Acanthochitona

Abstract: Twelve species of the polyplacophoran genera Notoplax, Leptoplax , Acanthochitona and Cryptoplax (Chitonida: Acanthochitonina: Cryptoplacoidea) were found in Vietnamese waters for the first time. Five of them, namely Notoplax conica, Leptoplax doederleini , Leptoplax richardi n. comb., Acanthochitona achates and A. biformis, are new to Vietnamese fauna. The remaining seven species are new to science, namely: Notoplax odysseyi n. sp., Leptoplax nhatrangi n. sp., L. tongkingi n. sp., Acanthochitona condaoi n. sp., A. lanae n. sp., A. nigra n. sp. and A.ostreaphila n. sp. Leptoplax richardi n. comb. was transferred from the original genus Notoplax based on the redefinition of the genus given herein. We confirmed the occurrences of 21 species of the superfamily Cryptoplacoidea in the Vietnamese fauna, which makes them the richest group of chitons in Vietnamese waters. A peculiar feature, a comb-like blade in the major uncinal teeth of the radula is found in two new species, L. tongkingi n. sp. and A. ostreaphila n. sp. A similar feature is known only in two other distinct groups: the genus Ferreiraella of the family Ferreiraellidae of the order Lepidopleurida and the genera Tonicella and Boreochiton of the family Tonicellidae of the order Chitonida. This is the first report of this feature other than those two groups.

Abstract: The present study describes the species composition and vertical distribution of chitons in tide pools and on exposed rock areas of the intertidal zone of Samara, Guanacaste, Pacific Costa Rica. Nine different species of chitons were recorded, and their densities and sizes were determined using quadrate sampling. Physical (period of emersion, temperature and salinity range) and biotic (presence and diversity of food resources) factors were examined to assess their influence on distribution and abundance of each species. Ischnochiton dispar was the predominant species with densities of up to 200 ind m−2, representing 85.4% of all sampled individuals (N = 4193). The size of I. dispar was positively correlated with the size of the inhabited boulders. Two species (I. dispar and Stenoplax limaciformis) showed segregation in size: I. dispar being negatively and S. limaciformis positively correlated to the distance from the shore. Two of the nine species (Chiton stokesii and Acanthochitona hirundiniformis) occurred mainly on rocky areas outside the tide pools with variable amounts of exposure to air during each tidal cycle. In both species the tide pool specimens were significantly smaller than those collected in the rocky areas. Distribution of all other species was restricted to the tide pools and species had their peak abundance in the zones with more moderate conditions and a higher diversity of algae, resulting in the highest chiton diversity in these areas.

Abstract: EnglishThe polyplacophoran fauna from the rocky-coralline system of Oaxaca, in the Mexican Tropical Pacific, consists of 13 species, including either endemic and widely distributed species. Chitons were collected in eight localities along the central area of Oaxaca, at 0-7 m of depth. Lepidochitona (L.) salvadorensis is recorded for the first time from Mexican waters. New data of distribution are reported for Lepidozona (L.) serrata, Stenoplax (S.) mariposa and Acanthochitona arragonites all previously known only from the Gulf of California. Chiton (C.) albolineatus is confirmed as an endemic species of the Mexican Tropical Pacific. Two species, Lepidochitona sp. and Ischnochiton sp., are probably new and will be described when morematerial will be available. Each species is systematically treated, commented and illustrated. italianoNegli ambienti di natura roccioso-corallina di Oaxaca, nel Pacifico Tropicale del Messico, sono state individuate 13 specie di chitoni. Sono presenti sia elementi endemici, sia elementi ad ampia distribuzione geografica. I chitoni studiati provengono da otto localita nel settore centrale di Oaxaca, e sono stati raccolti a profondita di 0-7 m. Lepidochitona (L.) salvadorensis, in precedenza nota solo per El Salvador, viene segnalata per la prima volta in acque messicane. Nuovi dati di distribuzione vengono riportati anche per Lepidozona (L.) serrata, Stenoplax (S.) mariposa e Acanthochitona arragonites, tutte note in precedenza solo per il Golfo di California. Chiton (C.) albolineatus risulta essere una specie endemica del Pacifico Tropicale del Messico. Vengono segnalate due specie, Lepidochitona sp. ed Ischnochiton sp., probabilmente nuove ed in attesa di essere descritte sulla base di materiale supplementare. Tutte le specie ritrovate sono trattate sistematicamente ed illustrate.