Unrolling the Systematics of a Southeastern Pacific Chiton
1
Departamento de Ecología y Biodiversidad, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 8370251, Chile
2
Zoological Institute, Russian Academy of Sciences, Universitetskaya nab. 1, St. Petersburg 199034, Russia
*
Author to whom correspondence should be addressed.
Taxonomy 2024, 4(4), 850-861; https://doi.org/10.3390/taxonomy4040045
Submission received: 23 September 2024
/
Revised: 5 November 2024
/
Accepted: 28 November 2024
/
Published: 3 December 2024
Abstract
:The species Chiton echinatus was first described by Barmes in 1824. Subsequently, it has been allocated to several widely distributed genera (e.g., Acanthopleura, Enoplochiton, Mesotomura) within the subfamily Acanthopleurinae. In order to resolve this species’ taxonomic uncertainty, specimens were collected throughout its entire distribution (i.e. from Peru and Chile) and subjected to a series of morphological and phylogenetic analyses. Scanning electron microscopy was used to improve this species’ morphological description, whereas publicly available sequences were used to infer its phylogenetic position. Morphological and phylogenetic analyses suggest that this species merits its own genus, endemic to the Southeastern Pacific. Of the aforementioned genera, Mesotomura appears to be the most appropriate designation. Therefore, it is proposed that the name Mesotomura echinata be restored, and the range of this species be extended to 39° S.
1. Introduction
Barnes [1] described five species of chitons, two of which inhabit Peru and Chile (i.e., Chiton echinatus Barnes, 1824 and Chiton niger Barnes, 1824). However, they have undergone several taxonomic changes, and it is still unclear to which genus each belongs. Shortly after these species were described, Frembly [2] described several species of chitons from northern Chile, including Chiton spiniferus Frembly, 1827 and Chiton coquimbensis Frembly, 1827. Some years later Gray [3] described two new genera, Corephium Gray, 1847 and Enoplochiton Gray, 1847, to designate Corephium echinatus and Enoplochiton niger , respectively. In addition, he suggested that Chiton spiniferus and Chiton coquimbensis would be synonymies of Corephium echinatus and Enoplochiton niger. Subsequently, Pilsbry (1893) transferred Corephium echinatus to the genus Acanthopleura Guilding, 1829 and to the newly established subgenus Mesotomura Pilsbry, 1893, proposing the new combination Acanthopleura (Mesotomura) echinata. Pilsbry [4] also suggested that Corephium is a synonym of Mesotomura. Almost a century later, in the last revision of the genus Acanthopleura, Ferreira [5] suggested that E. niger should belong to Acanthopleura, since its perinotum scales resemble the spines of A. spinosa (Bruguière, 1792). In addition, Ferreira (1986) synonymized both Mesotomura and Enoplochiton with Acanthopleura. Currently, these species are classified as Acanthopleura echinata (Barnes, 1824) and Enoplochiton niger (Barnes, 1824) and are latitudinally distributed between 4–37° S and 12°–30° S, respectively [6]. Both species are the largest chiton species along Peru and Chile (A. echinata > 200 mm, and E. niger > 150 mm) [7].
New molecular phylogenetic hypotheses have suggested Acanthopleura echinata is the sister species of Enoplochiton niger [6,8,9,10], and Alnashiri et al. [11] suggested assigning A. echinata to the genus Enoplochiton after a detailed examination of morphological characters. However, morphological and molecular information suggest that both species are too distant to belong to the same genus.
The present study provides a detailed morphological description of Acanthopleura echinata whilst also offering a comparative analysis to its closest relatives. Moreover, this study integrates a new phylogenetic hypothesis to elucidate its phylogenetic position.
2. Materials and Methods
2.1. Sampling
From 2011 to 2023, 273 specimens of Acanthopleura echinata were collected from different localities in Peru and Chile (Figure 1, Table 1). The chitons were collected during low tide period (~1–3 h) in each locality. The collected chitons were relaxed with 5% ethanol in seawater, flattened and preserved in 96% ethanol.
2.2. Morphology
For each specimen body length (BL, mm) and valve width (I-VIII, mm) were measured using a digital caliper. Small chitons (BL < 50 mm) were selected for scanning electron microscopy (SEM) for morphological analysis of valves, perinotum scales, and radula. These structures were dissected, mounted on tape, critical-point dried, coated with gold, and examined with SEM.
