>Is there anybody who can tell me the differences between the orders in Opisthobranchia and Pulmonata?

No; it actually is currently uncertain if the two can be distinguished.  Traditionally, the presence of a lung has been seen as the distinguishing feature of pulmonates, but this may have arisen more than once.

Likewise, exactly what constitute orders within this group of advanced euthyneurans remains debated.  Both the theoretical aspects of classification and the relationships among the groups are not fully clear.  For example, Rosenberg's Encyclopedia of Seashells demotes Pulmonata and Opisthobranchia to orders.

Thus, there is no definitive answer to your question.  You will have to decide for yourself the groups you want to recognize and go from there.

    Dr. David Campbell
    "Old Seashells"
    Biology Department
    Saint Mary's College of Maryland
    18952 E. Fisher Road
    St. Mary's City, MD  20686-3001 USA
    [log in to unmask], 301 862-0372 Fax: 301 862-0996
"Mollusks murmured 'Morning!'.  And salmon chanted 'Evening!'."-Frank Muir, Oh My Word!