A Hidden Diversity in the Atlantic and the SE Pacific: Hamatipedidae n. fam. (Crustacea: Tanaidacea)

A new family of paratanaoidean Tanaidacea, the hamatipedids, formerly part of the Typhlotanaidae, is established to accommodate three genera (Hamatipeda and two new). Deep-sea hamatipedids collected from four sites in the Atlantic (Argentine and Guiana basins) and 14 sites from the Southeast coast of Australia were studied using a taxonomic approach combining morphological and morphometric data. Four new species of Hamatipeda and one of a new genus are described from different deep-sea areas of the Atlantic and Pacific oceans. Hamatipeda sima originally classified within Hamatipeda, is transferred to a new genus. We observed that several morphometric characters (i.e., length of the last two pereonites) in different life-stages of one of the new Hamatipeda species (neuter, manca-2, and manca-3) are correlated with the total body length (TBL). Applying a morphometric approach, we aimed: (1) to identify those ontogenetic-dependent characters, and (2) to detect the characters, which can be used in discrimination of Hamatipedidae species, regardless their life-stage.


INTRODUCTION
Intensive exploration of the deep sea since the 1960s has uncovered a remarkable diversity of benthic organisms (Sanders et al., 1965;Sanders, 1968). The large number of new taxa discovered during each expedition unequivocally refute the 19th Century concept of the deep sea as unproductive and devoid of life ecosystem. These studies also revealed that many undescribed deep-sea species are often much smaller than their shallow-water counterparts, a reason why these have been overlooked over the decades of deep-ocean exploration (Larsen, 2005;McCallum et al., 2015;Frutos et al., 2016). The number of new species and their enormous diversity discovered during each deep-sea expedition, confirms that oceanic bottom is the last recognized ecosystem of the Earth (Ramirez-Llodra et al., 2011;Frutos and Sorbe, 2014;Costello and Chaudhary, 2017;Jażdżewska et al., 2018Jażdżewska et al., , 2021. A paucity of specialists and awareness of the role taxonomy for understanding and protection of the biodiversity has meant that collections of invertebrates from deep-sea expeditions were shelved in museums awaiting the attention of taxonomists and formal description (Brandt et al., 2007;Appeltans et al., 2012).
Among these organisms is the superfamily Paratanaoidea Lang, 1949, a monophyletic group of the crustacean suborder Tanaidomorpha (Kakui et al., 2011). It is represented by relatively small peracarids (<4 mm) of high diversity that is still underrecognized and undescribed (Błażewicz-Paszkowycz and Bamber, 2007;Błażewicz et al., 2019). It is currently represented by 19 recent families.
The Typhlotanaidae Sieg (1984) is one of the most diverse paratanaoidean families in the deep sea, comprising 17 genera and 119 species (Gellert et al., unpublished). Before the first phylogenetic approaches (Larsen and Wilson, 2002), typhlotanaids were grouped within the Leptognathiidae Sieg, 1976, although their morphological distinctiveness was often emphasized (Sieg, 1984). The Typhlotanaidae were characterized by a three-articulated antennule, six-articulated antenna (Sieg, 1984), and absence of eyes, which are considered evidence for a deep-water origin of the family (Błażewicz-Paszkowycz, 2007;Gellert et al., unpublished). The morphological distinctness of the ornamentation of their pereopods and their monophyletic origin is still being resolved, with the "true" typhlotanaids being defined by the presence of a "clinging apparatus" on the carpus of pereopods 4-6, which facilitates movement within their tubicolous domiciles. This apparatus includes several specialized sets of hooks, thorns, and pectinate spines rather than simple "bayonet" spines. Additionally, some genera have rounded and minutely spinulate structures called "prickly tubercles" (Błażewicz-Paszkowycz, 2007). Those structures are apparently absent in some genera such as Aremus Segadilha et al., 2018 andHamatipeda Błażewicz-Paszkowycz, 2007, leading to their affinity with Typhlotanaidae being questioned (Segadilha et al., 2018).
The basis for this paper is tanaid material collected during the pioneering expedition exploring the abyssal zone of the West Atlantic and slope off southeastern Australia. Those collections were deposited in the Museum of Comparative Zoology (Boston, MA, United States) and in the Melbourne Museum (Australia). The material was initially identified to the genus Hamatipeda, but closer identification has revealed a richer diversity allowing us to distinguish several taxa. Four of the species are formally described (three species from the SW Atlantic and one from SE Australia), two new genera are established, and analysis of morphological characteristics confirms that aspects of the attachment of the cheliped to the cephalothorax, pereopod setation, and the shape of the carpus cheliped enable us to define a new family.

