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| Scutopus variabilis Passos, Corrêa & Miranda, 2021 |
Aplacophorans are common inhabitants of the deep-sea, where many places remain unexplored regarding their biodiversity. Filling a gap in knowledge about these animals from the South Atlantic, Scutopus variabilis sp. nov. (Caudofoveata, Limifossoridae) is described; further, species distribution modelling (SDM) was performed to elucidate the distribution patterns of Atlantic species of Scutopus. The type materials of S. megaradulatus Salvini-Plawen (1972) and S. chilensis Salvini-Plawen (1972), were examined and a search was performed for specimens of Scutopus held in museum collections. Scutopus variabilis sp. nov. has a slender and highly variable body form and a very distinct suture line is present midventrally. Two dominant types of trunk sclerites were observed by Scanning Electron Microscopy (SEM): one elongated with lateral margins slightly concave in medial portion, and another longer, with narrower base; its radula bears up to eight rows of heavily sclerotized teeth bearing 12–16 small denticles. The species occurs in a wide bathymetric range (40–1300 m), being more abundant at the edge between the continental shelf and upper slope. Outside the areas from where these samples were obtained, suitable areas for S. variabilis sp. nov. were found in the Southern Caribbean Sea (from where S. megaradulatus is recorded) and in the Brazilian Northern coast; the Gulf of Mexico and the Brazilian Northeastern coasts were found as unsuitable. Species of Scutopus appear to exhibit different patterns of geographical distribution: the European S. ventrolineatus Salvini-Plawen (1968) and S. robustus Salvini-Plawen (1970) are known as widely distributed, while non-European representants, the American S. megaradulatus, S. chilensis and S. variabilis sp. nov., and the Japanese S. schanderi Saito and Salvini-Plawen (2014) and S. hamatamii Saito and Salvini-Plawen (2014) have more restricted distributions. However, clear and definite patterns of distribution of some of these species are probably blurred by sampling bias, for the European area is better studied. In the Atlantic, the SDM showed that species of Scutopus occur in a way that overlapping is minimized. Great sampling efforts combined with detailed descriptions based on SEM have revealed an interesting, abundant and up to now undescribed Brazilian deep-sea malacofauna.
Keywords: taxonomy, biogeography, species distribution modeling, Caudofoveata, Limifossoridae
Family Limifossoridae Salvini-Plawen, 1969
Genus Scutopus Salvini-Plawen, 1968
Type species: Scutopus ventrolineatus Salvini-Plawen, 1968
by original designation.
Remarks: Salvini-Plawen (1968) characterized S. ventrolineatus by its long, undivided, cylindrical body which coils up spirally when it is disturbed, its radula composed by multiple rows of paired teeth, each tooth bearing median denticles, an undivided or homogeneous, post-oral shield, and the presence of a long midgut sac or digestive gland, and by its sclerites that ventrally are positioned in a divergent way forming a clear external ventral sutural line. Later, Salvini-Plawen (1975) and Ivanov (1981) highlighted that the characters of the oral shield and the radula are typical of Scutopus species. The new species described herein has these main characteristics, as shown below.
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| Figure 1. Scutopus variabilis sp. nov. Photomicrographs under stereomicroscope of specimens of different sizes showing their variable body form and color (all in same scale). The body regions are shown in (A) (holotype) and (H), (B) and (D) had their soft parts dissolved for the extraction of their radulas [which are shown in Figures 4A,E, respectively and of their sclerites from the different body regions. The peribuccal region is protruded in (C) and (I). The midventral suture line is visible in (E) and (H); the main collar in (B), (F), (I), (K), (M), and (O); and the secondary collar in (H). The asterisks in (D), (E), (G), (J–N), (P), and (Q) show the anterior end. fgr - foregut region; mc - main collar; mgr - midgut region; msr - midgut sac region; pbr - peribuccal region; ppr - prepallial region; pr - pallial region; sc - secondary collar; sl - midventral suture line. Voucher numbers: (A) – ZUEC APL 277, (B) – ZUEC APL 285, (C) – ZUEC APL 287, (D) – ZUEC APL 284, (E) – ZUEC APL 279, (F) – ZUEC APL 282, (G) – ZUEC APL 306, (H) – ZUEC APL 298, (I) – ZUEC APL 286, (J) – MZSP 154099, (K) – ZUEC APL 286, (L) – ZUEC APL 326, (M) – MNRJ 23638, (N) – ZUEC APL 331, (O) – ZUEC APL 291, (P) – ZUEC APL 311, (Q) – ZUEC APL 283. |
Scutopus variabilis sp. nov. Passos, Corrêa and Miranda
Diagnosis. Body long, slender, up to 14 mm in length, often contorted, almost uniform in diameter; in most specimens divided in three parts: an anterior part separated by a main collar from a median part, and a slightly tapered posterior part. Oral shield post-oral, ventral to the mouth. Midventral suture line present. Two main types of sclerites: one elongated, with lateral margins slightly concave in medial portion, with base wider and about a half of the blade length, and another shorter, triangular, base and blade with continuous straight lateral margins; in both, blade ornamented with a central keel and weak adjacent longitudinal grooves. Radula distichous, with up to eight transversal rows of heavily sclerotized teeth (except for the two most proximal pairs); each tooth inwardly curved, with 12–16 small median bent denticles present in all the extension of the concave, inner margin.
Etymology. The name variabilis refers to the variable form and color exhibited by the specimens of this species.
Flávio Dias Passos, Paulo Vinicius Ferraz Corrêa and Marcel Sabino Miranda. 2021. Better Alone Than in Bad Company: New Species of Caudofoveate Limifossorid (Mollusca, Aplacophora) Unravels Patterns of Distribution Hidden in the Deep Atlantic. Front. Mar. Sci. 8:669478. DOI: 10.3389/fmars.2021.669478
