Introduction
Currently, the genus Sphyraena (barracudas) comprises 29 species worldwide (Froese and Pauly Reference Froese and Pauly2025), with a global distribution traversing temperate and tropical regions. In Mediterranean waters, the genus Sphyraena encompasses four species: the lessepsian S. chrysotaenia (Klunzinger, 1884) and S. flavicauda Rüppell, 1838, and the Atlantic–Mediterranean species S. sphyraena (Linnaeus, 1758) and S. viridensis (Cuvier & Valenciennes, 1829) (Pastore Reference Pastore2009). The European barracuda, S. sphyraena, is a widespread species, occurring in the eastern Atlantic (Bay of Biscay to Angola), including the Mediterranean and Black Sea, Canary Islands, and Azores (Ferri and Brzica Reference Ferri and Brzica2022). In the western Mediterranean, different parasitic taxa had been reported on this fish: Nematoda, Cestoda, Isopoda, Copepoda (Boussellaa et al. Reference Boussellaa, Neifar, Goedknegt and Thieltges2018), Digenea (Boussellaa et al. Reference Boussellaa, Neifar, Goedknegt and Thieltges2018; Looss Reference Looss1899), and Monogenea (Bouguerche Reference Bouguerche2019; Boussellaa et al. Reference Boussellaa, Neifar, Goedknegt and Thieltges2018; Euzet and Trilles Reference Euzet and J-P1960; Ktari Reference Ktari1971; Neifar, Reference Neifar1995; Radujkovic and Euzet Reference Radujkovic and Euzet1989).
To date, two polyopisthocotylan Monogenea have been reported from S. sphyraena in the western Mediterranean: the chauhaneid ‘Chauhanea mediterranea’ Euzet & Trilles, Reference Euzet and J-P1960 (Chauhaneidae) (Bouguerche Reference Bouguerche2019; Euzet and Trilles Reference Euzet and J-P1960; Ulmer and James Reference Ulmer and James1981) (currently accepted as Cotyloatlantica mediterranea (Euzet & Trilles, Reference Euzet and J-P1960) (Bravo-Hollis, Reference Bravo-Hollis1984); and the rhinecotylid Rhinecotyle crepitacula Euzet & Trilles, Reference Euzet and J-P1960 (Bouguerche Reference Bouguerche2019; Euzet and Trilles Reference Euzet and J-P1960). These two species had been scarily mentioned or investigated since their original description. Chauhanea mediterranea remains an intriguing species due to its reclassification across multiple genera (Bravo-Hollis Reference Bravo-Hollis1984; Euzet and Trilles Reference Euzet and J-P1960; Lebedev Reference Lebedev1969), underscoring the challenges and complexities associated with defining its taxonomic boundaries. Initially described from S. sphyraena in the Mediterranean and assigned to Chauhanea (Euzet and Trilles Reference Euzet and J-P1960), it was later reclassified into Pseudochauhanea (Yamaguti, Reference Yamaguti1965) based on the position of the vagina (Lebedev Reference Lebedev1969). However, Ulmer and James (Reference Ulmer and James1981) corrected previous misinterpretations of the female openings, showing that the median transverse opening, referred to as the vagina (Euzet and Trilles Reference Euzet and J-P1960), contained eggs within the associated duct, positioned in a way that suggests their emergence through this opening, indicating that it functions as a uterine opening. This reinterpretation of the position of the vagina blurred the distinctions between these genera. The creation of Cotyloatlantica (Bravo-Hollis Reference Bravo-Hollis1984) further complicated the taxonomy, highlighting the difficulties in using morphological traits to clearly define genus boundaries (Bravo-Hollis Reference Bravo-Hollis1984). The second conspecific species occurring on S. sphyraena, R. crepitacula described off Sète, France, Western Mediterranean (Euzet and Trilles Reference Euzet and J-P1960) is only known from a redescription from specimens from a distinct host, S. piscatorum Cadenat, 1964 and from a distinct locality, Ivory Coast, Eastern Central Atlantic Ocean (Euzet and Wahl Reference Euzet and Wahl1970).
