Náttúrufræðingurinn - 1985, Page 24

sem náttúruvalið verki á sambýlið í
heild sinni — en allir einstaklingar
sambýlis eru af sömu arfgerð (gena-
týpu), þar sem þeir eru myndaðir kyn-
laust af sama einstaklingi í upphafi (úr
blasta eða lirfu) — sé allur valþrýsting-
ur fljótur að segja til sín. Ef til vill gæti
F. sultana svarað slíkri samkeppni frá
P. repens á þennan hátt. Skýringarinn-
ar á því að báðar tegundirnar dafna
jafn vel og raun ber vitni sé því að leita
í árangursríkari framleiðslu lirfa F.
sultana, sem vegi upp að einhverju
leyti dreifingarhæfni og lirfufram-
leiðslu P. repens.
HEIMILDIR
Barnes, R.D. 1980. Invertebrate Zoo-
logy., 4. útgáfa. - Sounders College,
Philadelphia: 1089 bls.
Brown, C.J.D. 1933. A limnological study
of certain fresh-water Polyzoa with spe-
cial reference to their statoblasts. —
Trans. Am. Microsc. Soc. 52: 271—316.
Bushnell, J.H. 1966. Environmental rela-
tions of Michigan ectoprocta, and dyna-
mics of natural populations of Plu-
matella repens. — Ecol. Monogr. 36:
95-123.
Bushnell, J.H. & Rao, K.S. 1974. Dor-
mant or quiescent stages and structures
among the ectoprocta: Physical and
chemical factors affecting viability and
germination of statoblasts. — Trans.
Am. Microsc. Soc. 93(4): 524—543.
Fjeldsá, J. & Raddum, G.G. 1973. Þrjú ný
vatnadýr á íslandi. - Náttúrufr. 43:
103-113.
Heding, S.G. 1938. Freshwater Bryozoa.
- Zool. Icel. 4(66b): 3 bls.
Hyman, L.H. 1959. The Invertebrates:
Smaller Coelomate Groups. Vol. 5. —
McGraw-Hill Book Company, New
York: 783 bls.
Lacourt, A.W. 1968. A monograph of the
freshwater Bryozoa — Phylacto-
laemata. — Zool. Verh. Leiden 93: 1—
159.
Lindegaard, C. 1979. A survey of the
macroinvertebrate fauna, with special
reference to Chironomidae (Diptera)
in the rivers Laxá and Kraká, northern
Iceland. — Oikos 32: 281—288.
Marcus, E. 1940. Mosdyr. - Danmarks
fauna. G.E.C. Gads forlag, Kaup-
mannahöfn: 401 bls.
Mundy, S.P. 1980. A key to the British
and European freshwater Bryozoans.
- Freshw. Biol. Ass., Sci. Publ. 41: 1-
31.
Ryland, J.S. 1970. Bryozoans. — Hutch-
inson, London: 175 bls.
Thorpe, J.P. 1979. A model using deter-
ministic equations to describe some
possible parameters affecting growth
rate and fecundity in Bryozoa. — Syst.
Ass. Spec. 13: 113-120.
Woollacott, R.M. & Zimmer, R.L.
(ritstj.) 1977. Biology of Bryozoans. -
Academic Press, New York: 566 bls.
SUMMARY
Aspects of the life-cycles of
Fredericella sultana and
Plumatella repens
(Bryozoa : Phylactolaemata)
in the lake Urriðakotsvatn
south-west Iceland
by
Sigmar Arnar Steingrímsson
Marine Research Institute
Skúlagata 4
121 Reykjavík
A brief account on the general biology
of Bryozoans is given and the life-cycles of
Fredericella sultana (Blumenbach) and
Plumatella repens (Linnaeus) in the lake
Urriðakotsvatn south-west Iceland is
described (Fig. 1). The study was made in
April to September 1981.
Germination of statoblasts of F. sultana
started soon after the ice had melted in
early April (temperature range 3 to 8°C.
70