Morphological descriptions of the eggcases of skates (Rajidae) from the central-western Mediterranean, with notes on their distribution

PORCU, CRISTINA;MARONGIU, MARTINA FRANCESCA;BELLODI, ANDREA;CANNAS, RITA;CAU, ALESSANDRO;MELIS, RICCARDO;MULAS, ANTONELLO;SOLDOVILLA, GIUDITTA;VACCA, LAURA;FOLLESA, MARIA CRISTINA

2017-01-01

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Abstract

Eggcases of eight rajiform skates (Dipturus nidarosiensis, D. oxyrinchus, Leucoraja melitensis, Raja asterias, R. brachyura, R. clavata, R. miraletus and R. polystigma) present in the central-western Mediterranean are described, based on speci- mens obtained from shery surveys. Eggcase features such as dimensions, horns and apron lengths, and presence/ absence of lateral keels were crucial to discriminate the eggcases of the various species. Morphological and morpho- metric data, con rmed by the multivariate analysis, indicated that the eggcase of R. miraletus and L. melitensis were distinct from those of the other species for being unkeeled. Within the species having keeled eggcases, those of the genus Dipturus and R. brachyura were discriminated from the remaining group by having the largest dimensions and aprons. Sandy bottoms (<100–150 m depth) were identi ed as egg-laying sites (i.e. sites with females bearing eggcases in uteri) for many species belonging to genus Raja Raja asterias, R. brachyura, R. miraletus and R. polystigma). The nding of R. asterias and R. miraletus carrying eggcases yearly on the same sites, seems to con rm the theory that many rajid species demonstrate site delity, returning to the same depositional area on an annual basis. Some remarks on reproductive biology of these skates are also provided. The eggcase identi cation key reported here repre- sents the rst for the Mediterranean and may be useful, in the future, to identify egg-laying grounds of skates with a nonlethal method.