2.3. Phylogeny
Sequences of Cytochrome Oxidase I (COI), 16S rRNA (16s) and 18S rRNA (18S) of chitons belonging to the family Chitonidae were retrieved from previous studies [8,9,10] which were deposited in GenBank (Table 2). The sequences were aligned using MUSCLE [12] as implemented in MEGA XI [13]. Phylogenetic reconstruction was conducted using Maximum Likelihood (ML) via the IQ-TREE online server [14] and using the hill-climbing NNI tree search strategy [15]. The ModelFinder option [16] was used under a partition scheme for each gene (16S+COI+18S). Ultrafast bootstrap analysis was used with 1000 iterations to obtain node support [17]. The genus Chaetopleura Shuttleworth, 1853 was included as a sister taxon and Acanthochitona crinita (Pennant, 1777) was used as an outgroup. The phylogenetic tree was edited and visualized with FigTree v1.4 [18]. Finally, genetic distances (K2P, [19]) between species were calculated in MEGA XI.
3. Results
3.1. Morphology
Systematics
Family: Chitonidae Rafinesque, 1815
Genus: Mesotomura Pilsbry, 1893
Mesotomura echinata (Barnes, 1824)
Synonyms: Chiton echinatus Barnes, 1824: 71, pl. 3, fig 4a, b. Chiton spiniferus Frembly, 1827: 196, suppl. pl. 16, fig. 6; Sowerby 1833, pl. 1, fig. 47. Acanthopleura (Mesotomura) echinata Pilsbry, 1893: 105. Acanthopleura echinata: Dall 1909: 180, 248, pl. 23, fig. 6; Marincovich 1973: 44, fig.100; Ferreira 1986: 264–266, figs. 104–106. (bibliography and synonymy) Osorio 2002: 52. Mesotomura echinata Thiele, 1929: 22.
Material examined: Eight specimens of Mesotomura echinata from Museo Nacional de Historia Natural Chile: MNHNCL 400054, MNHNCL 400055, MNHNCL 400056, MNHNCL 400058, MNHNCL 400059, MNHNCL 400087, MNHNCL 400089. Two specimens of Mesotomura echinata from Zoological Institute, Russian Academy of Sciences, St. Petersburg, Russia: ZIN 2589 and ZIN 2591.
Comparative material examined: 13 specimens of Enoplochiton niger from Museo Nacional de Historia Natural Chile: MNHNCL 400050, MNHNCL 400051, MNHNCL 400052, MNHNCL 400094, MNHNCL 400096. One specimen of Enoplochiton niger from Zoological Institute, Russian Academy of Sciences, St. Petersburg, Russia: ZIN 2590.
Redescription: Body elongate, oval, depressed, up to 230 mm long, valves low (dorsal elevation 0.23–0.29) (Figure 2). Tegmentum varies in color: juveniles regularly show greenish color, turning with age to brownish with olive green tones and in some specimens with a bluish color. The central areas of the intermediate valvesshow a wide, longitudinal, dark brown line across the jugal area. Tegmentum sometimes with small blue spots. Larger individuals (BL > 50 mm) usually covered with red algae (i.e., Gelidium) on all valves and coralline algae on the spines (Figure 2).
Figure 2.
Pictures of live specimens of Mesotomura echinata at (A) Caleta Punta Arenas, Chile (~22° S) and (B) Antofagasta, Chile (~23° S).
Figure 2.
Pictures of live specimens of Mesotomura echinata at (A) Caleta Punta Arenas, Chile (~22° S) and (B) Antofagasta, Chile (~23° S).
Head valve semicircular (Figure 3A). Intermediate valves with a wavy front margin, convex at both sides of a narrow, strongly, forwardly produced jugal part; side margins little rounded, hind margin weakly concave at both sides of a pointed protruding apex, lateral areas little raised (Figure 3B,D,E). Tail valve semicircular, mucro posterior (Figure 3C,F). Head and tail valves are the smallest (mean width = 18.41 and 18.69 mm, respectively) with intermediate valves larger and in increasing width from II to V (Table 3).
Figure 3.
Valve morphology of Mesotomura echinata from Las Cruces (~33° S), Central Chile, collected on rocks, in intertidal pool, BL 28 mm (ZIN 2591), (A). Valve I, dorsal view. (B). Valve V, dorsal view. (C). Valve VIII, dorsal view. (D). Valve VII, detail of tegmentum in central and lateral areas. (E). Valve V, rostral view. (F). Valve VIII, lateral view.
Figure 3.
Valve morphology of Mesotomura echinata from Las Cruces (~33° S), Central Chile, collected on rocks, in intertidal pool, BL 28 mm (ZIN 2591), (A). Valve I, dorsal view. (B). Valve V, dorsal view. (C). Valve VIII, dorsal view. (D). Valve VII, detail of tegmentum in central and lateral areas. (E). Valve V, rostral view. (F). Valve VIII, lateral view.
