Introduction
The Mediterranean Sea has historically been one of the best-known marine areas in terms of Kinorhyncha fauna (Neuhaus, Reference Neuhaus and Schmidt-Rhaesa2013). Since the original works of Karl Zelinka, one of the most important researchers in the phylum during the late 19th and early 20th century (Zelinka, Reference Zelinka1928), numerous taxonomic contributions have focused on describing the mud dragons inhabiting the Mediterranean waters (e.g. Higgins, Reference Higgins1978; Sánchez et al., Reference Sánchez, Pardos, Herranz and Benito2011; Dal Zotto, Reference Dal Zotto2015). However, it is not uncommon to find new Mediterranean kinorhynchs still in recent days, especially in less explored regions (e.g. Yildiz et al., Reference Yıldız, Sørensen and Karaytuğ2016; Sánchez et al., Reference Sánchez, García-Herrero, García-Gómez and Pardos2018; Yamasaki et al., Reference Yamasaki, Neuhaus and George2018; Dal Zotto et al., Reference Dal Zotto, Neuhaus, Yamasaki and Todaro2019).
During a survey off the coast of Rovinj (Croatia, northern Adriatic Sea), a yet undescribed species of Meristoderes Herranz et al., Reference Herranz, Thormar, Benito, Sánchez and Pardos2012 was discovered in shallow waters. This echinoderid genus is characterised by partial cuticular divisions in lateroventral or ventrolateral position (corresponding to the tergosternal junction) on segment 2, so that the corresponding cuticular plate is not entirely complete (Herranz et al., Reference Herranz, Thormar, Benito, Sánchez and Pardos2012). Kinorhynch species previously known from the coasts of Rovinj are Antygomonas incomitata Nebelsick, 1990, Centroderes spinosus (Reinhard, 1881), Condyloderes agnetis Dal Zotto et al., 2019, Co. multispinosus (McIntyre, 1962), Echinoderes capitatus (Zelinka, 1912) and presumably E. gerardi Higgins, 1978 (Zelinka, Reference Zelinka1928; Nebelsick, Reference Nebelsick1990, Reference Nebelsick1992a, Reference Nebelsick1992b, Reference Nebelsick1993; Neuhaus et al., Reference Neuhaus, Pardos, Sørensen and Higgins2013; Dal Zotto et al., Reference Dal Zotto, Neuhaus, Yamasaki and Todaro2019). The latter species was reported by Zelinka (Reference Zelinka1928) as Echinoderes dujardinii Claparède, 1863, however, a recent review of both species by Sørensen et al. (Reference Sørensen, Goetz, Herranz, Chang, Chatterjee, Durucan, Neves, Özlem, Norenburg and Yamasaki2020) suggested that reports of E. dujardinii from the Mediterranean Sea are likely to correspond to E. gerardi.
Meristoderes is a moderately diverse genus of Kinorhyncha, currently numbering nine species. Since its monophyly is controversial (Sørensen et al., Reference Sørensen, Dal Zotto, Rho, Herranz, Sánchez, Pardos and Yamasaki2015; Herranz et al., Reference Herranz, Stiller, Worsaae and Sørensen2022), further phylogenetic analyses are still needed to determine its taxonomic validity. Nevertheless, this contribution sticks to the genus' defining morphology, assigning the newly discovered species to Meristoderes.
The present work highlights the need for additional meiofaunal samplings, even in areas relatively well known in terms of kinorhynch fauna, to determine the species inhabiting a given geographical area and to increase the knowledge of frequently overlooked animal groups, such as the mud dragons.
Material and Methods
Sandy sediment samples were collected on 20–21 June 2022 from a shallow subtidal depth of 12 m near Rovinj, northern Adriatic Sea, (Figure 1; Table 1) using a Higgins' meiobenthic dredge. Meiofauna were extracted from the sediment with the bubble-and-blot method (Higgins and Thiel, Reference Higgins and Thiel1988; Sørensen and Pardos, Reference Sørensen and Pardos2008, Reference Sørensen, Pardos and Smith-Rhaesa2020) and preserved in 96% ethanol.
