Orange Blob, Berthelina ilisima. Length: 3.0 cm (1.2 inches). Found under tidal rocks in the low surge zones along the coast of the greater Los Cabos area of Baja California Sur.

Phylogeny:  The Orange Blob, Berthellina ilisima (E.V. Marcus and E.R. Marcus, 1967), is a member of the Pleurobranchidae Family of Side-gill Slugs. The genus Berthellina is one of seven genera in this family, and there are fourteen species in this genus. They are also known as the Apricot Slug and Engel’s Gumdrop Slug and in Mexico as Blob Anaranjado.

Morphology: Orange Blobs are soft-bodied gastropods that lack an external shell. They have a thin, flat, unpigmented, internal shell.  Orange Blobs have an oval outline and a relatively high profile. Their dorsal surface is smooth. Their head is partially concealed by a prominent mantle. The mantle is rolled to produce two oral tentacles and two rhinophores on the head. Rhinophores (horn-like projections) are chemosensory organs help them to locate food and potential mates. They have a feathery gill located between the mantle and the foot, on their right side. They may be light yellow, orange, or red in color. Orange Blobs reach a maximum of 7.1 cm (2.8 inches) in length.

Habitat and Distribution: Orange Blobs are found on, and under, rocks, often in pairs intertidally to depths up to 30 m (98 feet). They are a tropical Eastern Pacific species. In Mexican waters they are found along the entire west coast, including the Gulf of California. During a 25-year study at Bahía de los Ángeles, Baja California, Berthellina ilisima was the third most common opisthobranch mollusk encountered.

Diet:   Orange Blobs are spongivores that feed on Demospongiae (porifera) sponges.

Predators: Orange Blobs are a poorly studied and understood species. Their skin can secret a compound containing sulfuric acid as a defense against predators. There are no documented predators of Orange Blobs.

Reproduction: Orange Blobs are simultaneous hermaphrodites (having both male and female reproductive organs). The reproduce sexually, with internal fertilization. During mating two slugs position themselves so that their genital openings are adjacent to one another, then they mutually exchange sperm. The fertilized eggs are laid as a circular, frilly ribbon, which is the same color as the animal. Reproductive activity occurs from May to July.

Ecosystem Interactions: Orange Blobs are a poorly studied and understood species and there is documentation of commensal, parasitic, or symbiotic relationships for this species.

Human Interactions:  The indigenous Seri people of the Gulf of California used Orange Blobs medicinally. Their name for this species means “sun in the sea”, referring to its brilliant color. Otherwise, Orange Blobs have no direct impact on human activities. From a conservation perspective they have not been formally evaluated however they are fairly common with a relatively wide distribution and should be consider to be of Least Concern.

Synonyms:  Berthellina engeli ilisima