Tegmentum sculpture is rather variable. The head valve, lateral areas of intermediate valves, and postmucronal areas of the tail valve are covered with radial rows of well-separated, roundish large pustules, with round ocelli, dispersed throughout. The jugum of the intermediate valves and antemucronal area of the tail valve are well separated by short grooves from the pleural areas of the valve, which are covered by longitudinal ribs, ten in intermediate valves and five in tail valve, on each side (Figure 3).
Figure 4.
Girdle ornamentation of Mesotomura echinata, Las Cruces (~33° S), Central Chile, collected on rocks in an intertidal pool, BL 28 mm (ZIN 2591), (A,B). Dorsal spike-like spines (aprox. Size) near the perinotum margin, surrounded by dorsal corpuscules and numerous sharply pointed spicules; (C). Closeup of two dorsal large spike-like spines separated by two dozen dorsal corpuscules; (D). ventral ribbed spicules.
Figure 4.
Girdle ornamentation of Mesotomura echinata, Las Cruces (~33° S), Central Chile, collected on rocks in an intertidal pool, BL 28 mm (ZIN 2591), (A,B). Dorsal spike-like spines (aprox. Size) near the perinotum margin, surrounded by dorsal corpuscules and numerous sharply pointed spicules; (C). Closeup of two dorsal large spike-like spines separated by two dozen dorsal corpuscules; (D). ventral ribbed spicules.
Articulamentum thick and white, with transverse, strongly engraved lines at the middle of valves, ventrally all valves show light brown coloration where insertion muscles attach, with coloration strongest towards the center. Sutural lamina large, rounded with an irregular pectinate insertion margin; jugal sinus connected by a short dentate jugal plate on the tail valve with a median indentation. Posterior valve with long insertion plate deeply pectinated outside, edge interrupted only by a single median-posterior slit. Slit formula 7–9/1/1–30, slits clear-cut, slit rays absent, eaves narrow, finely porous.
Girdle wide, green or dark reddish brown, dorsally covered with spike-like, bent spines (<8 mm long) and numerous small, calcareous, corpuscles (150–200 µm) (Figure 4). Margin of the perinotum devoid of large spines and small corpuscles but covered with small sharply pointed spicules (60–70 µm). Marginal needles small, sharply pointed (90–100 μm) with several obsolete riblets. Ventral side covered with small pointed spicules (50 × 30 µm) with five grooves on the upper surface (Figure 5A–C).
Radula 9 mm long in 28 mm specimen, with 43 transverse rows 164 of mature teeth (Figure 5D). Studied chiton with 71 adanal gills per side, which extend the whole length of the foot, nephridiopore situated between the 17th and 18th gills, gonopore situated between 20th and 21st gills from tail gills.
Distribution: This species inhabits is found from the intertidal to around 5 m depth, from Lobitos, Peru (−4.457817, −81.302748) to Biobio River, Chile (−36.806650, −73.176859) (Navarrete et al. 2020). In this study, we extend its distribution to Pilolcura, Chile (−39.666048, −73.352993).
Remarks: The main morphological differences between Mesotomura, Enoplochiton, and Acanthopleura are related to the structures of the perinotum and the shape of the insertion plates of the valves. Enoplochiton lacks insertion teeth on the terminal valve and has scales on the perinotum. Acanthopleura and Mesotomura have insertion teeth on the terminal plate, but these teeth are poorly developed in Mesotomura. Furthermore, Mesotomura is characterized by the presence of spikes, in contrast to the spines observed in Acanthopleura.
The main morphological features that distinguish Mesotomura from Enoplochiton are: (1) large dorsal spike-like spines (vs. separated, ribbed scales, of different sizes in Enoplochiton); (2) belt of sharply pointed dorsal spicules located above the girdle at the margin (which are absent in Enoplochiton; (3) radial rows of well-separated, rounded pustules on the head valve, lateral areas of the intermediate valves and antemucronal area of the tail valve (vs. concentric wavy grooves in Enoplochiton); (4) semicircular tail valve with posterior mucro (vs. triangular tail valve with terminal mucro in Enoplochiton); (5) slit formula 8/1/1-3 (vs. slit formula 8-9/1/0 (callus) in Enoplochiton); and (6) articulamentum white with small light brown spots in the middle of the valves (vs. articulamentum dark chocolate-brown in Enoplochiton).
Thus, we consider Chiton echinatus Barnes, 1824 as a representative of the genus Mesotomura.
