Acanthochitona fascicularis (Linnaeus, 1767)

Voncina, Katarzyna, Mikkelsen, Nina Therese, Morrow, Christine, Ang, Rory & Sigwart, Julia D., 2023, Clarification of the taxonomic status of Acanthochitona discrepans (Brown, 1827) with new data for the North-East Atlantic Acanthochitona (Polyplacophora, Acanthochitonidae), Biodiversity Data Journal 11, pp. 109554-109554 : 109554

Acanthochitona fascicularis (Linnaeus, 1767)

Chiton fascicularis : Linnaeus, 1767 - Linnaeus 1767: 1106; Poli, 1791 - Poli 1791: 10, pl. 4 fig. 3; Reeve, 1847 - Reeve 1827: pl. 10 sp. & fig. 53.

Chiton fascicularis non C. fascicularis : Sowerby, 1840a - Sowerby II 1840a: figs. 87, 87a, et mult. auct.

Acanthochites communis : Risso, 1826 - Risso 1826: 269.

Chiton fascicularis var. major : Philippi, 1836 - Philippi 1836: 108, pl. 7 fig. 2a, b.

Chiton crinitus : Sowerby, 1840: figs. 88-93; 1840a: 2.

Chiton crinitus non C. crinitus : Pennant, 1777 - Pennant 1777.

Chiton discrepans : Sowerby, 1840a: 2 (in synonymy of C. crinitus ; Sowerby, non Pennant, 1777); Forbes & Hanley, 1849 - Forbes and Hanley 1849: 396, pl. 58 fig. 4; Jeffreys, 1859 - Jeffreys 1859: 106, pl. 3 fig. 10, Jeffreys, 1869 - Jeffreys 1869: 198, pl. 5. fig. 4, et mult, auct.

Chiton discrepans non C. discrepans : Brown, 1827 - Brown 1827.

Acanthochites carinatus : H. Adams & Angas, 1864 Adams and Angas 1864.

Acanthochites carinatus non Acanthochites carinatus : Risso, 1826 - Risso 1826.

Chiton fascicularis var. rubra : Issel, 1870 - Issel 1870: 4.

Acanthochites discrepans var. minorflava : di Monterosato, 1878a - di Monterosato 1878: 78.

Acanthochites hamatus : de Rochebrune, 1882 - de Rochebrune 1882: 191; Thiele, 1909 - Thiele 1909: 43.

Anisochiton discrepans vars Anisochiton discrepans elongata , Anisochiton discrepans marmorata , Anisochiton discrepans nigrolineata : Dautzenberg, 1893 - Dautzenberg 1893: 25.

Acanthochites discrepans var. albina : Dautzenberg & Durouchoux, 1900 - Dautzenberg and Durouchoux 1900: 15.

Anisochiton (Acanthochites) discrepans var. viridis : Pallary, 1902 - Pallary 1902: 28.

Acanthochites discrepans var. violaceolimbata : Dautzenberg & Durouchoux, 1906 - Dautzenberg and Durouchoux 1906: 15.

Acanthochitona fascicularis Acanthochiton (a) Acanthochiton communis : Winckworth, 1926 - Winckworth 1926: 15, et mult. auct.

Acanthochiton heterochaetus : Bergenhayn, 1931 - Bergenhayn 1931: 20, pl. 1 figs. 38-42, pl. 3 figs 67-74.

Acanthochiton discrepans var. angustivalvus : Bergenhayn, 1931 - Bergenhayn 1931: 20.

Acanthochiton communis f. barashi : Leloup, 1969 - Leloup 1969: 1, figs. 1, 2D, 3D, G, 4B.

Acanthochitona bonairensis : Kaas, 1972 - Kaas 1972: 44, text figs 72-73, pl. 3 figs. 1, 2; Watters, 1981 - Watters 1981: 173 (in synonymy of A. communis ).

Acanthochitona fascicularis : Kaas, 1985 - Kaas 1985: 585, figs. 1-6.

Acanthochitona fascicularis Type material. Neotype: MNHN-IM-2000-5923, Muséum National d’Histoire Naturelle, Paris, France. Designated by Kaas (1985) (material not seen).

