Brachiopods have been at various times placed with the Mollusca, the Chaetopoda, the Chaetognatha, the Phoronidea, the Polyzoa, the Hemichordata, and the Urochordata.
In zoology, the mollusca are divided into cephalous and acephalous (Acephala), according as they have or have not an organized part of their anatomy as the seat of the brain and special senses.
Turtle and sea-snakes abound, as do mollusca, of which a few are peculiar, and zoophytes.
It will be remembered that, according to Spengel, the osphradium of mollusca is definitely and intimately related to the gill-plume or ctenidium, being always placed near the base of that organ; further, Spengel has shown that the nerve-supply of this olfactory organ is always derived from the visceral loop. Accord ingly, the nerve-supply FIG.
Time when the fact that the renal organ s,s', Nerves (right and of the Mollusca, as a rule, opens into the left) to the mantle.