The Morphology of the Nephridia and Genital Ducts of Cirriformia Spirobrancha
Thomas T. Gilbert
Hopkins Marine Station of Stanford University
Pacific Grove, California
1. Permanent Address:
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The Morphology of the Nephridia and Genital Ducts of Cirriformia Spirobrancha
I. Introduction
The object of this study was the polychaete annelid Cirriformia
spirobrancha (Moore, 1904). A member of the family Cirratulidae, C.
spirobrancha is a sedentary worm, up to six inches long and 1 inch in
diameter, living in black mud in intertidal and shallow subtidal mud flats
and sheltered tide pools. It lives burrowed with its anterior end just
below the substrate surface and its tentacles extended above the surface.
The literature of the nephridial anatomy of the annelidae is
scanty at best with the exceptions of the Nereidae (Jones, 1957) and
Lumbricus, an oligochaete. Goodrich's excellent summary (1945) covers
nearly all the known literature to date. Thus there is a limited back-
ground of well-described species with which to compare new findings.
Goodrich cites the work of E. Meyer (1887) describing the family Cirratulidae
in general terms. He found two types of nephridia, an anterior pair of
mixonephridia with very long excretory canal and numerous posterior mixo-
nephridia in the genital region composed almost entirely of large coelom-
ostomes. Goodrich also mentions Caullery and Mesnil's findings (1898) that
in Dodecaria concharum the anterior organs are as expected, but in epitokus
forms large coelomostomes develop late from the coelomic epithelium on the
anterior face of the posterior septa, fuze with the epidermis, and form pores
through which issue the genital products. No nephridial canal element was
found contributing to these genital ducts and possibly they represent
coelomostomes only.
It had been observed by students and faculty of this course prior
to this study that a pair of large anterior nephridia seemed to be present
in only about one-fifth of the C. spirobrancha individuals observed. Further,
no smaller nephridia or coelomoducts were seen posteriorly. The objectives
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of this study were thus to describe the nephridial anatomy of C. spiro-
brancha and to determine the extent and possible explanation of the
observed dimorphism.
This study determined that all individuals of C. spirobrancha
possess a single pair of large anterior mixonephridia and segmental nephridia
or coelomoducts in the genital region presumably serving as gonoducts.
The anterior organs have a unique sac-like morphology and an extensive
blood supply, while the genital organ's anatomy is not entirely clear.
II. Materials and Methods
Worms were collected from intertidal mud flats by municipal pier
fl, Monterey, California. Both live dissection and fixed and stained
serial sections in transverse, medial, and sagittal planes were used.
In dissection, the worms were anesthetized by addition of crystals of
magnesium chloride to sea water in a dissecting pan to a concentration
of approximately 7.5%. The body wall was opened by a lateral incision
along the dorsolateral row of setae. For prepared sections, worms were
relaxed in magnesium chloride, fixed in Bouin's fluid, embedded in paraffin,
cut at 10 and 14 microns, and stained according to Masson's trichrome
connective tissue technique as modified by Foot and by Coldner. A
series of camera lucida sketches on index cards was prepared to aid in
visualizing the internal anatomy of the nephridia.
III. Description of the Nephridia and Gonoducts
The nephridia are a pair of sac-like organs located in the
first two segments posterior to the prostomium ventrolateral to the pharynx.
They were not consistently observed early in the course because dissections
as a rule were made with dorsal or ventral incisions either missing or
destroying the nephridia.
The nephrostome is a large heavily ciliated funnel opening inte
the prostomial coelomic cavity in close proximity to the lateral body wall
and the extensive prostomial capillary beds. The funnel opening faces
dorsally and measures about 100 microns in diameter in fixed and stained
preparations. The whole funnel structure is 150 to 200 microns long. The
funnel narrows posteriorly as it passes through the septum and leads into
the cavity of the nephridium.
The body of the nephridium is about 6mm. long by 3 mm. high by
2 mm. wide and shows some involution in its outer wall. Its color varies
from light yellow to black over its surface; the darker colors are due
to blood capillaries in the outer wall. The wall is fragile and easily
torn in dissection. When opened, the interior surface of the nephridial
sac appears convoluted; in fixed and stained material subject to some
shrinkage and contraction, the interior of the sac is filled with these
convolutions. In dissection, the convolutions follow a characteristic
pattern. The dark color of blood vessels close to the surface is especially
evident on the convolutions. In fixed and stained preparations, the inter-
ior wall appears lightly ciliated, the cilia ocurring in tufts uniformly
distributed over the entire interior surface. The wall appears to be two
to three cell layers thick. The cell boundaries are indistinct; the outer
layer seems to be a continuation of the lining of the coelom. The wall
shows a lack of connective tissue or muscle fibers and is heavily supplied
with blood capillaries.
The nephridiopores are located posterior to the first septum and
lie on either side of the ventral nerve cord posterior to the point of
junction of the two circumpharyngeal connectives. The tubule leading to the
pore is 25-30 microns in diameter. The duct, unlike the body of the
nephridium, does not appear ciliated.
