Filter-feeding mechanisms in some brachiopods from New Zealand

Abstract

Summary All major types of lophophore in branehiopods, except the ptyeholophe, are represented among the growth stages of the five species described here. The basic ciliary mechanisms are uniform, and similar to those known in other species. The mantle cavity is always divided by the lophophore into inhalant and exhalant chambers with separate apertures; but the arrangement may change radically during ontogeny with the increasing complexity of the lophophore, which is attributed to a dimensional relation between food‐collecting capacity and metabolic requirements. The limited variety of lophophoral arrangements is taken to reflect an inherent limitation imposed by the basic structure and function of lophophores. The feeding mechanisms are compared briefly with those of other filter‐feeding animals.

Ciliary and mucus-net filter feeding, with special reference to fluid mechanical Characteristics

“…In the one type particles rent diameter. Middle, earliest functional lophophore stage; left, short segment of lophophore with filaments; right, cross section of filament, indicating path of particle from through current into surface current (modified from Rudwick, 1962Rudwick, , 1970. (C) Bivalve, upstream retention.…”

The lophophore and ciliary feeding mechanisms of the brachiopod Crania anomala (Müller)

“…3. Rowell (1961) has suggested that the inarticulate Discinisca may be a living representative of a type of spirolophous current-system postulated by Rudwick (1960) for the extinct Spiriferoidea, in which the interior of the spirals would be filled with exhalant water, the direction of filtration being reversed from that found in Crania, Lingula and Tegulorhynchia. Should this be confirmed by observation on living specimens, it will add support to the theory of an inherent limitation on the possible variety of spirolophous current-systems.…”

“…The current-system (Rudwick, 1960) of C. anomala, like that of all other brachiopods that have been investigated, consists essentially of one-way flow through a mantle cavity which is completely divided by the lophophore into separate inhalant and exhalant chambers, with separate inhalant and exhalant apertures to the exterior.…”

“…The spirolophe of Crania is unsupported by skeletal structures, and the body of the lophophore is a highly muscular structure (see Blochmann, 1892); the spirolophe of Tegulorhynchia is supported basally by skeletal crura and elsewhere only by a hydrostatic skeleton-the very thin-walled great brachial canal (see Atkins, 1962). This striking convergence in the filter-feeding system may reflect a fundamental inherent limitation on the variety of currentsystems which can possibly be produced by a spirolophe (see Rudwick, 1960).…”

Notes on the reproductive biology of brachiopods from southern New Zealand

“…Long (1964) dealt mainly with l'arval development, and reviews of the phylum by Hyman (1959) and Rudwick (1970) confirmed that little is known about breeding seasons, the varialbles influencing gonad ripening, or the mechanisms which trigger spawning. Water tempemture, day lenglth, and other physical variables governed by latitude are known to influence the breeding cycle in many invertebrates (see, for example, Thorson (1950) and Giese (1959», and the same can be expected in brachiopods (Rudwick 1962, Doherty 1976). …”