Buchnerillo atlanticus sp. nov., a new halophilic woodlouse (Isopoda: Oniscidea: incertae sedis) from the Atlantic coast of the Iberian Peninsula, with ecological remarks

. A new woodlouse species of the genus Buchnerillo Verhoeff, 1942 is described and illustrated from the Cantabrian Coast of Asturias (Eastern Atlantic Ocean of the Iberian Peninsula). Buchnerillo atlanticus sp. nov. is a halophilic woodlouse that lives under embedded rocks in ﬁ ne-grained sand areas of its type locality beach. Its morphological features, including secondary sexual characteristics, allow it to be distinguished from the other three known species of the genus Buchnerillo . Biological, ecological and ethological data of the new species are commented. To facilitate the separation of the four known species of Buchnerillo , the main diagnostic features are summarized and their known distribution is commented.


Description of collecting site
The population of the new species of Buchnerillo was located in the Conejera beach (Villaviciosa) in the Principality of Asturias (northern Spain) (Fig. 1A). The collecting area has an Atlantic macrobioclimate with supratemperate climate (Rivas-Martínez et al. 2017). The infl uence of the sea moderates the climate in the area. The area of Villaviciosa has a 12.8 ºC mean annual temperature and 1345 mm mean annual precipitation (data available at https://es.climate-data.org). Conejera is a heterogeneous beach composed by two different substrates: fi ne-grained sand and rocks. Fine-grained sand areas are characterized by the presence of boulders embedded in the substrate (Fig. 1B). No logs or plant remains were found in the study area. However, algae accumulations were common (Codium spp., Gelidium spp., among others) (Fig. 1B). The study area remains largely unchanged due to limited human impact.

Methodology
Surveys were carried out in the Principality of Asturias (northern Spain) in 2020 and 2021. After the discovery of a population of the new species of Buchnerillo, the locality was visited several times for ecological and ethological observations. Images of live specimens were taken in situ with a Nikon D5300 camera equipped with Tamron 90 mm macro lens and a Nikon D7000 camera equipped with the same lens. Several specimens were hand collected, stored and preserved in 75% ethanol. The collected specimens were dissected under a stereo microscope (Nexius-Z Euromex). For their morphological study, appendages, mouthparts and tergites were treated with Amann's lactophenol and mounted on microscope slides using Faure's liquid. Photographs of preserved specimens were taken with a digital microscope (Dino-Lite) and the main measurements were taken with the associated software (Dino-Capture ver. 2.0). Pencil drawings were prepared using a camera lucida attached to an Olympus CH-30 biological microscope and digitally inked according to the method described by Montesanto (2015) and with a drawing tablet (Wacom Intuos). A female specimen was examined and photographed by scanning electron microscope (Hitachi S-3400N). Photographs were edited with GIMP ver. 2.10.12. Maps were generated with ArcGis Desktop ver. 10.8.1. The type material has been deposited in the collections of the National Museum of Natural Sciences of Madrid and the Balearic Museum of Natural Sciences of Mallorca, both in Spain. The specimen used for SEM analysis is part of the fi rst author's personal collection.

Diagnosis
Species of Buchnerillo characterized by ovoid and endoantennal conglobation type. Cephalon, pereontergites and pleon-tergites smooth and covered with long setae regularly arranged. Frontal area striated, not grooved. Mandibles with dichotomized molar penicil. First pereon-tergite posterolateral corner without schisma. Endopod of male pleopod 1 with straight distal part.

Etymology
The name of the species comes from the Atlantic Ocean (concretely the Cantabrian Sea) which is the area where the specimens were collected. COLOUR. Cephalon and epimera pale. Rest of body reddish or yellow-orange with darker irregular reticulated spots, with slight variability (  rows of setae on cephalon and pereon-tergite 1; two rows on posterior half of pereon-tergites 2-7 and pleon; one row on pleotelson; setae emerge from cuticular pits (Fig. 3C).

