Gilled Freshwater Worm
Branchiura sowerbyi
Description
Defining feature: Branchiura sowerbyi is a large segmented worm that may grow well over
100 mm long. It has conspicuous external gills, resulting in a feather-like appearance of the
hind end (seen in the lower part of the photo), while the front (or head) end is simple, having
a dorsal lobe above the mouth. The species has no eye-spot.
Physical description: The visibly segmented worm is of red, blood-like colour when alive. It is
very delicate in that when handled it easily brakes into pieces along segment lines. In large
animals the feathery end is readily visible when the worm is placed into a water-filled dish.
Habitat
The Gilled Freshwater Worm lives on the bottom of running and standing waters in fine
sediment. It is a very common species, which attains highest population densities in streams
that are strongly loaded with bio-nutrient (Stream Health Class [SHC d] but disappears in
polluted waters (SHC f and g). (This is likely due to contamination with chemicals – other than
nutrients – in strongly and excessively polluted waters, being toxic to the sensitive skin of this
worm.)
Branchiura sowerbyi is tolerant of low oxygen levels in sediment and water because of its red
blood pigment (being very similar to the red blood of vertebrates, a rare trait in invertebrates).
This enables the worm to absorb and store a high amount of oxygen when available, and then
use it at times of low ambient oxygen levels. In addition to the red blood pigment, oxygen
absorption is facilitated through the external gills significantly increasing the body surface
area of this skin-breather.
Feeding
Branchiura sowerbyi is a detritivore sediment feeder, i.e. up-take of sediment to digest
organic matter, bacteria, fungi etc. attached to sediment particles.
Breeding
Like other Oligochaeta, B. sowerbyi reproduces sexually via the clitellum and asexually through
fragmentation. Sexual reproduction is highest in the warmer months.
Conservation
Status: Aquatic invertebrates are not listed under State and Federal Government
environmental legislation. This is due to the lack of knowledge about this species-rich
component of Australia’s fauna.
Additional information
Because of its sensitivity towards chemical pollutants, the Gilled Freshwater Worm is potentially a
suitable organism for uses in eco-toxicological tests in freshwaters.
Sources: Lobo H. & da Gama Alves R. 2011. Reproductive cycle of Branchiura sowerbyi (Oligochaeta: Naididae: Tubificinae) cultivated under
laboratory conditions. Zoologia 28: 427-431. OECD. 2008. Test No. 315: Bioaccumulation in sediment dwelling benthic Oligochaetes. OECD
Guidelines for the testing of chemicals, Section 3: Degradation and Accumulation. Photograph by Ulrike Nolte.
Distribution
The Gilled Freshwater Worm is found
throughout Australia. It is common in the
Moreton Bay Region and can be found in
all streams and dams that are slightly to
strongly impacted by biologically available
nutrients.
Legend:
Known distribution based
on species records
Moreton Bay Regional Council boundary