Pyrosomella verticillata
Life > Eukaryotes > Opisthokonta > Metazoa
(animals) >
Bilateria > Deuterostomia >
Chordata > Tunicata >
Thaliacea > Pyrosomatida > Family: Pyrosomatidae
> Genus:
Pyrosomella
Description
The zooids (individual filter-feeding animals
with inhalent and exhalent siphons) are formed into small oval to
oblong colonies up to 5 cm long and 3 cm in diameter, often
flattened (van Soest 1981). The wall of the colony is transparent
and colourless. Zooids are oval to slightly elongate in side view,
up to 3.9 mm long.
Distribution and habitat
This pelagic species has an Indo-Pacific distribution that includes southern African seas:
the distribution map for in van Soest (1981) shows three records
from this region.
Bioluminescence
Pyrosomella verticillata like most
members of the Pyrosomatidae is
bioluminescent and colonies are able to light up for sustained
periods. Each zooid in the colony has a pair of luminescent organs
flanking the orals siphon. Light production may be the result of
intracellular bioluminescent bacteria in the cells of these
luminescent organs but this needs to be confirmed. Bowlby et al.
(1990) showed how Pyrosomella verticillata and
Pyrosoma atlanticum
bioluminesce in response to light. If you shine light on zooids on
the one side of the colony, they bioluminesce and their light
stimulates adjacent individuals. In this way, the bioluminescence
spreads over the colony from the point where the zooids were
stimulated. A colony that lights up can in turn stimulate an
adjacent colony to light up as well. At the same time as lighting
up, the zooid closes its oral siphon and the cilia inside that cause
the water flow, stop beating. Colonies are negatively buoyant so
when water flow stops, the colony starts sinking slowly. It is
thought that the ability to bioluminesce in response to light
stimulation might be an adaptation to communicating about predators
and by also closing the water flow and sinking, they can move to a
depth where there are fewer predators (Bowlby et al. 1990).
Publications
- Bowlby MR, Widder EA, Case JF. 1990. Patterns of stimulated
bioluminescence in two pyrosomes (Tunicata: Pyrosomatidae).
Biological Bulletin 179: 340-350.
- van Soest RWM. 1981. A monograph of the order Pyrosomatida
(Tunicata, Thaliacea). Journal of Plankton Research 3(4):
603–631.
Text by Hamish Robertson |