During a parasitological study of polyopisthocotylans from S. sphyraena in the western Mediterranean, representatives of Ch. mediterranea and R. crepitacula were collected. Both species are redescribed and illustrated based on newly collected specimens, with novel morphometrical and anatomical data provided. An examination of the internal anatomy and of the organization of clamp sclerites led to a revision of the systematic status of the genera Chauhanea Ramalingam, Reference Ramalingam1953; Pseudochauhanea Yamaguti, Reference Yamaguti1965 and Cotyloatlantica Bravo-Hollis, Reference Bravo-Hollis1984.
Materials and methods
A total of 35 specimens of S. sphyraena were examined for gill parasites. Fish were collected by local fishermen from off the coast of Tamentfoust, Algeria (Division 37.1.1, Western Mediterranean Sea). Fish were stored on ice and transferred to the laboratory shortly after capture. Fish were identified using keys (Fischer et al. Reference Fischer, M-L and Schneider1987). Fish were dissected fresh on the day of purchase, and the gills were investigated for parasites. Gill arches were removed, separated by incision, placed in petri dishes filled with sea water, and thoroughly examined for the presence of parasites under a dissecting stereomicroscope. Specimens of Polyopisthocotyla were fixed in near-boiling saline and preserved immediately in 70% ethanol. Polyopisthocotylans were stained with acetic carmine, dehydrated using a graded ethanol series (70, 96, and 100% for 15 min each), cleared in clove oil, and mounted in Canada balsam (Bouguerche Reference Bouguerche2019). Polyopisthocotylans were identified on stained whole mounts. Drawings were made through a Nikon Eclipse i80 microscope (Nikon Eclipse Ni, Nikon, Tokyo, Japan) with DIC (differential interference contrast) and a drawing tube. Drawings were scanned and redrawn on a computer with Adobe Illustrator (Adobe Inc., San Jose, CA, USA). Measurements of whole mounts are in micrometers and indicated as the range followed by the mean. For high-level terminology of parasites, the systematics of Brabec et al. (Reference Brabec, Salomaki, Kolísko, Scholz and Kuchta2023) who elevated the former subclasses of ‘Monogenea’ to the level of classes is followed herein.
Results
Class Polyopisthocotyla Brabec, Salomaki, Kolísko, Scholz, Kuchta and 2023
Family Chauhaneidae Euzet & Trilles, Reference Euzet and J-P1960
Genus Chauhanea Ramalingam, Reference Ramalingam1953
Chauhanea mediterranea Euzet & Trilles, Reference Euzet and J-P1960 (Figures 1–4)
Synonyms: Cotyloatlantica mediterranea (Euzet & Trilles, Reference Euzet and J-P1960) (Bravo-Hollis, Reference Bravo-Hollis1984). Pseudochauhanea mediterranea (Euzet & Trilles, Reference Euzet and J-P1960) (Lebedev, Reference Lebedev1969).
Type-host: Sphyraena sphyraena (Linnaeus, 1758), the European barracuda (Sphyraenidae) (Euzet & Trilles, Reference Euzet and J-P1960).
Type locality: Sète, France, Western Mediterranean (Euzet and Trilles Reference Euzet and J-P1960).
Other localities: Central Mediterranean: Montenegro (Radujkovic and Euzet Reference Radujkovic and Euzet1989). Western Mediterranean: France (Euzet and Trilles Reference Euzet and J-P1960); Tunisia (Boussellaa et al. Reference Boussellaa, Neifar, Goedknegt and Thieltges2018; Ktari Reference Ktari1971; Neifar Reference Neifar1995). Tamenfoust, Algeria, present study.
