| Abstract: | The four, evolutionarily independent, lineages of suspension feeding
elasmobranchs have two types of branchial filters. The first is a robust,
flattened filter pad akin to a colander (e.g., whale sharks, mantas and
devil rays) while the second more closely resembles the comb-like gill
raker structure found in bony fishes (e.g., basking and megamouth
sharks). The structure and the presence of mucus on the filter elements
will determine the mechanical function of the filter and subsequent particle
transport. Using histology and scanning electron microscopy, we investigated
the anatomy of the branchial filters in 12 of the 14 species of
Chondrichthyian filter-feeding fishes. We hypothesized that mucus producing
cells would be abundant along the filter epithelium and perform
as a sticky mechanism to retain and transport particles; however, we
found that only three species had mucus producing goblet cells. Two of
these (Mobula kuhlii and Mobula tarapacana) also had branchial cilia,
indicating sticky retention and transport. The remaining filter-feeding
elasmobranchs did not have a sticky surface along the filter for particles
to collect and instead must employ alternative mechanisms of filtration
(e.g., direct sieving, inertial impaction or cross-flow). With the exception
of basking sharks, the branchial filter is composed of a hyaline cartilage
skeleton surrounded by a layer of highly organized connective tissue that
may function as a support. Megamouth sharks and most of the mobulid
rays have denticles along the surface of the filter, presumably to protect
against damage from large particle impactions. Basking sharks have
branchial filters that lack a cartilaginous core; instead they are composed
entirely of smooth keratin. Anat Rec, 00:000–000, 2013. VC 2013 Wiley
Periodicals, Inc.
Key words: histolog
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