Sampling
The 5,832 typhlotanaids specimens for the research were collected during the expeditions completed in the SW Atlantic (5,771 individuals) and SE Australia (61 individuals). From the Atlantic, the material included: 147 individuals from the expedition organized by Woods Hole Oceanographic Institution during 1971-1972 aboard the RV Knorr found in two places, e.g., the Guiana Basin and Argentine Basin at a wide depth range (1,022-3,317 m), and 61 individuals from the slope and abyss off the Australian coasts of New South Wales (off Eden) to Tasmania (off Freycinet Peninsula) at a wide depth range (49-2,900 m) collected during the SLOPE Program during 1979-1988. The distribution of the stations is given in Supplementary Table 1.
The samples were preserved in formalin. Distribution maps were prepared for each species using the QGIS 2.18 software (Szczepanek, 2017). The type-material and other materials studied for this research are deposited at Museums Victoria, Melbourne Museum (NMV) (Melbourne, Australia) and the Museum of Comparative Zoology (MCZ), Harvard University (Cambridge, MA, United States).

Morphological Analyses
Initial species identification was based on morphological observations with a dissecting microscope. The whole collection was sorted to several morpho-groups, and 208 individuals were preliminarily identified as Hamatipeda and were chosen for further comprehensive morphological study. From each group several individuals were designated for thorough morphological analysis and dissected with chemically sharpened tungsten needles. The dissected cephalothorax, pereon, and pleon appendages were mounted on slides using glycerin and sealed with molten paraffin . Morphological drawings were prepared using a light microscope (Nikon Eclipse 50i) equipped with a camera lucida. Digital pictures were completed using a graphic tablet following Coleman (2003).
Total body length (TBL) was measured along the central axis of symmetry, from the rostrum to the tip of the pleotelson. In contrast, body width was assessed perpendicular to the symmetry axis at the widest point (BW). Body width and length of cephalothorax, pereonites, pleonites, and pleotelson were measured on whole specimens. Hamatipeda mojito n. sp. (see below) was represented by numerous specimens of different ontogenetic stages. Observed variability of morphometric characters between life stages pose the question if the length of appendages changes proportionally to increasing body size during developmental growth (isometric growth) or not (allometric growth). In total, we measured ninetyseven specimens of H. mojito in three life stages: manca-2 (35 individuals), manca-3 (24 individuals) and neuter (38 individuals). For each specimen nine characters i.e., body length, pereonites 1-6 length, uropodal exopod and endopod configuration, were recorded. All measurements were assessed along the axis of symmetry and were made with a camera connected to the microscope (Nikon Eclipse Ci-L) and the NIS-Elements View software 1 .
Morphological terminology is largely as in Błażewicz-Paszkowycz (2007). The seta types are recognized as: (1) simple setae-without ornamentation, (2) serrate-with serration or denticulation, (3) penicillate-with a tuft of setules located distally and with a small knob on which a seta is fixed to the tegument and (4) rod setae-slightly inflated distally and with a pore followed Jakiel et al. (2020).

Statistical Analysis
The relationships between body size, body segments, and uropod rami measured at different developmental stages were presented as a power function (y = ax b ) and logarithmically linearized (log y = log a + b log x). All dimensions were log transformed before computing the regression equation. The slope of the regression line (b) represents the relative growth and was used to test the degree of allometry: isometry (b = 1), negative allometry (b < 1) or positive allometry (b > 1) (Hartnoll, 1982) (Supplementary Table 2).