Redescription
Based on 20 mature whole mounts. Morphometric data is presented in Table 1. Body elongated, with a visible constriction at a short distance from anterior end (Figure 1a). Haptor leaf-shaped, triangular, slightly asymmetrical, bearing 28 to 32 pedunculated clamps (Figure 1b): 17 to 19 on the right side and 11 to 15 on the left. Clamps Gastrocotyle type (Figure 1c).
Table 1. Comparative morphometric data for Cotyloatlantica mediterranea (Euzet & Trilles, Reference Euzet and J-P1960)
Abbreviations: CM, Central Mediterranean. WM, Western Mediterranean
Figure 1. Chauhanea mediterranea Euzet & Trilles, Reference Euzet and J-P1960 ex Sphyraena sphyraena. (a), whole body; (b), whole body showing the possible slender appearance; (c), clamp, ventral view; (d), anterior end showing septate oral suckers; (e), anterior part showing intestinal bifurcation; (f), cirrus and vagina; (g), egg.
Clamps formed by two jaws, anterior (Figure 2a) and posterior jaw (Figure 3b), supported by sub-peripheral marginal sclerites S.m. Proximally, marginal sclerites S.m. fold back and continued by basal oblique piece P.o. and an intermediate piece P.i. Anterior jaw with several ventral sclerosed costiform structures E.c. Costiform structures E.c. less numerous in posterior jaw (Figure 1c). Jaws connected by a central U-shaped piece, sagittal sclerite S.s. Ventral arm of sagittal sclerite S.s. longer. Proximally, sclerite S.s. widening and passing into posterior jaw. Dorsal arm of sagittal sclerite S.s. short and wide. Posterior jaw with two accessory sclerites S.a.; and articulating two superimposed pieces, a cordiform piece P.c. and an arched piece P.a. articulated on the base of dorsal arm of sagittal sclerite S.s.
Figure 2. Chauhanea mediterranea Euzet & Trilles, Reference Euzet and J-P1960 ex Sphyraena sphyraena, disposition of clamp sclerites. (a), ventral jaw; (b), dorsal jaw.
Figure 3. Chauhanea mediterranea Euzet & Trilles, Reference Euzet and J-P1960 ex Sphyraena sphyraena. (a), detail of the reproductive organs in the region of ovary, ventral view; (b), anterior end showing genital openings.
Mouth ventral, opening anteriorly. Oral suckers paired, opening on either side of oral cavity, elongated (Figure 1d). Pharynx muscular, median, followed by esophagus, which bifurcates into two caeca (Figure 1e). Caeca extending on either side of body to posterior part of haptor; with numerous transverse diverticula and not confluent posteriorly.
Testes numerous, 47–52 (48) in number, arranged in 3 groups: first group anterior to ovary, made up of testes arranged on either side of midline; second made up of para-ovarian testes, located on right side of midline and descending parallel to ovary; 3rd group represented by a batch of post-ovarian testes extending to anterior third of haptor. Vas deferens sinuous, continuing anteriorly to emerge, on left side of body, into a fusiform unarmed muscular cirrus (Figure 1f); cirrus asymmetrical, muscular, enclosed in a cirrus pouch.
Germarium voluminous, located on left side of the body, originating in a posterior mass, then ascending to form an anterior loop (Figure 3a). It descends and narrows into an oviduct in median region. Oviduct receiving genito-intestinal canal, which passes beneath the germarium and terminates in the left branch of the digestive tract. Oviduct then receiving vitelline reservoir. Uterus almost rectilinear, extending anteriorly, opening ventrally at anterior constriction of body through an oval pore (Figure 3b). Vitelline follicles highly developed, extending from genital pore and penetrating the haptor. Vitelline ducts Y-shaped, paired vitelline ducts long, joining in midline. Vagina opening into genital atrium lateral to cirrus. Eggs fusiform, with 2 filaments: anterior one and a shorter posterior one (Figure 1g).
