Boos, Karin

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Dental insights into ophiuroids: Feeding mechanisms and life styleKarin BoosBiologische Anstalt Helgoland/ Alfred Wegener Institut for Polar and Marine Research, PO Box 180, 27483 Helgoland; Karin.Boos@awi.deMICROPHAGEOUSa) The infaunal: surface and sub-surface deposit feeders, filter feeder, suspensionfeederb) The epibenthic-cryptic: filter feeder and suspension feederMACROPHAGEOUSThe epibethic: predators, scavengers and depositfeedersTop view of jaw element with teeth in Amphiura filiformis (Müller, 1776).Top view of jaw element with teeth in Acrocnida brachiata (Montagu, 1804).Top view on the mouth of Ophiothrix fragilis.Filter feeding posture of infaunal livingAmphiura filiformis. Photo by R.Rosenberg.Epibenthic lifestyle of Ophiura albida Forbes, 1839; Photo by Encyclopedia of Marine Life of Britain and IrelandEpibenthic cryptice lifestyle of OphiothrixFragilis (Abildgaard, 1789). Photo byEncyclopedia of Marine Life of Britain and Ireland.Top view of one jaw element in Ophiuraalbida.Ophiuroid echinoderms are highly specific towards different habitats reflecting lifestyles and feeding mechanisms. Previous studies have considered ophiuroids to be generally omnivorous macro- or microphageous feeders. According to their lifestyle, however, different feeding mechanisms may have evolved e.g. deposit feeding, filter feeding or predation. Most ophiuroids typically show more than one feeding mechanism along with their main feeding mode. In the present study, the morphology of teeth and associated papillae on individual jaw elements (see figure right) from ophiuroids performing different lifestyles (epibenthic, infaunal or epibenthic-cryptic) are compared and discussed in relation to reported feeding mechanisms and diets (for explanation on teeth and papillae see numbers in the pictures and adjacent text sections).Oblique view on the mouth in Ophiuraalbida. Lateral view of jaws with teeth in Ophiuraalbida. Top view of jaw element with teeth in Ophiothrix fragilis.Ophiura albida has three conical infradental papillae1and two or three broadened oral papillae2 located along the lateral sides of the jaw plates. Long and strongly pointed sharp teeth3 are found down the vertical jaw edges.Amphiura filiformis and Acrocnida brachiata both have a pair of slightly rounded infradentalpapillae1, as well as two pairs of long and pointy (A. filiformis) or one pointy pair and one leaf like (A. brachiata) pair of oral papillae2 along the sides of the jaw plates. The teeth3 along the vertical jaw edges are broad, almost square and flattened on the surface.In O. fragilis no oral or infradental papillae are present along the lateral jaw sides. A row of short and flat teeth3 located along the vertical jaw edges is surrounded by numerous dental papillae4, which are slightly longer than the teeth and have tapered tops. The front row of the dental papillae is shorter than the rest, seemingly representing infradentals.4312333Macrophageous epibenthic ophiuroidsMost representatives of the genus Ophiura live on different soft bottom sediments. They have been characterised to chiefly predate on epibenthic or infaunal organisms and to scavenge. Hunted or encountered prey is mostly gripped in arm slings or dug out of the sediment. Jaws, heavily armoured with strong and pointy teeth may be used in gripping or tearing flesh of captured prey. Interestingly, reports have designated Ophiura spp. to feed as surface and subsurface deposit feeders as well. In fact, stomach content analyses of O. albida revealed comparably high amounts of sediment (> 75%) in comparison to remains of small benthic organisms. Dabbing their tube-feet over the sediment surface looking for food particles may contribute to the active intake of sedimental particles. However, due to their predaceous dental equipment, the reported high amounts of deposit material are more likely the result of burrowing while searching for food and predating on infaunal organisms. Microphagoues infaunal ophiuroidsInfaunal lifestyles, e.g. as in A. filiformis or A. brachiata, typically reveal a rather stationary feeding mode, making active hunting for prey or scavenging unlikely, although this has been reported a probable feeding habit. In fact, A. filiformis has been designated to feed predominately as podial suspension feeder. By protracting three arms out of its burrow it can filter particles out of the water column or dab them up from the sediment surface. Grinding teeth for processing smaller organisms or deposit material, as opposed to raptorial instruments, best reflect the species’ microphageous feeding habits, and make predation or scavenging an unlikely feeding mode. Microphagoues epibenthic- cryptic ophiuroidsSimilar results to its infaunal relatives were found for O. fragilis, a rheophilic epibenthic suspension feeder. Yet, both grinding and carnassial teeth were found in O. fragilis.These may enable the animal to process larger particles or prey organisms by crushing or cutting them. This intermediate type of dental morphology between its epibenthic and infaunal living relatives presented here, confirms predation and scavenging, reported as a probable feeding mode in the cryptic O. fragilis, likely to occur.References: Eichelbaum, E., 1910. Über Nahrung und Ernährungsorgane von Echinodermen. Wiss. Meeresunters. Kiel 11, 187-274./ Feder, H.M., 1981. Aspects of the feeding biology of the brittlestar Ophiura texturata. Ophelia 20, 215-235./ Hayward, P.J., Ryland, J.S. (Eds), 1995. Handbook of the Marine Fauna of North-West Europe. Oxford University Press, Oxford./ Hughes, D.J., 1998. Subtidal brittlestar beds, vol. IV. An overview of dynamics and sensitivity characteristics for conservation management of marine SACs. Scottish Association for Marine Science (UK Marine SACs Project), 78 pp./ Jangoux, M., Lawrence, J.M. (Eds), 1982. Echinoderm Nutrition. A.A. Balkema, Rotterdam.12231 12231Schematic overview of the ‚mouth‘ side of an ophiuroid (from Hayward and Ryland, 1996) and a single jaw element.

Dental insights into ophiuroids: Feeding mechanisms and life style

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