Brachiopods have a rather simple nervous system compared to humans as they do not possess a true brain. They have a system consisting of 2 ganglia located above and below the oesophagus. The one above is known as the supra-oesophageal ganglion, the one below is the larger infra-oesophageal ganglion and they are both connected by oesophageal connective. The infra-oesophageal has a network of nerves that go to the dorsal mantle, arms and adductor muscles and two small ganglia which supply the ventral mantle lobe and the muscles of the peduncle. The majority of nerves are found in the mantle.
nervous system
Brachiopods have an open circulatory system where the coelomic fluid and blood mix. The blood passes from the front to the back by travelling through a network of vessels. The blood branches to the organs like the lophophore. The blood is colorless and is used to deliver nutrients to the organs. It is pumped by a muscular heart found in the dorsal region above the stomach.
Brachiopods absorb oxygen and eliminate carbon dioxide using the lophophore and mantle. Oxygen is distributed by the fluid of the coelom which is then circulated through the mantle. Distribution through the mantle occurs by contractions of the lining of the coelom or beating of the cilia. The lophophore is a crown of tentacles with cilia that help filter food particles out of water along with helping with respiration. It is reinforced by calciferous support. Hemerythrin is a respiratory pigment containing iron. This pigment is found in blood corpuscles within the fluid of the coelomic cavity. This is how oxygen is transported and carbon dioxide is removed. The coelomic fluid flows through canals but this is considered an open blood system, containing one true blood vessel. The walls only beat once every 30 minutes to keep fluid circulating throughout the body as a result the maximum consumption of oxygen is low in brachiopods.
respiratory system
circulatory system
FUN FACT!
The iron containing human hemoglobin and Brachiopod hemerythrin are both analogs derived from the same heme protein!
Generally, brachiopods have distinct sexes making them gonochoristics except for in three specific genera. As a result, reproduction has been found to occur sexually through the fertilization of an egg by a sperm cell. There are 4 gonads in brachiopods, 2 are in each valve. Once mature the gametes (egg and sperm) will be discharged into the metacoel. The egg and sperm are transported to the mantle cavity through excretory organs located on each side of the mouth called the nephridia. In most genera fertilization occurs outside the shell, however in some females it can occur inside the pouch like folds of the mantle. Once fertilized the egg develops into a free swimming larvae that settles to the bottom of the water bed.
Articulate and inarticulate brachiopods have some distinguishing reproductive features.
-
Articulate brachiopods have a free swimming period of only a few days whereas inarticulate brachiopods may last for up to a month.
-
The larvae pedicle is developed from the caudal region in articulates where as it develops from folds in the mantle along the valve margin.
-
The gonads of articulates are found in the channels of the mantle lobes while inarticulate’s have them near the gut region.
-
Larvae of inarticulate’s have valves, mantle lobes, a pedicle that coils in the mantle cavity and a small lopophore for feeding and swimming. Articulate larvae have a ciliated lobe that becomes the body and lophophore, a rear lobe that becomes the pedicle and a mantle.
-
Both types of juvenile brachiopods sink to the bottom once the shell becomes heavy enough during development.
Cell division in brachiopod embryos is radial, holoblastic and regulative. Their blastopores also close up because their mouth and anus develop from new openings instead of the more common way of developing through the deepening of the blastopore.
