Family Costasiellidae

Body broad, reching 3 mm, anteriorly tapering to a blunt tail. Rhinophores short, fused to each other anteriorly. Large eyes situated between rhinophores. Broad, thick ridge present from the base of each rhinophore to the anterior margin of head. Mouth lying in deep furrow between two ridges. Cerata black with whitish lighter-colored tips. Whitish patches surround eyes. Burrows into the sediment to feed and deposit egg masses. Lays small eggs that develop into lecithotrophic short-duration veliger larvae. Photo by Ángel Valdés.