Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza, 2022

Reyes-Gómez, Adriana, Flores-Garza, Rafael, Galeana-Rebolledo, Lizeth, Hernández-Vera, Gerardo, Galván-Villa, Cristian M., Torreblanca-Ramírez, Carmina, Flores-Rodríguez, Pedro, García-Ibañez, Sergio & Ríos-Jara, Eduardo, 2022, Intertidal chitons (Mollusca: Polyplacophora) from the rocky coastline of Guerrero, México, with the description of a new species, Zootaxa 5155 (4), pp. 451-492 : 478-484

Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov.

Figures 16A–J ; 17A–O , 18A–D .

Lepidochitona sp. Reyes-Gómez, 2016: 98 a–c, 99, 100a–b.

Type material. Holotype, EMU 11417 consisting of a whole specimen, and eight paratypes, EMU 11418.

Type locality. Majahua , Acapulco, Guerrero, México, 16°50'58.2"N, 99° 54'1.8"W, in intertidal 1–1.5 m. Etymology. Named after Acapulco, Guerrero where it appears to be most common .

Material examined. Majahua, Acapulco , Guerrero, 16°50'58.2"N, 99° 54'1.8"W, in intertidal 1–2 m, in surf areas on large rocks, holotype, BL 9.1 mm, 02.05.2009. 5 paratypes, BL 2.9–11.90 mm, in intertidal 1.2 m on medium boulders bury in sand .

The following chiton material was found in intertidal between 1– 2 m.

(n=4), BL 3.9, 5.8, 6.1, 7.4 mm, CNMO 5234 , CNMO 5271 , CNMO 5782 , CNMO 5792 , Las Salinas, Marquelia, 16°35' 49.5''N, 99°05'43.7''W, 09.04.2009; (n=1) , BL 4.5 mm, CNMO 5236 , Majahua, Acapulco, 16°50'58.2"N, 99° 54'2.4"W , 02.052009; (n=1), BL 7.9 mm, CNMO 5779 , Piedra Tlacoyunque, Tecpan de Galeana , 16°19' 35.4''N, 98°34' 12.6''W, 16.04.2009; (n=1) , BL 5.1 mm, CNMO 5780 , (n=1), BL 5.1 mm, CNMO 5795 , Tlacopanocha, Acapulco, 16°50' 41.5''N, 99°54'25''W, 01.05.2009; (n=2) , BL 5.6, 7.8 mm, CNMO 5781 , CNMO 5784 , Playa Ventura, Copala, 16°32'8.3"N, 99°54'44.6"W , 10.052009; (n=1), BL 7.2 mm, CNMO 5785 , Pie de la Cuesta, Acapulco, 16°52' 25.6''N, 99°56' 34.6''W, 08.05.2010; (n=2) , BL 5.7, 8.1 mm, CNMO 5793 , CNMO 5794 , Punta Maldonado, Cuajinicuilapa, 16°19' 35.4''N, 98°34'12.6''W, 07.04.2009; (n=1) , BL 4.4 mm, CNMO 6061 , La Angosta, Acapulco, 16°60' 29.8''N, 99°54' 55.7''W, 04.05.2010; (n=1) , BL 6.7 mm, CNMO 6069 , Playa Manzanillo, Acapulco, 16°50' 27.9''N, 99°54' 38.1''W, 05.05.2010; (n=1) , BL 6.8 mm, UAGRO 0045 , Casa de Piedra , Copala, 16º32'10.1"N, 98º53'47.3''W, 10.05.2009; (n=1) , BL 7.3 mm, UAGRO 0046 , Ojo de Agua , Petatlán, 17°18' 01.8''N, 101°03' 05.8''W, 17.04.2009; (n=1) , BL 7.4 mm, UAGRO 0047 , Barra de Potosí , Teniente José Azueta, 17°31' 43.5''N, 101°27' 08.2''W, 16.05.2009; (n=1) , BL 8.2 mm, UAGRO 0048 , Las Gatas, Zihuatanejo de Azueta , 17°37' 17.5''N, 101°33' 14.2''W, 15.05.2009; (n=1) , BL 7.6 mm, UAGRO 0049 , Troncones, La Unión, 17°47' 35''N, 101°44' 46.6''W, 17.05.2009; (n=1) , BL 4.9 mm, UAGRO 0049 , La Barrita, Petatlán, 17°24' 32.7''N, 101°10' 51.3''W, 15.03.2014 .

