_??_1995 The Japan Mendel Society Cytologia 60: 205-210, 1995

Comparative Karyological Studies and Shell Measurements of Two Egyptian Marine of Genus (Prosobranchiata-)

Ahmed E. Yaseen, Abdel-Based M. Ebaid and I. S. Kawashti*

Cytogenetic Laboratory, Zoology Department, Faculty of Science (Qena) Assiut University, Egypt

Accepted December 12, 1994

In recent years, especially since 1960, a considerable amount of information has been accumulated on variable taxa of . This recent interest may be attributed to the boon in the field of cytogenetics (Nakamura 1986). Chromosome number of gastropods belonging to order Mesogastropoda have not yet been reported for many species. Patterson and Burch (1978) reported that the haploid chromosome number of several species of this order ranges from n=7 to n=18, with the exception of some species of families Thiaridae and Cypraeidae which have higher haploid chromosome numbers ranging from n=20 to n=60 which is attributed to the presence of polyploid phenomena. Although there has been considerable development of cytotaxonomic studies in the last twenty years, marine invertebrates have usually been disregarded by karyologists especially in Egypt. As far as the available literature indicates, no information are existing regarding the chromosomal studies and shell measurements of these two species, Cerithium adustum and C. nodulosum in Egypt, so the aim of the present work is to determine the chromosome number, describe the karyotype and shell measurement in details for these two species.

Materials and methods

The specimens of Cerithium adustum and C. nodulosum were collected during low tide at day time along the coasts of the northwestern part of the Red Sea. They were housed in the Laboratory tanks of aerated sea water, they were fed continuously on lettuce, wheat germ and tetra-min fish food to promote somatic growth (Dixon and Clarke 1982).

Chromosomal preparations Chromosome preparations were made by the warm-dry method (Corni and Mancini 1986, Nakamura 1986) as follows: following an intraperitoneal injection of 20ƒÊl of 0.05% colchicine after 1hr, testes, ovaries and gills were diced under 1% sodium citrate and kept there in 20min, fixed in Carony fluid for 30min, treated in 60% acetic acid on warm slide and stained with Giemsa (pH 7) for 15-20min at room temperature. Chromosome were examined and photographed. Centromere position is described according to criteria established by Levan et al. (1964).

Shell measurements About fifty individuals from each species were used in the morphological analysis of shell parameters. Four shell dimentions which are length (L), width (W), aperature length (AL) and aperature width (AW) were measured for each snail using a dial caliper. Spire shape

* Zoology Department, Faculty of Science, Al-Azhar University. 206 Ahmed E. Yaseen, Abdel-Based M. Ebaid and I. S. Kawashti Cytologia 60

(L/AL), shell shape (L/W) and aperture shape (AL/AW) were calculated as shown in Table 3 a according to James (1968).

Results and discussion

The cell spread and karyotype of the two species Cerithium adustum and C nodulosum was found to have a diploid chromosome number of 18 and 16 and fundamental number of 36 and 26 respectively as shown in Fig. 1 and 3. Arm ratio, relative length and centromeric indices are given in Table 1 and 2. An idiogram (Figs. 2, 4) was constructed from relative length and centromeric indices with the centromeres drawn at the same level to make visual comparison easier. The karyotype of Cerithium adusttum consists of: six metacentric pairs (arm ratio 1.00 -1.44) and three submetacentric pairs (arm ratio 2.00-2.46), while the karyotype of C.

Fig. 1. A cell spread [a] and karyotype [b] of the Fig. 3. A cell spread [a] and karyotype [b] of the Cerithium adustum (2n=18). Cerithium nodlosum (2n=16). Table 1. Classification and average measurements of chromosomes in ten cell spreads of Cerithium adustum.