Imaging
The scanning electron microscope work was performed on a Phenom Pro X (Department of Invertebrate Zoology and Hydrobiology, University of Lodz, Poland) to examine fine morphological details in a subset of specimens from the MCZ collection. Specimens were frozen at −10 • C and analyzed using a temperature-controlled sample holder. Confocal laser scanning microscopy (CLSM) images were obtained with LSM 780 (Zeiss) microscope equipped with Plan-Apochromat 63x/1.4 objective using InTune tuneable excitation laser system (set to excitation wavelength 555 nm). Specimens were stained for 24 h with equal volume mixture of saturated water solutions of Congo red and acid fuchsin. Before dissection and mounting in 100% glycerol, stained animals were washed thoroughly with 50% aqueous glycerol solution. Fluorescence was registered in single emission channel: 561-695 nm. Images were recorded as Z-stacks with 12.6 µs pixel dwell and two times line averaging with optical cross section of 0.5 µm. Collected data was pseudo-colored in gold and reconstructed into a 3D image stack by maximum intensity projection using ZEN software (Zeiss). Diagnosis: Body long > 10 L:W. Pereonite-1 long (subequal or longer than cephalothorax), without hyposphenium. Pereonites 1-5 longer than wide (pereonites 2-3 over 1.5 L:W). Antennule three-articled. Mandible molar process wide, crushing surface and irregular edge, without tubercles and teeth. Cheliped basis not reaching pereonite-1, posterior lobe enfolded by sclerite. Pereopods 1-3 with seta on coxa; pereopods 4-6 coxa fused with body. Pereopod-1 more slender than others. Pereopods 2-3 often robust, with short setae and small spines. Pereopods 4-6 merus and carpus with two (or three * ) hooks and one molariform spine, carpus without prickly tubercles; unguis trifurcate (or bifurcate * ). Pleopods small, vestigial; setae always plumose. Uropod endopod one or two-articled; exopod one-articled. 2 Male: Unknown.
Remarks: The robust carpal hooks of pereopods 4-6 in the absence of a prickly tubercle are an autapomorphy for the new family and the character that distinguishes its members from the Typhlotanaidae. The Hamatipedidae lack both a hyposphenium on the pereonite-1 and the prickly tubercles on the carpus of pereopods 4-6, both characteristic of "true" typhlotanaids. So far, six typhlotanaid genera, i.e., Paratyphlotanais Kudinova-Pasternak and Pasternak, 1978, Meromonakantha Sieg, 1986, Obesutanais Larsen et al., 2006, Targaryenella Błażewicz and Segadilha, 2019Typhlamia Błażewicz-Paszkowycz (2007) and Aremus lack the prickly tubercles, although they have robust spines or bayonet setae (or "bayonet-like spines, " Bird and Holdich, 1988) on the carpus of pereopods 4-6. There are several other features which distinguish the Hamatipedidae from those genera and these genera can be segregated into two groups based on the setation of pereopods 1-3: the first, Meromonakantha, Paratyphlotanais, and Targaryenella differ from all other typhlotanaid and hamatipedid genera in having simple (or bayonet-like) spines on the carpus (and merus to lesser extent). The second group, Aremus, Obesutanais, and Typhlamia share the general setation pattern of the hamatipedids and typhlotanaids (sensu stricto) but the first lacks pleopods in females and has an articulated spine on the antennule apex, Obesutanais is characterized by a short and compact body (3.0-6.0x L:W) and only a pair of hooks on the carpus of pereopods 4-6, inter alia, and Typhlamia by its long antennule article-3 (about 14x L:W) and long setae, and more elongate merus, carpus and propodus of pereopods 1-3. Hamatipedidae have elongated pereonites and the cheliped basis posterior lobe separated from the pereonite-1 (Figure 1), making it similar to Typhlamia at first glance. However, hamatipedids have a shorter antennule than Typhlamia, and their carpal clinging apparatus of pereopods 4-6 is different. In hamatipedids it is formed by hooks (naked or serrated), which are sometimes apically flattened (molariform). In Typhlamia the spines are small, slender, and only distally flattened (Gellert et al., unpublished). The morphological phylogeny of Typhlamia and Hamatipedidae should be corroborated in future analysis implementing molecular techniques.