Map showing the sampling area. (A) General map of the Western Mediterranean Sea. The green box shows the specific sampling area. (B) Detailed map of the Istrian Peninsula; blue dots show additional samples (see Table 1); orange dot shows the sample where the new species was found.
Records of Meristoderes zmaj sp. n. accompanying fauna collected in the vicinity of Rovijn, with sediment granulometry data. Bold font indicates the new species
After extracting the meiofauna, remaining sediment samples were preserved in 96% ethanol and air-dried to remove debris. Sediment granulometry was then determined following the methods given in Guitián and Carballas (Reference Guitián and Carballas1976).
Kinorhyncha specimens were sorted under a ZEISS Stemi SV6 stereomicroscope. For light microscopy, kinorhynchs were dehydrated through a series of glycerine and were kept in 100% glycerine for 24 h. Subsequently, they were mounted on glass slides with dimethyl hydantoin formaldehyde resin (DMHF). Specimens were studied and photographed with an Olympus BX51 microscope with differential interference contrast optics equipped with an Olympus DP70 camera. For scanning electron microscopy (SEM), the animals were transferred to 100% ethanol and then chemically dried through a gradient of hexamethyldisilazane (HMDS) and ethanol. For their observation, specimens were mounted on stubs, sputter coated with gold and examined with a JEOL Ltd. JSM-6335F at CNME (National Centre for Electron Microscopy, Complutense University of Madrid). Line art illustrations and image compositions were done with Adobe Photoshop and Illustrator 2022.
Identification to genus level was done following the keys provided in Sørensen and Pardos (Reference Sørensen, Pardos and Smith-Rhaesa2020). Taxonomic measurements were done following the procedures provided in González-Casarrubios et al. (Reference González-Casarrubios, Cepeda, Pardos, Neuhaus, Yamasaki, Herranz, Grzelak, Maiorova, Adrianov, Dal Zotto, Di Domenico, Landers and Sánchez2023). Measurements can be consulted in the Kinorhyncha Measurement Database (González-Casarrubios and Yamasaki, Reference González-Casarrubios and Yamasaki2022) and in the additional material of the present contribution (see Supplementary Table S1). The type material of the new species is deposited at the Natural History Museum of Denmark (NHMD).
Results
Ten Kinorhyncha species were found in the soft sediment samples taken in the northern Adriatic Sea (Table 1), namely Cristaphyes carinatus (Zelinka, 1912), E. capitatus, E. ferrugineus Zelinka, 1928, E. gerardi, E. hispanicus Pardos et al., 1998, Pycnophyes communis Zelinka, 1908, P. robustus Zelinka, 1928, P. zelinkaei Southern, 1914 and Semnoderes armiger Zelinka, 1928, plus the new species of Meristoderes which is herein formally described.
Description of the new species
Class Cyclorhagida (Zelinka, 1896)
Family Echinoderidae Carus, 1885
Genus Meristoderes Herranz et al., 2012
Meristoderes zmaj sp. n.
urn:lsid:zoobank.org:act:111E50DB-0478–46C3-A23A-77479A294289
(Figures 2–6 and Tables 2 & 3)
Line art drawing of adults of Meristoderes zmaj sp. n. (A) Female, dorsal overview. (B) Female, ventral overview. (C) Male, dorsal view of segments 10–11. (D) Male, ventral view of segments 10–11. dpl, dorsal placid; id, incomplete division; lbh, long bracteate hairs; ldss, laterodorsal sensory spots; ldtu, laterodorsal tube; ltas, lateral terminal accessory spines; lts, lateral terminal spines; lvgcoI, lateroventral type 1 glandular cell outles; lvtu, lateroventral tube; mdgcoI, middorsal type 1 glandular cell outlet; mds, middorsal spine; mdss, middorsal sensory spot; mlss, midlateral sensory sopt; mltu, midlateral tube; mvpl, midventral placid; pdgcoI, paradorsal type 1 glandular cell outlet; pdss, paradorsal sensory spot; ppf, primary pectinate fringe; ps, penile spines; sdss, subdorsal sensory spots; sdtu, subdorsal tube; te, tergal extensions; vlss, ventrolateral sensory spots; vltu, ventrolateral tube; vmgcoI, ventromedial type 1 glandular cell outlet; vmss, ventromedial sensory spots. Number after abbreviations indicate the corresponding segment. Scalebar: 100 μm.
