Personalized Birthday Mermaid Girls Party Long Sleeve T-Shirt. Birthday mermaid Long Sleeve T-Shirt - White girls party photo idea with blue mermaid tail. Pre-shrunk 100% cotton 6.1 ounce long sleeve t-shirt. Double-needle stitched neckline and sleeves. Quarter turned. Shoulder-to-shoulder taping. Adult: S, M, L, XL, 2XL, 3XL