Description: As in other Flabelliferan isopods, the uropods are flattened and are lateral to the pleotelson rather than ventral or terminal. The exopodites of the uropods do not arch over the pleotelson and pereopod 1 is not greatly enlarged. This family is unusual for an isopod because the head (cephalon) is not attached broadly to the pereon so the head can rotate, and the uropods are unusually small. The first thoracic (pereon) segment in Limnoria is about twice as long as the rest. In this species the pleon has 4-5 visible pleonites plus the pleotelson. The animal can roll up into a ball. The uropods are small, and the exopodites of the uropods are somewhat clawlike. The incisor process of the right mandible has file-like ridges, and the incisor process of the left mandible has rasplike scales (but the mandibles have no teeth). The dorsal surface of the pleotelson has a small median ridge that splits into two ridges posteriorly but does not have 3 or 4 small tubercles. Bores into wood. Usually less than 4 mm long.
How to Distinguish from Similar Species:Limnoria algarum bores into kelp holdfasts. Limnoria tripunctata bores into wood but it has 3 small tubercles on the dorsal pleotelson instead of the bifurcating ridge.
Geographical Range: In temperate and polar waters of the northern hemisphere. From Kodiak Alaska to Point Arena, California on our coast.
Depth Range: Intertidal to 20 m
Habitat: Boring into wood
bores into wood near the intertidal zone, such as pilings and
Its boring rate is about 1-3 cm/year, and it can eventually do
damage. The burrows of this isopod are far smaller in
that of the shipworms (bivalves which also bore into wood), being only
about 1 mm in diameter (photo).
digging, they jerk their head back and forward while turning slowly in
the burrow. They typically start to burrow into the wood at a
angle rather than digging straight in. They swallow the wood
which pass through the gut as rapidly as 80 minutes. Besides
of much smaller diameter, the burrows of gribbles are much shallower
those of shipworms, going only a centimeter or two into the
Also, unlike shipworms, they often dig interconnections between their
Although this species has several
ciliated protozoan symbionts, some of which also produce cellulases, it
is a very unusual animal because it appears to produce the cellulase
necessary for digesting the cellulose in the wood itself. The
where the wood is digested, appears to be sterile, with very few or no
bacteria or protozoans within it. One further problem with
cellulose from wood is that much of the cellulose is bound in lignin,
is very difficult to digest. A related species (L.
quadripunctata, see King et al., 2010) has high amounts of
in its gut which may produce phenoloxidase. The phenoloxidase
be used to break up lignin, plus may explain why bacteria seem absent
the gut since phenoloxidase is toxic to bacteria. Various
can be found on the outer surface, especially the pleopods, and may be
important in providing nitrogen to the animal.
Females of this species carry around 22 large eggs in their marsupium
or pouch between the front legs. The eggs are nearly 1/4 the
of the body. They do not hatch into a larval stage
hatch like small adults which begin burrowing. Therefore
colonies in wood are quite localized and spread slowly across the wood
surface as they reproduce and start more burrows. Young and
can be found year-round, but peak breeding in the Salish Sea area is in
April and May. Not only do the young not normally swim, but
do not even seem to be chemically attracted to wood, as many other
are attracted to their appropriate substrates when settling.
they simply remain on the wood in which they are born and begin
there by default. Later in life, some adults do swim away,
in the spring and summer. During this migration phase they do
positively to wood (see references in Cragg
et al., 1999). Their preference for wood seems to
by the presence of fungus or fungal metabolites on the surface or the
of other gribbles.
Flora and Fairbanks, 1966
Kozloff, 1987, 1996
Elshanshoury, A.R., M.H. Mona, F.A. Shoukr, and A.M. Elbossery, 1994. The enumeration and characterization of bacteria and fungi associated with marine wood boring isopods, and the ability of these microorganisms to digest cellulose and wod. Marine Biology 119:3 pp 321-326
King, Andrew J., Simon M. Cragg, Yi Li, Jo Dymond, Matthew J. Guille, Dianna J. Bowles, Neil C. Bruce, Ian A. Graham, and Simon J. McQueen-Mason, 2010. Molecular insight into lignocellulose digestion by a marine isopod in the absence of gut microbes. Proceedings of the National Academy of Sciences 107:12 pp 5345-5350 (for a related species, L. quadripunctata)
Richards, B.R. and C.I. Belmore, 1976. Occurrence of
Limnoria-lignorum (Rathke) at Amchitka Island, Alaska.
the Fisheries Research Board of Canada 33:7 pp 1642-1644
General Notes and Observations: Locations, abundances, unusual behaviors:
This is the piece of washed-up driftwood from which the Limnoria lignorum photographed above was extracted. The ruler is included for scale.
Authors and Editors of
Salish Sea Invertebrates web site provided courtesy of Walla