PHYLUM MOLLUSCA - MOLLUSKS

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Mollusks
soft
NUMBER OF SPECIES: 110,000 (2nd to atheropods)
HABITATS: Marine, FreshWater, Terrestrial
SIZE: snails 1 millimeter high to clams 4 - 5 feet across to squid > 60 feet long (largest of all invertebrates)
. Phylum Characteristics
Head-Foot
includes the more active portion of body associated with feeding, sensory functions & locomotion
Visceral Mass:
includes internal organs associated with digestion, circulation, respiration, excretion & reproduction
FOOT
ventral flattened muscular structure typically used for locomotion
VISCERAL MASS
dorsal to foot, comprising most of the internal organs
MANTLE
fold of the body wall that usually secretes a shell and encloses a space called the MANTLE CAVITY* which typically contains the gills
Trestial-lung
Marine-gills
GILLS
used for respiration and filter feeding (in some)
RADULA
toothed, tongue-like structure typically used for feeding
gastropods
snails, slugs, nudibranchs
bivalves
clams, mussels, scallops, oysters
cephalopods
octopuses, squids, nautiluses, cuttlefishes
Circulation
1)most with open circulatory system similar to arthropods
2. respiratory pigments: HEMOGLOBIN (RED) and HEMOCYANIN (BLUE)
Respiration
1. aquatic species use gills in mantle cavity
2. terrestrial species use mantle cavity as a lung
Water Balance and Excretion
(meta)nephridia similar to annelids
2. nitrogenous waste products: aquatic species excrete ammonia; terrestrial species excrete uric acid
CORNEA
transparent outer covering
IRIS
pigmented portion that regulates amount of light that enters eye by controlling size of pupil
PUPIL
opening to eye
LENS
structure that focuses or concentrates light which enters eye
RETINA
layer of light-sensitive cells
CILIARY MUSCLES
control position of lens (focusing)
control position of lens (focusing)
• There is no blind spot, nerve cells come off the back of each photoreceptor
• Humans have an optix disc where bundles of nerve cells exit to form an optic nerve
• Osphradia
- groups of cells in mantel cavtity that taste water and function to detect food
Unque to cephalopods (except nodules ) adaptaions due to lack of protective shell and predators
1)rapid color changes
2)Inc glands