Many species of both water vertebrates and invertebrates invented independently various mechanisms to obtain the neutral buoyancy and so that to save much of their energy: swim bladder of the Ostheichthyes and some of the Syphonophores, the liver of the Chondrichthyes, etc. Can the main digestive gland play the same role for shrimps?
Good question, Andrey!
I don't think shrimps have neutral buoyancy....never seen one static in the water column. They are often heavier (denser) so tend to be pulled down. Many live in the water column, but even so I don't believe they have neutral buoyancy, they swim actively to keep their position. Of course, these often possess strong, developed pleopods and pereopodal exopods furnished with plumose setae, which makes this energy expensive task easier (the plumose setae may actually help to slow down the "fall" of the shrimp by diminishing the rate weight/superficial area). If the digestive system plays any role in the process (maybe lighter lipids on fat tissues) it needs to be investigated.
Thank you for the comment!
Unfortunately, I can hardly investigate a living shrimp. Novosibirsk is too far from sea.
On the other hand, it was a rather long chain of steps that led me to this question. I am not a biologist, just a hepatobiliary surgeon. The first step was surgery and pathogenesis investigations of certain congenital biliary disorders in the human followed by the liver and the gallbladder embryonical development study. It is known that there is a wide gap ('lacuna') between the liver and the gallbladder' bud development at the 28th day of gestation and this of the intrahepatic ducts app. on the 15th week. If the gallbladder function is to collect bile, it should be quite the contrary, the bile ducts first, the gallbladder afterwards.
Further was reading on the comparative anatomy, so that I could find out that the liver and the gallbladder are basic organs for the Vertebrates, and they arised seemingly in that polyphyletic group called 'the Ostracodermes'. So, why those creatures could invest the liver and, very probably, the bone tissue simultaneousely? It was this from the question about the neutral or positive buoyancy appeared.
Sincerely,
Andrey
I see...interesting thought line.
In fact we are far from knowing all the invertebrate species in the world, and along with that are our knowledge on their physiological features. It is a whole new world to explore! I believe more and more comparative studies are for coming when these new discoveries on invertebrate species with bizarre structures and habits be found.
Best regards,
Paulo
Thank you, Paulo.
I wonder if the main digestive gland of a frozen shrimp is suitable for the measurement. The question is a rhetorical one, though... Would you be so kind as to give me some reference on the invertebrates main digestive gland, please? There must have been some investigations performed concerning its general structure, histology, etc. I could find the very specific papers about a carbonite accumulation in the crabs and other stuff of the same kind.
Sorry Andrey, can't be of great help on that: my expertise is on taxonomy and systematics, other things regarding biology of these animals I read occasionally on books and articles...
However, typing on Google Scholar I spotted these papers that may be helpful:
>>> THE FUNCTIONAL ANATOMY OF THE DIGESTIVE TRACT OF A SHRIMP METAPENAEUS BENNETTAE RACEK & DALL* (CRUSTACEA : DECAPODA : PENAEIDAE) by W. Dall (1967)
LINK: http://www.publish.csiro.au/?act=view_file&file_id=ZO9670699.pdf
>>> Functional cytology of the hepatopancreas of Penaeus semisulcatus
(Crustacea: Decapoda) during the moult cycle by S.Y. AI-Mohanna 1 and J.A. Nott (1989)
LINK: http://download.springer.com/static/pdf/161/art%253A10.1007%252FBF00541656.pdf?auth66=1412167446_cb473caab1f3232308f1feb38ade360c&ext=.pdf
>>> Internal Anatomy and Physiological Regulation edited by Linda H. Mantel
LINK: http://books.google.com.br/books?hl=pt-BR&lr=&id=FOuar4vjSa0C&oi=fnd&pg=PA1&dq=digestive+gland+crustacea+flotation&ots=Ohq2ez1fkz&sig=3rbJf9q4-5cFJoXbgTW0oEHZ8ho#v=onepage&q=digestive%20gland%20crustacea%20flotation&f=false