Chiton (Chiton) granosus

Ibáñez, Christian M, Pardo-Gandarillas, M Cecilia, Méndez, Marco A, Sellanes, Javier, Sigwart, Julia D & Sirenko, Boris, 2021, Phylogenetic position and morphological descriptions of Chiton species from the south-eastern Pacific, Zoological Journal of the Linnean Society 191 (3), pp. 695-719 : 706-710

CHITON (CHITON) GRANOSUS FREMBLY, 1827

( FIGS 4D , 7C , 12 , 13 )

Chiton granosus Frembly, 1827: 200 , suppl. pl. 17, fig. 1; Plate, 1902: 56, pl. 4, fig. 190; Pilsbry, 1893: 167, pl. 30. figs 27, 28; Dall, 1919: 247. Chiton (Chiton) granosus: Marincovich, 1973: 43 , fig. 98. Chiton (Chondroplax) granosus: Bullock, 1988b: 185 , figs 96, 97, 103, 140, 141, 143 and 144. Chiton (Chiton) granosus: Kaas et al., 2006: 116 , fig. 38, map 14 (bibliography and synonymy).

Type material: NHMUK 20190537 /1, neotype from the Hugh Cuming collection from ‘ Valparaiso, Chili’ , designated herein .

collection; these specimens have been designated as the lectotype ( Fig. 7A ) and paralectotypes ( Fig. 7B ) on this basis. The teratological paralectotype ( NHMUK 20190538 /2) has a coalescence between valve II and valve III; the fragmented valve is visible on the ventral side but the dorsal view appears to be a simple hypomeric seven-valved chiton, as described by Type locality: ‘ Valparaiso , Chili’ (Valparaiso, Chile) .

Description of neotype specimen: Dried specimen 91 mm long by 59 mm wide, overall colour black with pale central stripe divided by a darker midline in intermediate valves ( Fig. 6C ). Head valve with approximately 13 irregular radiating lines of large, round, raised granules; intermediate valves lateral areas with three to four radiating lines of widely spaced elongate raised granules, solid black; central areas of intermediate valves with anterior-posterior ribs formed in part of fused granules creating a latticed appearance, with symmetrical colour blocks forming the midline stripe, from distal to proximal black, pale cream, dark brown, grey-brown and centrally dark brown to black. Tail valve antemucronal area as central areas of intermediate valves; postmucronal area with approximately 13 irregular radiating lines of elongate granules of similar size but slightly smaller than those on the lateral areas of intermediate valves. Articulamentum blue in middle areas of valves. Girdle perinotum covered in black, imbricating scales; hyponotum with fine elongate flat sclerites.

Descriptive notes: Size: animals of medium to large size, typically 76 mm long by 51 mm wide ( Table 2). Colour: black with brown or green tone, usually eroded and sometimes with white lines on the central area ( Fig. 4D ). Body shape: oval with moderate dorsal elevation. Slit formula: 12–18/1/14–17. Plates: head valve with <20 ribs composed of large granules ( Fig. 4D ). Juvenile head valve with large granules forming <ten ribs ( Fig. 12A ). Commonly eroded intermediate plates, central area with many fine ribs, valve slightly wider than long, sloping postmucronal tilt ( Fig. 13A ). Intermediate plates with one slit. Articulamentum: apophyses rounded, short and wide, connected by a pectinate jugal lamina, insertion plates pectinate with short insertion slit ( Fig. 12B ). Perinotum: wide, solid black with rounded scales arranged irregularly ( Fig. 13B, C ). Radula: central tooth rounded, major lateral tricuspid ( Fig. 12D ).

Distribution: Paita (~ 5°S), Peru to Boca del Guafo (~ 43°S), Chile ( Marincovich, 1973; Osorio et al., 2005). In this study, we found this species from Chiclayo (~ 8°S), Peru to Peninsula Taitao (~ 46°S), Chile ( Fig. 1 ).

