Larval development of Canadian Atlantic oregoniid crabs (Brachyura: Majidae), with emphasis on Hyas coarctatus alutaceus Brandt, 1851, and a comparison with Atlantic and Pacific conspecifics

Abstract

Larval development of Hyas coarctatus alutaceus Brandt, 1851, consisting of two zoeal stages followed by a megalopa, is described for the first time from larvae of known parentage. Mean duration of the first and second zoeal stages was 41 and 30 days at ambient temperature (3–12 °C) and 30 and 36 days at 9 °C, respectively. First megalopae appeared after 69 and 62 days post-hatching at ambient temperature and 9 °C, respectively. For comparison, all larval stages of Hyas araneus, Hyas coarctatus coarctatus, and Chionoecetes opilio were also cultured from local populations. Zoeae of all these species were found to be very similar. Larvae of H. c. alutaceus were significantly larger than those of H. c. coarctatus, surpassing even those of H. araneus. Laboratory-reared and wild-caught larvae from different geographic areas were also compared. Characters potentially useful in the interspecific and subspecific differentiation of zoeae are presented. These include (i) relative dimensions of the carapace, spinules on carapace spines, setae on antennal exopodites, lateral abdominal spines relative to abdominal somites, spines on the telson furca, and dorsolateral spines on abdominal somite 3; (ii) presence or absence of spinules on lateral abdominal spines and knobs on eyestalks; (iii) setation of appendages; and (iv) pigmentation. Megalopae are also compared morphometrically and meristically. Larvae vary more than appeared previously. A key for the identification of larval stages of C. opilio and Hyas spp. is provided.