Redescription of Pseudobenedenia lauriei Szidat 1965 (Monogenea: Capsalidae) from Notothenia neglecta in Laurie, Peterman, and South Orkney Islands, South Antarctica

Nataliya Y Rubtsova1* and Paula Marcotegui2

Keywords: Pseudobenedenia lauriei; Redescription; Notothenia neglecta; South Antarctica

Introduction

The first species of Pseudobenedeniae – Pseudobenedenia nototheniae Johnston, 1931 was described in 1931 and 1937 [1, 2] from the body surface of Notothenia microlepidota Hutton, 1875 and Paranotothenia magellanica (Forster, 1801). In 1965, Szidat described Pseudobenedenia lauriei Szidat, 1965 from the pectoral fins and body surface of Notothenia neglecta Nybelin, 1951 [3]. No type material was designated by Szidat [3] and information on the number of specimens used for the description was missing [3]. In 1968 Hargis, et al. [4] described Pseudobenedenia shorti Hargis et Dillon, 1968 from nototheniid fish of the genus Trematomus [4] and Yamaguti [5] described Pseudobenedenia elongate Yamaguti, 1968, Pseudobenedenia merinthe Yamaguti, 1968 and Pseudobenedenia ovalis Yamaguti, 1968 from Hawaiian fish [5]. In 1976, Gibson [6] revised the genus Pseudobenedenia and transferred P. shorti to the genus Pseudobenebenoides Szidat, 1969 [6, 7]. He established the new genus Parabenedenia Gibson, 1976 and transferred to it Pseudobenedenia nototheniae, Parabenedenia noblei [8], Pseudobenedenia elongate, Pseudobenedenia merinthe and Pseudobenedenia ovalis. The same year Gibson corrected himself by replacing the name of the genus Parabenedenia with Menziesia Gibson, 1976, and transferring to this genus P. noblei, P. elongate, P. merinthe, and P. ovalis. He also transferred Pseudobenedenia nototheniae back to the genus Pseudobenedenia Johnston [9]. Gibson [6] also synonymized Pseudobenedenia lauriei with Pseudobenedenia nototheniae without studying any collections of this species. Later on, Timofeeva, et al. [10] described Pseudobenedenia gibberifrons Timofeeva, Gaevskaja, Kovaleva, 1987 from Gobinotothen gibberifrons (Lönnberg, 1905) and Pseudobenedenia dissostichii Timofeeva, Gaevskaja, Kovaleva, 1987 from Dissostichus eleginoides Smitt, 1898. More recently, a new species Pseudobenedenia coriicepsi Rubtsova, Chaudhary, Salganskiy, Kuzmina, 2023 was described from Notothenia coriiceps [11].

This work aimed to redescribe P. lauriei using museum collections of P. lauriei from the Argentine Museum of Natural Sciences Bernardino Rivadavia, Buenos Aires, Argentina, collected by Szidat, Bellizio in 1963 and Szidat and Groussac in 1968. We intended to provide additional information on this species, designate lectotype and paralectotypes, and establish that P. lauriei is a valid species.

Materials and Methods

Our study based on five whole-mounted museum specimens, fixed in Canada balsam. Measurements and microphotographs were made in the Ichthyoparasitology Laboratory, Institute of Marine and Coastal Research (IIMyC), Faculty of Exact and Natural Sciences, National University of Mar del Plata, Argentina, with microscope Leica LED2500, x10, x40 magnification). Microphotographs made by Leica DFC 295 camera. Line drawing and analysis of data made in the Institute of Parasitic Diseases (IPD) Scottsdale, AZ, USA.

Results

The Argentine collection at hand included two specimens collected in 1963 by Szidat and Bellizio near Laurie Island. These two specimens possibly were used for the original description of P. lauriei published two years later. Szidat and Groussac collected three other specimens of P. lauriei in 1968 in other locations – Peterson and South Orkney Islands. All this information we revealed by studying hand-written inscriptions on labels of the museum specimens.

