Acanthochitona avicula ( Carpenter, 1864 )

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 : 166

Acanthochitona avicula ( Carpenter, 1864)

( Figures 3E , 10A–F )

Acanthochites avicula Carpenter 1864: 18–27 . Chresonymy and synonymy in Watters (1990).

Type material. Lectotype by designation of Watters (1981), ANSP 349330 .

Type Locality. Catalina Island , California, USA .

Material examined. One specimen, BL 9.6 mm.

Habitat. In the intertidal zone, in an exposed area with semi–wet rock mounds during low tide. The chiton was collected from the lower part of a rock semi–buried in sand with brown and red crusty algae patches.

Remarks. Acanthochitona avicula exhibits pustules with numerous (10–16) micraesthetes ( Fig. 10D ). The jugum exhibits a smooth surface with the micraesthetes openings visible ( Figs. 10B, C ). Girdle densely covered by curved, striated hyaline spicules ( Fig. 10E ). Radula with tricuspid major lateral teeth, the middle cusp is longer than the other two; minor lateral tooth very reduced; the central tooth is an elongated, apically hook–like plate ( Fig. 10F ).

Acanthochitona avicula was considered a synonym of A. angelica Dall, 1919 by several authors ( Thorpe 1971; Abbott 1974; Kaas & Van Belle 1990). However, Smith (1977) indicated that the tegmentum color pattern of A. angelica does not correspond to the variations in color observed in A. avicula . Watters (1990) recognized both species as independent, considering the distribution of A. angelica in the Gulf of California, without specifying the sampling sites, which were somewhere in the Bahía de los Ángeles, Baja California (BC), and Islas Tres Marías, Nayarit. Moreover, he indicated that A. avicula has a wider distribution, from the Bahía la Choya to Puerto Peñasco, Sonora. He reported it as a common species in the intertidal and up to 20 m depth.

Watters (1990) provided a detailed morphological description of the Acanthochitona species from the eastern Pacific and provided for all of them SEM images of the valve pustules. This author showed that the jugum of A. avicula has 8 to 12 deep longitudinal grooves and that the pustules of the tegmentum are drop–shaped, densely covering the lateropleural areas. Conversely, A. angelica has a jugum with 7 to 10 more superficial grooves, the pustules are smaller and slightly rounded. The A. avicula specimen obtained in the present study showed that the pustules adjacent to the jugum are elongated, the peripheral pustules are less elongated, and the jugum is smooth on its center.

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 10. Scanning electron microscope images (A–F) of Acanthochitona avicula CUCBACM 00494. A. Dorsal view of head valve. B. Dorsal view of intermediate valve IV. C. Dorsal view of tail valve. D. Dorsal view of Valve IV detail of pustules. E. Portion of girdle, shows the dorsal girdle spicules. F. Portion of radula, show the central, minor and major lateral teeth. Acanthochitona exquisita CUCBACM 00497 (G–L). G. Dorsal view of head valve. H. Dorsal view of intermediate valve IV. I. Dorsal view of tail valve. J. Dorsal view of valve pustules of valve IV. K. Magnification of valve IV pustules. L. Radular teeth.