Light micrographs of the holotype of Meristoderes zmaj sp. n. the main trunk characters. (A) Dorsal view of segments 1–4. (B) Ventral view of segments 1–4. (C) Dorsal view of segments 4–6. (D) Ventral view of segments 4–6. (E) Dorsal view of segments 7–8. (F) Ventral view of segments 7–8. id, incomplete division; ltas, lateral terminal accessory spines; lts, lateral terminal spines; lvs, lateroventral spine; lvtu, lateroventral tube; mds, middorsal spine; ppf, primary pectinate fringe; sdtu, subdorsal tube; vltu, ventrolateral tube. Number after abbreviations indicates the number of the corresponding segment. Sensory spots marked as dashed circles; type 1 glandular cell outlets marked as continuous circles. Scalebars: A–F: 10 μm.
Light micrographs of the holotype (A–C, E) and paratype (D) of Meristoderes zmaj sp. n. showing overviews and detailed trunk characters. (A) Ventral overview. (B) Close-up of the incomplete division and ventrolateral tube of segment 2. (C) Ventral view of segments 10–11. (D) Detail of the midventral long bracteate hairs. id, incomplete division; ltas, lateral terminal accessory spines; lts, lateral terminal spines; te, tergal extensions; vltu, ventrolateral tube. Scalebars: A: 50 μm; B–D: 10 μm.
Scanning electron micrographs of additional female of Meristoderes zmaj sp. n. showing overviews and detailed trunk characters. (A) Dorsal overview. (B) Dorsal view of segments 4–5. (C) Dorsal view of segments 8–9. (D) Dorsal view of segments 6–7. (E) Dorsal view of segments 10–11. ltas, lateral terminal accessory spines; lts, lateral terminal spines; mds, middorsal spine; ppf, primary pectinate fringe. Number after abbreviations indicate the number of the corresponding segment. Sensory spots marked as dashed circles; type 1 glandular cell outlets marked as continuous circles. Scalebars: A: 100 μm; B–E: 10 μm.
Scanning electron micrographs of additional female of Meristoderes zmaj sp. n. showing overviews and detailed trunk characters. (A) Lateral overview. (B) Lateral view of segments 1–2. (C) Detail on the middorsal sensory spot of segment 2. (D) Detail on the acicular spine and paradorsal sensory spots of segment 6. (E) Dorsal view of segments 10–11. (F) Lateral view of segments 10–11. (G) Close-up on the laterodorsal tube of segment 10. ltas, lateral terminal accessory spines; lts, lateral terminal spines; mds, middorsal spine; mltu, middlateral tube; ppf, primary pectinate fringe; sdtu, subdorsal tube; ss, sensory spot; te, tergal extension. Number after abbreviations indicate the number of the corresponding segment. Sensory spots marked as dashed circles; type 1 glandular cell outlets marked as continuous circles. Scalebars: A: 100 μm; B, E–F: 10 μm; C, G: 1 μm; D: 3 μm.
