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Graziella Mura

Abstract

Fairy shrimps have recently been considered for use in larval fish rearing, because of their size and their nutritional value. This study presents the results obtained for Thamnocephalus platyurus, a species from Central and South America, which was already mass cultured successfully in the United States in a flow-through system. Cysts and instar I nauplii have an unfavourably large size: mean diameter 278 μm and 240 μm for untreated and decapsulated cysts, respectively; mean naupliar length 436 μm. However, the species shows an interesting pattern in its fatty acid methyl ester (FAME) profile, especially with regard to polyunsaturated fatty acids (PUFA). In particular, T. platyurus cysts are characterized by significant levels of the 18:2 and the 20:5w3, and by the presence of the 22:6w3, which are normally absent in Artemia cysts.

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Graziella Mura

Abstract

La distribuzione stagionale di Artemia salina e Brancfainella spinosa (Anostraca) è stata studiata in una pozza temporanea salmastra della costa occidentale della Sardegna. Artemia è presente da sola a salinità superiori al 70%, mentre per valori inferiori è presente anche Branchinella. Uno studio dettagliato della fluttuazioni annuali dei parametri chimicofisici ha dimostrato che il ciclo vitale di quest'ultima specie è assai più limitato in confronto a quello di Artemia. La biologia delle due specie è stata studiata in termini di schiusa, velocità di crescita, maturazione sessuale e riproduzione. Entrambe coesistono allo stadio di adulto per un lasso di tempo strettamente dipendente dagli eventi climatici. La breve sovrapposizione dei cicli osservata ha inoltre sollevato la questione di una possibile competizione, o di eventuali meccanismi per evitarla. Comunque le significative differenze rilevate per quanto concerne i tratti fondamentali del ciclo, e le differenze di dimensioni delle due specie in esame fanno ritenere che esista una separazione di nicchia. I risultati ottenuti vengono discussi e confrontati con altri casi segnalati in letteratura.

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Graziella Mura

Abstract

Morphology of the molar surface of the mandibles is examined via SEM and discussed in relation to possible functions, after reviewing and reconsidering the existing literature on the subject. A comparison of mandibular (present work) and trunk limb morphology (Daborn, 1978, 1979) reveals some discrepancies between mandible structure and supposed feeding habits of some fairy shrimp species.

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Graziella Mura

Abstract

Occasional reports on mandibular morphology in some Anostracans by means of optical (Ocioszynska-Bankierowa, 1933; Lynch, 1937; Linder, 1941; Mahoon, 1960; Fryer, 1966) and SEM microscopy (Tyson & Sullivan, 1981; Fryer, 1983; Schrehardt, 1987; Mura, 1991; Mura & Del Caldo, 1992, 1993) posed the question whether this character might be taxonomically relevant. This view was supported by the findings of Edwards (1980) on cladocerans, and of Martin (1988) on conchostracans, thus suggesting to perform a wider inquiry. This SEM study examined the morphology of the molar surfaces in a large number of representatives of the 8 existing Anostraca families, in order to obtain further information. The results are contrasting, and vary depending on the families considered. The observed differences, when present, are detectable only at the genus level and never extend to species, except on rare occasions (for example in the branchinectids). The observations concern both shape and ornamentation (number of teeth and spines at the posterior tips and on the dorsal margins, texture of the transition area, extension of the antero-ventral area, and so on). The most evident variation was expected between non-related genera, but this was shown to be invalid in many cases, and did not depend on the systematic position of the taxa examined. Moreover, even within a family, intergeneric diversity was frequently not observed (like in chirocephalids and branchipodids). Finally, intraspecific variation was also recorded, at least for those species where a great number of specimens was available for study.