3.2. Phylogeny
The ML phylogeny shows higher bootstrap values in all nodes (>90) supporting the monophyly of Chiton, Acanthopleura, Tonicia and Mesotomura+Enoplochiton (Figure 6), demonstrating that Mesotomura echinata is a sister species of Enoplochiton niger, and together they are a sister clade of Tonicia (Figure 6). This demonstrates that M. echinata does not belong in/to the genus Acanthopleura. Furthermore, the branch length found between M. echinata and E. niger (0.064–0.073) is greater than that found within the genera Tonicia (0.015–0.032) and Chiton (0.027–0.058), suggesting that M. echinata does not belong in the genus Enoplochiton. In addition, genetic distances of COI between M. echinata and E. niger (K2P:0.22492) were similar to comparisons of the former species with Acanthopleura (K2P: 0.24422–0.21557), Tonica (K2P: 0.21812–0.23453), and Chiton (K2P: 0.20878–0.26265) species, suggesting M. echinata and E. niger did not belong to the same genus.
4. Discussion
The detailed morphological descriptions complemented with the molecular phylogeny of the present study allow us to restore the taxonomic status of the genus Mesotomura. Of all the described genera, in which M. echinata has been historically included, Mesotomura is the most suitable, and thus we restore the name Mesotomura echinata.
4.1. Morphology
The sculptural elements of the tegmentum of M. echinata (i.e., longitudinal ribs and large pustules on lateral areas) are similar to those of the northern ecotypes of Tonicia calbucensis Plate, 1898 and T. chilensis (Frembly, 1827) [21], whereas the sculptural elements of Enoplochiton niger (i.e., postmucronal areas have radiating ribs) are more similar to those of T. swainsoni (G. B. Sowerby I, 1832) and T. forbesii P. P. Carpenter, 1857 [8,20]. Resemblence of the genera Mesotomura and Enoplochiton to the genus Tonicia is also found in the morphology of their egg hulls. Hull projection in Mesotomura echinata is cilindrical with six to seven spikes [22], which are similar to Tonicia [23] but different from the genera Acanthopleura Guilding, 1830 and Liolophura Pilsbry, 1893 [23,24].
The principal morphological distinctions between Mesotomura, Enoplochiton, and Acanthopleura pertain to the shape of the front margin of intermediate and tail valves, structures of the perinotum, and the configuration of the valve insertion plates. Mesotomura echinata differs from Acanthopleura species and E. niger by having a narrow margin covered by sharply pointed spicules [25]. Moreover, M. echinata contrasts from Acanthopleura by having conspicuous, transverse, strongly engraved lines in the central part of articulamentum; longitudinal grooves in the central area of intermediate and antemucronal areas of the tail valves; and wavy front margin in intermediate and tail valves. Enoplochiton is characterized by the absence of insertion teeth on the terminal valve and the presence of large scales on the perinotum [5]. In contrast, Acanthopleura and Mesotomura exhibit insertion teeth on the tail valve, although these are particularly poorly developed in Mesotomura [5]. The current morphological description and comparison allow us to resolve the taxonomic status of both Mesotomura and Enoplochiton species. The general appearance of both species (M. echinata and E. niger) is contrasting as they possess several notable differences in the size and shape of their valves and perinotum (Figure 7). The plates of both species contain concentric wavy striae and granules along the diagonal line. M. echinata also contains numerou radial granules (10–12) on the cephalic plate (Figure 3). The perinotum of Enoplochiton is thick and includes large and elongated scales (Figure 7). The plate morphology of E. niger is unique among species of the family Chitonidae inhabiting the Southeastern Pacific. For example, the tail plate (VIII) is elongated triangular, and the cephalic plate (I) is semicircular like most chitons (Figure 7). In addition, the apophyses of E. niger are dark brown to black, while most chitons (including M. echinata) have white apophyses.
4.2. Distribution
Mesotomura echinata is a common and abundant species in lower intertidal of Chile and Peru [6,7]. The distribution of this species has been recorded from Lobitos, Peru (−4.457817, −81.302748) to Biobio River, Chile (−36.806650, −73.176859) [6]. In this study, we extend its distribution around 300 km south to Pilolcura, Chile (−39.666048, −73.352993. Figure 7). This species was not known to occur further south than 37° S (Navarrete et al. 2020) which could be because it can become rare and difficult to find at its northernmost and southernmost distribution.
