On the Ciliary Mechanisms and Interrelationships of Lamellibranchs: PART I: New Observations on Sorting Mechanisms

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Abstract
Accounts are given of the ciliary feeding mechanisms in: A, Nuculana minuta (Muller);B, Glycymeris glycymeris (L.), and Area tetragona Poli; C, Heteranomia squamula (L.), Monia squama (Gmelin), and Monia patelliformis (L.); D, Pteriahirundo (L.); and E, Solenmargina tus Montagu, Ensis siliqua (L.), Ensis arcuatus (Jeffreys), and Cultellus pellucidus (Pennant). These Lamellibranchs agree in possessing a certain ciliary sorting mechanism on the gills themselves, namely adjoining tracts of frontal cilia beating in opposite directions on the same gill filament or leaflet. In Pteria, Solen, and Ensis, bivalves with plicate and heterorhabdic lamellae, this occurs on the ordinary and apical filaments only, and is complicated by a difference in the direction of the frontal currents in the plical grooves and on the crests, such as is already known in Pecten, Ostrea, and Lima. In Cultellus it is found on both lamellae of the inner demibranch, but on the ascending lamella only of the outer demibranch. The types of frontal ciliation of the gill filaments dealt with in the papers of Part I are given in Table I. Tracts of fine frontal cilia, beating continuously, convey particles intended for consumption, while tracts of coarse cilia, fully active only when stimulated, transport material intended to be rejected. In all, except the Protobranch Nuculana, unwanted material is carried to the ventral edges of the demibranchs, which are generally ungrooved or slightly grooved, rarely deeply grooved. In the Arcidae and Anomiidae the current along the edge is posterior in direction, so that such of the unwanted material as does not fall on the mantle is transported directly to the exterior. In Pteria, Solen, Ensis, and Cultellus the marginal current is oralward, but if the load be heavy much falls on the mantle, and is conveyed posteriorly by its recurrent tracts and finally ejected on sudden closure of the valves. In the Anomiidae the sorting mechanism on the gills was not observed functioning satisfactorily under experimental conditions, in that there was no appreciable transportation of intended food particles dorsally, and it would seem that members of this family feed mainly after the manner of the Ectoproct Polyzoa, that is on particles brought directly to the broad dorsal food grooves by the water current set up by the lateral cilia. In Nuculana minuta the highly specialized method of sorting on the small gills would seem to have been inherited from a form in which the gills played a considerably greater part in the nutrition of the animal than they do in this Protobranch.

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