Sea pens or pennatulaceans (Phylum Cnidaria, Order Pennatulacea) are colonial marine octocorals that typically anchor themselves into soft sediment. They make large colonies from the intertidal zone down to the abyssal plain that provide an important structural habitat to other organisms. In the present study, the morphological and histological characteristics of the dominant species of Virgularia gustaviana, the dominant sea pen species of the Persian Gulf, were surveyed. Samples of V. gustaviana were collected along the coastal intertidal zone of the Soru and Bandar Abbas beaches, located at the northeast of the Persian Gulf. The sea pens were then fixed in Bouin's solution. Histological sections were prepared using routine histological techniques and stained with hematoxylin and eosin. V. gustaviana morphologically consisted of two major parts, including the rachis and peduncle, originated from the early polyp. Rachis with leaf-like plates consisted of autozooids and siphonozooids that were located at the ventral and dorsal surfaces of the rachis, respectively. The peduncle was the lower part of the sea pen with a smooth structure and the bubble-shaped end. The body wall (coenenchyme) of V. gustaviana consisted of three layers including the epithelium, mesogloea, and gastrodermis. There was a calcareous rod, with the dark and light concentric circles, called the axis at the center of the body of the sea pen. A layer of calcified sponge-like tissue called sclerite was observed around the axis. Sclerite was connected to the body wall of the sea pen by four thin tissue septa that divide the coelom into four water canals. Another water canal was found between the axis and the sclerite, which is considered the fifth water canal of the sea pen. In conclusion, V. gustaviana have the basic histological structure like other studied species.
