Gnorimosphaeroma oregonensis

Gnorimosphaeroma oregonensis
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Malacostraca
Order:	Isopoda
Family:	Sphaeromatidae
Genus:	Gnorimosphaeroma
Species:	G. oregonensis
Binomial name
Gnorimosphaeroma oregonensis (Dana, 1853)
Synonyms
Sphaeroma oregonensis Dana, 1853

Gnorimosphaeroma oregonensis, the Oregon pill bug, is a small intertidal macroinvertebrate isopod crustacean. It is an oval-shaped organism roughly 12 mm in length, and about twice as long as it is wide. G. oregonensis is covered in a grey-coloured rigid shell, which is roughly uniform in colour except for a thin band that extends from the head to the end of the organism, and progresses from dark grey to light grey respectively. At the head, G. oregonensis possesses antennae, a mouth (for feeding), and eyes, and its body is lined with seven pairs of small legs, used for crawling when the organism is young, and for swimming later in life. Gills are located on the animal's belly, and is the mechanism by which the animal breathes.

Feeding

Other than for transport, G. oregonensis uses its legs for scavenging dead organic material from the substrata of ponds and streams. G. oregonensis is therefore a primarily a detrivore, although it also feeds on diatoms and the eggs of other organisms. It generally prefers a herbivorous diet. G. oregonensis is preyed on by a wide variety of consumer species, including other isopods and invertebrates, as well as many species of fish.

Habitat

The primary habitat of G. oregonensis is the mid-Californian to Alaskan coast, where it inhabits tidal pools and the intertidal region up to twenty-two metres from shore. They live in very large and frequent families, with dozens or even hundreds being found per tenth of a metre in places where they are most abundant, such as the San Francisco Bay, where they are the most common isopod found. Their substrata of choice are gravel, sand, and loose rocks on rocky beaches in the aforementioned areas, although they can be found living amongst algae as well. They also have a tendency to prefer dark habitats, such as crevices, empty shells, and under large rocks.

Tolerance of abiotic factors

The salinity that G. oregonensis is commonly found in ranges from nine to thirty-one ‰, which is a relatively wide range, although they prefer areas of lower salinity. Osmoregulation in G. oregonensis is primarily dependent on where the population originated, and the organism is very proficient in adapting to changes in salinity, temperature, and humidity, meaning in can withstand fairly large ranges of all three of these factors. G. oregonensis also has the ability to tolerate relatively low levels of oxygen, which is common to polluted water. Competition with other marine isopods and crustaceans, as well as mussels and barnacles, is a biotic factor that limits the range of G. oregonensis, but its aforementioned abilities to withstand many changes in its environment as well as to survive in polluted water make it a fairly successful competitor.

References

• Segal and Burbanck, 1963. The Biology of Crustacea Volume 5. Academic Press Inc.
• Rickets, E., Calvin, J. and Hedgpeth, J. 1985. Between Pacific Tides, 5th Edition. Stanford University.
• Schultz, G. 1969. The Marine Isopod Crustaceans. WM. C. Brown Company Publishers.
• Warburg, M.R. 1978. Evolutionary Biology of Land Isopods. Springer – Verlag Berlin Heidelberg.