The large size, high trophic level and wide distribution of Hexanchiformes (cow and frilled sharks) should position this order as important apex predators in coastal and deep‐water ecosystems. This review synthesizes available information on Hexanchiformes, including information not yet published, with the purpose of evaluating their conservation status and assessing their ecological roles in the dynamics of marine ecosystems. Comprising six species, this group has a wide global distribution, with members occurring from shallow coastal areas to depths of c. 2500 m. The limited information available on their reproductive biology suggests that they could be vulnerable to overexploitation (e.g. small litter sizes for most species and suspected long gestation periods). Most of the fishing pressure exerted on Hexanchiformes is in the form of commercial by‐catch or recreational fishing. Comprehensive stock and impact assessments are unavailable for most species in most regions due to limited information on life history and catch and abundance time series. When hexanchiform species have been commercially harvested, however, they have been unable to sustain targeted fisheries for long periods. The potentially high vulnerability to intense fishing pressure warrants a conservative exploitation of this order until thorough quantitative assessments are conducted. At least some species have been shown to be significant apex predators in the systems they inhabit. Should Hexanchiformes be removed from coastal and deep‐water systems, the lack of sympatric shark species that share the same resources suggests no other species would be capable of fulfilling their apex predator role in the short term. This has potential ecosystem consequences such as meso‐predator release or trophic cascades. This review proposes some hypotheses on the ecology of Hexanchiformes and their role in ecosystem dynamics, highlighting the areas where critical information is required to stimulate research directions.

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The reproductive biology of the angel shark Squatina guggenheim was described based on 584 animals sampled in the San Matías Gulf, Argentina, between January and December 1996. Both sexes of S. guggenheim reached similar total length and matured at similar sizes (between 73 and 76 cm total length). In males, testes were paired and showed diametric development. Adult males were predominant in the austral autumn and winter, and were capable of mating all year round. In females, only the left ovary was functional. The maximum follicular diameter recorded (6 cm) was observed during the austral autumn and winter, with ovulation occurring during spring and summer. The size distribution of the follicles indicated that adult females presented different maturational stages in all the seasons. No post-ovulatory follicles were distinguished in any of the females examined. The seasonal analysis showed significant differences in sex abundance. Adult males were predominant in autumn and winter, juvenile males in spring, and adult females in summer. Only a few pregnant animals were caught in January, May and September. The results suggest that S. guggenheim females show a biannual reproductive cycle with gestation taking at least one year, and that the San Matías Gulf is not one of their main breeding areas.