Diagnosis. Small chitons; tegmentum micro-granular; central areas of the intermediate valves with a fine corrugated sculpture forming a network-like pattern present in the pleural areas of intermediate valves. The lateral areas are indicated by the diagonal ridge that forms a somewhat elevated rib. If the tegmentum is not eroded, the head valve may show 2–3 slightly elevated radial ribs, located near the posterior margin of both sides of the valve. Girdle covered with longitudinally striated spicules of rounded anterior margin and hyaline curved spicules, interspersed on the whole girdle surface and arranged in tufts of 3–8 spicules, located near the valve’s sutures and the girdle base.

Description. Body shape oval; up to 11.2 mm long. Tegmentum color variable: dark to lighter orange-brownish, with dark gray and lighter patches of brown and cream, scattered with irregular dark gray and cream dots on the central areas of intermediate valves. Girdle usually shows irregular bands in the same colors as the tegmentum in light brown, orange, and cream. Tegmentum micro-granular; the head valve may show 2–3 slightly elevated radial ribs on each side of the posterior margin; the rib next to the margin is usually wider than the others which can be observed in uneroded individuals. The lateral areas are indicated by a slightly raised rib. Central areas of each intermediate valve exhibit a finely corrugated sculpturing, arranged in an irregular network pattern; jugal area usually smooth.

The aesthete system is comprised of megalaesthetes with a diameter of 10–12 µm, each surrounded by 6–9 micraesthetes.

Head valve semicircular, wider than long; posterior margin widely v-shaped and notched. Intermediate valves are round backed (dorsal elevation of 0.27), semi rectangular in outline, with rounded side margins, becoming wider and shorter in length from valves V to VII. Tail valve wider than long, anterior margin straight; mucro somewhat elevated, central to slightly postmedian; postmucronal area is depressed; postmucronal slope is somewhat concave.

Articulamentum white, translucent, thin; insertion plate teeth irregular in size and shape; apophyses subrectangular shaped, somewhat elevated and separated by a wide, smooth jugal plate; slit rays present in all valves and on the jugal area; eaves spongy; slit formula 8–12/1–2 occasionally/9–13.

Girdle dorsally covered with small spicules apically rounded and finely ribbed; additional hyaline spicules between 180–210 µm, interspersed individually and bunched in groups of 3–8, located mainly in the valve sutures throughout the girdle surface; usually the hyaline spicules are broken. Anteriorly (around the head valve) and posteriorly (between VII-VIII), 6–8 tufts of hyaline curved spicules are present, grouped in 4–6 ranging between 190–350 µm of length. The marginal spicules are finely ribbed and 165–260 µm length.

Radula with central tooth of 42 x 23 µm, sub-rectangular outlined, apically wider and bending outwards; the minor lateral teeth are long narrow plates, anteriorly flattened; major lateral teeth tricuspid, the central denticle wider than the other two, and the inner cusp narrower and slightly longer than the others.

Distribution. From Isla Venados, Mazatlán, Sinaloa: 23°15'09''N, 106°30'59''W to Estacahuite, Puerto Ángel, Oaxaca, México: 15°40'18''N, 96°29'45''W (e.g., CNMO 5868); including Sayulita, Nayarit: 20°52'10''N, 105°26'27''W and Bahía Chamela, Jalisco: 19°31'38''N, 105°04'24''W; shallow subtidal to 12 m depth, in rocky and coralline substrate.

Habitat. Adult individuals found in surf areas on medium-sized rocks covered with red crustose algae. Juveniles found in subtidal to 8 m depth under rocks buried in sand.