Material
CEPHALON. With frontal and suprantennal ridges, delimiting frontal shield; upper margin regularly curved; lower margins concave, delimiting on each side hollows in which antennae are housed during conglobation (Fig. 3A). Frontal shield surface covered with fi ne transverse striae (Fig. 3A). Eyes formed by one ocular spot, not well-defi ned as ommatidium.
FIRST ANTENNA. Two articles; fi rst article slightly longer than second; second article with two long apical aesthetascs (Fig. 4B).  SECOND ANTENNA. Thick and short, with long setae on peduncular articles; fl agellum with three articles; two aesthetascs on second fl agellar article (Fig. 4C).
PEREOPODS. Short, with one long divided seta on carpus. Dactylus with long and plumose dactylar seta.

Remarks
Buchnerillo atlanticus sp. nov. is distinguished from the other three known species of the genus, in addition to other morphological characteristics, by the lack of dorsal tubercles and by having long sensory setae. According to the respective original descriptions, it also differs from the other species by having the mandibles with dichotomized molar penicil, instead of semi-dichotomized. In addition to these morphological features, it is distinguished from B. litoralis by its ovoid rather than spherical conglobation (Vandel 1960a), by the shape of the endopod of the fi rst male pleopod, which in B. atlanticus is almost straight with a very wide basal part and in B. litoralis has a curved distal part, apically dilated (Vandel 1960a). Both species have the frontal area of the cephalon not excavated, but covered with fi ne transverse striae. In addition to the characteristics already mentioned, B. atlanticus is distinguished from B. oceanicus by the cephalic structure, with striated instead of grooved frontal area (Ferrara 1974). Buchnerillo atlanticus, B. litoralis and B. oceanicus share the lack of schisma in the fi rst pereontergite and presence of a short lobe in its ventral part. Finally, B. atlanticus is also distinguished from B. neotropicalis by the absence of schisma in the fi rst pereon-tergite and by the shape of the male fi rst pleopods, among other characteristics (Taiti et al. 2018). The most distinctive morphological features of the four known species of Buchnerillo are presented in Table 1.

Distribution
Buchnerillo atlanticus sp. nov. is only known from its type locality of Conejera beach in Villaviciosa (Asturias, Spain) ( Fig. 1A-B). Although several localities with similar ecological conditions were visited, no specimens were found. Up to date, each species of Buchnerillo belong to different coastal areas of the world: Buchnerillo litoralis occurs on the Mediterranean shores, B. oceanicus on the coasts of the Indian Ocean, B. neotropicalis on the coasts of the Pacifi c Ocean and B. atlanticus on the Cantabric coast of the Atlantic Ocean (Fig. 7).

Ecology
Buchnerillo atlanticus sp. nov. was always found in Conejera beach areas with fi ne-grained sand. All the specimens were adherent to the lower face of large highly humid stones embedded in the substrate.  (Fig. 1B). Several specimens seemed to be seen feeding on small patches of algae and other organic material adhered to the rocks. Apparently, the presence of B. atlanticus was not altered by frequent survey and handling of the same stones in the short sampling period. Buchnerillo shared habitat with three other halophilic woodlice: Armadilloniscus candidus Budde-Lund, 1885, Halophiloscia couchii (Kinahan, 1859 and Ligia oceanica (Linnaeus, 1767). Buchnerillo atlanticus did not present particular conspecifi c aggregations. Other arthropods present in the area were the pseudoscorpion Neobisium maritimum Leach, 1817 and the chilopod Geophilus easoni Arthur et al., 2001 both potential predators of B. atlanticus. Several species of halophilic Collembola, staphylinid Coleoptera and tiny mites were also present in the study area, in addition to some other accidental arthropod taxa from the cliff. Regarding its behaviour, it was always seen moving slowly among the organic material and small grains of sand stuck to the lower face of the stone ( Fig. 2A-B). In case of disturbance the individuals rolled into an ovoid ball that remained adhered to the surface due to the humidity (Fig. 2C). The shape and colour of Buchnerillo provides this woodlouse with an almost perfect camoufl age, looking like one more sand grain in the microhabitat under the stone ( Fig. 2A). In case of a major or continuous disturbance it ended up opening slightly and releasing itself from the stone, falling to the substrate where they turn complete untraceable. The specimens showed some photophobic behaviour (Supplemental material). When the stones were lifted, B. atlanticus moved into the shade. This species is thought to be very sensible to dehydration. When specimens were removed from their habitat it only took a few minutes 3,000 6,000 9,000 12,000 Km to die. Buchnerillo atlanticus needs constant humidity, present in its habitat under stones embedded in humid substrate. Its habitat is subject to tidal infl uence with occasional submersion. Specimens of B. atlanticus were seen between July and September, with a slightly variation in population abundance among consecutive days.

