Parallel to the prototroch, a postoral band of shorter cilia, the metatroch
, encircles the body and beats with an effective stroke from posterior to anterior, opposing the beat of the prototroch.
The velar edge had the ciliary bands typical of feeding veligers: prototroch, metatroch
, and food groove (Fig.
elegans are free-swimming planktotrophic animals with a ciliated prototroch and metatroch
and a collar (Fig.
By 3 days after fertilization, larvae had developed a nearly complete set of external ciliary structures: an apical tuft composed of a group of long cilia surrounded by shorter cilia, three equatorial ciliary bands (a preoral prototroch, circumoral food groove, and postoral metatroch
), and a ventral neurotroch (Fig.
Sparse cilia were also located below and within the mouth of the trochophore, although they did not form the distinct band of cilia characteristic of a true metatroch
The feeding larvae of Littorina spp., like those of all known feeding larvae of gastropods, capture food particles between two "opposed bands" of compound cilia (the prototroch and metatroch
) borne on the edge of large velar lobes; particles are then carried to the mouth by short cilia in the gap between the opposed bands, the food groove (Fig.
Two bands of ciliated cells, the prototroch and metatroch
, and an intervening food groove with shorter cilia ran along the periphery of each velar lobe, which also had patches of yellow pigment.
This feeding mechanism, in which a preoral band of compound cilia (the prototroch) beats from anterior to posterior, and a postoral band of compound cilia (the metatroch
) beats in the opposite direction, trapping particles between them, was described in the larvae of serpulid annelids (Strathmann et al., 1972), close relatives of the sa-bellariids (Kupriyanova and Rouse, 2008).
For instance, the accessory trochoblast cells that contribute to the formation of the prototroch in many spiralians (2q derivatives) have been co-opted to form the secondary opposed feeding band ("metatroch
") in C.
One common arrangement of cilia is circumferential opposed preoral and postoral bands of cilia (prototroch and metatroch
) bordering a ciliated food groove (Fig.
Most annelid larval forms, feeding or not, can be readily related to the trochophore ground plan, which Nielsen (2001, 2004) defined as a larva bearing an apical tuft, a preoral ciliated band derived from trochoblasts (prototroch), an adoral ciliary zone, and postoral metatroch
, gastrotroch, and telotroch, all of which bands consist of multiciliate cells with compound cilia.
Surprisingly, Pernet (2003) observed complete downstream-collecting ciliary systems with pro-totroch, adoral ciliary zone, and metatroch
in larvae of the sabellid polychaetes Schizobranchia, Demonax, Myxicola, and Pseudopotamilla.