ABSTRACT
The phylum Cycliophora contains a few marine epizoic species on nephropid lobsters only known from the northern hemisphere. Microscopic sessile feeding stages with a ciliated buccal funnel, oval trunk and adhesive disc lives as filter feeding commensals on the host mouthparts. The feeding structures are continually replaced from internal budding cells. The life cycle consists of an asexual and a sexual part where attached feeding stages alternates with brief non-feeding free stages. The embryo is brooded inside a female and develops into a chordoid larva. Electron microscopy shows that cycliophorans are acoelomates and have a differentiated cuticle, compound cilia and protonephridia. The latter is only found in the chordoid larva. The embryology is poorly studied, and genomic data are scarce. However, transcriptomes and an EST library are available. The males are dwarfs and consist of few cells. Still, the body architecture is complex, which contradicts the assumption about correlation of complexity of the body plan and the number of cells and cell types. Future exploration of the cycliophoran genome could provide insights into how high body plan complexity can be achieved with few cells.