Species included: Hamatipeda kohtsukai
Remarks: Until this study, Hamatipeda included four species 3 . The first to be described, Hamatipeda longa, was collected off the Falkland Islands and placed in the genus Typhlotanais (Kudinova-Pasternak, 1975). Later, Błażewicz-Paszkowycz (2007) described Hamatipeda trapezoida from Drake Passage and assigned it to a new genus, Hamatipeda. This genus was supplemented with two other species, Hamatipeda sima by  recovered in SE Australia (Eastern Bass Strait and Flinders Island), and Hamatipeda prolata from the SE Brazilian coast (Segadilha et al., 2019). Recently, Kakui and Hiruta (2021) has described another species -H. kohtsukai, which was the first record of the genus in the Northern Hemisphere. Because it lacked a trifurcate unguis in the pereopods 4-6 (a key-character for the genus), the definition of the Hamatipeda was extended (Kakui and Hiruta, 2021).
During our examination of the SW Atlantic and SE Australia specimens, we observed a high variety of morphological features (character of the antennule, antennule ornamentation, and character of their pereopods) and decided to extract H. sima from Hamatipeda. It is deposited it in a new genus Yarutanais n. gen. (see below). In addition, Rakaduta n. gen. is established to accommodate a new hamatipedid species from SE Australia.
Etymology: The name is given after the popular Brazilian cocktail drink -caipirinha.
Remarks: Hamatipeda caipirinha n. sp., from the SW Atlantic, can be distinguished from other members of the family by the uropod endopod slightly shorter than exopod. Similar equal-length uropod rami are present in  H. trapezoida from the Antarctic (Błażewicz-Paszkowycz, 2007), but H. caipirinha has a two-articled endopod (one-articled in H. trapezoida) and ischial seta on pereopods 4-6 (two in H. trapezoida).

Hamatipeda caipiroska
Etymology: The name is given after the well-known Brazilian cocktail drink-caipiroska.
Remarks: Hamatipeda caipiroska n. sp. is an abyssal species of the SW Atlantic. It can be distinguished from other members of the genus by the presence of a relatively stout cheliped carpus (1.6 L:W) that is more slender in other Hamatipeda species (at least 2.0x L:W). Moreover, H. caipiroska has a two-articled uropodal endopod, as in H. longa, H. prolata, H. caipirinha, and H. mojito, but only H. prolata, known from the Brazilian slope, shares with H. caipirinha parallel margins on pereonites 4-6. These two species are also distinguished by the shape of pereonites 1-3, which are rectangular in H. prolata and trapezoidal in H. caipiroska (Supplementary Table 1).
Hamatipeda caipiroska and H. caipirinha were collected by dredging at the same station in the abyssal of Argentina Basin. They can be distinguished by the length of the uropod rami (almost equal in H. caipirinha, and with exopod clearly shorter 0.7x endopod in H. caipiroska), the length of pereonite-4 (long 1.7 L:W) in H. caipirinha, and short (1.4 L:W in H. caipiroska), and the aspect ratio of the cheliped carpus  ventrodistal seta; propodus ventrodistal simple seta. Pereopods 4-6 ischium with two setae; carpal molariform spine smooth. Uropod exopod 0.8x endopod; endopod two-articled.
Etymology: The name is given after the famous Cuban cocktail drink -mojito; as noun in apposition.
Remarks: Hamatipeda mojito n. sp. is the only member of the genus that has a smooth carpal molariform spine on pereopods 4-6 (Supplementary Table 3 and Figure 8A). The other species that has possibly similar smooth molariform spine is H. longa, known from the Falkland Islands, although preservation of the holotype of H. longa and its long-term storage in formalin did not allow for observation of the minute ornamentation. Nevertheless, H. longa has a much shorter uropod exopod (0.5x endopod), that is clearly longer (0.8x endopod) in H. mojito.
Etymology: The name is given after the Australian drink: Lemon, Lime and Bitters (LLB) which is a combination of clear lemonade, lime cordial, and bitters.
Cheliped ( Figure 10A) basis 1.5 L:W; merus wedge-shaped, with ventral seta; carpus 1.9 L:W, with two long ventral setae, two distal and subproximal short setae on the dorsal margin; chela slender, 3.0 L:W, 0.9x carpus; palm 1.2x fixed finger, with seta on inner side, and seta near dactylus insertion; fixed finger with two ventral setae (one longer than the other); cutting edge with three setae and three weak, blunt teeth distally; seta of dactylus not observed.
Distribution: SE Australia, from New South Wales to Victoria, south of Point Hicks, at depths of 1,119-2,600 m (Figure 14). Remarks: Hamatipeda lelibi n. sp. from the slope off SE Australia can be distinguished from other Hamatipeda species by the distinctive projections on the anterior margins of the tergites of pereonites 2-5 (Supplementary Table 1). These are a unique character in the Paratanaoidea, although a similar process is present on the anterior margin of pleonite-1 of the paratanaid Pseudobathytanais gibberosus Larsen and Heard, 2001 (p.17, Figure 8A).

