Dear Getulio, godd morning!

I agree with you about the deep-water elsmobranchs descriptions and records from Brazil and that the deep water diversity is really higher than expected. In other hand, several species from Northern and Eastern Atlantic and even from Indian and Eastern Pacific have been reported from our coast in the the last 10-15 years (examples are species of Aulopidae, Synodontidae, Bramidae, Merluccidae, Ateleopodidae, Grammicolepididae, among many others). So I assume that deep waters fishes, mainly Actinopterygii, even being of very wide distribution, are more speciose than we thougth years ago but much more research must be done to answer your first question. 

Best wishes,

Alfredo

no, the Elasmobranchiis it is one under class of the Chondrichtyeses that are brackish waters

I am uncertain whether deep water fishes can be considered more diversified or not, but part of the problem rely on the level of knowledge of certain regions in specific oceans. For instance, in some places (e.g., the Pacific coast of South America) deep sea fishes are very incompletely known. Some recent deep-sea expeditions have discovered many new fishes (most of which still remain undescribed) but also new records for non-deep see waters. In this case, many of those new records have been explained as results of El Nino or La Nina Phenomenon or currents that have significant changes in the marine biodiversity. To my best knowledge, the area of origin of a group is something more complex than to be explained using number of species in an specific area (e.g., deep-sea waters).