Lophotrochozoans

Lophotrochozoans are a major clade of animals within the superphylum Spiralia, one of the primary divisions of the protostomes. The group is defined largely by molecular phylogenetics and includes a diverse array of phyla, ranging from segmented worms to mollusks and several lophophorate lineages.

The name reflects two historically recognizable features that occur in many members: a feeding organ called the lophophore in the lophophorates, and trochophore-type larval development in many trochozoans. However, not all members retain these features throughout life, and characteristics can vary among lineages.

Major lineages are divided into two components: the Lophophorata (lophophore-bearing phyla such as Phoronida, Brachiopoda, and Ectoprocta/Bryozoa) and the Trochozoa (which include Mollusca, Annelida, and several related phyla such as Nemertea and Sipuncula). These groups display a wide range of body plans, lifestyles, and developmental strategies. Most lophotrochozoans show spiral cleavage during embryogenesis, and many have trochophore larvae at some stage, although direct development is common in several lineages.

Ecologically, lophotrochozoans occupy diverse habitats, from marine and freshwater environments to terrestrial systems, and include free-living worms, shelled molluscs, and colonial bryozoans. Their fossil record extends back to the early Paleozoic, with early molluscs and annelids providing substantial evidence of early diversification.

Modern studies rely on molecular data to resolve relationships within the clade, and some traditional groupings have shifted as a result.