Annotated Bibliography

Ph. Sipuncula, Fam. Golfingiidae

Purschke, G., et. Al.1997. Ultrastucture of the nuchal organ and cerebral organ in Onchnesoma squamatum (Sipuncula, Phasolionidae). Zoomorphology 117:23-31.

The position of Sipunculans in the phylogenetic tree is still being discussed. Two general hypotheses link these organisms to either the annelids or the molluscans. An in depth look at the nuchal and cerebral organ of a Onchnesoma squamatum is done to determine whether these structures may be homologous to the well known nuchal and cerebral structures of the polychaetes (annelids).

This is the first in depth study of the nuchal and cerebral organs. By determining whether these structures are homologous to those of the polychaetes, a firmer link to either hypothesis can be made. If they are similar, this could be more evidence to link the sipunculans to the annelids.

1828 species were collected, anaesthetized and examined under both scanning and transmission electron microscopes. Nuchal organs are found to always be unpaired, and these organisms lack an olfactory chamber.

When compared to the polychaete nuchal and cerebral organ, major differences were found. Nuchal organs are paired in polychaetes and unpaired in sipunculans. Furthermore, the sensory nerves to the nuchal organ in polychaetes have microvillia in the olfactory chamber. It is concluded that not only does the study not support the homology of the nuchal organs in the Sipuncula and Annelida, but it also suggests that the organ has a different function in the two taxa.

Ph. Sipuncula, Fam. Golfingiidae

Blanco, G. A., et. Al. 2005. Hydrogen Peroxide Induces Apoptotic-Like Cell Death in Coelomocytes of Themiste petricola (Sipuncula). Biological Bulletin. 209:168-183.

Do the species of Sipuncula and other coelomocytes use apoptosis to respond to infected, injured, or mutated cells? Will exposure to hydrogen peroxide cause apoptotic-like processes in sipunculans?

Apoptosis is important in immunity, and its regulation in coelomocytes could be significant to the sipunculan immune system. Hydrogen peroxide is known to produce apoptosis in the cells of animals from protozoa to mammals. It induces apoptosis by a massive depolarization of mitochondria.

Adult specimens with an average weight of 100mg were collected and their coelomocyte fluid drained. Suspensions of 1x1⁶ cells/ml were exposed to 100mM H₂O₂ and assayed for different apoptotic indicators at several points. It was observed that several characteristics of apoptosis were taking place such as chromatin condensation, nuclear segmentation, cell volume decrease, membrane blebbing, and formation of apoptotic bodies.

Hydrogen peroxide did induce apoptotic like processes. This indicates that apoptosis may be used for the regulation of cell numbers during times of stress and for immune responses.

Ph. Sipuncula, Fam. Phascolosomatidae

Tzetlin, A. B. and G. Purschke. 2006. Fine structure of the pharyngeal apparatus of the pelosophera lava in Phascolosoma agassizii (Sipuncula) and its phylogenetic significance. Zoomorphology. 125:109-117.

The buccal organ in sipunculans is considered homologous to either the pharyngeal organ in polychaetes or the radular apparatus of the mollusks. The larva of phascolosoma agrassizii studied to determine which homologous structure the buccal organ is more closely related.

The determination of whether this organ is more like the homologous structures found in the molluscs or the annelids can help support either as being more closely related to the sipunculans in hopes of placing them correctly on the tree of life.

Adults were collected and kept until gametes were released. The larva which resulted were fixed, dehydrated and prepared into slides of ultra thin sections. These slides were observed using transmission electron microscopy. The results show great structural similarities between sipunculan’s buccal organ and the polychaetes pharynx. No similarities were seen between the buccal organ and the radular apparatus of the molluscs.

This lends to the evidence that sipunculans are more closely related to annelids than to molluscs.