S. Tekaya et al., ULTRASTRUCTURAL AND CYTOCHEMICAL STUDY OF THE VITELLARIA IN THE MARINE TRICLAD SABUSSOWIA-DIOICA (PLATYHELMINTHES, TRICLADIDA, MARICOLA), Journal of submicroscopic cytology and pathology, 30(2), 1998, pp. 249-256
The development of vitelline cells (or vitellocytes) within the vitell
aria of the marine triclad Sabussowia dioica has been studied by menas
of ultrastructural and cytochemical investigations. Maturing vitelloc
ytes have a small nucleus with some patched chromatin and a well-devel
oped nucleolus; the abundant cytoplasm contains free ribosomes, mitoch
ondria, RER and Golgi complex, along with several types of inclusions:
egg-shell globules, yolk globules, lipid droplets and glycogen. Vitel
locytes are associated with acessory cells which externally surround t
he vitellarium to form a kind of lamina or tunica and internally envel
ope vitellocytes by their long, flat cytoplasmic projections. The egg-
chell globules appear to arise from repeated coalescence of small Golg
i derived vesicles and at the onset of formation show a multigranular
pattern. Later on, after vesicle fusion, they reach a diameter of 2.5-
2.7 mu-m and show a peculiar pattern with an electron-dense content, r
eacting positively to the test for polyphenols, which is interrupted b
y some small spots or narrow channels consisting of proteins. Yolk glo
bules are membrane-bound inclusions of about 2-2.5 mu-m in diameter co
ntaining a loose, granular material of medium electron-density which i
s completely digested by pronase and does not react with the Thiery te
st. Numerous lipid droplets, usually surrounded by glycogen granules,
are also present. A comparative analysis of the egg-shell globule stru
cture in the marine triclads studied to date suggest that the content
of this type of inclusions in S-dioica (family Cercyridae) has an inte
rmediate pattern with respect to those previously described in Cercyra
hastata (family Cercyridae) and Procerodes lobata (family Procerodida
e).