Morphometry and sexual maturity in the spider crab Maja squinado (Decapoda: Majidae) in Galicia, Spain

Ontogenetic changes in the relative growth of males and females of the spid er crab Maja squinado were analyzed and related to their reproductive (matu rity) status in order to define criteria to assign individuals to each grow th phase. The sampling was carried out in two different areas of southern G alician waters, northwestern Spain, in shallow water (<10 m) with mixed roc ky-sandy bottoms (juvenile and postpubertal adult areas) and deep water (>2 0 m) with soft bottoms (adult habitat). A Principal Component Analysis (PCA ) of morphometric variables and a nonhierarchic K-means cluster of PCA scor es differentiated two morphometric groups defined as juvenile and adult pha ses. A significant change in allometry of cheliped size was detected in juv enile males with a break point at a 109-mm carapace length (CL). This point may indicate a change in the relative growth of juveniles, separating the immature and adolescent phases. Histological analysis of a subsample of mal es showed that sperm were present in most adolescent crabs, but not in imma ture crabs. Bivariate morphometric linear discriminant functions allow for the identification of juvenile and adult males (classified previously by K- means cluster) with over 99% correct classification using CL and the length or height of the right cheliped. Carapace length at the onset of sexual ma turity was estimated to be 132.7 mm (50% of adult males), although in a bro ad range, 112-165 mm, the size of juveniles and adults overlap. The life hi story of male spider crabs shows 3 phases differentiated by the relative gr owth rate of chelipeds separated by two 2 critical molts: prepubertal molt (immature-adolescent) determines a slight increase in allometry, and pubert al or terminal molt (adolescent-adult) determines an increase in the relati ve size and allometry of chelipeds and the onset of functional maturity. Fe males showed only 2 phases separated by the terminal molt. Growth of chelip eds in females showed no changes in allometry and was similar to juvenile m ales. Juvenile females presented a smaller relative width and a higher allo metry of the abdomen with regard to adult females. Unlike juvenile females with a flat abdomen, adult females with a domed abdomen have well-developed pleopods, gonads, and seminal receptacles. Carapace length at the onset of sexual maturity was estimated to be 130.4 mm (50% of adult females). The r ange of overlap of the size of juveniles and adults (114-143 mm) was smalle r than in males.