4.3. Phylogeny
Despite current classifications of Mesotomura echinata and Enoplochiton niger in the subfamily Acanthopleurinae, phylogenetic analyses from this study suggest a common ancestor of these two species with Tonicia, which would place them in the subfamily Toniciinae. At least part of the species from these subfamilies are now attributed to the genera Acanthopleura and Liolophura close by morphological characters to genus Onithochiton J. E. Gray, 1847. The kinship relationship of the last genus was confirmed even by the fact when describing Acanthopleura rehderi Ferreira, 1986. Ferreira [5] placed it in the subfamily Acanthopleurinae, but not in the subfamily Toniciinae, although all characters of the genus Onithochiton were present in this species. These comparisons suggest some Acanthopleurinae are Toniciinae and we need a revision of subfamilies inside Chitonidae.
The present study evidences the monophyly of Mesotomura and Enoplochiton as sister group of Tonicia as in support of previous studies [6,8,9,10,11]. The divergence of Enoplochiton, Mesotomura, and Tonicia was estimated during the Paleogene (~50 Mya) and for both species (Mesotomura and Enoplochiton) during the Eocene (~35 Mya) [8].
5. Conclusions
The present study clarifies the taxonomic confusion around several names of the species Mesotomura echinata. The morphological similarity of Mesotomura and Enoplochiton with Tonicia, its phylogenetic relatedness, and recent divergence times suggest all belong to the subfamily Toniciinae.
Author Contributions
C.M.I. conceptualization, sampling, analysis, writing. B.S. sampling, analysis, writing. All authors have read and agreed to the published version of the manuscript.
Funding
This research was funded by FONDECYT 1130266.
Data Availability Statement
Sequences used in this study are available on GenBank.
Acknowledgments
We are very grateful to Konstantin Benken (ZIN) for his technical assistance with SEM procedures, Katja Nefedova who prepared the digital plates. The research was performed using equipment of the “Taxon” Research Resource Center (http://www.ckp-rf.ru/ckp/3038/, accessed on 22 September 2024) of the Zoological Institute of the Russian Academy of Sciences (St. Petersburg) Center (ZIN). This work is based on the taxonomic collection of ZIN and was supported by the State scientific program “Taxonomy, biodiversity and ecology of invertebrates from Russian and adjacent waters of World Ocean, continental water bodies and damped areas” No. 122031100275-4. We Thanks to Felipe Torres and Adriana Halvonik-Sanchez the great help in the review and proofreading of this manuscript.
Conflicts of Interest
The authors declare no conflicts of interest.
References
- Barnes, D.H. Description of five species of Chiton. Am. J. Sci. Arts 1824, 7, 69–72. [Google Scholar]
- Frembly, J. A description of several new species of chitons, found on the coast of Chili, in 1825; with a few remarks on the method of taking and preserving them. Zool. J. 1827, 3, 193–205. [Google Scholar]
- Gray, J.E. On the genera of the family Chitonidae. Proc. Zool. Soc. Lond. 1847, 15, 63–70. [Google Scholar]
- Pilsbry, H.A. Polyplacophora. In Manual of Conchology; Tryon, G.W., Ed.; Academy of Natural Sciences: Philadelphia, PA, USA, 1893; Volume 14, pp. 129–350, pls. 31–68. [Google Scholar]
- Ferreira, A.J. A Revision of the Genus Acanthopleura Guilding, 1829 (Mollusca: Polyplacophora). Veliger 1986, 28, 221–279. [Google Scholar]
- Navarrete, A.H.; Sellanes, J.; Pardo-Gandarillas, M.C.; Sirenko, B.; Eernisse, D.J.; Camus, P.A.; Ojeda, F.P.; Ibáñez, C.M. Latitudinal distribution of polyplacophorans along the Southeastern Pacific coast: Unravelling biases in geographical diversity patterns. Mar. Biodiver. 2020, 50, 45. [Google Scholar] [CrossRef]
- Ibáñez, C.M.; Waldisperg, M.; Torres, F.I.; Carrasco, S.A.; Sellanes, J.; Cecilia, M.; Sigwart, J.D. Environmental and ecological factors mediate taxonomic composition and body size of polyplacophoran assemblages along the Peruvian Province. Sci. Rep. 2019, 9, 15934. [Google Scholar] [CrossRef]
