Invertebrates

Lophophorata: Phylum Phoronida, Brachiopoda, and Bryozoa

Lophophorata is a clade composed of three Phyla: Phoronida, Brachiopoda, and Bryozoa. They are grouped like this due to one uniting structure, the lophophore.

Introduction

Lophophorata is a clade composed of three Phyla: Phoronida, Brachiopoda, and Bryozoa. They are grouped like this due to one uniting structure, the lophophore (Jang & Hwang, 2009; Temereva & Kuzmina, 2017).

Morphology

Let’s begin with the pièce de resistance: the lophophore. It is a feeding structure, similar to a bunch of ciliated tentacles, that surround the mouth; therefore, lophophorates are suspension feeders. The cilia create strong water circulation, allowing for gas exchange, the exportation of gametes, and food particle delivery. The lophophore is thought to be the result of convergent evolution (Halanych, 1996). The gut of a lophophorate is U-shaped, so the direction of water flow prevents the mixing of food and waste products.

Phylum Phoronida

Phoronids are also known as horseshoe worms and build chitinous tubes to protect and support their soft bodies (Abele, Gilmour, & Gilchrist, 1983). Phoronids can retract and extend their lophophore, and cilia manipulate food into their mouth. Phoronids actively assess the flow of the water current and can reorient themselves as water flow changes to maximise their food-capturing ability. Their diet includes zooplankton, detritus, and invertebrate larvae.

Phoronis australis.

Phylum Brachiopoda

Please don’t be a pleb and confused them with Bivalvia. Brachiopoda has upper and lower valves, as opposed to left and right valves of bivalves. Anyway, they don’t even share the same ancestry.

The lophophore is connected to the lower brachial valve and is supported by cartilage and, sometimes, a brachidium (calcareous support attached to the brachial valve). Most brachiopods attach themselves to hard substrates by a stalk called the pedicle, a connective tissue that is part of the upper pedicle valve.

Inarticulate brachiopods (Lingula anatine).

Class Articulata

This class is defined by its “tooth-and-socket” hinge arrangement and a simple muscle strategy that opens and closes the hinges.

Class Inarticulata

This class has untoothed hinges and a more complex muscular strategy for aligning the valves.

Phylum Bryozoa

Bryozoans resemble phoronids, except bryozoans are microscopic, typically about 0.5mm in length. All genera, except one, form colonies that resemble moss. Each individual is called a zooid and has a hard casing called a cystid and a polypide that holds the organs in place. Within the colony, individual zooids may share resources through internal connections, and some zooids may specialise in a function. Vibracula zooids have a long bristle thought to function as defence or vibrate to keep the colony from becoming covered with sediment.

A freshwater bryozoan species.

References

Abele, L. G., Gilmour, T., & Gilchrist, S. (1983). Size and shape in the phylum Phoronida. Journal of Zoology, 200(3), 317–323.

Halanych, K. M. (1996). Convergence in the feeding apparatuses of lophophorates and pterobranch hemichordates revealed by 18S rDNA: an interpretation. The Biological Bulletin, 190(1), 1–5.

Jang, K. H., & Hwang, U. W. (2009). Complete mitochondrial genome of Bugula neritina (Bryozoa, Gymnolaemata, Cheilostomata): phylogenetic position of Bryozoa and phylogeny of lophophorates within the Lophotrochozoa. Bmc Genomics, 10(1), 1–18.

Temereva, E. N., & Kuzmina, T. V. (2017). The first data on the innervation of the lophophore in the rhynchonelliform brachiopod Hemithiris psittacea: what is the ground pattern of the lophophore in lophophorates?. BMC evolutionary biology, 17(1), 1–19.

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