Measurements of female holotype (NHMD – 1699747) and male paratype (NHMD – 1699748) of Meristoderes zmaj sp. n. ac, acicular spine; CL, cumulative length; LD, laterodorsal; LTAS, lateral terminal accessory spines; LTS, lateral terminal spines; LV, lateroventral; MD, middorsal; ML, midlateral; MSW, maximum external width; S, segment; SD, subdorsal; SW, standard sternal width (measured at segment 10); TL, total length; tu, tube; VL, ventrolateral. Number after abbreviations indicate the corresponding segment. All measurements are taken in microns (μm) unless is specified
Summary of nature and arrangement of cuticular characters of Meristoderes zmaj sp. n. ac, acicular spine; gcoI, type 1 glandular cell outlet; LA, lateral accessory; LD, laterodorsal; ltas, lateral terminal accessory spines; lts, lateral terminal spines; LV, lateroventral; MD, middorsal; ML, midlateral; ne, nephridiopore; PD, paradorsal; ps, penile spines; SD, subdorsal; SL, sublateral; ss, sensory spot; tu, tube; VL, ventrolateral; VM, ventromedial. ♂ and ♀ shows dimorphic characters
Material examined
Holotype. Adult female, collected on 20 June 2022 at Rovinj (Croatia, northern Adriatic Sea): 45°04′30.1″N 13°36′39.5″E at 12 m depth; mounted in DMHF, deposited at NHMD under accession number: NHMD – 1699747.
Paratype. Adult male, same collection data as holotype, deposited at NHMD under accession number: NHMD – 1699748.
Additional material. Adult female, same collection data as holotype, mounted for SEM, stored at the UCM meiofauna collection.
Diagnosis
Meristoderes with middorsal acicular spines on segments 4, 6 and 8 and lateroventral acicular spines on segments 6–9, progressively increasing in length towards the posterior segments. Long tubes in subdorsal, midlateral and ventrolateral positions of segment 2 and in lateroventral position of segment 5, and short tubes in laterodorsal position on segment 10. Tubes on segment 10 express sexual dimorphism in length, being longer in males. Type 2 glandular cell outlets and female papillae absent. Lateral terminal spines long and slender (LTS/TL ratio of ca. 75–78%).
Etymology
The species is named after Zmaj (змај), a medieval representation of a dragon-like, giant reptilian creature from the Slavic folklore. In the Croatian mythology, Zmaj were powerful beings forces of good who protected mankind from evil.
Description
Adult with head, neck and 11 trunk segments. See Table 2 for measurements and dimensions, and Table 3 for summary of spine, tube, nephridiopore, glandular cell outlet and sensory spot locations.
Head. With retractable mouth and introvert. None of the examined specimens had the introvert everted, hence no details on number, arrangement and morphology of the oral styles and scalids can be provided.
Neck. With 16 trapezoidal placids. Midventral placid widest (ca. 12 μm wide at base, 12–13 μm long), remaining ones narrower (ca. 6–8 μm wide at base, 12–13 μm long) (Figures 2A, B). Four dorsal and two ventral trichoscalid plates associated with trichoscalids; dorsal trichoscalid plates rounded, small; ventral ones larger, rhomboidal.
Trunk. With 11 cuticular segments (Figures 2A, B, 4A, 5A, 6A). Segment 1 as a closed cuticular ring; segment 2 as a cuticular ring with incomplete tergosternal divisions in lateroventral/ventrolateral position and a midventral fold; segments 3–11 with one tergal and two sternal plates (Figures 2A, B, 3A, B, 4B). Sternal plates reach their maximum width at segment 8, tapering towards the posterior segments; sternal plates narrow compared to the total trunk length (MSW8/TL ratio ca. 22%), giving the animal a slender outline (Figures 2A, B, 4A, 5A, 6A). Cuticular hairs acicular, bracteated (except for those of segment 1), emerging from rounded to oval perforation sites (Figures 5B–E, 6B, E, F). Cuticular hairs distributed in 1–2 straight, transverse rows on segment 1; in 2–3 straight, transverse rows on segment 2 and in 3–9 rows becoming wavy in ventrolateral and subdorsal positions on segments 3–10; sternal plates of segments 3–6 with a patch of 3–4 long bracteated hairs in paraventral position and those of segments 7–10 with a paraventral patch of regular-sized hairs (Figures 2A, B, 4D). Primary pectinate fringe long, straight, serrated, with equal length tips (Figures 2A, B, 3B, 5D, 6F). Secondary pectinate fringe not observed.
Segment 1. Without spines and tubes. Type 1 glandular cell outlets in middorsal and lateroventral positions. Sensory spots in subdorsal, laterodorsal and ventromedial positions. Sensory spots on this and following segments oval, with one or two central pores surrounded by 3–5 concentric rings of micropapillae, sometimes flanked by a pair of long hairs (Figures 2A, B, 3A, B, 6B).
