OF SOME SHELL FEATURES OF VALVATA CRISTATA 0 . F . MOLLER , 1774 ( PROSOBRANCHIA , VALVA TIDAE ) FROM FISHPOND IN LIGOT A-ZABRZEG ( UPPER SILESIA )

Height and breadth of shells of Valvata cristata O. F. Müller, 1774 were measured; growth lines on the shells were counted. The shell height was found to range from 0.5 to 1.4 mm, while the shell breadth from 1.0 to 3.5 mm; there was no significant correlation between the shell size and growth 1ines number. Samples of 50 individuals chosen at random each month (from May to October) were divided into sizeclasses and the distribution pattern of the classes in the vegetation period was analysed. Young individuals were found to appear in July. key woRDs: shell, seasonal variability, Silesia, Poland http://dx.doi.org/10.12657/folmal.002.006 Folia Malacol. 2: 77–82 Folia Malacologica 2/1988 was originally published as No. 1112 of Scientific Bulletins of University of Mining and Metallurgy, Cracow. This digitalised version was prepared by the Association of Polish Malacologists and first published on-line on December 30th, 2016. ZESZYTY NAUKOWE AKADEMII G6RNICZO·HUTNICZEJ IM. STANISlAWA STASZICA Nr 1112 Folia Malacologica z. 2 Krak6w 1988


INTRODUCTION
Valvata cristata O.F. MUller, 1774 was never found in sinkhole ponds and sand pits in Uppersilesian Industrial Region (Strzelec, Serafi~ski 1984) nor in fish-ponds in Golysz and Landek (Kownacka l963) , In my previous•sfudy on snails of fish-ponds in Silesia and its vicinity (Rembecks in press) this species was found in only two ponds per thirteen~In one of them: Sok6l D V. CFistata constituted 19.30% of all the snails • found.It was the reason for more detailed studies on the populat ion living there and for comparison of the results with the data from other territories.
The aim of the present study is to show the variation in V. cristata shell and to analyse the seasonal changes in its mean width in the fish-pond.

THE DESCRIPTION OF THE STUDlED AREA
The fish-pend Sok6£ 0 is situated in the borderland of the katowickie and bielskie voivodships in llgota-Zabrzeg village.The pond area amounts to 3.5 ha., the depth to 0.3 -0.4 m. ' The pond is supplied ~1ith infiltrating water and never dries out.Its Bottom is slimy-clayey .There is a lot of organic s~spension in the water.The water hardness oscillated in the study period from 6.67°g to 8.15°g.The vegetation in the pond is composed mainly of Salvinia natans (L.), Alisma plantago-aguatica L., Lemna trisulca L., Phragmites communis Trin., Acarus calamus L., ~ latifolia L.

MATERIAL AND METHODS
Specimens of V. cristata were collected from May to October at•• month intervals in three different sites.Fifty individuals were taken out a.t random from every sample and height acrd width of each shell were measured.Additionally, the number of growth lines on the Shell were counted.
All the results were statistically analysed.The specimens were divided in seven classes according to the width of shell (measured wi'th accuracy up to 0.1 mm): class I~ 1. 3 mm; class II 1.4-1.7 mm; class III 1.8-2.1 mm; class IV 2.2-2.5 mm; class V 2.6-2.9 mm; class VI 3.0-3.3mm; class VII>3.3 mm.The increase of individual size in vegetation season was analysed on this base.

A. Shell characteristic
The shape of shells of V. cristata is slightly variable (Fig. 1).Among 300 specimens only in one shell the last whorl was not stuck.Most of the shells were yellowish grey beige, with transverse stripes.Sometimes they were tran~lucent, and occasionally dark brown, matt and more solid, with organic coat.
In the studied material 281 shells were characterized by distinct, transverse growth stripes in number from 1 to 5. No significant correlation between the shell size and number of those stripes was observed (r = +0.27).In the material of the same month there occurred the specimens of the same size, but with various number of growth lines, e.g. the shell 1.0 mm high and 2.7 mm wide had 5 lines, whereas another of similar size had 2 lines only.that the wid~h of tne shell is mar~ variable than the height (Vy = 22.20%, .Vx =. 16.B6%).

C. SeasonaL s~ell variability
The analysis of the seasonal var~abilit~ in the shell (Fig. 2) shows that the smallest individuals appear i~ July, their number increases in August and September and then decreases in October.It seems that the breeding period of, V. cristata starts in June and continues at least to October.In spring the individuals of classes V and VI occur and only in summer the smaller individuals (of classes II and Ill) appear numerov.~ly.In autumn all t~e size classes occur in similar numbers .
Urba"ski (1957) and Piechocki (1979) consider that V. cristata prefers stagnant water bodies with muddy bottom and rich vegetation.Hubendick ( 194 7) considers, however, tha t this species lives on clayey bottom covered with detritus in neyer drying out water bodies.Boycott (1936) considers that v, cristata prefers slimy bottom with rish vegetation and slow water current.
In the present study both the proportions of t~is species in the whole sample and the size of the shells suggest, that in the studied pond the V. cristata population found very good conditions,namely the clayey--slimy bottom and rich vegetation.The informations about the V. cristata Piechocki (1979) considers that the breeding the embryonal development is lasting 30 -40 -pond the reproduction did not start before end of September.biology are very scarce.period begins in spring and days.In the studied fish-June and went on till the The growth lines in Planorbidae are frequently considered the result of the inhibited growth during hibernation.Recently it has been found (Strzelec 1985) that they may appear in the reprod~ction period ~s well.In V. cristata the growth lines are not correlated with size, what enables the supposition that they are not only an effect of seasonal factors, but a result of endogenous mechanisms of growth as well.
This would be the subject of further studies.

CONCLUSIONS
1.There is no significant correlation between the shell size and the number of growth lines (r = +0.27).
2. The maximal height and width of the V. cristata shell are, on the average, somewhat greater than the• given by some authors.
3. It seems that the breeding period starts in late spring and goes on till autumn.