50. Bryozoa

Gonzalo Giribet; Gregory D. Edgecombe

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50. Bryozoa

Gonzalo Giribet
Gonzalo Giribet

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and Gregory D. Edgecombe
Gregory D. Edgecombe

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This chapter is in the book The Invertebrate Tree of Life

50BRYOZOABryozoans or “moss animals” are benthic (mostly sessile, but some walking spe-cies are known), aquatic colonial lophophorates. Despite being found in abundance in most marine and some limnic habitats—they are among the top three to five most diverse animal phyla (the others being Annelida, Arthropoda, Cnidara, and Porifera) in some littoral hard-bottom communities based on metabarcoding anal-yses (Wangensteen et al., 2018)—and being a diverse group, they are often neglected in many biodiversity studies. Bryozoa is also called Ectoprocta for having the anus located outside the lophophore region (as opposed to Entoprocta; see chapter 51). This phylum includes more than 6,300 living species (Cook et al., 2018) but is rep-resented by even greater extinct diversity, with about 15,000 species, its fossil rec-ord enhanced by the calcareous skeleton in most members of the group. An esti-mated 808 extant genera are surpassed by some 1,289 extinct genera (Taylor and Waeschenbach, 2015) (fig. 50.1).A typical bryozoan colony is formed after a founding individual is produced by budding, giving rise to new zooids and extrazooidal parts, each zooid of mi-croscopic size. The founding individual, the ancestrula (fig. 52.2 B), is produced from a larva resulting from sexual reproduction, but new colonies can also develop from resting bodies after wintering in colder waters. The term used for colony de-velopment is “astogeny.” Colonies can be monomorphic or polymorphic, with spe-cialized zooids performing different functions. Each zooid is composed of a pro-tective box or tube-shaped body wall called the “cystid” and the moveable polypide that consists of the soft parts (gut, muscles, and the lophophore around the mouth). The cuticle of the cystid can be flexible and contain chitin (in the ctenostomes and phylactolaemates), whereas it is rigid and can contain calcium carbonate in the cheilostomes and cyclostomes, where it is called the “zooecium” (Nielsen, 2012a). The polypide extends the lophophore for feeding through an opening—covered by a protective operculum in some species—in the “skeleton.”Bryozoan colonies can be encrusting, arborescent, or even free living, and some of the arborescent calcified colonies can have a substantial role in reef building (Ernst and Königshof, 2008) and providing habitat for many other organisms. Due to their suspension feeding habits (Bullivant, 1968), bryozoans can be ecologically important. In the Indian River Lagoon of Florida, it has been estimated that colo-nies of Amathia verticillata clear and recirculate an average of 48,000 gallons of sea-water per m2 of seagrass bed per day (Winston, 1995). Bryozoans are thus not only a major evolutionary lineage of animals but also one with underappreciated eco-logical roles.

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50BRYOZOABryozoans or “moss animals” are benthic (mostly sessile, but some walking spe-cies are known), aquatic colonial lophophorates. Despite being found in abundance in most marine and some limnic habitats—they are among the top three to five most diverse animal phyla (the others being Annelida, Arthropoda, Cnidara, and Porifera) in some littoral hard-bottom communities based on metabarcoding anal-yses (Wangensteen et al., 2018)—and being a diverse group, they are often neglected in many biodiversity studies. Bryozoa is also called Ectoprocta for having the anus located outside the lophophore region (as opposed to Entoprocta; see chapter 51). This phylum includes more than 6,300 living species (Cook et al., 2018) but is rep-resented by even greater extinct diversity, with about 15,000 species, its fossil rec-ord enhanced by the calcareous skeleton in most members of the group. An esti-mated 808 extant genera are surpassed by some 1,289 extinct genera (Taylor and Waeschenbach, 2015) (fig. 50.1).A typical bryozoan colony is formed after a founding individual is produced by budding, giving rise to new zooids and extrazooidal parts, each zooid of mi-croscopic size. The founding individual, the ancestrula (fig. 52.2 B), is produced from a larva resulting from sexual reproduction, but new colonies can also develop from resting bodies after wintering in colder waters. The term used for colony de-velopment is “astogeny.” Colonies can be monomorphic or polymorphic, with spe-cialized zooids performing different functions. Each zooid is composed of a pro-tective box or tube-shaped body wall called the “cystid” and the moveable polypide that consists of the soft parts (gut, muscles, and the lophophore around the mouth). The cuticle of the cystid can be flexible and contain chitin (in the ctenostomes and phylactolaemates), whereas it is rigid and can contain calcium carbonate in the cheilostomes and cyclostomes, where it is called the “zooecium” (Nielsen, 2012a). The polypide extends the lophophore for feeding through an opening—covered by a protective operculum in some species—in the “skeleton.”Bryozoan colonies can be encrusting, arborescent, or even free living, and some of the arborescent calcified colonies can have a substantial role in reef building (Ernst and Königshof, 2008) and providing habitat for many other organisms. Due to their suspension feeding habits (Bullivant, 1968), bryozoans can be ecologically important. In the Indian River Lagoon of Florida, it has been estimated that colo-nies of Amathia verticillata clear and recirculate an average of 48,000 gallons of sea-water per m2 of seagrass bed per day (Winston, 1995). Bryozoans are thus not only a major evolutionary lineage of animals but also one with underappreciated eco-logical roles.

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