Description:
Gnorimosphaeroma oregonense (formely oregonensis) is a small intertidal crustacean (Phylum Arthropoda, Order Isopoda) that is related to the roly-polys found on land. They have a segmented, oval-shaped body about 1 cm in length, which is covered by a grey exoskeleton. Like all isopods, their body is flattened from top to bottom (dorsoventrally), and they have seven pairs of visible legs of similar size (hence the name isopoda, iso = same, poda = foot) (Rudy et al. 2013).
Their head has two pairs of antennae, which may be difficult to see. One pair is used for smell and taste. The second pair of antennae are used for touch. They also have two small black compound eyes. These eyes are likely highly sensitive to movement which would allow G. oregonense to detect the movement of fast moving predators. Chewing mouthparts are located on the bottom surface of the head (Rudy et al. 2013).
The many overlapping plates protect G. oregonense from predators, allowing G. oregonense to curl into a ball when threatened (Rudy et al. 2013). This behaviour protects the isopod's legs and softer underbody and can also reduce water loss. Legs are used for crawling and holding onto the substratum. The first pair of legs can also be used to hold food. The hindmost region has five pairs of flattened legs, which are used for gas exchange and for swimming.
Their head has two pairs of antennae, which may be difficult to see. One pair is used for smell and taste. The second pair of antennae are used for touch. They also have two small black compound eyes. These eyes are likely highly sensitive to movement which would allow G. oregonense to detect the movement of fast moving predators. Chewing mouthparts are located on the bottom surface of the head (Rudy et al. 2013).
The many overlapping plates protect G. oregonense from predators, allowing G. oregonense to curl into a ball when threatened (Rudy et al. 2013). This behaviour protects the isopod's legs and softer underbody and can also reduce water loss. Legs are used for crawling and holding onto the substratum. The first pair of legs can also be used to hold food. The hindmost region has five pairs of flattened legs, which are used for gas exchange and for swimming.
Ecology:
Gnorimosphaeroma oregonense inhabits coastal areas from Alaska to California and Hawaii (Kozloff 1973; Rudy et al. 2013). They can be found amongst algae and sea grasses, under mussels, around barnacles and under damp rocks, logs and other woody debris in the intertidal zone to subtidal depths of 24 m. They are particularly abundant in areas that have fresh water seepage (Rudy et al. 2013).
G. oregonense are preyed upon primarily by fish, but are also eaten by other invertebrates, mammals and birds (Rudy et al. 2013). They rely, in part, on blending into the substratum to avoid being detected by these visual predators.
G. oregonense are preyed upon primarily by fish, but are also eaten by other invertebrates, mammals and birds (Rudy et al. 2013). They rely, in part, on blending into the substratum to avoid being detected by these visual predators.
Life History:
Gnorimosphaeroma oregonense has separate sexes; however, distinguishing between males and females is difficult unless the female is carrying eggs. Females carry their fertilized eggs in a special fluid-filled pouch on their ventral surface, which protects the eggs from drying out. The eggs hatch into small individuals that look like adults. There is no larval stage (Rudy et al. 2013).
References cited:
Kozloff EN. 1973. Seashore Life of Puget Sounds, the Strait of Georgia, and the San Juan Archipelago. Vancouver BC: JJ. Douglas Ltd.
Rudy P, Rudy LH, Shanks A, Butler B. 2013. Gnorimosphaeroma insulare. University of Oregon Libraries and the Oregon Institute of Marine Biology. [accessed 2016 Aug 10].
https://scholarsbank.uoregon.edu/xmlui/bitstream/handle/1794/12708/G_insulare_2016_final.pdf?sequence=3&isAllowed=y
For more information:
Aikins S, Kikuchi E. 2001. Studies on habitat selection by amphipods using artificial substrates within an estuarine environment. Hydrobiologia 457: 77–86.
Lagerspetz KYH, Vainio LA. 2006. Thermal behaviour of crustaceans. Biological Reviews. 81(2): 237–258.
Nilsson DE, Nilsson HL. 1981. A crustacean compound eye adapted for low light intensities (Isopoda). Journal of Comparative Physiology A. 143(4): 503–510.
Rees CP. 1975. Competitive interactions and substratum preferences of two intertidal isopods. Marine Biology. 30(1): 21-25.
Riegel JA. 1959. A revision in the sphaeromid genus Gnorimosphaeroma Menzies (Crustacea: Isopoda) on the basis of morphological, physiological and ecological studies on two of its "subspecies”. The Biological Bulletin. 117(1): 154-162.
Standing JD, Beatty DD. 1978. Humidity behaviour and reception in the sphaeromatid isopod Gnorimosphaeroma oregonensis (Dana). Canadian Journal of Zoology. 56(9): 2004-2014.
Warburg MR. 1964. The response of isopods towards temperature, humidity and light. Animal Behaviour. 12(1): 175-186.
Rudy P, Rudy LH, Shanks A, Butler B. 2013. Gnorimosphaeroma insulare. University of Oregon Libraries and the Oregon Institute of Marine Biology. [accessed 2016 Aug 10].
https://scholarsbank.uoregon.edu/xmlui/bitstream/handle/1794/12708/G_insulare_2016_final.pdf?sequence=3&isAllowed=y
For more information:
Aikins S, Kikuchi E. 2001. Studies on habitat selection by amphipods using artificial substrates within an estuarine environment. Hydrobiologia 457: 77–86.
Lagerspetz KYH, Vainio LA. 2006. Thermal behaviour of crustaceans. Biological Reviews. 81(2): 237–258.
Nilsson DE, Nilsson HL. 1981. A crustacean compound eye adapted for low light intensities (Isopoda). Journal of Comparative Physiology A. 143(4): 503–510.
Rees CP. 1975. Competitive interactions and substratum preferences of two intertidal isopods. Marine Biology. 30(1): 21-25.
Riegel JA. 1959. A revision in the sphaeromid genus Gnorimosphaeroma Menzies (Crustacea: Isopoda) on the basis of morphological, physiological and ecological studies on two of its "subspecies”. The Biological Bulletin. 117(1): 154-162.
Standing JD, Beatty DD. 1978. Humidity behaviour and reception in the sphaeromatid isopod Gnorimosphaeroma oregonensis (Dana). Canadian Journal of Zoology. 56(9): 2004-2014.
Warburg MR. 1964. The response of isopods towards temperature, humidity and light. Animal Behaviour. 12(1): 175-186.