Compare three aspects of the early development of a squirrel (a chordate) and a garden snail (a moll

The familiar garden snail, slug, winkle, sea hare, sea slug, abalone, pond snail, and conch are all gastropods.  Gastropods are characterized by torsion, a process in which the mantle cavity is rotated anti-clockwise up to 180 degrees, until it faces forwards and is positioned over the head. This occurs early in larval development and means that the digestive, reproductive, and excretory systems all discharge through the one opening in the shell. Gastropods feed in a wide variety of ways: they may be hunters, browsers, or grazers; some are suspension or deposit feeders; some are parasitic.
Mollusks all have the following characteristics:

• All Mollusks have a true coelom.

• The body has three distinct parts: the muscular foot, the head, and the visceral mass.

• Mollusks have organ systems for circulation, respiration, digestion, excretion, nerve impulse conduction, and reproduction.

• Most Mollusks are bilaterally symmetrical and have one or more shells.


The three features unique to chordates and found in all of them at least during early development are: the notochord, composed of gelatinous tissue and bound by a tough membrane; a tubular nerve cord (or spinal cord), located above the notochord; and gill slits leading into the pharynx, or anterior part of the digestive tract (the throat, in higher vertebrates). In addition, all have blood contained in vessels, and the tunicates and vertebrates have a ventrally located heart. All have a postanal tail, that is, an extension beyond the anus of the notochord or backbone and of the body-wall musculature, containing no internal organs.