Eleutheromenia sierra
Creators: name: Cobo, M. Carmen
name: Farris, William J.
name: Kocot, Kevin M.
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Solenogastres
Cavibelonia
Pruvotinidae
Eleutheromenia
Eleutheromenia sierra

description: Eleutheromenia sierra (Pruvot, 1890)
Paramenia sierra Pruvot, 1890: XIII.
Eleutheromenia sierra – Salvini-Plawen 1967: 398.
Eleutheromenia carinata Salvini-Plawen & Öztürk, 2006: 220, n. syn.
Gephyroherpia impar Zamarro, García-Álvarez & Urgorri, 2013: 435, n. syn.
MATERIAL EXAMINED. — Corsica (France) • 1 specimen (used for sclerite preparations, histology, and DNA extraction); CORSICABENTHOS 2 (Table 2); 40 m depth; MNHN-IM-2019-1749; GenBank: OR456216; OR458913 (1 microscope slide with sclerites, 1 SEM stub; 15 slides with 5 µm serial sections).
DESCRIPTION
White animal, elongate body (12 × 1.5-2.5 mm) with a median discontinuous serrated keel, with at least 17 lobes (Fig. 4B; 9A). Hollow sclerites somewhat protruding from the cuticle. With one type of hook-shaped sclerite (80-120 × 8 µm; the inner part of the hook is 30 µm long) (Fig. 9B, C, D) and acicular sclerites of different sizes: big and slightly curved sclerites (160-180 × 8 µm) (Fig. 9B); curved and thin sclerites (80-100 × 3-4 µm); straight and long acicular sclerites (190-210 × 6-7 µm), the latter mostly located in the ventral region of the body (Fig. 9E). Hook-shaped sclerites in the ventral region of the body. Hook-shaped sclerites occupying the sides of the dorsal lobes, with some thin acicular sclerites among them. Bigger curved acicular sclerites at the apical regions of the lobes (Fig. 9A). With knife-shaped scales of the pedal groove (80 × 25 µm). Atrium with single and paired atrial papillae (Fig. 13A), divided into three parts in its posterior region. Mouth and atrium separated by a muscular wall without cuticle (Fig. 13B). With a single pedal fold. Ventrolateral foregut glands of type A / Pararrhopalia type (Fig. 13D). With a distichous radula formed by hook-shaped teeth without medial denticles (Fig. 13D, D’). Very glandular esophagus. Midgut with an antero-dorsal caecum (Fig. 13D) and lateral constrictions. With respiratory folds (Fig. 13G). With seminal vesicles (Fig. 13E, E’). With abdominal spicules in a pair of ventral pouches of the mantle cavity (Fig. 13F).
REMARKS
The specimen was placed in the subfamily Eleutheromeniinae Salvini-Plawen, 1978 based on its resemblance to three known species of the subfamily that also have a discontinuous serrated keel: both species of Eleutheromenia (E. sierra (Pruvot, 1890) and E. carinata Salvini-Plawen & Öztürk, 2006) and Gephyroherpia impar Zamarro, García-Álvarez & Urgorri, 2013. The classification within this subfamily is also justified by the presence of hook-shaped sclerites, ventrolateral foregut glands of type A and the absence of a dorso-pharyngeal papilla gland (García-Álvarez & Salvini-Plawen 2007) (Table 4).
The specimen from Corsica has a keel with clearly differentiated lobes, at least 17, mostly in the anterior region of the body, that were more easily distinguishable when the animal was alive. The serial sections reveal a separation between the lobes as described by Salvini-Plawen (2003) for E. sierra. The keel of E. sierra has been reported to consist of between 15 and 16 lobes (Pruvot 1890; Salvini-Plawen 2003: fig. 11). In E. carinata the keel is continuous but the lobes “vary somewhat in height” (Salvini-Plawen & Öztürk 2006: fig. 2). The keel in G. impar was described as “continuous that varies somewhat in its height along its course and shows, in the medial body region, 10 lobulations,” although in the image of the holotype at least 15 lobes can be distinguished (Zamarro et al. 2013: fig. 8). We observed that the lobes in the Corsica specimen are less evident after fixation and thus the external aspect can be compared with all three species mentioned here. The observed differences in the keel among the three species may be due to the preservation of the specimens.
In the specimen from Corsica, we did not observe serrated sclerites, described for the Eleutheromenia species but not in G. impar (Zamarro et al. 2013: fig. 8). We did find harpoon-shaped sclerites (Fig. 9F), described for E. carinata (Salvini-Plawen 2003; fig. 8b) but not E. sierra (Salvini-Plawen & Öztürk 2006: fig. 3) or G. impar (Zamarro et al. 2013: fig. 8). The lack of observation of a specific type of sclerites, such as the serrated acicular sclerites, may be because SEM images or sclerite preparations were obtained from a region of the body where that type does not occur. Our SEM images were taken only from a small piece of the mid-body region, for example. In addition to the study of the mid body region sclerites under SEM, we prepared sclerites from other body regions by dislodging them with a thin needle in an attempt to observe any body region-specific sclerite types, but it is of course possible that particularly rare or fragile sclerite types were missed. Therefore, a thorough study of additional specimens would be desirable. Given the impossibility of differentiating these three Eleutheromeniidae species based on the sclerites and keel, it is necessary to study the internal anatomy.
