon sp. [= probably Rhizoprionodon acutus (Rüppel)] [10] off the eastern Australian coast. Gibson and Colin [15] designated it as a junior synonym of the inadequately described Terranova brevicapitata (Linton, 1901) from G. cuvier in the western North Atlantic, but Deardorff [11] resurrected T. scoliodontis, pointing out that it differs from the former species mainly in the presence of the ventral postcloacal plectane. Based on the LM examination of syntypes, T. scoliodontis was subsequently redescribed by Bruce and Cannon [10]. Moravec and Justine [29] were the first to study this species using SEM (see above).

Discussion
The genus Terranova was erected by Leiper and Atkinson [25] to accommodate their new species Terranova antarctica Leiper et Atkinson, 1914, which was poorly described and based on a single female 32 mm long, collected from the gummy shark Mustelus antarcticus (Günther) (Triakidae, Carcharhiniformes) in Bay of Islands, New Zealand [24,25]. The genus was characterized as follows: "An Ascarid with three large simple lips. No interlabia. Oesophagus simple. Gut with anterior caecal prolongation. No oesophageal appendage." However, later the type specimen of T. antarctica was re-examined by Baylis [2], who had assigned it to Porrocaecum Railliet et Henry, 1912. Baylis and Daubney [4] considered Terranova to be a synonym of Porrocaecum, which was followed by some subsequent authors.
Nevertheless, Karokhin [23] proposed the division of Porrocaecum into two subgenera based on the presence or absence of interlabia: Porrocaecum [type species P. crassum (Deslongchamps, 1824)] including parasites of birds and Terranova [type species T. decipiens (Krabbe, 1878)] comprising species from elasmobranchs, teleosts, aquatic reptiles and marine mammals. However, since Terranova Karokhin, 1946 has a different type species than Terranova Leiper et Atkinson, 1914, these names are homonyms according to the International Code of Zoological Nomenclature (ICZN) [16].
Johnston and Mawson [18] resurrected Terranova Leiper et Atkinson, 1914 as an independent genus, assigning to it eight other species previously listed in Porrocaecum. Of these, Mozgovoy [32] excluded T. kogiae Johnston et Mawson, 1939, a parasite of pygmy sperm whales, on the basis of the excretory pore allegedly situated at the level of the nerve ring [17], and created a new genus Pseudoterranova Mozgovoy, 1953 to accommodate it. However, Gibson [14] proved in type specimens of T. kogiae that their excretory pore is situated between subventral lips as in other species listed in Terranova (sensu lato). Mozgovoy [32] listed a total of 13 species in Terranova (s. l.), excluding those described from larvae parasitizing fishes.
Gibson [14], on the basis of some morphological differences, placed the species of Terranova (s. l.) parasitizing mammals in a separate genus Pseudoterranova Mozgovoy in Skryabin et al., 1951 [sic], with Phocanema Myers, 1959 [type species P. decipiens (Krabbe, 1878)] as a junior synonym, and this has been followed by subsequent authors (e.g. [26,28,44]). However, Mozgovoy [30] listed "Pseudoterranova nov. gen." in his paper of 1950, but this is a nomen nudum according to the ICZN, because no other information was provided. In 1951, Mozgovoy [31] published a paper dealing with anisakids of mammals in the then USSR (see [39]), but Pseudoterranova is not mentioned in it; on the contrary, he listed Terranova to be a valid genus for T. decipiens. Therefore, the name Pseudoterranova accompanied by information on the type species, was first available in the monograph of Mozgovoy (1953) [32], and consequently, this genus should be correctly cited as Pseudoterranova Mozgovoy, 1953 (see ICZN, Articles 50 and 21).