Remarks
The organization of the clamps sclerites was investigated herein. Cotyloatlantica mediterranea shares with Co. pretiosa Bravo-Hollis, Reference Bravo-Hollis1984 the subdivision of the basal oblique sclerite (P.o.), which is a continuation of the marginal sclerite (S.m.) in the anterior jaw of the clamps. Proximally, the marginal sclerites (S.m.) fold back and continue as a basal oblique piece (P.o.) and an intermediate piece (P.i.) (Figure 4). As this feature was previously used to distinguish Cotyloatlantica from Chauhanea and Pseudochauhanea, and since this sclerite organization was confirmed in Ch. mediterranea, Cotyloatlantica is synonymized with Chauhanea. Given that Chauhanea has priority over Cotyloatlantica (1953 vs. 1984), species of Cotyloatlantica are transferred to Chauhanea (see Discussion for the resulting new combinations). Therefore, Ch. mediterranea is used from this point onwards.
Figure 4. Micrographs of clamps of Chauhanea mediterranea Euzet & Trilles, Reference Euzet and J-P1960 ex Sphyraena sphyraena, showing the clear subdivision of the basal oblique piece P.o. (arrows).
Inaccuracies in previous interpretations of the female openings of Ch. mediterranea are also highlighted herein. The anterior median transverse opening at the level of the body constriction, previously referred to as the vagina, is associated with a thin-walled duct containing eggs, indicating that it corresponds to the uterine aperture. A lateral position of both the cirrus and the vaginal opening is confirmed. Since the primary character used to distinguish Chauhanea from Pseudochauhanea – the midventral opening previously misidentified as the vagina – was actually a misinterpretation of the uterine opening, the distinction between these two genera is no longer valid. Consequently, synonymization of Chauhanea and Pseudochauhanea is proposed. Given that Chauhanea has priority over Pseudochauhanea (1953 vs. 1965), species of Pseudochauhanea are transferred to Chauhanea (see Discussion for the resulting new combinations).
The differences between the previous description and our observations justify the need to amend the diagnosis of the genus: uterine opening median, vaginal opening lateral, and clamps with subdivision of the basal oblique sclerite as a continuation of the marginal sclerite of the anterior jaw.
Chauhanea Ramalingam, Reference Ramalingam1953
Amended generic diagnosis
Chauhaneidae. Body lanceolate, without stalk for haptor. Haptor asymmetrical, not delineated from body proper, with numerous clamps of Gastrocotyle type; terminal lappet and terminal anchors absent. Oral suckers paired, muscular, septate or aseptate. Ceca with numerous diverticula, occasionally extending into haptor, and terminating separately at or near posterior end of haptor. Testes numerous, pre-, para-, and post-ovarian. Cirrus pouch present; cirrus unarmed, may or may not protrude into genital atrium; genital pore submarginal. Germarium complex, in mid-region of body. Vagina unarmed, opening laterally. Uterine opening post-bifurcal opening, mid-ventrally. Eggs elongate, filamented at both ends. Vitellaria co-extensive with caeca except for their posterior-most portion. Gill parasites of marine teleosts.
Type species: Chauhanea madrasensis Ramalingam, Reference Ramalingam1953, on Sphyraena acutipinnis off Chennai, India, Eastern Indian Ocean (Ramalingam Reference Ramalingam1953).
Family Rhinecotylidae Lebedev, 1979
Genus Rhinecotyle Euzet & Trilles, Reference Euzet and J-P1960
Rhinecotyle crepitacula Euzet & Trilles, Reference Euzet and J-P1960 (Figures 5–6)
Type-host: Sphyraena sphyraena (Linnaeus, 1758), the European barracuda (Sphyraenidae) (Euzet and Trilles Reference Euzet and J-P1960).
Figure 5. Rhinecotyle crepitacula Euzet et Trilles, 1960 ex Sphyraena sphyraena. (a), whole body; (b), anterior small clamp; (c), posterior large clamp; (d, e), disposition of sclerites in ventral (d) and dorsal (d) jaw in anterior small clamps; (f, g), disposition of sclerites in ventral (f) and dorsal (g) jaw in posterior large clamps; (h), genital atrium; (i), egg.