Regarding the anterior internal anatomy, Gephyrohepia and Eleutheromenia (García-Álvarez & Salvini-Plawen 2007) are distinct as the atrium and mouth are separate in Gephyrohepia while Eleutheromenia species have an atrio-buccal cavity (Pedrouzo et al. 2022). In the Corsica specimens mouth and atrium are partially separated. As discussed above for the subfamily Pruvotininae, the atrio-buccal cavity is also an ambiguous character in Eleutheromeniidae. The reconstructions included in the original descriptions of E. carinata (Pruvot 1891: fig. 16) and E. sierra (Salvini-Plawen & Öztürk 2006: fig. 4) show the mouth opening into the posterior part of the atrium, but Salvini-Plawen (2003), in the description of a specimen identified as E. sierra, states that “mouth opening in the dorso-posterior area of the common atrio-buccal cavity, connected with the sensory region by a groove (ridge).” According to the original descriptions of G. antarctica and G. impar, the mouth is separated from the atrium by a cuticularized ridge with musculature (Salvini-Plawen 1978; Zamarro et al. 2013). Nevertheless, Salvini-Plawen describes this ridge in G. antarctica Salvini-Plawen, 1978 as “a tegumental ridge without spicules”. In the same way, a cuticle with sclerites is not evident in the section of G. impar presented by Zamarro et al. (2013: fig. 10a, b) and the separation between the two cavities is consistent with what we have observed in the sections of the Corsica specimen (Fig. 12B), which lacks cuticle and sclerites in this area. The specimen from Corsica shares other anterior internal characteristics with G. impar (Zamarro et al. 2013) that are all comparable with what was described also for both E. sierra and E. carinata (Salvini-Plawen & Öztürk 2006): atrium posteriorly trilobed; central region of the atrium forming a blind pouch with single or paired atrial papillae; one pedal fold; hooked radula teeth without medial denticles; glandular esophagus; unpaired antero-dorsal midgut caecum. The only distinctive posterior characteristic of G. impar compared with E. sierra and E. carinata is the lack of abdominal spicules (Pruvot 1890; Salvini-Plawen & Öztürk 2006; Zamarro et al. 2013). In the Corsica specimen there are abdominal spicules (Fig. 12F) and their shape and position correspond with those described in both E. sierra and E. carinata (Salvini-Plawen 2003; Salvini-Plawen & Öztürk 2006). However, although not described for G. impar, the internal reconstruction of the holotype of this species shows a ventro-anterior pouch of the pallial cavity (Zamarro et al. 2013: fig. 9b) that corresponds with the position of the abdominal spicules in both Eleutheromenia species (Salvini-Plawen 2003; Salvini-Plawen & Öztürk 2006) and in G. antarctica (Salvini-Plawen 1978). Finally, the presence of epidermal papillae is a diagnostic character for the genus Gephyroherpia (Salvini-Plawen 1978) whereas the diagnosis of Eleutheromenia indicates the absence of these structures. In studying the available images of sections of G. impar, we did not observe epidermal papillae (Zamarro et al. 2013; fig. 10). There are no epidermal papillae in the Corsica specimen.
Considering all the above, it is not possible to make a distinction between G. impar and E. sierra based on anatomy. Furthermore, the only clear difference between E. sierra and E. carinata is the length of the paired region of the spawning duct and the exact position of its opening in the mantle cavity (Salvini-Plawen & Öztürk 2006), but the description of E. carinata was based on a juvenile. Therefore, we propose the synonymy of E. sierra, E. carinata and G. impar Consequently, the specimen from Corsica is identified as E. sierra. In addition, the phylogenetic analysis of COI and the results of both species delimitation methods (Fig. 2) indicate that the Corsica specimen is the same species as a specimen from Norway identified as E. sierra. Therefore, and considering that the separation between atrium and mouth is not a good diagnostic character, we propose a new classification for the subfamily Eleutheromeniinae: Eleutheromenia Salvini-Plawen, 1978 including E. sierra and E. antarctica n. comb. for G. antarctica Salvini-Plawen, 1978 and the monospecific genus Luitfriedia García-Álvarez & Urgorri, 2001 (with L. minuta García-Álvarez & Urgorri, 2001) differing by the lack of radula.
Given the synonymy proposed here, the distribution of E. sierra is extended and includes Portaló Island, Cabo de Creus (Spain), Bay of Izmir (Turkey) and Corsica Island (France) in the Mediterranean Sea (40-75 m depth) and the NW of the Iberian Peninsula in the Atlantic Ocean (598 m depth) (Salvini-Plawen & Öztürk 2006; Zamarro et al. 2013; García-Álvarez et al. 2014). As previously collected specimens, the specimen from Corsica was collected from a sandy bottom.
description: Published as part of Cobo, M. Carmen, Farris, William J. & Kocot, Kevin M., 2024, New data on the biodiversity of Solenogastres (Mollusca, Aplacophora) in the Mediterranean Sea: findings from the program " Our Planet Reviewed " Corsica 2019 - 2022, pp. 543-576 in Zoosystema 46 (21) on pages 566-568, DOI: 10.5252/zoosystema2024v46a21, http://zenodo.org/record/13744725