Segment 2. With long tubes in subdorsal, midlateral and ventrolateral positions. Type 1 glandular cell outlet in middorsal position. Sensory spots in middorsal (posterior to the glandular cell outlet), laterodorsal and ventromedial positions (Figures 2A, B, 3A, B, 4B, 6B).
Segment 3. Without spines and tubes. Type 1 glandular cell outlet in middorsal position. Sensory spots in subdorsal and midlateral positions (Figures 2A, B, 3A, B).
Segment 4. With long middorsal acicular spine surpassing the posterior margin of the following two to three segments. Type 1 glandular cell outlets in paradorsal and ventromedial positions (Figures 2A, B, 3A, D, 5B).
Segment 5. With long tubes in lateroventral position. Type 1 glandular cell outlets in middorsal and ventromedial positions. Sensory spots in subdorsal, midlateral and ventromedial positions (Figures 2A, B, 3C, D, 5B).
Segment 6. With long middorsal acicular spine surpassing the posterior margin of the two following segments, longer than that of segment 4, and also with long acicular spines in lateroventral position. Type 1 glandular cell outlets in paradorsal and ventromedial positions. Sensory spots in paradorsal, midlateral and ventromedial positions (Figures 2A, B, 3C, D, 5D, 6D).
Segment 7. With long acicular spines in lateroventral position. Type 1 glandular cell outlet in middorsal and ventromedial positions. Sensory spots in subdorsal, midlateral and ventromedial positions (Figures 2A, B, 3E, F, 5D).
Segment 8. With long middorsal acicular spine surpassing the posterior margin of the tergal extensions, longer than that of segment 6, and also with long acicular spines in lateroventral position. Type 1 glandular cell outlets in paradorsal and ventromedial positions. Sensory spots in paradorsal and midlateral positions (Figures 2A, B, 3E, B, 5C).
Segment 9. With long acicular spines in lateroventral position. Type 1 glandular cell outlets in paradorsal and ventromedial positions. Sensory spots in paradorsal, subdorsal, midlateral and ventrolateral positions (Figures 2A, B, 5C). Nephridiopore in sublateral position.
Segment 10. With laterodorsal tubes differing in length among sexes (those of males slightly longer). Two type 1 glandular cell outlets in middorsal position, longitudinally aligned. Sensory spots in subdorsal position (Figures 2A–D, 4C, 5E, 6E–G).
Segment 11. With long, slender lateral terminal spines (LTS/TL ratio ca. 75–78%). Females with paired, relatively short lateral terminal accessory spines (LTAS/LTS ca. 17%). Males with three pairs of penile spines, first and third pairs longer and filiform, second pair shorter and thicker. Type 1 glandular cell outlet in middorsal position. Two pairs of sensory spots in subdorsal position, one on central position of the segment and the other one on the tip of the tergal extensions. Hairy middorsal protuberance conspicuous in SEM observation. Tergal extensions triangular, long, distally pointed (Figures 2A–D, 4C, 5E, 6E, F).
Discussion
Taxonomic remarks of the new species
The new species belongs to the genus Meristoderes as it fulfils all the diagnostic characters of Echinoderidae and, in addition, has a single cuticular plate on segment 2 with incomplete subcuticular divisions in a lateroventral/ventrolateral position, which allows it to be differentiated from other echinoderid genera (Herranz et al., Reference Herranz, Thormar, Benito, Sánchez and Pardos2012; Sørensen and Pardos, Reference Sørensen, Pardos and Smith-Rhaesa2020). Given that the partial ventral fissures characteristic of Meristoderes as well as that the existence of the genus is questioned according to phylogenetic analyses, the new species is then compared with all members of the Echinoderidae.