- Ibáñez, C.M.; Eernisse, D.J.; Méndez, M.A.; Valladares, M.; Sellanes, J.; Sirenko, B.; Pardo-Gandarillas, M.C. Phylogeny, divergence times, and species delimitation of Tonicia (Polyplacophora: Chitonidae) from the Eastern Pacific Ocean. Zool. J. Linn. Soc. 2019, 186, 915–933. [Google Scholar] [CrossRef]
- Ibáñez, C.M.; Pardo-Gandarillas, M.C.; Méndez, M.A.; Sellanes, J.; Sigwart, J.; Sirenko, B. Phylogenetic position and morphological descriptions of Chiton species from the Southeastern Pacific. Zool. J. Linn. Soc. 2021, 191, 695–719. [Google Scholar] [CrossRef]
- Ibáñez, C.M.; Carter, M.J.; Aguilera, M.A.; Pardo-Gandarillas, M.C.; Rezende, E.L. Body size variation in polyplacophoran mollusks: Geographic clines and community structure along the Southeastern Pacific. Glob. Ecol. Biogeogr. 2021, 30, 1781–1795. [Google Scholar] [CrossRef]
- Alnashiri, H.; Thomas, L.; Thaikkottathil, M.; Philip, S.; Kutty, R.; Sivanpillai, S.; Abo Rasain, A.M. Phylogenetic Affinities of Acanthopleurinae Dall, 1889 Chitons (Mollusca: Polyplacophora: Chitonidae) from Jazan Coast in the Red Sea and Western Indo-Pacific. J. Mar. Sci. Eng. 2023, 11, 158. [Google Scholar] [CrossRef]
- Edgar, R.C. MUSCLE: Multiple sequence alignment with high accuracy and high throughput. Nucleic Acids Res. 2004, 32, 1792–1797. [Google Scholar] [CrossRef] [PubMed]
- Tamura, K.; Stecher, G.; Kumar, S. MEGA11: Molecular evolutionary genetics analysis version 11. Mol. Biol. Evol. 2021, 38, 3022–3027. [Google Scholar] [CrossRef] [PubMed]
- Trifinopoulos, J.; Nguyen, L.T.; Von Haeseler, A.; Minh, B.Q. W-IQ-TREE: A fast-online phylogenetic tool for maximum likelihood analysis. Nucleic Acids Res. 2016, 44, W232–W235. [Google Scholar] [CrossRef] [PubMed]
- Nguyen, L.T.; Schmidt, H.A.; Von Haeseler, A.; Minh, B.Q. IQ-TREE: A fast and effective stochastic algorithm for estimating maximum-likelihood phylogenies. Mol. Biol. Evol. 2015, 32, 268–274. [Google Scholar] [CrossRef]
- Kalyaanamoorthy, S.; Minh, B.Q.; Wong, T.K.F.; Von Haeseler, A.; Jermiin, L.S. ModelFinder: Fast model selection for accurate phylogenetic estimates. Nat. Methods 2017, 14, 587–589. [Google Scholar] [CrossRef]
- Minh, B.Q.; Nguyen, M.A.; Von Haeseler, A. Ultrafast approximation for phylogenetic bootstrap. Mol. Biol. Evol. 2013, 30, 1188–1195. [Google Scholar] [CrossRef]
- Rambaut, A. FigTree v1.4. 2009. Available online: http://tree.bio.ed.ac.uk/software/tracer (accessed on 11 June 2024).
- Kimura, M. A simple method for estimating evolutionary rate of base substitutions through comparative studies of nucleotide sequences. J. Mol. Evol. 1980, 16, 111–120. [Google Scholar] [CrossRef]
- Kaas, P.; Van Belle, R.A.; Strack, H.L. Monograph of Living Chitons. (Mollusca: Polyplacophora) 6, Suborder Ischnochitonina (Concluded): Schizochitonidae; Chitonidae; Additions to Volumes 1–5; Koninklijke Brill NV: Leiden, The Netherlands, 2006; 463p. [Google Scholar]
- Sirenko, B.I.; Ibáñez, C.M. Comparative morphology of Tonicia (Polyplacophora) geographical ecotypes from Southeastern Pacific. Ruthenica 2022, 33, 27–45. [Google Scholar] [CrossRef]
- Gaymer, C.F.; Guisado, C.; Brokordt, K.B.; Himmelman, J.H. Gonad Structure and Gamete Morphology of the Eastern South Pacific Chiton Acanthopleura echinata Barnes, 1824. Veliger 2004, 47, 141–152. [Google Scholar]
- Sirenko, B.I. New outlook on the system of chitons (Mollusca: Polyplacophora). Venus 2006, 65, 27–49. [Google Scholar]
- Sirenko, B.I. Revision of the system of the order Chitonida (Mollusca: Polyplacophora) on the basis of correlation between the type of gills arrangement and the shape of the chorion processes. Ruthenica 1993, 3, 93–117. [Google Scholar]
- Leloup, E. Reports of the Lund University Chile Expedition 1948–49. 27. Polyplacophora. Lunds Univ. Arsskriften N.F. Avd. 1956, 52, 1–94. [Google Scholar]
Figure 1.