Gibson and Colin [14] considered Terranova-like species from marine mammals to belong to Pseudoterranova (see above) and those having no distinct lips from elasmobranchs and teleosts to Pulchrascaris Vicente et dos Santos, 1972 (type species P. caballeroi Vicente et dos Santos, 1972). The validity of the latter genus was confirmed by Deardorff [11], who redefined it and carried out a detailed review. Pulchrascaris has been recognized by subsequent authors (e.g. [10,36]). The remaining nominal species of Terranova (s. l.) were split by Gibson and Colin [14] into five groups distinguished by the width of the labial prolongations or by their host types, with a sixth group containing species inquirendae or incertae sedis. Without supporting data, they also synonymized several species, but Deardorff [11] and Bruce and Cannon [10] disagreed with that action and resurrected four species.
According to Bruce and Cannon [10], there are important interspecific morphological features among Terranova spp., such as the presence/absence of lateral alae, plectanes or a gubernaculum, and especially labial characters, which might be used for splitting the genus. In our opinion, the most important differences occur, as in many other nematode groups, at the cephalic end, i.e. the lips and their equipment with teeth. Unfortunately, some significant morphological details, e.g. labial structures, are not readily visible in these fairly large nematodes under the LM and, consequently, these were either inadequately described or undescribed in the great majority of Terranova species. To date, only a few Terranova-like species from poikilothermic hosts have been studied using the SEM [10,11,29,35,36,42].
Since T. antarctica, the type species of Terranova, is known only from a single female, and the majority of taxonomically important morphological features in Terranova spp. are found in the male, Bruce and Cannon [10] designated this species as a nomen dubium or species inquirenda, because it cannot be positively identified. However, a genus is objectively determined by its type species (ICZN, Article 61); if T. antarctica is a species inquirenda, then the respective genus becomes a genus inquirendum. Consequently, until T. antarctica [species inquirenda] is redescribed from a newly collected topotypical material or molecular data can be extracted from the type specimen, Terranova cannot be considered a valid genus.
Although the type specimen of T. antarctica is still available at the Natural History Museum in London, its possible re-examination with the use of LM would be useless. Morphological details of its mouth require to be studied under the SEM, which can hardly be carried out on the sole type specimen without the risk of its destruction and with uncertain results. Since the original description of T. antarctica, no adult specimens of this species have been reported. Larvae designated as Phocanema antarctica were found in fish by Reimer [34], but this identification is doubtful.
Consequently, we propose two new genera, Euterranova n. gen. and Neoterranova n. gen., to accommodate some species previously listed in Terranova (s. l.) from poikilothermic hosts. Since these are based mainly on labial characters, only the species in which these features are clearly described are included; all other species of Terranova (s. l.) are considered to be species inquirendae and their generic appurtenance can only be elucidated by subsequent studies. These are: T. amoyensis, T. antarctica, T. cephaloscyllii, T. circularis The authors are aware that a molecular analysis is needed to confirm the present results, which will be a matter of future studies.
Terranova (s. l.), previously considered a junior synonym of Porrocaecum [4], was resurrected as a valid genus as early as 75 years ago [18], which has been followed by the great majority of subsequent authors (see above). Any similarity of F. Moravec and J.-L. Justine: Parasite 2020, 27, 58 representatives of these two genera is based solely on the presence of an intestinal caecum, but otherwise they are unrelated and belong to different ascaridoid families [1,25]. Nevertheless, until recently, ascaridoid species attributed to Porrocaecum have sometimes been reported as parasites of elasmobranchs and teleost fishes. For example, Sood [40], in his comprehensive monograph devoted to fish nematodes from South Asia, has reported 17 nominal species (all adults) of Porrocaecum, including 14 species parasitic in teleosts and three, P. galeocerdonis Thwaite, 1927, P. bengalensis Lakshmi et al., 1986 and P. tigrini Lakshmi, 1992, from the same host species, the tiger shark Galeocerdo tigrinum (= G. cuvieri); except for P. galeocerdonis (= Euterranova galeocerdonis), all the 16 above-mentioned species from India are poorly described and illustrated, and should be considered species dubiae and incertae sedis. Nevertheless, that is why Porrocaecum is included in the following key to some ascaridoid genera.
Key to the genera of adult Porrocaecum-like ascaridoid nematodes: