Nuttallina crossota ( Berry, 1956 )

Reyes-Gómez, Adriana, Vargas-Ponce, Ofelia, Galván-Villa, Cristian, Salgado-Barragán, José, Esqueda-González, Ma. Del Carmen & Ríos-Jara, Eduardo, 2023, Inventory of chiton species (Polyplacophora) from the rocky intertidal of the Northern Gulf of California, with an illustrated taxonomic key, Zootaxa 5296 (2), pp. 147-178 : 164

Nuttallina crossota ( Berry, 1956)

( Figures 3C , 9A–I )

Nuttallina crossota Berry, 1956: 71–74 . Chresonymy and synonymy in Ferreira (1982).

Type material. Holotype, SBMNH 34423 from the “Berry collection 15133”.

Type locality. Puerto Peñasco , Sonora, México.

Material examined. Forty-one specimens, BL 8.5– 7.1 mm.

Habitat. In the upper intertidal on medium–sized and small rocks, on exposed rocky massifs, among brown algae that were also under large rocks buried in sand.

Remarks. Nuttallina crossota exhibits irregular granulose sculpture arranged in quincunx ( Figs. 9A–D ); the lateral areas are reduced with 2 elevated thick radial ribs ( Figs. 9B, C ); jugal area with the sculpture, however, usually very much eroded in adult specimens ( Figs. 9B, C ). Girdle densely covered with small elongated, striated spicules and interspersed, thick hyaline spicules ( Figs. 9E–F ). Major lateral radular tooth tricuspid, minor lateral reduced, smaller and shorter than central tooth; central tooth appears as a sub–rectangular plate with its apical edge slightly bent outwards ( Figs. 9H–I ).

The genus Nuttallina was considered a member of the family Callistoplacidae (Pilsbry 1893; Smith 1960) due to the similarity of the insertion slits of the articulamentum and the ribs of the valve tegmentum. Later, this genus was included in the family Lepidochitonidae (see Thiele 1929; Thorpe 1971; Van Belle 1977) based on four characteristics: 1) the tegmentum has granules, 2) the tail valve is smaller than the head valve, 3) the major lateral tooth is tricuspidate, and 4) the girdle scales are small.

Nuttallina crossota is endemic and the only species of this genus in the Gulf of California. At Puerto Peñasco (the type locality), the species was not found, while at Playa Cementerio, the number of the collected individuals was three and at Las Palmas, Bahía Kino two specimens were found. However, at Pie de Faro , Bahía San Felipe, the number of individuals collected was high (36 individuals). Most of the individuals showed an eroded tegmentum on the jugal area of the intermediate valves; some were eroded in the lateral areas as well. At Pie de Faro , Bahía San Felipe, the specimens were found sheltered among brown algae densely covering a large volcanic rock massif with a rough surface, 1.60 m high and 12 m long. During low tide, the rock massif was totally exposed and dry with Nuttallina crossota covered by the algae. In the lower part of the beach, they were observed on (large) submerged rocks semi–buried in sand and buried on the base of the rock massif.

Figures

FIGURE 3. Chiton species obtained from the Northern Gulf of California. A. Dorsal and lateral view of Dendrochiton lirulatus CUCBACM 00479. B. Dorsal view of Lepidochitona beanii CUCBACM 00486. C. Dorsal and lateral view of Nutallina crossota CUCBACM 00488. D. Dorsal view of Chiton virgulatus CUCBACM 00491. E. Dorsal view of Acanthochitona avicula CUCBACM 00494. F. Dorsal view of Acanthochitona exquisita CUCBACM 00497.

FIGURE 9. Scanning electron microscope images of Nuttallina crossota CUCBACM 00488. A. Dorsal view of head valve. B. Dorsal view of intermediate valve IV. C. Dorsal view of half of intermediate valve IV shows the lateral areas. D. Dorsal view of tail valve. E. Segment of girdle in dorsal view shows the hyaline spicules. F. Radular teeth. G. Portion of girdle showing the ornamentation of spicules. H. Portion of radula. I. Detail of central, minor, and major lateral teeth.