The region of ocurrence of the presumed gonoducts corresponds very
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closely with the region of production and storage of the gametes. The
ducts were not seen in fixed and stained material due to tearing of the
sections by grit in the gut. In dissection they appear white in color and
lie just posterior to each septum in this region one pair to a segment. They
are about O.3 mm. long and about 50 microns in outside diameter. They
appear to open to the outside at the level of the ventrolateral ros of setae.
No obvious funnel was present at the inner end of the duct and the duct was
not seen to pierce the septum. There appeared to be little or no blood
supply. The inner end lies close to the venteral nerve cord and ventral
blood vessel at the base of the coelomic cavity.
IV. Discussion
The nephridia do not have the convoluted tubule morphology described
for the Nereidae (Jones, 1957). However, the nephridial anatomy described
for C. spirobrancha is reasonable. The worm is sedentary, yet does not
irrigate its burrow as do some other burrowing polychaetes. Thus it
must excrete its waste products at its anterior end. The worm does not
appear to move enough to be able to leave its wastes behind it as it burrows.
Waste products presumably are carried in the blood from the posterior parts
of the body to the capillary nets in the nephridia or to those lining
the coelomic cavity of the prostomium into which the nephrostome extends.
These capillary nets are the locus of exchange of solutes between blood and
coelomic fluid. The nephridia then pump out the dissolved wastes in the
urine. The cilia in the nephrostome provide the current of fluid through
the nephridium. The cilia and the convolutions in the wall of the organ
help direct the flow and keep the fluid near the walls in constant motion
facilitating exchange. Reabsorbtion of substances from the coelomic fluid
to the blood is similarly accomplished. Contractions of the extensive
musculature associated with the pharynx and body wall in the region of the
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nephridia may also help provide a fluid flow.
It would be interesting to follow the embryological development
of these organs to facilitate comparison with the tubular nephridia of
other polychaetes. Physiological work on the functions of the organs is
also necessary.
In line with the preceeding discussion, it is presumed that the
posterior gonoducts do not function as nephridia. Their location posterior
to the anterior septum in each segment suggests they may consist of
nephridial tissue and may function as simple nephridia. Caullery and
Mesnil (1898) noted in Dodecaria concharum that coelomostomes with short
ducts developed at the time of spawning. The present study was carried
out when most worms were spawning and the ducts observed could have been
in the process of development. They may be absent or vestigial during the
rest of the yaer or the rest of the worms' life cycle.
V. Conclusions
1. The nephridia of Cirriformia spirobrancha have been described to
be a pair of sac-like organs with a large blood supply and extensive
internal surface area located in the first two post-prostomial segments.
2. The presumed gonoducts have been described to be simple tubules
located in the genital region.
3. Possible functions for both nephridia and gonoducts have been
postulated.
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Figure Captions
Figure 1. Camera lucida sketch of a transverse section at the level of
the first septum. Note the extensive capillary beds and the large size
of the nephrostome.
Figure 2. Camera lucida sketch of a transverse section of the body of the
nephridium showing the large size of the cavity.
Figure 3. Camera lucida sketch of a sagittal section. The ventral body
wall is shown at the bottom; anterior is to the right.
Figure 4. Diagram of ventral view showing the location of the nephridia
in the body.
Figure 5. View from dorsally of the interior ventrolateral body wall in
the genital region showing the presumed gonoducts.
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Key to Figures
Body wall
Blood vessel
Coelomic cavity
Capillary bed
Circumpharyngeal connective
Nephridial cavity
Prostomial coelom
Gut musculature
Gonoduct
Longitudinal muscle
Circular muscle
Nephridial wall tissue: For clarity
wall blood vessels have been omitted
from all figures except figure 2
where they were not as extensive as
usual.
Body of Nephridium
Ventral nerve cord
Duct from nephridium to nephridiopore
Nephridiopore
Nepkrostome
Prostomium
Septum
Setae and setal musculature
Ventrolateral row of setae
Ventral blood vessel and nerve cord
Acknowledgements:
I would like fo thank Roger Szal and Bruce Belman for teaching me,with
great patience, all the techniques used in this work and for much good
advice.
This work was supported in part by the undergraduate research participation
program of the National Science Foundation, grant+ GY-4369.
Footnote:
1. Jones, R. MeC., MeClung's Handbook of Microscopical Technique, p. 249-50.
Literature Cited
1. Goodrich, E. S. 1945, The Study of Nephridia and Genital Ducts since
1895, Quart. J. Microscop. Sci. 86:113-392.
2. Jones, M. L. 1957, On the Morphology of the Nephridium of Nereis
Vexillosa Grube, Biol. Bull. 113:407-13.
3. Jones, R. McC., ed., MeClung's Handbook of Microscopical Technique,
ded., Haffner Publishing Co., New York, 1950.
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