Alguns aspectos da biologia de Subulina octona (Bruguiere,1789) (Gastropoda, Pulmonata, Subulinidae) em condições de laboratório

Abstract

In order to understand the biology Subulina octona (Bruguiére, 1789) under laboratory conditions the following reproductive and developmental characteristics have been studied: oviposition; size of the eggs; period of incubation; occurence of self-fertilization; growth of the shell; and the development of specimens fed with different diets (lettuce; lettuce plus concentrated ration). The study 42 individually isolated specimens of S. octona during 182 days indicated that oviposition occur between 10 pm and 10 am with maximum peak between 10 pm and 4 am. The number of oviposition per snail varied from 11 to 19 with two to eight eggs per cluster and a total of 42 to 112 eggs were layed by a singles snails during the period of study. The interval between ovipositions was from seven to 31 days with 76% of the cases concentrated between seven to 15 days. Measurements of 180 eggs showed that the value for the greatest axis varied from 1.5 to 2.0 mm (1.6 mm, was the most frequent) while that of smallest axis varied from 1.2 to 1.6 mm (1.3 mm was the most frequent). The period of incubation of 137 eggs (layed in February 1990) varied from one to 14 days. Self-fertilization in S. octona was observed among 32 snails, individualy isolated for 154 days; eggs were detected in 38 to 50-days-old sanils; total number of ovipositions varied from six-nine; number of eggs per cluster, one-nine; total number of eggs per snail, 16-56. A period of incubation of one to 15 days and a viability of 94.8% were observed for eggs layed in July of 1990 by these isolated snails. Thirty-two specimens were measured to determine length of shell of recently ecloted snails and growth rates. The lenght of shell of recently ecloded snails was 1.3-1.8 mm. Growth rates were established after detection of the first egg-bearing specimen, with 15 days interval measurements; during the first 45 days shells grew 0.8 to 1.5 mm and during the last 75 days, 0.2-1.0 mm. Snails fed for 30 days with lettuce achieved less than half of the lenght of snails fed with lettuce plus concentrated ration.