Let S = φ be a two-fold connected orthogonal polygon in the plane. Assume that S is starshaped via staircase paths and K is any component of KerS, the staircase kernel of S. Let B be the bounded component of R 2 \S. If B contains one kind of north, east, south and west dents then KerS is either one component or two and the positions of these components agree with the kind of dents. But if B contains two kinds of north, east, south and west dents then either K er S is one component or S is not starshaped via staircase paths.

Matured brood stock of Pinctada radiata were collected from Afamia region in Lattakia coast. Three sets of spawning and larval rearing experiments were conducted during the period from July - October 2016 and the pearl oysters were successfully spawned at average temperature 31.5 ± 0.26 °C. After about 60 min, oocytes presented no germinal vesicle, rounded and measured 47.5-55 μm with an average of 50 ± 3.95 μm in diameter. Early stages of embryonic development were recorded and the polar body was observed 15 min after fertilization, trefoil stage at 1 h and 30 min, morula at 3 h and 30 min, blastula at 4 h and 50 min, gastrula at 6 h, trochophore larva at 8 h and veliger larva at 20 h. Veliger larva dimensions were 61.88 ± 3.82 μm for average length along the antero-posterior axis and 51.26 ± 5.14 μm for height along the dorso-ventral axis.