Figure 6. Rhinecotyle crepitacula Euzet et Trilles, 1960 ex Sphyraena sphyraena. (a), anterior end showing genital atrium; (b), detail of the reproductive organs in the region of the ovary.
Type locality: Sète, France, Western Mediterranean (Euzet and Trilles Reference Euzet and J-P1960).
Other hosts: Sphyraena piscatorum Cadenat, 1964, the Guinean barracuda (Sphyraenidae) (Euzet and Wahl Reference Euzet and Wahl1970).
Other localities: Lagune Ebrié, Ivory Coast, Eastern Central Atlantic Ocean (Euzet and Wahl Reference Euzet and Wahl1970). Tamenfoust, Algeria, Western Mediterranean, present study.
Redescription
Based on 14 mature whole mounts. Morphometric data is presented in Table 2. Body elongated, terminating posteriorly by a broad haptor (Figure 5a). Body flattened dorso-ventrally. Haptor separated from body proper by a slight constriction, oblong, with a characteristic shape of a ‘spoon’ as defined by Euzet and Trilles (Reference Euzet and J-P1960); its ventral concavity divided by a longitudinal septum and a series of transverse muscular septa, giving the appearance of two parallel rows of loculi. Haptor marked by two rows of loculi, bearing numerous clamps arranged in two series: anterior (Figure 5b) and posterior clamps (Figure 5c) highly dissimilar.
Table 2. Comparative morphometric data for Rhinecotyle crepitacula Euzet & Trilles, Reference Euzet and J-P1960
Abbreviations: ECA, Eastern Central Atlantic. WM, Western Mediterranean
Clamps of anterior series relatively small, consisting of two jaws: anterior jaw and posterior jaw. Anterior jaw (Figure 5d) with a median piece a1. On proximal side, a1 terminating in T-shape. Distally, median piece a1 curving into a2, which passes into posterior jaw. Anterior jaw supported by two blade-like lateral sclerites b1. Proximally, sclerites b1 curving and forming a short extension into posterior jaw. In posterior jaw (Figure 5e), sclerite a2 continuing into a lateral expansion a3 which ends in two lobed expansions forming a shallow V. Below a3, a relatively long posterior median piece f is articulated. Posterior jaw supported by two lateral sclerites c.
Clamps of posterior series larger. Anterior jaw (Figure 5f) with a long median sclerite a. On distal side, median sclerite a ending in a pronounced T-shape. Anterior jaw supported by two lateral sclerites b, forming a semicircle in anterior and posterior halves of clamps. The two semicircles separated by a shallow curvature. A slight asymmetry is due to the degree of curvature and length of these sclerites. On proximal side, sclerites b curving into posterior jaw. Posterior jaw (Figure 5g) narrower than anterior jaw. On proximal side and the midline, a long sclerite f articulating on median sclerite a. Posterior jaw supported by two lateral sclerites c. In anterior half of clamp, sclerites c more or less parallel to median sclerite a; in posterior half of clamp, lateral sclerites c forming a semicircle.
Mouth ventral, sub-terminal mouth. Oral suckers paired, muscular, opening laterally, transversely elongated; ventrally, each sucker subdivided by three septa into four subequal chambers; edges of oral suckers lined with tiny papillae (Figure 6a). Pharynx muscular, globular, opening mid-ventrally. Oesophagus short. Intestinal bifurcation pre-atrial. Caeca with numerous lateral and axial diverticula; extending on either side of body reaching the haptor; caeca not confluence posteriorly.
Testes distributed in intercaecal space of posterior quarter of body, irregular in shape, superposed and often obscured by vitelline follicles. Vas deferens paired, wide and sinuous, extending up the midline to anterior end, opening at base of genital atrium. Genital atrium spherical, with muscular walls, opening dorsally. Genital atrium armed with small hooks (Figure 5h), arranged in three groups: an anterior semicircle of 9 to 11 small tight spines; a second group of 9 to 10 large spines. Male opening in the atrial lumen by a seedling of few slightly curved pointed spines.
