|Beroe forskalii Milne Edwards, 1841, top; B. cucumis Fabricius, 1780, 2nd; B. gracilis Kunne, 1939, 3rd; B. abyssicola Mortensen, 1927, 4th
Phylum Ctenophora / Order Beroida / Family Beroidae
Beroid ctenophores are a remarkable group that preys voraciously on other comb jellies. Unlike their cydippid relatives, Beroe lack tentacles throughout the life cycle. The body resembles a swimming sac, with a large forward directed mouth. Instead of sticky tentacles or large oral lobes, the cavernous mouth is used to engulf prey whole. Small Beroe use modified mouth cilia (the macrocilia) to bite off pieces of comb jelly prey; larger individuals also use the macrocilia to grab and swallow whole prey.
Using the eight comb rows for propulsion, Beroe are relatively strong swimmers. They swim constantly in search of prey, which are encountered blindly. Following a heavy meal, the meridional digestive canals (lying just below the comb rows) are readily visible – those in Beroe cucumis and Beroe abyssicola branch but do not connect, while those in Beroe forskalii form a network of connected branches. Beroe forskalii is an impressive comb jelly, attaining lengths of up to 15 cm. It has a broader mouth than the other three species and is particularly fond of lobate comb jellies like Leucothea and Bolinopsis B. forskalii can swell to ridiculous proportions after consuming an entire individual (bottom photo). Beroe gracilis is a more modest 3 cm, while the more common Beroe cucumis can reach lengths of 6 to 10 cm.
B. cucumis will dine on other species of Beroe and in captive situations inevitably wins out; it also preys on lobate and cydippid ctenophores and can be found in dense surface aggregations of several hundred within a small area. Beroe abyssicola is more of a deep water species, where it has an attractive rose coloration. This coloration tends to be lost when it visits surface waters, but the distinctive dark color of the pharynx often remains. Like other comb jellies, these Beroe have bioluminescent areas of the body. Beroe are a popular display for public aquariums featuring jellies. Since culturing them is not feasible, they must be collected. Feeding is a problem unless a reliable supply of comb jelly prey is available.