Bath Sponge (Spongia officinalis)

Spongia officinalis, or Bath Sponge, thrives in the clear Mediterranean waters around Malta. Divers can explore its unique lobed structure and vibrant marine environment, especially at sites like Ras il-Ħobż in Gozo.

How to Identify a Bath Sponge

Spongia officinalis, commonly known as the Bath Sponge, is a commercially used sea sponge. These sponges grow in large lobes with small openings and are formed by a mesh of primary and secondary fibers. They are light grey to black in color and feature fine, slightly elevated openings with cone-shaped voids (conules). Oscula can be scattered or at the tip of the lobes.

Where are Bath Sponges Found?

Spongia officinalis is found throughout the Mediterranean Sea, including the waters around the Maltese Islands. They inhabit shallow waters (1-10 meters) down to depths of 100 meters, growing on littoral rocky surfaces, sandy bottoms, and vertical walls in well-oxygenated water.

Interesting Facts about Bath Sponges

Taxonomy: Belongs to the genus Spongia, family Spongiidae, order Dictyoceratida, class Demospongiae, phylum Porifera, and kingdom Animalia.
Historical Use: Mentioned by Aristotle around 350 BC, the Bath Sponge has been used since ancient times. Greeks spread its use across Europe during the Middle Ages for various purposes, including padding in Roman soldiers‘ helmets, surgical absorbents, digestive aids, and primitive contraceptives.
Skeleton Structure: The Bath Sponge has an ectosomal skeleton of primary and secondary fibers forming conulose openings and a choanosomal skeleton with a dense mesh of polygons. Primary fibers are 50-100 nanometers in diameter, while secondary fibers are 20-35 nanometers.
Reproduction: They reproduce asexually via budding or fragmentation and sexually through dioecious or sequential hermaphroditism. Sperm is spawned into the water, captured by females, and fertilization peaks from October to November.
Larval Development: Embryos develop in choanosomal tissue, with parenchymella larvae released from June to July. These larvae are lecithotrophic and settle on a benthic surface to grow into adults.

Where can I see a Spongia officinalis?

You can see Spongia officinalis while diving in various site around Goo in Malta. One notable dive site to observe these sponges is Ras il-Ħobż, also known as Middle Finger, on Gozo’s south coast. This site offers a perfect opportunity to explore the natural habitat of the Bath Sponge.

The photo of this Bath Sponge was taken at a depth of 30m at Ras il-Ħobż, also known as Middle Finger, on Gozo’s south coast.