Species of the class Bivalvia have soft bodies (characteristic
of their phylum, Mollusca) and are enclosed in a hard shell. Bivalve mollusks
include many species of clams, oysters, mussels, and scallops. All the bivalves
have shells divided into two halves, hence their name.
Filter Feeders
Most bivalves are filter-feeders that trap fine food particles in mucus
that coats the gills and then use hair-like cilia to transport the particles
to the mouth. Water flows into the gill chamber through an incurrent siphon,
passes over the gills, and then exits the mantle cavity through an excurrent
siphon. Being filter-feeders, most bivalves lead rather sedentary lives.
Soft Bodies with Strong Parts
Bivalves, being mollusks, are soft-bodied animals (from the Latin molluscus,
"soft"). They are protected by two hard shells made of calcium
carbonate which are drawn together by powerful muscles.
All bivalves have a similar body plan with three main parts: a muscular
foot usually used for movement, a body mass containing most of the internal
organs, and a mantle, a heavy fold of tissue that drapes over the body
mass and may secrete a shell. Mussels secrete strong threads that tether
to rocks, docks, boats, and the shells of other animals.
Basic Characteristics of an Arachnid
There are over 57,000 species of scorpions, spiders, ticks, and mites
in the world that belong to Class Arachnida. Arachnids have one or two
main parts while insects have three. Arachnids have eight pairs of appendages
rather than six (chelicerae, pedipalps, four pairs of walking legs) and
are primarily terrestrial.
Lips for Arms
Spiders use their fanglike chelicerae (from the Greek cheilos,
"lips," and cheir, "arm"), equipped with poison
glands, to attack prey. As the chelicerae and pedipalps chew the prey,
the spider spills digestive juices onto the torn tissues. The food softens,
and the spider sucks up the liquid meal.
Endangered Species
Of the 25 000 species of invertebrates that are known in British Columbia,
many are threatened by loss or degradation of their habitats and are at
risk because their ecosystems are at risk.
In the South Okanagan, hardly anything is known about the six species
of sun scorpions that are known from the south Okanagan and few specimens
of the Western Ridge Mussel have been found.
The environmentally sensitive, Western
Ridge Mussel (Gonidea angulata), is a rare and endangered
mollusc in the Thompson-Okanagan belonging to Class Bivalvia, Order Unionoida.
The sun-shy, Sun Scorpion (Eremobates
gladiolus), is an example of an endangered arachnid of the
Class Arachnida, Order Solpugida that lives in dry southern interior of
the Okanagan valleys of British Columbia.
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