Regarding Meristoderes, the new species can be distinguished from its congeners by its spine and tube pattern. Meristoderes zmaj sp. n. has middorsal spines on segments 4, 6 and 8 and lateroventral spines on segments 6–9. This spine distribution is shared with four species: Meristoderes boylei Herranz and Pardos, 2013, M. elleae Sørensen et al., 2013, M. herranzae Sørensen et al., 2013 and M. macracanthus Herranz et al., 2012 (Herranz et al., Reference Herranz, Thormar, Benito, Sánchez and Pardos2012; Herranz and Pardos, Reference Herranz and Pardos2013; Sørensen et al., Reference Sørensen, Rho, Min, Kim and Chang2013). The remaining congeners have middorsal spines on more (segments 4–8 in M. taro Sánchez et al., 2019) or fewer segments (segments 6 and 8 in M. okhotensis Adrianov and Maiorova, 2018 and only on segment 4 in M. galatheae Herranz et al., 2012), or lack lateroventral spines on segments 6 and 7 (M. glaber Sørensen et al., 2013 and M. imugi Sørensen et al., 2013) (Sørensen et al., Reference Sørensen, Rho, Min, Kim and Chang2013; Adrianov and Maiorova, Reference Adrianov and Maiorova2018; Sánchez et al., Reference Sánchez, Pardos and Martínez Arbizu2019).
Additionally, the new species has three pairs of long tubes on segment 2 in subdorsal, midlateral and ventrolateral positions. Only M. glaber, M. herranzae, M. imugi and M. okhotensis have similar tubes on segment 2 (Sørensen et al., Reference Sørensen, Rho, Min, Kim and Chang2013; Adrianov and Maiorova, Reference Adrianov and Maiorova2018). However, M. glaber and M. imugi lack tubes in lateral position, M. okhotensis has an extra pair in laterodorsal position and the dorsal ones of M. herranzae are located in laterodorsal instead of subdorsal position and it also lacks the lateral ones. Taking all into account, it seems that M. herranzae is the most similar species to M. zmaj sp. n., but the possession of lateral accessory tubes on segment 8 and only two pairs of these structures on segment 2 in the former allows their differentiation (Sørensen et al., Reference Sørensen, Rho, Min, Kim and Chang2013).
Finally, M. boylei, M. elleae, M. herranzae, M. imugi and M. macracanthus (Herranz et al., Reference Herranz, Thormar, Benito, Sánchez and Pardos2012; Herranz and Pardos, Reference Herranz and Pardos2013; Sørensen et al., Reference Sørensen, Rho, Min, Kim and Chang2013) have conspicuous extra tubes in the lateral series besides the lateroventral spines. All of them have these tubes in lateral accessory position, except for M. imugi and M. okhotensis in which tubes are located sublaterally and midlaterally, respectively (Herranz et al., Reference Herranz, Thormar, Benito, Sánchez and Pardos2012; Herranz and Pardos, Reference Herranz and Pardos2013; Sørensen et al., Reference Sørensen, Rho, Min, Kim and Chang2013; Adrianov and Maiorova, Reference Adrianov and Maiorova2018). Therefore, M. zmaj sp. n. follows a general arrangement of cuticular appendages, but the combination of spine and tube pattern is a unique within the genus.
