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Phascolosoma nigrescens

Rodrigo Zorrilla Gonzalez (2014)


Fact Sheet



Physical Description


Life History & Behaviour

Reproduction & Development


Musculature and Movement

Anatomy & Physiology


Evolution & Systematics

Taxonomy and Synonyms

Biogeographic Distribution

Conservation & Threats

References & Links


Phascolosoma nigrescens (Keferstein, 1865) is a bilaterally symmetrical, unsegmented marine worm-like species of the phyla Sipuncula. The use of sipunculids as fish bait has been known to fisherman since as early as the 16th century (Saiz, 1993). The first scientific article on the Sipuncula phyla was published by Guillaume Rondelet in 1555. Figure 1 depicts a reproduction of Rondelet's paper. Much controversy exists surrounding the phylogeny of this phyla, and recent evidence suggests all Sipuncula may be a subgroup of the Annelid phylum. P.nigrescens has an introvert usually as long as the trunk (though this varies between individuals) and at least 30 rows of hooks – the main feature used to identify this species. The external body wall is covered with conical papillae, and the introvert bears distinctive black pigment bands on the dorsal surface. P. nigrescens uses its introvert, as well as biochemical processes to bore into coral rocks and is considered a deposit feeder. Little is known about P. nigrescens, but it is generally accepted that they are dioeceous. A study on the movement and musculature of P. nigrescens was conducted at the University of Queensland, and anatomical sections were prepared. Four potential locomotion types were identified, but mainly, it  was determined that P. nigrescens has very limited mobility outside of its coral burrow. 

Figure 1: Reproduction of the first scientific paper on the Phyla Sipuncula, from Rondeletti, 1555 in Saiz, 1993