Germarium dorsal, complex, folded on itself, located in intercaecal space of posterior third of body (Figure 6b). Oviduct crossing part of germarium and receiving vitelline reservoir on midline. Genito-intestinal canal projecting right caecum. Uterus dorsal, rising medio-longitudinally and opening in genital atrium. Vitelline follicles well-developed delimiting caeca laterally and terminating at posterior end of the body. Vitelline ducts Y-shaped, paired vitelline ducts long. Vagina absent. Eggs Spindle-shaped with two unequal polar filaments (Figure 5i).
Discussion
Chauhanea mediterranea Euzet & Trilles, Reference Euzet and J-P1960
The newly collected specimens of Chauhanea correspond morphometrically to the data on Ch. mediterranea reported in the literature off Sète, France (Euzet and Trilles Reference Euzet and J-P1960), and off Naples, Italy (Ulmer and James Reference Ulmer and James1981). Comparative measurements revealed no significant differences between our material and that described by the previously mentioned authors, suggesting the presence of a single species in the western Mediterranean.
Chauhanea mediterranea was first described from the gills of S. sphyraena from the French coast, western Mediterranean by Euzet and Trilles (Reference Euzet and J-P1960), who assigned it to the genus Chauhanea. The latter was created by Ramalingam (Reference Ramalingam1953) to accommodate Ch. madrasensis Ramalingam, Reference Ramalingam1953 from the Sharpfin barracuda S. acutipinnis off Chennai (referred to as ‘Madras’), India, Eastern Indian Ocean. It was subsequently placed in the genus Pseudochauhanea (Lebedev Reference Lebedev1969), created to accommodate P. sphyraenae Yamaguti, Reference Yamaguti1965 from the great barracuda S. barracuda off Hawaii, Eastern Central Pacific (Yamaguti Reference Yamaguti1965); then in the genus Cotyloatlantica, created to accommodate C. pretiosa from S. barracuda and the Guachanche barracuda S. guachancho, off Mexico, Western Central Atlantic (Bravo-Hollis Reference Bravo-Hollis1984).
Pseudochauhanea was distinguished from Chauhanea based on the position of the vagina, considered median and transverse at the level of the body constriction in Pseudochauhanea vs. lateral in Chauhanea (Yamaguti Reference Yamaguti1965). However, Ulmer and James (Reference Ulmer and James1981) highlighted inaccuracies in previous interpretations of the female openings of Ch. mediterranea, as the individual median transverse opening at the level of the body constriction was referred to as the vagina (Euzet and Trilles Reference Euzet and J-P1960), while eggs were seen within the duct associated with this median opening and were in such a position to indicate their emergence through (Ulmer and James Reference Ulmer and James1981). This observation is herein deep-rooted, as the thin-walled duct leading to the aforementioned median aperture indeed contained eggs, and thus, it is confirmed that the uterus opens medioventrally. Hence, the median aperture considered by Yamaguti (Reference Yamaguti1965) to be a vaginal opening is, in fact, a uterine opening. Additionally, the lateral position of the cirrus and the opening of the vagina of the examined specimens herein agree with those described by Ulmer and James (Reference Ulmer and James1981) for Ch. mediterranea and especially with those by Ramalingam (Reference Ramalingam1953) for Ch. madrasensis. The midventral opening referred to as the vagina by Yamaguti (Reference Yamaguti1965) in Pseudochauhanea is, in fact, the uterus. Since the primary character used to distinguish Chauhanea from Pseudochauhanea was based on a misinterpretation of the uterine opening, the distinction between these two genera is no longer valid. Consequently, Chauhanea and Pseudochauhanea are considered synonyms. Given that Chauhanea has priority over Pseudochauhanea (1953 vs. 1965), Pseudochauhanea species are transferred to Chauhanea, with the following new combinations: Ch. elegans Fuentes-Zambrano, 1997 n. comb.; Ch. elongata Kritsky, Bilqees & Leiby, 1972 n. comb.; Ch. macrorchis Lin, Liu & Zhang in Zhang, Yang & Liu, 2001 n. comb.; Ch. mexicana Lamothe, 1967 n. comb.; Ch. sphyraenae Yamaguti, Reference Yamaguti1965 n. comb.