Key for identification of Hamatipeda (neuters). See also
Type species: Rakaduta inexcessis n. sp. (by monotypy). Etymology: In the Aboriginal language Walpiri, "rakadu" means "deep, " which reflects deeper distribution of the genus in relation to Yarutanais, which occurs on the continental shelf. The ending "ta" are two first letters from Tanaidacea.

Etymology:
The name of the species is for the Australian rock band (INXS) formed in Sydney, New South Wales.
Pleopods 1-5 ( Figure 12H) basal article naked. Endopod 2.1 L:W, with one proximal and eight distal setae on outer margin. Exopod 2.0 L:W, with one proximal and six distal setae on outer margin.
Remarks: As for the genus because of monotypy.
Distribution: Australia, from off Nowra, New South Wales to Eastern Bass Strait, 50 km NE of Babel Island, Tasmania, at depths 49-1,000 m (Figure 14).
Remarks: Yarutanais sima is the only Yarutanais species on the shelf and slope off SE Australia. It can be distinguished from other members of the Hamatipedidae by the presence of a cheliped carpal shield and five setae on the carpus pereopods 2-3 (Błażewicz-Paszkowycz and Bamber, 2012: figure 116 A,C-D) and short antennule article-3 (only little longer than article-3; Figure 13E). Moreover, the antennule article-1 has ventral and ventrolateral robust microtrichia that are absent in other hamatipedids ( Figure 13D).

Diversity and Distribution
As a result of our study, the Hamatipedidae includes three genera (two new for science) and ten species (five new for science). The most speciose genus is Hamatipeda, with the two other genera Rakaduta and Yarutanais monotypic.
The Hamatipedidae is a wide-spread element of the benthic community in the Southern Hemisphere (Figure 14), and underestimated element of benthic deep-sea communities. In the Atlantic, the most northern record of the family is H. mojito, found off French Guiana. Except for Yarutanais sima that occurs in the shallow Bass Strait, all hamatipedids inhabit greater depths beyond the continental shelf, i.e., on the continental slope (seven species) and only two are known from the abyssal.

Morphometrics
Analysis of the relationships between body size, body segments, and uropod rami measured at different developmental stages of Hamatipeda mojito indicates allometric growth. Positive allometry was calculated for pereonite-6, isometry for pereonites 4-5, and negative allometry for the carapace, pereonites 1-3, and uropod endopod and exopod (Figure 15 and Supplementary  Table 2). Moreover, two size stages of neuters were observed.

