Structure and Function of Metazoan Ciliary Bands and Their Phylogenetic Significance

Abstract

Ciliated epithelia, especially the ciliary bands used in swimming and filter feeding, of representatives of the following phyla have been investigated: Porifera, Cnidaria, Annelida, Mollusca, Sipuncula, Nemertini, Platyhelminthes, Entoprocta, Ectoprocta, Rotifera, Pterobranchia, Phoronida, Brachiopoda, Echinodermata and Enteropneusta. The trochaea theory predicts that Porifera and Cnidaria have only monociliate cells and lack ciliary bands used in filter‐feeding, that the gastroneuralian larvae have downstream‐collecting ciliary bands with prototroch and metatroch of compound cilia on multiciliate cells, and that notoneuralian larvae have an upstream‐collecting neotroch on monociliate cells. The observations generally fit these predictions and the exceptions are discussed. In all the ciliated epithelia, except that of the sponge larva, each ciliated cell has an accessory centriole perpendicular to the basal body of the cilium and situated on its downstream side.

Downstream collecting in ciliary suspension feeders: the catch-up principle

“…The structure of the velum of gastropod and bivalve larvae is well known through several studies, for example the gastropods Crepidula (Werner 1955), and Mitrella (Nielsen 1987) and the bivalves Ostrea (Waller 1981), Barnea (Nielsen 1987), Mercenaria (Gallager 1988) and Codakia (Gros et al 1997). Most species have early, non-feeding, trochophora-like stages with a large prototroch, but later on develop into feeding veligers with an adoral ciliary zone and metatroch (Gros et al 1997).…”

“…These larvae have a preoral prototroch of long compound cilia, a postoral metatroch of shorter compound cilia, and an adoral ciliary zone of separate cilia (the food groove); these ciliary bands are carried by multiciliate cells (Nielsen 1987; only the larva of the polychaete Owenia has separate cilia and monociliate cells, see Emlet & Strathmann 1994). A very similar system is found in the rotifers, where the prototroch is usually called trochus and the metatroch cingulum (Strathmann et al 1972, Nielsen 1987. The prototroch usually consists of 1 row of compound cilia, but 2 rows of cells with compound cilia are found in some annelid and mollusc larvae (for example Polygordius, see Hatschek 1878, and Ostrea, see Erdmann 1935, Waller 1981.…”

“…Planktotrophic filter-feeding larvae with prototroch and metatroch are known from the families Opheliidae (Armandia, Hermans 1978), Capitellidae (Mediomastus, Hansen 1993), Oweniidae (Owenia, Emlet & Strathmann 1994), Serpulidae (Spirobranchus, Serpula, Pomatoceros, Galeolaria, Segrove 1941, Strathmann et al 1972, Grant 1981, Nielsen 1987, and Polygordiidae (Polygordius, Woltereck 1902). The echiurids are now regarded as specialized annelids by some authors (Nielsen 1995, McHugh 1997, and both Echiurus and Urechis have planktotrophic trochophores (Balzer 1917, Newby 1940.…”

“…Upstream collecting ('single-band system') has been described in larvae of phoronids, brachiopods, echinoderms and enteropneusts, and on the tentacles of adult phoronids, brachiopods and pterobranchs (Strathmann et al 1972, Nielsen 1987, Emlet & Strathmann 1994. In general, the mechanisms involved in separating food particles from the currents set up by the ciliary bands in upstream collecting organisms are poorly understood.…”

“…The metatroch beats anteriorly, toward the prototroch. In larvae that have this feeding mechanism (with the exception of the mitraria larva of Owenia), the prototroch consists of compound cilia that may reach lengths of about 30 to 140 µm during the development of different species (Nielsen 1987, Emlet & Strathmann 1994. Between these parallel ciliary bands lies a food groove (the adoral ciliary zone), with separate cilia that beat toward the mouth.…”