Remarks. The history of confusing names leading to the currently broad concept of Lepidochitona Gray, 1821 has been reviewed by Eernisse (1986). A substantial revision by Kaas & Van Belle (1981) extended the name to multiple temperate European species with similar more or less smooth valves and only small girdle elements.

Ferreira (1982b) broadened the concept of the genus even further to include similar temperate and tropical Eastern Pacific species, most of them previously assigned to other genera. Eernisse (1986) revised the temperate northeastern Pacific species and did not accept synonymies proposed by Ferreira (1982b) and described three new species. Eernisse (2004) reported biogeographic and molecular (16S + cox1) support for reviving Cyanoplax Pilsbry, 1892 for a monophyletic grouping apart from Lepidochitona , whose temperate northeastern Pacific members were never intended to include L. beanii (D. J. Eernisse, pers. communication, contrasting WoRMS that incorrectly reports this species as Cyanoplax beanii ). García-Ríos (2010, 2011, 2015) and others have documented the presence of previously unnoticed species diversity in Lepidochitona in the Caribbean and Pacific. We assign Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. to Lepidochitona along with other Temperate Eastern Pacific or Caribbean species ( Lepidochitona beanii ; Lepidochitona salvadorensis ; L e pidochitona liozonis , Lepidochitona pseudoliozonis ) whose close morphological affinities are also given by their continuous distribution.

Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. was initially recorded as Lepidochitona sp. ( Reyes-Gómez et al. 2010), collected at Puerto Ángel, Oaxaca. Later, Flores-Garza et al. (2012) and GaleanaRebolledo et al. (2014) misidentified the same species from Guerrero as several species: Lepidochitona beanii Carpenter, 1857 , Lepidochitona hartwegii ( Carpenter, 1855) , Dendrochiton flectens ( Carpenter, 1864) , and Lepidochitona sp. The subsequent revision of those specimens using SEM imaging ( Reyes-Gómez 2016), revealed that all of them were conspecific, including the specimens from Oaxaca identified as Lepidochitona sp. by ReyesGómez et al. (2010).

Ferreira (1982b) reported Lepidochitona beanii ( Carpenter, 1857) (lectotype BMNH 1857.6.4.906, tablet 906), with the type locality at Mazatlán, Sinaloa. This author also designated Chiton bipunctatus as lectotype (LACM 74–11, and BMNH 1978147 both as possible syntypes, both from Isla Lobos de Afuera, Perú). Based on the type material and on additional specimens from Perú (lot of 32 chitons LACM 74–6, by J.H. McLean), Ferreira (1982b) considered this species to range between 33°N and 7°S, from southern California to Perú and throughout the Gulf of California. However, the southern records of this species seem to be doubtful due to insufficient information on the labels of the type due to the morphological inaccuracies shown in the figures that Ferreira presented in his review. The image of a L. beanii specimen of 11.5 mm BL from Isla Lobos de Afuera ( Ferreira 1982b: Fig. 12 ; LACM 74–6, collected in 1974) shows an oval body shape and it seems that it has more girdle tufts than the original description by Carpenter (1857), which also exhibit an interspersed arrangement. However, the specimen of 7.8 mm BL ( Ferreira 1982b Fig. 15–17 ) from Punta Fermin Los Ángeles, California (which might correspond to a juvenile of Tonicella lineata ) has an oval-elongate body shape. In addition, a new species (that it is in the process to be described by Ibáñez Christian) of Lepidochitona was identified from Perú that differs morphologically and genetically from L. beanii (from Bahía Kino, Sonora). This recent finding also contributes to the hypothesis that L. beanii might not be distributed as far away down to Isla Lobos de Afuera as Ferreira (1982b) claimed.

