In order to analyze chromosomes for possible numerical and structural alterations in response to exposure to organotin(1V) compounds, gastropod Truncatella subcylindrica specimens were treated with dibutyltin(1V) and tributyltin(1V) chloride solutions with different exposure times.Experimental evidence suggests that tributyltin(1V) chloride is more toxic to this organism than dibutyltin(1V) dichloride at low concentrations. Furthermore, the toxicity responses to these organotin(1V) derivatives seem to be proportional to both concentration and exposure time.The following structural lesions have been identified by comparative analysis of spermatocyte chromosomes from untreated specimens and specimens treated with organotin(1V) compounds: (1) breakages; (2) bridging; (3) irregular outline; and (4) light areas after staining with acetic orcein. In this respect, dibutyltin(1V) and tributyltin(1V) chlorides seem to have an effect similar to that of colchicine.

We have studied mitotic and meiotic chromosomes in the males of two species of Blaps: B. gigas and B. gibba.Karyological characteristics such as the occurrence of a multivalent configuration at diakinesis and two types of metaphase-II spreads support the notion that multiple-chromosome sex systems involving five chromosomes in B.gigas and eight chromosomes in B. gibba have developed in these species. Results obtained by means of silver staining and C-banding techniques suggest that the complex sex systems occurring in B. gigas and B. gibba may have originated from exchanges of terminal ribosomal genes among the Y chromosome and some autosomes.

In the present investigation the diploid numbers 2n = 45, 2n = 46, 2n = 47, and 2n = 48 have been determined for Gobius paganellus. Specimens of different sex were found to have exactly the same karyotype. This species is characterized by two fundamental numbers: NF = 47, and NF = 48. Chromosome polymorphism due to different chromosome rearrangements within the A-type complement is present in this species.

In order to obtain chromosome preparations from early‐developing embryos of Anilocra physodes, a squash technique has been successfully employed. Results gathered after exposure of this material to bis[dimethyltin(IV)chloro]protoporphyrin IX {[(CH3)2SnCl]2 ‐ Protoporphyrin IX} solutions at different exposure times suggest that this chemical complex is capable of producing abnormal metaphase and anaphase figures in proportion to its concentration and not to exposure length. Essentially, all of the chromosome abnormalities are classifiable as chromosome fragments mainly observed at the metaphase stage; chromosome bridges; and large decondensed chromosome regions.

The diploid numbers 2n= 48, and 2n= 47 have been determined for the greater amberjack, Seriola dumerili. A chromosome polymorphism due to Robertsonian fusion is present in this species. A simple sex-determining mechanism has not been observed