Bell Pettigrew Museum
of Natural History
Interpretative Panels
Text: Dr Iain Matthews
Design: Steve Smart & Cavan Convery
A University of St Andrews Development Fund Project
School of Biology
http://biology.st-andrews.ac.uk
14:4 Cycliophora
P hy l u m
Cycliophora
S u b p hy l u m
Super class
Class
The most recently described phyla, Cycliophora
was discovered in 1995 and currently contains only
a single species, Symbion pandora.
S. pandora has a very complex life cycle, with a
number of well-defined sessile and free swimming
stages. None of the short-lived, free-swimming
stages feed, and the majority of the lifecycle is spent
as a relatively large (c. 350 µm), solitary, sessile
feeding stage that attaches to the setae of the
crustacean, Nephrops norvegicus.
While attached to the host, the feeding stage
reproduces asexually from internally produced
buds. However, when the lobster begins to moult,
the cycliophoran undergoes a complex chain of
sexual reproduction events. Dwarf males,
incapable of feeding, emerge and seek feeding
stages containing developing females. After
fertilization a ciliated free-swimming chordoid
larva is released that can seek out new hosts and
continue the life cycle.
Lobster lip life
Body Plan:
• Bilaterally symmetrical
• Triploblastic
• U-shaped through gut
• Lacks circulatory and
gaseous exchange systems
• Funnel-shaped feeding organ
with compound cilia
Gut
Endoderm
Body Cavity
Mesoderm
Ectoderm
The body of S. pandora comprises a ciliated funnelshaped feeding structure, a trunk housing the
brain, a U-shaped through gut and a cuticular stalk
with a circular attachment disc. All stages lacks
circulatory and gaseous exchange systems, but the
sexually produced larval stage does have a pair of
protonephridia. On the basis of ultrastructural
research, the cycliophorans were originally allied
to the phyla Entoprocta and Bryozoa, however
subsequent molecular data suggests they may be
related to Rotifera and Acanthocephala. The
phylogenetic position of Cycliophora is still
uncertain.
Classification
within
Cycliophora
Class: Eucycliophora
Order: Symbiida
See specimen.
The phylum Cycliophora currently
contains only one species. This
makes it the smallest of all the
phyla, although new species may
still await discovery.
Cycliophora is also the most
recently discovered phylum, only
being described for the first time
in December 1995. It was
discovered by 2 Danish scientists,
Peter Funch (University of Aarhus)
and Reinhardt Møbjerg Kristensen
(Natural History Museum of
Denmark , University of
Copenhagen).
The single known species of
cycliophoran, Symbion pandora,
lives on the bristles surrounding
the mouth of the Norway lobster,
Nephrops norvegicus, a
crustacean which is commonly
eaten in Scotland as scampi.