In this study, we analyzed and compared only specimens of Lepidochitona species distributed closer to the type localities of Lepidochitona beanii and Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. ( Table 4 ). Our new species resembles L. beanii as redescribed by Kaas & Van Belle (1985) based on the study of its lectotype at a first glance since both species are limited to small body size and have brown, orange, or grayish color. However, Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. bears a distinctive, irregularly corrugated sculpturing on the pleural areas of intermediate valves in contrast to L. beanii , which shows a microgranular quincunx pattern ( Kaas & Van Belle 1985: figs 53 [1–3, 6]; see also Figs. 21 [B-D]). Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. also has more girdle tufts (observed in 25 of 29 examined specimens) which are irregularly interspersed on the girdle, and consistently more (3–8) hyaline spicules per girdle tufts than L. beanii (3–4). Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. display intermediate valves with lower dorsal elevation (0.27) than L. beanii (0.35). The intermediate valves of our new species have a more rectangular shaped outline, and the lateral areas can be indicated by a slightly raised diagonal ridge ( Figs 17 C–F ), which is lacking in L. beanii ( Kaas & Van Belle 1985: Figs 53 [3]; see also Fig. 21 [C]). The girdle of Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. has dorsal spicules with rounded apex; the spicules are longitudinally striated. By, contrast the spicules of L. beanii are bluntly pointed ( Kaas & Van Belle 1985, figs 53 [11–13]; see also Fig. 17N ).

The comparison of the sympatric Lepidochitona salvadorensis García-Ríos, 2006 to our new species revealed that L. salvadorensis exhibits longer hyaline spicules (0.4–0.8 mm) and has a smoother tegmentum ( García-Ríos 2006: Fig. 1 vs. Figs. 17A–C ) than Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. The radular central tooth of L. salvadorensis is wider and more flattened than the one in our new species, which is bent outwards on its apex, and the minor lateral teeth are thinner than those in L. salvadorensis ( García-Ríos 2006: fig. 10 vs. Figs 17K, M ).

We also compared Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. with Caribbean chitons. The examination of Lepidochitona bullocki García-Ríos, 2011 and Lepidochitona rufoi García-Ríos, 2010 revealed that these two species can attain 4–5.5 mm of body length, the lateral areas are somewhat elevated, the girdle is reduced, the mucro is located in antemucronal position, and the postmucronal slope in both species is almost straight. Lepidochitona bullocki shows a long sub-rectangular central radular tooth that is somewhat curved on its apical end, and the minor lateral teeth appear as a slender plate. Lepidochitona rufoi displays minor lateral teeth and the central teeth are excessively reduced, appearing as thin, small plates, which differ greatly from the teeth our new species radular teeth. The length and number of the hyaline spicules in the girdle tufts are also distinctive for each species. Lepidochitona bullocki has a spicule length of 0.5 mm and has an average of 10 spicules per tuft. Lepidochitona rufoi exhibits individual spicules (70 µm length) interspersed on the girdle. Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. shows tufts with 3–8 spicules (180–210 µm length). The examination of L. liozonis and L. rosea revealed that both species have a sub-rectangular shaped tegmentum and their mucro is located in antemucronal position. Lepidochitona liozonis differs from our new species in displaying 2–3 spicules per tuft. Lepidochitona rosea bears individual spicules that rise from chitinous cups that are interspersed on the girdle surface.

The morphologic comparisons place Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. close to L. bullocki , since both species show a fine sculpturing on the tegmentum, that has raised lateral areas, a protruding apex, a concave posterior margin and a tail valve with a postmucronal slope semi-concave to concave. The apophyses of both species are about of the same length and shape, and the girdle tufts display numerous hyaline spicules. Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. differs more strongly from the eastern Pacific Lepidochitona species ( L. beanii and L. salvadorensis ), regarding tegmentum shape and sculpturing, morphology and disposition of the hyaline spicules of the girdle, and regarding the morphology of the radular teeth (see above). Lepidochitona salvadorensis differs most from Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. Both species are sympatric in the Mexican Tropical Pacific (from Mazatlán to Oaxaca, México).

Lepidochitona acapulcoensis Reyes-Gómez & Flores-Garza sp. nov. differs from all the species reviewed by: (a) having a fine net-like sculpture in the pleural areas of intermediate valves, (b) 2–3 radial ribs on both sides of the posterior valve margin of the head valve with, (c) the distinctive central tooth which is apically folded inwards, and (d) 6–8 tufts located around the head and tail valve that can bear 4–6 longer hyaline spicules, and the girdle tufts that have 3–8 hyaline spicules. All examined Lepidochitona species have a distinctive central and a small lateral radular tooth morphology and differs from each other also in the number and length of the hyaline spicules per tuft indicating that these characters are diagnostic on the species level. The tegmentum sculpturing seems to be distinctive for a few species, however, most of the members within the genus present microgranular sculpturing and appear to be smooth to the naked eye.