Compared to other species of Echinoderidae, the new species can also be distinguished by its unique pattern of tubes and spines. The presence of middorsal spines on segments 4, 6 and 8, lateroventral tubes on segment 5 and lateroventral spines on segments 6–9 is the second most common pattern within the family, shared by 28 species. Nevertheless, 20 of them also possess tubes in the lateral series on segment 8, a feature absent in the new species. Only eight species share with M. zmaj sp. n. the referred distribution of spines and the absence of lateral tubes in segment 8, namely E. apex Yamasaki et al., Reference Yamasaki, Neuhaus and George2018, E. bermudensis Higgins, Reference Higgins1982, E. hamiltonorum Sørensen et al., Reference Sørensen, Rohal and Thistle2018, E. joyceae Landers and Sørensen, Reference Landers and Sørensen2016, E. legolasi Grzelak and Sørensen, Reference Grzelak and Sørensen2022, E. multiporus Yamasaki et al., Reference Yamasaki, Neuhaus and George2018, E. schwieringae Yamasaki et al., Reference Yamasaki, Neuhaus and George2019 and E. shenlong Sánchez et al., Reference Sánchez, Pardos and Martínez Arbizu2019. However, all these species have only one pair of tubes on segment 2 (in lateroventral or ventrolateral position), except for E. abbreviatus Higgins, Reference Higgins1983 (subdorsal and lateroventral tubes), E. legolasi (no tubes) and E. shenlong (no tubes), whereas M. zmaj sp. n. has three pairs of tubes on this segment. Several species with the same spine pattern resemble the new species by also having three tubes on segment 2, namely E. belenae Pardos et al., Reference Pardos, Herranz and Sánchez2016, E. hispanicus, E. newcaledoniensis Higgins, Reference Higgins1967, E. peterseni Higgins and Kristensen, Reference Higgins and Kristensen1988, E. xiphophorus Adrianov and Maiorova, Reference Adrianov and Maiorova2021; but, as referred above, all of them possess tubes on segment 8, among other differences. Therefore, the pattern of spines and tubes of M. zmaj sp. n. is also unique within the whole family.
Kinorhyncha community
Among the six kinorhynch species previously reported from Rovinj, named A. incomitata, C. spinosus, C. agnetis, C. multispinosus, E. capitatus and E. gerardi (Zelinka, Reference Zelinka1928; Nebelsick, Reference Nebelsick1990, Reference Nebelsick1992a, Reference Nebelsick1992b, Reference Nebelsick1993; Higgins, Reference Higgins1969; Neuhaus et al., Reference Neuhaus, Pardos, Sørensen and Higgins2013; Dal Zotto et al., Reference Dal Zotto, Neuhaus, Yamasaki and Todaro2019), only the two Echinoderes were also found in the present survey (Table 1). Most of the remaining species collected in the samples represented new reports for Croatia, but their presence is not an exceptional finding, as they were already known from the nearby waters of Trieste (less than 100 km away, northeast Italy). That is the case of C. carinatus, E. capitatus, E. ferrugineus, P. communis, P. robustus and S. armiger (Zelinka, Reference Zelinka1928; Nebelsick, Reference Nebelsick1992b; Yamasaki and Dal Zotto, Reference Yamasaki and Dal Zotto2019).
It is noteworthy that four of the local species were not found in our study (Zelinka, Reference Zelinka1928; Nebelsick, Reference Nebelsick1990, Reference Nebelsick1992a, Reference Nebelsick1992b, Reference Nebelsick1993; Higgins, Reference Higgins1969; Neuhaus et al., Reference Neuhaus, Pardos, Sørensen and Higgins2013; Dal Zotto et al., Reference Dal Zotto, Neuhaus, Yamasaki and Todaro2019). This fact could be partly explained by the depth of the samples, most of them collected in very shallow waters, whereas C. agnetis was discovered from relatively deep areas off Rovinj (Dal Zotto et al., Reference Dal Zotto, Neuhaus, Yamasaki and Todaro2019) and C. spinosus and Condyloderes multispinosus are commonly collected in deeper sediment samples (Neuhaus et al., Reference Neuhaus, Pardos, Sørensen and Higgins2013). All this suggests that future samplings around Croatia could provide numerous novel reports and even hidden species of kinorhynchs that are still waiting to be discovered.
Supplementary material
The supplementary material for this article can be found at https://doi.org/10.1017/S0025315423000875.
Acknowledgements
This contribution was partially funded by the project Fauna Ibérica XII: Escalidóforos de la Península Ibérica y Baleares (PGC-2018 095851-B-C62), of the MICINN (Ministerio de Ciencia, Innovación y Universidades), Spain.
Author contributions
N. S. and F. P. designed the sampling. A. G.-C., N. S., D. C. and F. P. participated in the sampling campaign to collect the specimens. A. G.-C. separated, mounted, identified and photographed the specimens. A. G.-C., D. C. and N. S. wrote the manuscript. A. G.-C. and F. P. made the image compositions. All authors reviewed and accepted the latest version of the manuscript.
Competing interests
None.
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