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Pattern of Mandibular Morphology in Anostraca with Some Taxonomical Remarks

Graziella Mura
Crustaceana
Vol. 69, No. 2 (Mar., 1996), pp. 129-154
Published by: Brill
Stable URL: http://www.jstor.org/stable/20105185
Page Count: 26
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Pattern of Mandibular Morphology in Anostraca with Some Taxonomical Remarks
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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. /// Osservazioni occasionali, compiute precedentemente sia con il microscopio ottico (Ocioszynska-Bankierowa, 1933; Lynch, 1937; Linder, 1941; Mahoon, 1960; Fryer, 1966), che con il microscopio a scansione (Tyson & Sullivan, 1981; Fryer, 1983; Schrehardt, 1987; Mura, 1991; Mura & Del Caldo, 1992 e 1993), hanno sollevato la questione circa la validità della morfologia mandibolare negli Anostraci da un punto di vista tassonomico. Tale ipotesi, trova conferma nelle osservazioni di Edwards (1980) sui Cladoceri, e di Martin (1988) sui Concostraci, e ci ha indotti pertanto ad indagare ulteriormente. Questo studio al SEM ha preso in esame la morfologia mandibolare di un gran numero di rappresentanti delle 8 famiglie di Anostraci oggi conosciute, allo scopo di ottenere la maggior quantità possibile di informazioni. Le differenze osservate, quando esisteóno, sono risultate rilevabili solo a levello di genere, e non si estendono mai alle specie, salvo rare occasioni (ad esempio nei Branchinectidae). Le osservazioni compiute concernono sia la forma che la ornamentazione (numero di denti e spine presenti sul polo posteriore e sui margini dorsali, tessitura dell'area di transizione, estensione dell'area antero-ventrale, etc.). Le maggiori differenze, attese in particolar modo tra generi non affini, sono risulate in molti casi inesistenti, e comunque indipendenti dalla posizione sistematica dei taxa presi in esame. Inoltre, persino nell'ambito di una stessa famiglia non sono state in molti casi osservate differenze intergeneriche (ad esempio nei Chirocephalidae e nei Branchipodidae). Infine, e'stata anche riscontrata una certa variabilità intraspecifica, almeno nell'ambito di quelle specie per le quali erano disponibili un gran numero di esemplari.

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