In this study, the organization of the clamps of Ch. Mediterranea was investigated for the first time, and the latter species shares with Co. pretiosa Bravo-Hollis, Reference Bravo-Hollis1984 the subdivision of the basal oblique sclerite P.o., which is the continuation of the marginal sclerite S.m. of the anterior jaw of the clamps, along a cordiform piece P.c. and an arched piece P.a., articulated on the distal end of the sagittal sclerite S.s. of the posterior jaw of the clamps. The previously mentioned criteria were used to distinguish the genus Cotyloatlantica from Pseudochauhanea and from Chauhanea sensu Euzet and Trilles (Reference Euzet and J-P1960). This sclerites organization has been confirmed herein in Ch. mediterranea, leading to the synonymization of Cotyloatlantica and Chauhanea. Similarly, since Chauhanea has priority over Cotyloatlantica (1953 vs. 1984), Cotyloatlantica species are transferred to Chauhanea, with the following new combinations: Ch. mediterranea Euzet & Trilles, Reference Euzet and J-P1960 n. comb. and Ch. pretiosa (Bravo-Hollis, Reference Bravo-Hollis1984) n. comb.
Rhinecotyle crepitacula Euzet & Trilles, Reference Euzet and J-P1960
Herein, a simultaneous occurrence of Ch. mediterranea, found coexisting on the gills of its host S. sphyarena alongside another polyopisthocotylan species R. crepitacula, is reported. The attribution of the newly collected specimen to the genus Rhinecotyle Euzet & Trilles, Reference Euzet and J-P1960 was straightforward due to distinctive morphological features of the haptor examined herein. The possession of an oblong haptor with a ventral concavity divided by a longitudinal septum and an additional series of transverse muscular septa, creating the appearance of two parallel rows of loculi, are unique features for the genus Rhinecotyle (Euzet and Trilles Reference Euzet and J-P1960; Euzet and Wahl 1960).
This dual parasitic occurrence is not unusual within Polyopisthocotyla. In previous studies in the western Mediterranean, up to four species were encountered on the sparid host, the bogue Boops boops (Linnaeus, 1758): the microcotylid Microcotyle isyebi Bouguerche, Gey, Justine & Tazerouti, 2019; the gastrocotylid Pseudaxine trachuri Parona & Perugia, 1890; and the diclidophorids Cyclocotyla bellones Otto, 1823 occurring simultaneously on their sparid host B. boops (Bouguerche et al. Reference Bouguerche, Gey, J-L and Tazerouti2019b, Reference Bouguerche, Tazerouti, Gey and Justine2019c; Bouguerche et al. Reference Bouguerche, Tazerouti, Gey and Justine2020; Bouguerche et al. Reference Bouguerche, Tazerouti, Gey and Justine2021a; Bouguerche et al. Reference Bouguerche, Tazerouti and Justine2022), along with an undescribed species of Choricotyle (Diclidophoridae). Similarly, the Atlantic horse mackerel Trachurus trachurus (Linnaeus, 1758) hosts three gastrocotylids, P. trachuri, Gastrocotyle trachuri van Beneden & Hesse, 1863; Allogastrocotyle bivaginalis Nasir & Fuentes Zambrano, 1984; and the heteraxinids Cemocotyle trachuri Dillon & Hargis, 1965 (Bouguerche et al. Reference Bouguerche2019; Bouguerche et al. Reference Bouguerche, Tazerouti and Justine2021b). Hence, despite their small size sometimes, fish hosts still accomplish their role as a shared ecological niche.
