Diagnostic morphological characteristics of laboratory-reared Cancer oregonensis (Brachyura: Cancridae) with recommendations for identifying cancrid zoeae in the Salish Sea

Abstract

Cancrid larvae are among the most abundant decapods in the meroplankton in the Northeast Pacific; however, their study remains problematic because of difficulty discriminating among larvae of sympatric congeners. We addressed this issue by providing morphological characteristics from laboratory-reared Cancer oregonensis zoeae that can be used to distinguish this species from published descriptions of zoeae of other species of Cancer found in the Salish Sea (C. magister, C. productus, C. gracilis, C. antennarius). The angle of lateral exospines projecting from the furca of the telson and the length of the exospines relative to the length of the furcal branches of C. oregonensis are smaller in comparison to all stages of C. magister and C. productus. The setal formula on the inner margin of the telson furca and the number of setae on the exopod of the second maxilliped also vary between certain stages of C. oregonensis, C. magister and C. productus. The carapace length of C. oregonensis becomes noticeably longer than that of C. antennarius and C. gracilis as zoeal stages progress. The ratio of the length of the posterolateral spines projecting from the third and fourth abdominal somite to the length of the subsequent abdominal somite is greater in C. oregonensis than in C. antennarius and C. gracilis, and may be especially useful for identification when size differences are less apparent at early stages. We also observed stage duration and mortality of zoeae reared at ~13°C, which were consistent with previous estimates reported for laboratory-reared cancrid larvae.