Table 2. Classification and average measurements of chromosomes in ten cell spreads of Cerithium nodulosum. 208 Ahmed E. Yaseen, Abdel-Based M. Ebaid and I. S. Kawashti Cytologia 60

Fig. 2. Idiogram of the chromosomes of Cerithium Fig. 4. Idiogram of the chromosomes of Cerithium adustum. Idiogram was wonstructed relative to nodulosum. Idiogram was constructed relative to relative (I) and to centromeric index (II). relative length (I) and to centromeric index (II).

nodulosum consists of: two metacentric pairs (arm ratio 1.03-1.23), three subtelocentric pairs

(arm ratio 3.23-3.38) and three telocentric pairs (arm ratio •‡). Shell measurements were carried out on 50 samples of each species. In Cerithium adustum the shell has a broad to fairly broad shaped shell measuring L/W ratio range from 1.1 to 1.3, the 1995 Comparative Studies of Genus Cerithium 209

Table 3a. Showing the appoved description and ranges of shell spire and aperture shapes

Table 3b. Summary of ranges of some shell measurements of the two species studied

L=Length, AL=Aperture Length, W=Width, AW=Aperture Width.

shell spire ranges from short to medium with a mean L/AL ratio range from 1.4 to 1.6 and the shell aperature is wide to fairly wide measuring about 1.3 to 1.5. While in C. nodulosum the shell has narrow to very narrow-shaped shell measuring L/W ratio from 12.6-54, the shell spire ranges from short to medium with a mean L/AL ratio from 1.4 to 1.6 and the shell aperature is narrow to very narrow measuring about 1.5 to 1.8 as shown in Table 3b. The cytogenetic findings of the present investigation of the two species, Cerithium adustum and C. nodulosum are in complete agreement with those recorded using the classical morphol ogical and anatomical methods for . Therefore these two species which belong to the same genus Cerithium, are not only different in diploid chromosome number 18 and 16 respectively, but they also differ in the distribution of chromosomes among karyotype groups. Furthermore, the fundamental number (FN) of 36 of the first and 26 of the second species demonstrated still another aspect of difference. The net result of these facts would ultimately leads to the conclusion that the distinction between the two species karyologicaly and morphoogically is quite justifiable.

Summary

Cerithium adustum and Cerithium nodulosum collected from the rocky shore on the Red Sea were karyotyped. These two species showed a distinct differentiation in the diploid chromosome number (2n=18 and 16 respectively). The karyotype of Certhium adustum consists of: six metacentric pairs and three submetacentric pairs while the karyotype of C. nodulosum consists of: two metacentric pairs, three submetacentric pairs and three telocentric pairs. Shell measurements of these species are also described in details in this paper. These results are reported for the first time in Egypt. 210 Ahmed E. Yaseen, Abdel-Based M. Ebaid and I. S. Kawashti Cytologia 60

References Corni, M. G. and Mancini, T. 1986. A chromosome study of Cnamelea gallina (L.) (Bivalvia: Veneridae). Bull. Zool. 53: 23-24. Dixon, D. R. and Clarke, K. R. 1982. Sister chromatin exchange a sensetive method for detecting damage caused by exposure to enviromental mutagens in chromosomes of adult Mytilus edulis. Marine Bial. Letters 3: 163-172. James, B. L. 1968. The characters and distribution of the subspecies and varieties of Littorina saxatalis (Olivi) in Britain. Cah. Biol. Mar. 9: 143-165. Levan, A., Fredga, K. and Sandberg, A. A. 1964. Nomenclature for centromeric position on chromosomes. Hered. 52: 201-220. Nakamura, H. K. 1986, Chromosomes of the Archaeogastropoda (Mollusca-Prosobranchiata) with some remarks on their cytotaxonomy and phylogeny. Pubp. Seto. Mar. Biol. Lab. 31 (316): 191-267. Patterson, C. M. and Burch, J. B. 1978. Chromosomes of pulmonate molluscs. In: V. Fretter and J. Peakeeds, Pulmonate. Vol. II: 171-217 Academic Press, New York.