The genus Rhinecotyle was created by Euzet and Trilles (Reference Euzet and J-P1960) with the type species R. crepitacula collected from the gills of S. sphyraena off Sète, France, Western Mediterranean. At present, this genus is bispecific and exclusively related to the Sphyraenidae with R. crepitacula (see below for hosts) and R. deloyai Bravo-Hollis, Reference Bravo-Hollis1980 from S. barracuda (Edwards, 1771) (Bravo-Hollis Reference Bravo-Hollis1980). Rhinecotyle crepitacula was redescribed based on specimens from a distinct host, S. piscatorum Cadenat, 1964 in the Ivory Coast, Eastern Central Atlantic Ocean. The Mediterranean specimens (off Algeria) examined herein differed from the Atlantic specimens (off Ivory Coast) by the front-series clamps number (16–32 vs. 18–22), the posterior series clamps number (14–26 vs. 12–20), by having smaller front-series clamps (34–48 × 55–65 vs. 30–45 × 50–60), and smaller posterior series clamps (115–145× 55–90 vs. 110–130 × 50–80). Most importantly, the Mediterranean specimens of R. crepitacula examined herein differed from the Atlantic populations from a different host by having fewer spines in the genital atrium. Hence, although R. crepitacula was previously considered to be a transatlantic species (Euzet and Wahl Reference Euzet and Wahl1970), the conspecificity of the Mediterranean and Atlantic populations should be investigated further. Herein, as our Rhinecotyle specimens were collected from the type-host S. sphyraena and given the proximity of the geographic location (Algeria, Western Mediterranean, 775 km from the type locality Sète, France), a conservative position was taken in ascribing the specimens to R. crepitacula. Algeria and North Africa represent new locality records for this parasite. Future studies will likely reveal that the Atlantic R. crepitacula population, described on a distinct host (S. piscatorum) and from a different locality (Ivory Coast, Eastern Central Atlantic Ocean) (Euzet and Wahl Reference Euzet and Wahl1970), corresponds to a different species.
Authors’ contribution
CB conducted experiments, collected and analysed data, prepared figures, wrote and edited the manuscript.
Availability of data and materials
All data and materials are freely available.
Acknowledgements
The author is grateful to all the participants of ‘The Ocean Fellowship’ (edition 2021), especially Graziano Meneghin and Markus Reymann. Thanks are extended to the local fishermen from Tamentfoust, Algeria, for kindly helping with fish acquisition.
Financial support
Chahinez Bouguerche was supported individually by framework agreement projects: 1. ‘the DeepBlue Project: Distance Crossborder Traineeship Programme’/ DEEP BLUE: Developing Education and Employment Partnerships for a Sustainable Blue Growth in the Western Mediterranean Region, hosted by Muséum national d’Histoire naturelle (MNHN), issued by OGS – National Institute of Oceanography and Applied Geophysics, Italy; co-financed by The European Maritime and Fisheries Fund (EMFF) (MNHN-SJ N°176/20), for the analysis, interpretation of data, and writing of the manuscript in framework of the project ‘Exploring the fascinating biodiversity of marine polyopisthocotyleans from marine fishes of the southern Mediterranean Sea’. 2. ‘The Ocean Fellowship’ (edition 2021), offered by the TBA21 Academy, held at Ocean Space in Venice, Italy, in the context of the exhibition The Soul Expanding Ocean#1: Taloi Havini and the transdisciplinary program The Current III (The Mediterraneans: ‘Thus waves come in pairs’, after Etel Adnan). 3. the Swedish Taxonomy Initiative, Artdatabanken, Swedish University of Agricultural Sciences, within the scope of the project ‘Systematics and integrative taxonomy of Monogenea parasitizing fishes of Sweden’ (SLU.dha 2023.4.3-248) during the writing of the manuscript.
Competing interests
The author declare that they have no conflict of interest.
Ethical standard
All applicable institutional, national, and international guidelines for the care and use of animals were followed.
Open access
