Haigai（Tegillarca granosa）and Chirimen yukigai(Meropesta sinojaponica)
Both the Haigai (Tegillarca granosa) and the Chirimen yukigai (Meropesta sinojaponica) currently inhabit areas south of the Seto Inland Sea and the Ariake Sea, but it has been discovered that the Haigai was present in the Oga Peninsula around 8,000 years ago and in Hachirogata around 7,000 years ago.
The Chirimen yukigai expanded its distribution to as far north as Chiba Prefecture on the Pacific coast about 6,000 years ago.At that time, this shell species was also present in Hachirogata.
During this period, it is believed that the shell lived along the coastline of the Sea of Japan south of Akita, but so far, no discoveries have been made in that area.
Ogata Village is the only known location for Chirimen yukigai in the entire Sea of Japan.
From about 8,000 to 6,000 years ago, during a period of warming, warm ocean currents became stronger, bringing various marine species from the southern seas to the north.
In Ogata Village, in addition to the Haigai and Chirimen yukigai, other shell species such as Itabogaki (Ostrea denselamellosa), Shiofuki (Mactra veneriformis), Murasakigai (Soletellina adamsii), Hamaguri (Meretrix lusoria), and Kushikemasuo (Cryptomya elliptica) have been found.