Discussion
The recent discovery of a fourth species of Buchnerillo that inhabits the Atlantic coasts of Europe represents an important breakthrough to continue studying hard-to-fi nd halophilic woodlice such as the species of this genus. Although the Atlantic coastal fauna of the continent has been explored intensively since the end of the 19 th century (Vandel 1960a;Legrand 1953aLegrand , 1953bLegrand , 1954aLegrand , 1954bHarding & Sutton 1985;Gregory et al. 2012;Cherpitel et al. 2019;Garcia & Robla 2021), this species was never reported. There are records of Buchnerillo litoralis in the Atlantic coastal areas of Portugal (da Gama et al. 2000) and the island of Madeira (Vandel 1960b). However, these specimens were poorly described or documented with fi gures to ensure that it was really the Mediterranean species described in the midtwentieth century. It is possible that these records correspond to B. atlanticus sp. nov. This hypothesis is supported by the fact that several specimens, apparently identical to the new species, were collected years ago in the Canary Islands (S. Taiti pers. com.). However, it remained undescribed because only one female was preserved and the rest of the specimens could not be located (S. Taiti pers. com.). It cannot be completely ruled out that B. litoralis may be distributed beyond the Mediterranean Sea. However, B. litoralis seem to have an endogean way of life and are not usually found associated with driftwood or other remains susceptible to be transported by currents. Taiti et al. (2018) also remarked that the record of B. litoralis in the Florida Keys, on the Atlantic coast of North America (Paoletti & Stinner 1989), is very doubtful and should be reviewed. It is interesting to note that the four known species of Buchnerillo are linked to different marine basins. Consequently, gene fl ow among their populations might have been hindered by the separate ocean current systems for millions of years. A complete and exhaustive review of the genus based on molecular data would be of great interest in establishing the phylogenetic relationships among species of Buchnerillo as well as the taxonomic position of the genus. However, at the moment there is very little material available. The small size and cryptic habits of species of Buchnerillo probably have hindered the discovery of these species and could also affect the collection of more specimens. It will be necessary to develop more meticulous and appropriate sampling techniques (Nöel & Séchet 2017) and to actively explore other shores around the world to fi nd new populations of Buchnerillo and maybe new species of this unknown genus of uncertain systematic position. Regarding its ecology, species of Buchnerillo are poorly known. The few bibliographic records correspond to taxonomic or faunistic works, revealing an important gap in ecological and ethological knowledge.
Since the habitat of Buchnerillo atlanticus slightly differs from that of other species (algae vs plant remains), more studies are needed to assess the species habitat preferences. However, this species was found in the same microhabitat of other species of Buchnerillo (Vandel 1960a;Chelazzi & Ferrara 1978;Pezzino 2015). In addition, although the interactions between species of Buchnerillo and other woodlice are far from known, B. atlanticus has been found coexisting with other halophilic species as those found in other locations (Chelazzi & Ferrara 1978;Nöel & Séchet 2017;Garcia & Robla 2021). Regarding ethology, little is known about the behaviour of species of Buchnerillo. Chelazzi & Ferrara (1978) carried out an exhaustive ecological study that involved Buchnerillo oceanicus. They discovered that B. oceanicus is a nocturnal and stationary strictly halophilic woodlouse limited to very humid places. We observed that B. atlanticus always occurs in very humid microhabitats, has a slight photophobic behaviour and moves slowly under stones, fi tting with previous references (Chelazzi & Ferrara 1978). However, the accessible information is scarce, and the life cycle and way of living remains unsolved. Finally, variations in the abundance and detectability among consecutive days probably depend on climatic and tidal conditions as seen in other isopod populations from coastal areas (Messina et al. 2016;Garcia & Robla 2021).
In conclusion, distribution, ecological and biological knowledge of species of Buchnerillo continues to be scarce and insuffi cient. With a new species described and with the data provided, it is necessary to carry out sampling campaigns to locate new populations, to carry out new studies to understand the biology of Buchnerillo atlanticus sp. nov. and the other species and to solve the uncertain taxonomic position of the genus Buchnerillo.