Acanthochitona fascicularis Type locality. Algeria, coast of Barbary ( Linnaeus 1767); Algeria, Oran ( Kaas 1985).

Materials

Type status: Other material. Occurrence: individualID: SMF 373027; individualCount: 1; lifeStage: adult; otherCatalogNumbers: BOLD:AAJ3296, NIB_CCM_0522; associatedSequences: BOLD:CCMMO043-21, GenBank: OR526595 ; occurrenceID: 55E89EFE-E8B6-5D86-9019-A160AFE8A3EF; Taxon : scientificNameID: Acanthochitona fascicularis; Location : country: Ireland; county: Galway; locality: Bealadangan ; verbatimCoordinates: 53°18'43"N 9°37'26"W; Event: eventDate: 21/09/2021; eventRemarks: Christine Morrow leg.; Record Level: collectionCode: Malakologie- SMF; basisOfRecord: PreservedSpecimen Type status: Other material. Occurrence: individualID: SMF 373030; individualCount: 1; lifeStage: adult; otherCatalogNumbers: BOLD:AAJ3296, NIB_CCM_0537; associatedSequences: BOLD:CCMMO046-21, GenBank: OR526596 ; occurrenceID: 6110752C-8064-5DE9-97C2-8AEC5CDCECFD; Taxon : scientificNameID: Acanthochitona fascicularis; Location : country: Ireland; county: Galway; locality: Aillwee ; verbatimCoordinates: 53°21'21"N 9°38'45"W; Event: eventDate: 24/09/2021; eventRemarks: Christine Morrow leg.; Record Level: collectionCode: Malakologie- SMF; basisOfRecord: PreservedSpecimen Type status: Other material. Occurrence: individualID: SMF 373028; individualCount: 1; lifeStage: adult; otherCatalogNumbers: BOLD:AAJ3296, NIB_CCM_0523; associatedSequences: BOLD:CCMMO044-21, GenBank: OR526597 ; occurrenceID: 474B14EF-848E-5AB3-9408-AE88C534A0F1; Taxon : scientificNameID: Acanthochitona fascicularis; Location : country: Ireland; county: Galway; locality: Bealadangan ; verbatimCoordinates: 53°18'43"N 9°37'26"W; Event: eventDate: 20/09/2021; eventRemarks: Christine Morrow leg.; Record Level: collectionCode: Malakologie- SMF; basisOfRecord: PreservedSpecimen Type status: Other material. Occurrence: individualID: 360506-4; individualCount: 1; lifeStage: adult; associatedSequences: GenBank: OR145409 ; occurrenceID: 459DF758-0C45-5ACA-8467-6F6403CEE765; Taxon : scientificNameID: Acanthochitona fascicularis; Location : country: Portugal; stateProvince: Azores; county: Galway ; locality: Ponta Delgada : Rosto do Cao ; verbatimCoordinates: 37°44.567'N 25°38.167'W; Event: eventDate: 29/07/2013; eventRemarks: Julia Sigwart, Laura Sumner-Rooney & Nicholas Carey leg.; Record Level: collectionCode: Malakologie- SMF; basisOfRecord: PreservedSpecimen Type status: Other material. Occurrence: individualID: SMF 373029; individualCount: 1; lifeStage: adult; otherCatalogNumbers: BOLD:AAJ3296, NIB_CCM_0524; associatedSequences: BOLD:CCMMO045-21, GenBank: OR526598 ; occurrenceID: F1DC0BB9-0B94-5DEE-A0A8-766B86D322C2; Taxon : scientificNameID: Acanthochitona fascicularis; Location : country: Ireland; county: Galway; locality: Bealadangan ; verbatimCoordinates: 53°18'43"N, 9°37'26"W; Event: eventDate: 20/09/2021; eventRemarks: Christine Morrow leg.; Record Level: collectionCode: Malakologie- SMF; basisOfRecord: PreservedSpecimen

Description

(See Jones and Baxter (1987), Dell’Angelo and Smriglio (2001), Bonfitto et al. (2011), Schmidt-Petersen et al. (2015) for additional descriptions that pertain to Acanthochitona fascicularis ). Small to large size (in examined material, BL: 9-30 mm, BW: 5-18 mm, BL/BW ratio: 1.7), outline oval, flat to moderately elevated, semi-carinated, slightly protruding apices; girdle very wide and spiculose. Dorsal colouration variable; usually green and brown variously combined; some specimens can be uniform and brightly coloured, yellow or orange (Fig. 1 D-E).

