Tooth morphology and food processing in Ophiothrix fragilis (Abildgaard, in O.F. Müller, 1789) and Ophiura albida Forbes, 1839 (Echinodermata: Ophiuroidea)

Based on the main feeding modes of two common European brittlestars, Ophiothrix fragilis and Ophiura albida, the pre­sent study relates the species’ tooth morphology to their function in processing food items of different structural quality. Clusters of grinding dental papillae in the suspension feeding O. fragilis seem most appropriate for loosening compound food items, i.e., food boli, or potentially for grazing. Large triangular teeth are considered to be used as crushing and cut­ting instruments, most likely for processing loosened or broken up food masses into smaller digestible portions. In the mostly predating and scavenging O. albida, sharp and pointy or broad scale-like oral papillae may serve in gripping and fixing live benthic prey organisms or carrion, while the larger spine-like teeth may be applied as carnassial instruments thrusting into the flesh of a prey organism and tearing off pieces. Designating the two species either as grinders and cutters processing compound and hard structured food or as grippers and tearers handling softer textures, still awaits confirmation through feeding experiments and observational documentation.

Growth rates and prey selection of two congeneric predatory caddisflies (Trichoptera: Rhyacophilidae)

Rhyacophila fuscula (Walker) and R. melita Ross inhabit cool southern Ontario streams, often together. In laboratory experiments, R. fuscula and R. melita showed significant weight gains in 2 weeks on four common prey taxa occurring in the field (Diptera: Chironomidae and Simuliidae; Ephemeroptera: Baetidae; and Trichoptera: Hydropsychidae). Rhyacophila melita grew significantly less than R. fuscula on three prey, but significantly better on Chironomidae. The prey eliciting highest growth rates from R. fuscula (Prosimulium, Baetis) and R. melita (Chironomidae) are most abundant in the habitats occupied by each of these predators. Prosimulium and Baetis are common on the surface of rocks in headwater regions where R. fuscula are at high densities, and chironomids are the most abundant prey organism in the marl (travertine) microhabitat of R. melita farther downstream. Where the two predators co-occur, they may compete for foraging areas in the spring, when prey and microhabitat resources are reduced by flood scour.