The morphology of the branchial skeleton of heterocongrines (Anguilliformes: Congridae) and its relation to their diet.

Members of the subfamily Heterocongrinae (Congridae) are a peculiar group of anguilliform eels that construct sandy borrows, form large colonies, and are popularly recognized as garden eels. They live with most of their bodies inside self-constructed borrows exposing their heads and trunk to feed on zooplankton, preferably copepods, that are brought passively by currents. As plankton feeders there was a suspicion that their branchial skeleton would have structures that could aid in the filtering process, such as highly developed or modified branchial rakers, which are observed in other suspension-feeding fishes, such as anchovies and sardines. Branchial rakers, however, were considered to be absent across Anguilliformes (except for Protanguilla). Nonetheless, specimens that were examined using clearing and staining and computed tomography showed, in all cases, branchial rakers associated with their gill arches. Heterocongrines have branchial rakers across their first to fourth branchial arches. These rakers are conical and apparently unossified, but further studies are necessary to attest its degree of ossification or its complete absence. Their pharyngeal tooth plates are reduced, a condition that may reflect their preference for smaller food items. Additionally, they may use crossflow filtering to feed, although detailed studies are necessary to clarify if hydrosol sieving may also aid in food capture. Furthermore, the present study proposes that the presence of branchial rakers should be better investigated in Anguilliformes with similar feeding habits as heterocongrines, considering that these structures may be more widespread within the group than previously considered.

A new congrid eel (Teleostei: Anguilliformes: Congridae) from the Western Pacific, with an analysis of its relationships.

A new species of congrid eel, Bathycongrus villosus sp. nov., is described from the Philippines and Vanuatu. It is similar to some of the small-toothed species currently placed in Bathycongrus and to the species of Bassanago. In this paper we compare the new species to Bassanago albescens (Barnard, 1923) and to Bathycongrus parviporus Karmovskaya, 2011, which it most closely resembles. An analysis of 19 characters shows that it agrees with Bat. parviporus in 16 characters and with Bas. albescens in one. In two characters, the three species are all different. We therefore place it in Bathycongrus.