Head valve much wider than long, semicircular, with five barely-raised rays, posterior margin almost straight, no notch and apex (Fig. 7 A). Intermediate valves from triangular to trapezoid, apex slightly protruding; raised, clearly separated from lateropleural areas, wedge-shaped and striated jugum (Fig. 1 D-E, Fig. 7 B). Tail valve almost circular with central elevated mucro (Fig. 1 D, Fig. 6 C).

Tegmentum uniformly and thickly covered (density from 42 to 70 granules per 1 mm2, mean = 52, n = 7 specimens) by small, round granules arranged in arched lines on the valves; each granule with 0-6 aesthetes randomly distributed, without a clear separation between macro- and microaesthetes; some granules with an incision in the middle of the granule posterior margin (Fig. 1 D, Fig. 4 C, Fig. 7 , Fig. 8 B).

Articulamentum well-developed; apophyses wide, rectangular, separated at jugum, rounded at anterolateral margins; insertion plates wide, continuous with apophyses, slits deep, extending dorsally into shallow channels (slit formula: 5/1/2) (Fig. 7 ).

Girdle very wide and fleshy, deeply encroaching sutural areas. Colours ranging from creamy-yellow to olive-green and brown, with different degrees of blotches in which white, green and brown variously combined; sometimes yellow or orange (Fig. 1 D-E). Dorsal perinotum densely covered with two kinds of spicules: shorter, slender, pointed, but usually broken spicules and longer and thicker spicules interspersed amongst them (Fig. 8 D). Sutural tufts with 55-120 long and slim bristles, surrounded by shorter, thinner, also smooth needles. Hyponotum densely covered with lanceolate, flattened spicules, finely striated near the top, of size up to 100 x 18 µm (Fig. 8 C).

Central radula teeth elongated, almost straight at the top and keeled near base; first lateral tooth wing-shaped and smaller than the central; second (major) lateral elongated with accessory plate tricuspidate with central denticle longer than the others; cusps pointed and triangular in outline (Fig. 8 A).

Gills merobranchial, 15-17 ctenidia on each side.

Diagnosis

Acanthochtiona fascicularis , can be easily distinguished from other NE Atlantic relatives by the triangular shape of valves, raised and clearly separated jugal area, small and round, densely-packed tegmental granules and small number of aesthetes (0-6) without clear separation between micro- and macroaesthetes. For comparison, see the Remarks section for A. crinita and A. discrepans .

Distribution

This species is widely distributed in the North-East Atlantic, with a range from the west coast of Ireland (molecular data and SEM photos from this study), south to the Azores (molecular data and SEM photos from this study) and the Mediterranean Sea (literature records and GenBank sequences).

Figures

Figure 1. Images of the adult specimens of Acanthochitona, dorsal view. A A. crinita from England, BL not measured; B A. crinita from the Azores, BL not measured; C A. discrepans from Norway, BL 17 mm; D A. fascicularis from Ireland, BL 23 mm; E A. fascicularis from the Azores, BL 13 mm.

Figure 4. Morphology of the granules of tegmentum with the macro- and microaesthetes. A Acanthochitona crinita; B A. discrepans; C A. fascicularis.

Figure 6. Acanthochitona discrepans from Northern Ireland (A-E) and Norway (F). A Radula; B Valve VII, detail of the tegmentum in the lateropleural area; C One of the 18 tufts of spicules on the girdle; D Dorsal spicules; E Dorsal and marginal spicules; F Dorsal, marginal and ventral spicules.

Figure 7. Acanthochitona fascicularis from Ireland. All in dorsal view. A Valve I; B Valve V; C Valve VIII.

Figure 8. Acanthochitona fascicularis from Ireland. A Radula; B Valve V, detail of the tegmentum in the lateropleural area; C Ventral spicules; D Dorsal spicules.