Which of the following characteristics helps define gastropods?
Gastropods have a muscular foot which is used for “creeping” locomotion in most species. In some, it is modified for swimming or burrowing. Most gastropods have a well-developed head that includes eyes, 1-2 pairs of tentacles, and a concentration of nervous tissue (ganglion).
Which type of coiling is common in gastropod?
The most frequent form of coiling in gastropods, however, is helicoidal, with asymmetrical coiling of the shell around a line producing a skewed turbinate coil.
What are the three main types of gastropods?
Traditionally, the three main gastropod groups are the prosobranchs (subclass Prosobranchia), the opisthobranchs (subclass Opisthobranchia), and the pulmonates (subclass Pulmonata); however, many authorities classify the pulmonates as a subgroup within subclass Opisthobranchia.
What period are gastropods from?
Cambrian Period
The earliest undisputed gastropods date from the Late Cambrian Period, around 500 million years ago. Some paleontologists think gastropods are even older, based on a small, shelly fossil called Aldanella, known from Lower Cambrian rocks, but others think Aldanella is a worm.
Why are gastropods called gastropods?
Snails and slugs are known as gastropods, which mean ‘stomach foot’. This describes the way in which the body and internal organs of slugs and snails has been twisted back so that the stomach lies above the large fleshy foot of these animals.
What gastropod means?
Definition of gastropod : any of a large class (Gastropoda) of mollusks (such as snails and slugs) usually with a univalve shell or none and a distinct head bearing sensory organs.
What is torsion and Detorsion in gastropods?
Torsion allows foot to be retracted after the head for better protection of head. DETORSION. Detorsion is reversal of torsion which takes place when during evolution shell is lost or a type of shell evolves that has openings on the opposite sides. In such situations twisting of visceral mass is not necessary.
What is shell coiling in gastropods?
The condition is most noticeable among gastropods (Gastropoda) and cephalopods (Cephalopoda), where it is obvious that the shell is a hollow cone, coiled up to a greater or lesser extent. If the coiling does not remain in a single plane but moves down the axis (translation), a helically coiled shell results.
Why is it called a gastropod?