Figures

FIGURE 1. Location of sampling sites within the coastline of Guerrero, from north to south:A) Troncones, B) Isla Grande, C) El Capricho, D) Las Gatas, E) Barra de Potosí, F) La Barrita, G) Puerto Vicente Guerrero, H) Ojo Agua, I) Tlacoyunque, J) Pie de la Cuesta, K) Parque de la Reina, L) Muelle, M) Manzanillo, N) Tlacopanocha, O) Palmitas, P) Majahua, Q) Playa Ventura, R) Casa de Piedra, S) Las Salinas, T) Peñitas, U) Punta Maldonado.

FIGURE 12. Chiton articulatus, SEM images of a specimen BL 28.3 mm length; A, detail of girdle scales; B, radular teeth; C, detail of central and minor lateral teeth. Tonicia forbesii, BL 19.5 mm, Isla Grande, Zihuatanejo deAzueta (CNMO 5255). Valves in dorsal view, D, head valve; E, intermediate valve IV; F, tail valve. Valves in ventral view, G, head valve; H, intermediate valve IV; I, tail valve; J, detail of lateral and central area of intermediate valve IV; K, detail of lateral area ocelli.

FIGURE 15. Lepidochitona salvadorensis, disarticulated valves of a specimen BL 10.74 mm, Barra de Potosi Protegida, Zihuatanejo de Azueta (CNMO 5332). valves in ventral view, A, intermediate valve IV; B, tail valve; C, detail of the tail valve and girdle tufts. SEM images of a specimen BL 10.7 mm, valves in dorsal view show the tegmentum details; D, head valve IV; E, intermediate valve IV; F, tail valve; G, intermediate valve IV in ventral view, H, central and minor lateral teeth detail.

FIGURE 16. Lepidochitona acapulcoensis Reyes-Gómez and Flores-Garza sp. nov., holotype, EMU 11417, Majahua,Acapulco, Guerrero, whole specimen of 9.10 x 5.31 mm, A, in dorsal view; B, lateral view; C, detail of head valve; D, detail of central areas sculpturing and tail valve; E, detail of girdle. Paratypes, whole specimens in dorsal view, F, specimen of 8.2 x 4.8 mm, and G in lateral view; H, specimen of 6.2 x 3.7 mm; I, specimen of 11.1 x 6.5 mm; J, same specimen in lateral view.

FIGURE 17. Lepidochitona acapulcoensis Reyes-Gómez and Flores-Garza sp. nov.; paratypes, EMU 11417, Majahua, Acapulco, Guerrero, SEM images of a specimen BL 9.4 mm (A, C, D, G, H, J-O) and BL 9.1 mm (B, E, F, I); A, head valve in dorsal view, and B in ventral view; C, intermediate valve IV in dorsal view, D, detail of aesthetes of valve IV; E, dorsal view of valve IV; F, insertion teeth and eaves detail of valve IV; G, dorsal view of tail valve; J, lateral view of tail valve. K, radular teeth; L, detail of the major lateral tooth cap; M, detail of the minor lateral and centra teeth. N, girdle spicules ornamentation; O, section of the girdle, shows the tufts detail.

FIGURE 18. Lepidochitona acapulcoensis Reyes-Gómez and Flores-Garza sp. nov.; paratype, EMU 11417, Majahua,Acapulco, Guerrero, SEM images of a specimen of 9.4 mm length; A, Girdle hyaline spicules of anterior tufts (between valve I and II), B and C, hyaline tufts detail; D, marginal spicules.

FIGURE 21. Lepidochitona beanii, Bahía Kino, Sonora; 7.3 mm BL. Dorsal view of: A whole specimen; B head valve; C, intermediate valve IV, D, tail valve.