Remarks: This species is easily confounded with C. barnesii (see remarks for C. barnesii ). Sanhueza & Ibáñez (2016) erroneously stated that C. granosus was a nomen nudum, but the original description is sufficient, complete and appropriately published, and the name is valid. The International Code for Zoological Nomenclature requires seven qualifying conditions ( ICZN Art. 75.3). A neotype is designated herein to clarify the taxonomic status of the species and prevent confusion with similar species ( ICZN Art. 75.3.1). The characters that differentiate the species are included in the descriptive notes above ( ICZN Art. 75.3.2). Prior descriptions, and our additional remarks and novel genetic data from additional specimens, are sufficient to ensure the species can be correctly recognized and identified, and this description is consistent with the selected neotype ( ICZN Art. 75.3.3). The original description does not include a specific designation of type material ( Frembly, 1827). Therefore, the original type material is not lost or destroyed, but a type specimen was never previously designated. From the historical context, we understand that the relevant material was all deposited in NHMUK. One of us ( JDS) has examined every known specimen in the relevant part of the polyplacophoran collections of NHMUK and could not find any specimen that convincingly matches the illustration in the original description ( Frembly, 1827: pl. 17, fig. 1). We note that the illustration is somewhat stylized, and may not be sufficiently accurate to match an individual specimen, including the description of specimens in the text of the original description. We have concluded that it is not possible to connect the original description to an extant specimen ( ICZN Art. 75.3.4). The designated neotype specimen was selected to ensure consistency with what is known of the material in multiple specimens collected by Frembly and which informed the original description. The neotype is connected to the type locality, and of the available specimens, the individual closest to the generalized dimensions stated in the original description ( ICZN Art. 75.3.5) is as follows: neotype dimensions, 4.8 × 3.2 cm compared to original description approx. 4.4 × 3.3 cm, ‘length 1 3/ 4 inches, breadth 1 3/10’ (Frembly, 1927: 201). The type locality is clearly stated as Valparaiso, Chile ( Frembly, 1827) and the selected specimen is also clearly recorded as from Valparaiso ( ICZN Art. 75.3.6). As the specimen is part of the permanent collections of NHMUK, it is the property of a recognized institution with appropriate facilities for maintaining this specimen ( ICZN Art. 75.3.7).

Circumstantial evidence suggests that some or all of Frembly’s material was and is present in the collections of NHMUK (see remarks under C. cumingsii , above). The type material for this species was already noted as ‘location of type unknown’ in a prior revision ( Bullock, 1988b). We were unable to identify any individual specimen or specimen lot that could be connected to the original description or to Frembly. Among the contemporary (early 19 th century) specimens, two lots from J. E. Gray were considered as potential Frembly-associated material. One lot has two specimens mounted on a card with handwriting that matches the designated lectotype for C. cumingsii and has a pencil circle drawn around one specimen. We note that the Gray material is potentially relevant to future research, but these specimens have no locality data, whereas the type locality for C. granosus is clearly stated in the original description as Valparaiso. There is also one lot of three specimens of C. granosus

710 C. M. IBÁÑEZ ET AL.

in the Senckenberg Gesellschaft für Naturforschung , Frankfurt am Main , Germany, donated by Cuming. These specimens also have no documented connection to Frembly and the locality is given only as ‘ Chili’. Therefore, we selected a neotype specimen from the Cuming collection (contemporary to Frembly) in the NHMUK with their collecting locality as Valparaiso .

Figures

Figure 1. Map showing sampling localities. Lines represent the geographical distribution of each Chiton species: 1, Chiton stokesii; 2, Chiton granosus; 3, Chiton cumingsii; 4, Chiton magnificus; 5, Chiton barnesii.

Figure 4. Pictures of Chiton species from the south-eastern Pacific. A, Chiton barnesii live specimen from La Pampilla, Coquimbo, Chile (29°26’11’’S, 71°18’20’’W). B, Chiton stokesii live specimen from Santa Rosa, Ecuador (2°12’39’’S, 80°56’45’’W). C, Chiton cumingsii live specimen from Lagunillas, Coquimbo, Chile (30°06’13’’S, 71°22’59’’W). D, Chiton granosus live specimen from Antofagasta, Chile (23°40’10’’S, 70°24’29’’W). E, Chiton magnificus live specimen from Lagunillas, Coquimbo, Chile (30°06’13’’S, 71°22’59’’W). F, Chiton magnificus live specimen from Puerto del Hambre, Punta Arenas, Chile (53°36’44’’S, 70°55’43’’W).

Figure 6. Chiton barnesii, Chile, Coquimbo, BL 20.0 mm, 05.01.2015:A, C, dorsal and ventral scales and marginal spicules; B, D, radula, head of major lateral tooth has one denticle.

Figure 7. Type specimens of chitons: A, lectotype of Chiton cumingsii NHMUK 20190538/1; B, paralectotype of Chiton cumingsii NHMUK 20190538/2; C, neotype of Chiton granosus NHMUK 20190537/1. Scale bar 10 mm.

Figure 12. Chiton granosus, Chile, Las Cruces, BL 9.5 mm, 20.11.2008: A, valve I, dorsal view; B, valve V, dorsal view; C, valve VIII, dorsal view; D, valve V, ventral view; E, valve V, detail of tegmentum in central and lateral areas; F, valve V, rostral view; G, valve VIII, lateral view.

Figure 13. Chiton granosus, Chile, Las Cruces, BL 9.5 mm, 20.11.2008: A, valve V, detail of tegmentum and apophyses; B, C, dorsal and ventral scales and marginal spicules; D, radula, head of major lateral tooth has three denticles.