Sampling localities (red dots) for Mesotomura echinata. For locality names see Table 1.
Figure 1.
Sampling localities (red dots) for Mesotomura echinata. For locality names see Table 1.
Figure 5.
Girdle elements and radula of Mesotomura echinata from Las Cruces (~33° S), Central Chile, collected on rocks, in intertidal pool, BL 28 mm (ZIN 2591), (A). Two dorsal large spike-like spines, several dorsal corpuscules, numerous dorsal sharply pointed spicules, several marginal needles, and ventral ribbed spicules; (B,C). Dorsal sharply pointed spicules near margin, marginal needles, and ventral ribbed spicules; (D). Radula.
Figure 5.
Girdle elements and radula of Mesotomura echinata from Las Cruces (~33° S), Central Chile, collected on rocks, in intertidal pool, BL 28 mm (ZIN 2591), (A). Two dorsal large spike-like spines, several dorsal corpuscules, numerous dorsal sharply pointed spicules, several marginal needles, and ventral ribbed spicules; (B,C). Dorsal sharply pointed spicules near margin, marginal needles, and ventral ribbed spicules; (D). Radula.
Figure 6.
Maximum likelihood phylogeny of Chitonidae species. Color boxes highlight the monophyletic clades (green = Chiton, yellow = Acanthopleura, light blue = Enoplochiton+Mesotomura, pink = Tonicia).
Figure 6.
Maximum likelihood phylogeny of Chitonidae species. Color boxes highlight the monophyletic clades (green = Chiton, yellow = Acanthopleura, light blue = Enoplochiton+Mesotomura, pink = Tonicia).
Figure 7.
Pictures of (A) Enoplochiton niger, Coquimbo, Chile, 29°56′ S 71°20′ W, rocks, intertidal, BL 22 mm (ZIN 2590). (B) Mesotomura echinata, Pilolcura, Chile, 39°40′ S, 73°24′ W, rocks, intertidal pool, BL 58 mm (ZIN 2589).
Figure 7.
Pictures of (A) Enoplochiton niger, Coquimbo, Chile, 29°56′ S 71°20′ W, rocks, intertidal, BL 22 mm (ZIN 2590). (B) Mesotomura echinata, Pilolcura, Chile, 39°40′ S, 73°24′ W, rocks, intertidal pool, BL 58 mm (ZIN 2589).
Table 1.
Sampling locality, coordinates, sample size, and body length (mm) of Mesotomura echinata from the Southeastern Pacific.
Table 1.
Sampling locality, coordinates, sample size, and body length (mm) of Mesotomura echinata from the Southeastern Pacific.
| Locality | Latitude | Longitude | Sample Size | Body Length (mm) |
|---|---|---|---|---|
| −4.4522 | −81.2883 | 33 | 25.2–73 |
| −8.0825 | −79.1248 | 1 | 98 |
| −12.0671 | −77.1591 | 3 | 51.5–79 |
| −12.4799 | −76.8009 | 8 | 69–100 |
| −13.8486 | −76.2822 | 3 | 68–71 |
| −17.6408 | −71.3520 | 6 | 23–44 |
| −18.5280 | −70.3225 | 13 | 35–99 |
| −20.3092 | −70.1365 | 5 | 35.8–103 |
| −21.0008 | −70.1653 | 26 | 30–151 |
| −23.6696 | −70.4081 | 15 | 42–106 |
| −27.0667 | −70.8333 | 20 | 29–193 |
| −29.4366 | −71.3058 | 4 | 46–119 |
| −29.4800 | −71.3106 | 7 | 93–141 |
| −30.1036 | −71.3833 | 8 | 93–128 |
| −30.5190 | −71.6945 | 2 | 116–125 |
| −31.9787 | −71.4993 | 18 | 65.4–140 |
| −31.4233 | −71.5932 | 18 | 49–183 |
| −32.7433 | −71.4969 | 11 | 42–135 |
| −33.1828 | −71.6856 | 7 | 29–108 |
| −33.4258 | −71.7044 | 8 | 24–62 |
| −34.3930 | −72.0255 | 28 | 53–113 |
| −34.4247 | −72.0438 | 5 | 41–95 |
| −36.6066 | −72.9790 | 8 | 95–127 |
| −36.7669 | −73.1714 | 3 | 78–137 |
| −36.7669 | −73.1714 | 10 | 86–135 |
| −36.8125 | −73.1749 | 3 | 34–133 |
Table 2.
GenBank accession numbers of chiton species’ sequences included in the phylogenetic analysis.
Table 2.
