Idotea wosnesenskii: Isopod–The Race Rocks Taxonomy

 

1– Global Distribution: Ranges from Alaska (and Russia) to Estero Bay, San Luis Obispo County.

2- Habitat: You can find it under rocks, under cobble at the edges of tide pools, in blades of seaweed, attached to floats and on eelgrass. Hangs onto holdfasts stalks, worm tubes and other objects. But the most common place is under rocks on the shore.

3- Physical Description: They are large isopods, measuring up to 3-4 cm long and quite dark. Generally their color is olive-green but it may vary from bright green to brown or nearly black. The abdominal region is mostly unsegmented and their terminal portion is rather smoothly rounded, except for a tiny blunt tooth at the tip See the ventral image on the left.
4- Feeding: It feeds on algal detritus and reproductively mature plants, but avoids non-fertile individuals. It doesn’t eat immature plants by the algae’s cuticle.

5- Predators: Other arthropods and invertebrates, fishes, birds, reptiles and mammals.

6- Reproduction: “During reproduction, the male isopod carries the female for a short period known as pre-copula which lasts until the moult at which time copulation occurs. The sperm are transferred from the male to the female genital duct. In most species, the female releases the eggs into a ventral brood chamber where they are incubated until after hatching.” Idotea wosnesenskii incubate their eggs and juveniles in pockets of the body which open from the brood chamber. “Unlike crabs and shrimps isopods are not released as free-swimming zoea larva. Instead, when hatched they look very much like adults but have 6 rather than 7 pereonal segments. Some species care for their young after leaving the chamber but most species do not.” (Quoted from source b)

7- An Interesting Fact: It does not look like much of a swimmer, but it is surprisingly agile and graceful when it does swim. The paddlelike appendages on the underside of its abdomen propel it with seeming effortlessness, while the legs are spread as if to take hold of any firm object that comes along

8- References:

a) EZIDweb-Idotea wosnesenskii. October 1, 2002.
Webmaster: Beach Watcher Joan Gerteis. November 13th 2005.
http://www.beachwatchers.wsu.edu/ezidweb/animals/Idoteawosnesenskii2.htm
b) Biology of Isopods. 1996.
© Museum Victoria Australia. November 13th 2005.
http://www.mov.vic.gov.au/crust/isopbiol.html

c) Edward F. Ricketts, Jack Calvin, Joel W. Hedgpeth. Between Pacific Tides. 5th Edition.

d) Kozloff, Eugene N. Seashore Life of Pudget Sound, The Strait Of Georgia, and The San Juan Archipelago.

e) Yates, Steve. Marine Wildlife From Pudget Sound Through The Inside Passage.

Other Members of the Phylum Arthropoda at Race Rocks.

taxonomyiconReturn to the Race Rocks Taxonomy
and Image File
pearsonlogo2_f2The Race Rocks taxonomy is a collaborative venture originally started with the Biology and Environmental Systems students of Lester Pearson College UWC. It now also has contributions added by Faculty, Staff, Volunteers and Observers on the remote control webcams. This file was originally written by Claudia Aliaga, Chile, Pearson College student , Year 32 -2006

 

Ligia pallasii: Sea Slater –The Race Rocks Taxonomy

video of sampling of populations of Ligia sp

 

During the Johan Ashuvud project 2004, students explored the intertidal with Garry. They examined various organisms as well as the artificial tidepool.

In this video, we also get a chance to meet all the students taking part in the project

The central part of this video has a section on Ligia sp.

Sexual dimorphism in body proportions is marked in L.pallasii. Males, with their large, laterally expanded ephemeral plates, have a length/width ratio of about 1.6; females and immature males are narrower, with a corresponding ratio of about 2.1. Half- moulted males are occasionally found in which the rear half of the body has moulted and is abruptly significantly wider than as yet unmoulted front half, an odd sight, usually several days after the posterior moult.On the walls of cliffs and sea caves, the larger and broader males often cover and shield the females and juveniles.

L.Pallassi prefers sea cliffs. At Race Rocks, the loose upper intertidal rocks and crevasses on the Western side of the main island provide ideal habitat. There are differences in the osmoregulatory responses shown by these species associated with their behavior and ecology.The slower -moving pallasii lives permanently in cool, moist habitats characterized by fluctuating hypo-saline condition. L.Pallasii are air breathers with gill-like pleopods not equipped with tracheal trees.The respiratory pleopods must be kept moist to function properly.This is done by immersion or by dipping the tail in water in such away that the uropods serve as capillary siphons.

Ligia species are fed upon by birds, especially gulls, and by the intertidal crab. Life span of L.pallasii is 1.5 to 2 years , with breeding occurring in spring and early summer, and the average brood size is 48 plus or minus 11 young.The overall sex ratio is 1:1.

Domain Eukarya
Kingdom Animalia
Phylum or Division Arthropods
Class Crustacea (crustaceans)
Order Isopoda
Family Ligiidae
Genus Ligia
Species pallasii

COMMON NAME:sea slater

pearsonlogo2_f2The Race Rocks taxonomy is a collaborative venture originally started with the Biology and Environmental Systems students of Lester Pearson College UWC. It now also has contributions added by Faculty, Staff, Volunteers and Observers on the remote control webcams. Dec 2005- Palwasha Hussain Khel