trochophore

[Greek trokhos, wheel (from trekhein, to run) + -PHORE.]

A generalized but distinct type of free-swimming larva found in several invertebrate groups, including nemerteans, marine turbellarians, brachiopods, bryozoans, phoronids, mollusks, sipunculids, and some annelids. The form is somewhat pear-shaped (see illustration), and it is provided externally with a prominent circlet of cilia (a troch) and one or sometimes two accessory circlets. Anterior and posterior apical ciliary tufts and eyespots are often present. The digestive tract is complete and functional; paired nephridia with excretory tubules are present; muscle and nerve fibers, sense organs, and a band of mesoderm complete the internal structure. Presumably, the larva, which develops ontogenetically along many divergent lines, indicates the close evolutionary relationships of the groups it represents. See also Annelida; Brachiopoda; Bryozoa; Mollusca; Phoronida; Turbellaria.

annelid. (After T. I. Storer et al. General Zoology, 4th ed., McGraw-Hill, 1976)">
Some trochophore larvae. Pear-shaped form is common in all groups. (a) Bryozoan. (b) Patella, a mollusk. (c) Polygardius, an annelid. (After T. I. Storer et al. General Zoology, 4th ed., McGraw-Hill, 1976)

trochophore
A - episphere
B - hyposphere
1 - ganglia
2 - apical tuft
3 - prototroch
4 - metatroch
5 - nephridium
6 - anus 8 - gastrointestinal tract
9 - buccal opening
10 - blastocoele

Bright-field microscope image of trochophore of annelid Pomatoceros lamarckii (family Serpulidae)

A trochophore (pronounced /ˈtrɒkɵfɔər/; also spelled trocophore) is a type of free-swimming planktonic marine larva with several bands of cilia.

By moving their cilia rapidly, a water eddy is created. In this way they control the direction of their movement. Additionally, in this way they bring their food closer, in order to capture it more easily.

Contents 1 Occurrence 2 Feeding habits 3 Life cycle 4 External links

Occurrence

Trochophores are found in the trochozoan phyla, which include the entoprocts, mollusks, annelids, echiurans, sipunculans and nemerteans. Together, these phyla make up part of the Lophotrochozoa; it is possible that trochophore larvae were present in the life cycle of the group's common ancestor.

Feeding habits

Trochophore larvae are often planktotrophic; that is, they feed on plankton.

Life cycle

Ontogeny of the Polyplacophora: First image shows the trochophore, second shows the stadium in metamorphosis, third is a juvenile Polyplacophoran

Trochophores are hatched from eggs. The stadium of a trochophore larva lasts for a few hours and then it changes into another free-swimming veliger larva (in some gastropods and in some bivalves) or into a metatrochophore or into a postlarvae juvenile which lands on the substrate.

SEM Image of development of the annelid Pomatoceros lamarckii (family Serpulidae) showing the trochophore in images D-F.
D - early trochophore
E - complete trochophore
F - late trochophore
G - metatrochophore

9-hour-old trochophore of the marine gastropod Haliotis asinina
sf - shell field

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External links

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