DISCUSSION
The proposed new family is the twentieth recent family of the Paratanaoidea and the eleventh that apparently radiated in lightdeprived environments such as the deep-sea. The lack of eyes in many paratanaoideans is suggested as evidence of the place of this origin, although in some cases, e.g., the blind Tanaissuidae Bird and Larsen (2009), Bird (2002, 2012 the lack of eyes is considered an adaptation for tubicolous life-style. The earliest paratanaoidean families to be recognized were relatively straightforward for taxonomic classification. The presence of the multi-articled uropods (Leptocheliidae Lang, 1973), lateral plumose seta on pleonites 1-4 (Paratanaidae Lang, 1949;Teleotanaidae Bamber, 2008), cheliped attached directly/posteriorly to the cephalothorax (Agathotanaidae Lang, 1971 andAnarthruridae Lang, 1971) or one pair of the oostegites (Pseudotanaidae Sieg, 1976), were sufficiently diagnostic for these families. Later classification of the Paratanaoidea and the definitions of the newly established families were less obvious and required use of morphometry, dissection of the mouthparts and having of at least basic experience in tanaidacean taxonomy to capture specific and often fine details in morphological structures. The definition of more recently erected families based on character of pereopod setation (Jóźwiak et al., 2009;Błażewicz et al., 2019), proportion of the uropods rami (Larsen and Wilson, 2002;Bird and Larsen, 2009;Błażewicz-Paszkowycz and Bamber, 2009) or shape of the sclerite that links the cheliped with cephalothorax .
The application of molecular data in taxonomic studies can promote the validation of morphological data that, although indispensable for taxonomists, can be deficient for proponents of Linnaean taxonomy. Undeniably, integrative taxonomy, in which morphology supplemented with molecular and other data e.g., biology, ecology; (Kaiser et al., 2018;Jakiel et al., 2019Jakiel et al., , 2020, allows to reliable "group related species into genealogical trees, which represent the evolutionary lineage of modern organisms from common ancestors" (Paterlini, 2007). It serves an ideal way for establishing any new taxa. Nevertheless, decent quality in molecular data is extremely difficult to obtain when studying small deep-sea crustaceans, as they are often represented by single and small-sized specimens, or when historical collections are inappropriate for molecular analysis, i.e., fixed/preserved with formalin. For this reason, only requisite preservation and processing of the collection warrant successful molecular investigations (Riehl et al., 2014).
The decision here to establish the family Hamatipedidae is based solely on morphological observation and focused primarily on a unique setation of the carpus of pereopods 4-6, that has uniquely short, robust and bent spine that was termed a "hook" when the type-genus Hamatipeda was established (Błażewicz-Paszkowycz, 2007) to emphasize their unique character. Here, the three new species, whose ornamentation of these legs clearly indicates close affinity with earlier described species of Hamatipeda, are supplemented with two species, related, but sufficiently different to warrant two new genera (Rakaduta and Yarutanais) and place them in the new family.
Ornamentation and setation of crustacean legs are important components in understanding evolutionary relationships of modern organisms and their ancestors. In the most recent system proposed by Garm and Watling (2013), which simplified earlier setae classification (Garm, 2004;Garm and Watling, 2013), the setae were divided into seven categories depending on the function, ornamentation, articulation and the presence of terminal/subterminal pore that extends to an internal lumen and innervation ( Figure 8D). The carpal spines (= hooks) which are diagnostic characters for the Hamatipedidae might be classified as cuspidate setae in Garm and Watling's classification since they lack a terminal pore and reveal residual articulation (Figures 8B,C,E) unlike setae ( Figure 8F). Loss of flexibility and articulation of the setae implies their purely mechanical function related for tube-life. Imaging of prickly tubercles ( Figure 8G) shows that they are a separate structure from the three (spinulate) spines on the carpus and are probably derived from microtrichia and associated region of the carpal cuticle.
The low abundance of deep-sea populations often represented by a few individuals in the samples precludes studying a life cycle of deep-sea Tanaidacea. The knowledge we currently have on life history and reproductive strategies of deep water tanaids comes from observations on only a few shallow-water species that we extrapolate to deepwater species (see Esquete et al., 2012;Rumbold et al., 2014;Gellert and Błażewicz, 2018;Stępień et al., 2021). The material we investigated was unique, as one species -H. mojito was represented by 127 individuals at different developmental stages, which allowed us to make a series of measurements of total body length, body segments and uropodal rami. Our results have indicated the presence of two postmarsupial manca stages, as those observed for several shallow-water species (e.g., Bückle Ramírez, 1965;Fonseca and D'Incao, 2003). Although we did not observe females with developed oostegites in our material (neither fully developed nor oostegite buds), some neuters were clearly bigger than others. Without a thorough histological analysis assessing the degree of ovarian development, it is impossible to determine unequivocally the life history of H. mojito; however, it can be assumed that this species may breed at least twice in a lifetime, like other shallowwater tanaidomorphs (e.g., Lang, 1952;Bückle Ramírez, 1965;Johnson and Attramadal, 1982;Błażewicz-Paszkowycz, 2001;Toniollo and Masunari, 2007;Bamber, 2014). Our data also demonstrate that the last undeveloped last thoracomere (pereonite-6) of H. mojito grows about twice as fast as other pereonites. A similar observation was made for the pereonite-5 although it grows slower than in pereonite-6. Nevertheless, relative length of the last two pereonites cannot serve as a reliable diagnostic character. Conversely, the length of the uropod rami of M. mojito is constant during ontogenesis, offering a favorable diagnostic character.
Discovering and understanding the biodiversity of the deepest parts of the ocean is written in the priorities of recent marine biology, that is essential for efficient protection of the fragile deep-sea ecosystems. The pressure to apply modern and sophisticated research methods discourages us from focusing on unworked historical collections. Our results, however, demonstrate that investigation of even a small part of historical materials can substantially increase the knowledge of deep-sea diversity. This serves as a reference point for future analyses crucial for developing conservation strategies, and particularly important in the context of the global warming observed in recent decades, which affects also still unknown deep sea.

AUTHOR CONTRIBUTIONS
MG: taxonomic identification, statistical, and manuscript writing. MB: concept of the manuscript, taxonomic identification, manuscript writing, and discussion. GB: manuscript writing and discussion. AS: statistical analysis and manuscript writing. MS: confocal imaging. All authors contributed to the article and approved the submitted version.