GenBank accession numbers of chiton species’ sequences included in the phylogenetic analysis.
| Species | COI | 16S | 18S |
|---|---|---|---|
| Acanthochitona crinita (Pennant, 1777) | MG680030 | MG679963 | AF120503 |
| Acanthopleura gemmata (Blainville, 1825) | MK016468 | MK097373 | MK480245 |
| Acanthopleura granulata (Gmelin, 1791) | MZ467321 | AY377608 | AY37765 |
| Chaetopleura angulata (Spengler, 1797) | KF369121 | AY377591 | AY37763 |
| Chaetopleura apiculata (Say, 1834) | MZ091411 | AY377590 | AY377636 |
| Chaetopleura benaventei Plate, 1899 | MK480272 | MK480249 | MK097377 |
| Chaetopleura hennahi (J. E. Gray, 1828) | MK480272 | MK480267 | MK097396 |
| Chaetopleura peruviana (Lamarck, 1819) | MK480272 | MK480257 | MK097385 |
| Chaetopleura roddai A. J. Ferreira, 1983 | MK480272 | MK480259 | MK097387 |
| Chiton barnesii J. E. Gray, 1828 | MK016433 | MK097397 | MK480268 |
| Chiton cumingsii Frembly, 1827 | MK016399 | MK097378 | MK480250 |
| Chiton glaucus J. E. Gray, 1828 | MK016469 | MK097380 | MK480252 |
| Chiton granosus Frembly, 1827 | MK016402 | MK097382 | MK480254 |
| Chiton magnificus Deshayes, 1827 | MK016408 | MK097383 | MK480255 |
| Chiton olivaceus Frembly, 1827 | PP94579 | AY37760 | AY377651 |
| Chiton stokesii Broderip, 1832 | MK016411 | MK097388 | MK480260 |
| Enoplochiton niger (Barnes, 1824) | MK016416 | MK097390 | MK480262 |
| Mesotomura echinata (Barnes, 1824) | MK016459 | MK097371 | MK480243 |
| Sypharochiton pelliserpentis (Quoy & Gaimard, 1835) | MK016472 | AY37760 | AY377653 |
| Tonicia calbucensis Plate, 1898 | MK016439 | MK097402 | |
| Tonicia chilensis (Frembly, 1827) | MK016458 | MK097421 | MK480284 |
| Tonicia disjuncta (Frembly, 1827) | MK097423 | MK480285 | |
| Tonicia fremblyana Kaas, 1957 | MK016450 | MK097407 | MK480274 |
| Tonicia lebruni Rochebrune, 1884 | MK097414 | MK480279 | |
| Tonicia swainsoni (G. B. Sowerby I, 1832) | MK016444 | MK097403 | MK480272 |
Table 3.
Mean, minimum (Min), maximum (Max), and standard deviation (SD) of valve width (mm) of 273 Mesotomura echinata specimens.
Table 3.
Mean, minimum (Min), maximum (Max), and standard deviation (SD) of valve width (mm) of 273 Mesotomura echinata specimens.
| Valve | Mean | Min | Max | SD |
|---|---|---|---|---|
| I | 18.41 | 5.00 | 34.00 | 6.626 |
| II | 21.15 | 6.00 | 40.00 | 7.820 |
| III | 24.18 | 6.00 | 47.00 | 9.244 |
| IV | 26.14 | 6.00 | 50.00 | 10.097 |
| V | 26.72 | 6.00 | 51.00 | 10.259 |
| VI | 26.15 | 6.00 | 50.00 | 10.279 |
| VII | 24.07 | 5.00 | 46.00 | 9.472 |
| VIII | 18.69 | 4.00 | 36.00 | 7.438 |
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content. |
© 2024 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
Share and Cite
MDPI and ACS Style
Ibáñez, C.M.; Sirenko, B. Unrolling the Systematics of a Southeastern Pacific Chiton. Taxonomy 2024, 4, 850-861. https://doi.org/10.3390/taxonomy4040045
AMA Style
Ibáñez CM, Sirenko B. Unrolling the Systematics of a Southeastern Pacific Chiton. Taxonomy. 2024; 4(4):850-861. https://doi.org/10.3390/taxonomy4040045
Chicago/Turabian StyleIbáñez, Christian M., and Boris Sirenko. 2024. "Unrolling the Systematics of a Southeastern Pacific Chiton" Taxonomy 4, no. 4: 850-861. https://doi.org/10.3390/taxonomy4040045
APA StyleIbáñez, C. M., & Sirenko, B. (2024). Unrolling the Systematics of a Southeastern Pacific Chiton. Taxonomy, 4(4), 850-861. https://doi.org/10.3390/taxonomy4040045