In Table 1, we present the results of our measurements of five specimens of P. lauriei from N. neglecta – two collected by Dr. Lothar Szidat together with Dr. N. Bellizio (full name of researcher unknown) near Lauriei Island in 1963 and four collected by Szidat and Groussac (full name unknown) in 1968 at Peterman and South Orkney Islands (Table 1). For comparison, we added existing measurements of the type species of genus Pseudobenedenia (P. nototheniae) and a few other species described from other nototheniid fish from Antarctica. We excluded from this table records that we consider to represent mixed data from a few hosts that were measured together or misidentifications (except for P. nototheniae, that we consider a species complex [11].

*Type species of the genus; we consider it a species complex [11]. Table 1: Comparative morphometric data on Pseudobenedenia species from its different specific hosts.

Discussion

Some specimens from the museum that we studied were in a very poor state, but we tried to measure them as precisely as possible. There was a sixth specimen marked as P. lauriei from N. neglecta in the museum collection that was completely unsuitable for research. If we took into account only two specimens collected in 1963 by Szidat and Bellizio, they still differed from the published material by Szidat in 1965 in the original description. The diameter of pharynx differs (0.5 and 0.46 from 0.3 in the original description as well as accessory sclerite and anterior hamuli are slightly longer than in the description of P. lauriei [3], while other measurements correspond to those published in the description). This indicates that the original description was based on more than these two specimens collected in 1963 or (less likely) that the author did not use these specimens for the description at all. What matters is that they were collected by the author in the same location and the same host and were never designated for this species deposited in the museum until the present.

According to our data, we can see that the original measurements of P. lauriei lay in the range of our measurements of the P. lauriei collected by the author [3]. The original description was missing data on the ovary, testes, bursa, haptor diameter, and egg. The only parameter that was out of the range is the length of the tiny sclerotized structure - the posterior hamulus that was 0.1 in Szidat`s description [3] and 0.22 in ours. Therefore, by the metric parameters and by host specificity our data and Szidat’s description form the harmonic unity. Despite the somewhat poor quality of these 60-year-old specimens, we tried to create a more detailed drawing of the whole view of P. lauriei together with more detailed images of sclerotized structures of haptor (Fig. 2, b-d). In the studied whole mounts, sclerotized structures never appeared perfectly in profile, as needed for taxonomical studies, and extremely difficult to achieve while working with such big monogeneans as Capsalidae are [11].

Our results suggest that synonymizing P. lauriei with P. nototheniae, [6] was in error. Intuitively Gibson [6] may have detected that something with his synonymy was not right. He wrote about the surprisingly low degree of host-specificity of P. nototheniae, which markedly contrasts with the related Entobdella solae Kearn, 1967, which has strict host specificity. He also had the right notion that there is something wrong with such a wide range of hosts, emphasizing that P. nototheniae being a skin parasite should be susceptible to any immune factors present in the mucus of its host [6].

The host of P. lauriei, Notothenia neglecta Nybelin, 1951 is a valid fish species, the closest sister species to Notothenia coriiceps Richardson, 1844 [12, 13]. Notothenia neglecta is spread along the coast of the Antarctic continent, Antarctic Peninsula, South Georgia, South Shetland, South Orkney Islands, and Peter I Island, according to Fish Base [14].

While studying Capsalids from twenty-three species of notothenoid fish, including fourteen representatives of family Nototheniidae, over few years in Atlantic part of Antarctica, Timofeeva, et al. [10] have formulated few patterns that are common for these monogeneans. All Pseudobenedeniae specimens collected from one species of host were different from ones from other fish species by body size, size of haptor, sizes of its sclerotized attachment structures of haptor and by their shape, sizes and relative position of sexual organs [10]. The localization on the body of the individual hosts was often different, and there was a difference in parameters of infection [10]. That corresponds with our published data [11] and our data that are in press. Thus, different nototheniid fish harbor close but different species of Pseudobenedenia, as well as two other genera of Pseudobenedeniella Timofeeva, Gaevskaja, Kovaleva, 1987 and Pseudobenedenoides Szidat, 1969 [1, 7, 10]

Acknowledgments

Our gratitude goes to Alejandro Tablado, Argentine Museum of Natural Sciences Bernardino Rivadavia, Buenos Aires, Argentina, for his help with museum collections.