Pleurobranchidae Family of Side-gill Slugs

Two Side-gill Slugs of the Pleurobranchidae Family can be found in this website:

Phylogeny: Side-gill Slugs of the Pleurobranchidae Family belong to the phylum Mollusca. They are in the class Gastropoda, the subclass Heterobranchia, the infraclass Euthyneura, the subterclass Ringipleura, the  superorder Nudipleura, the order Pleurobranchida, and the superfamily Pleurobranchoidea. The Pleurobranchidae Family is one of three families in this superfamily. The Pleurobranchidae Family contains seven genera and seventy-one species. The name Pleurobranchidae comes from the Greek and means “lateral gill” or “side gill”. Species in this family are commonly known as Pleurobranchids.

Morphology: Side-gill Slugs are  soft-body gastropods that, unlike sea snails, lack an external shell. Most have a thin, unpigmented fragile internal shell that is shaped like that of a limpet or abalone. Some species even lack an internal shell. Side-gill Slugs have an oval profile and most are somewhat flat. Their head is partially concealed by a prominent mantle that is rolled to produce 2 oral tentacles and 2 rhinophores on the head. The rhinophores (horn-like projections) are chemosensory organs that help locate food and potential mates. They have a feathery gill between the mantle and the foot on their right side. The dorsal surface may be bumpy, have calcareous spiracles or be smooth. Side-gill Slugs are generally drab in color. They range in size from 1.5 cm (0.6 inches) to 20 cm (7.9 inches) in length.

Habitat and Distribution: Most Side-gill Slugs are found on hard substrates, but some have the ability to bury in soft substrates. They range in depth from the intertidal zone to over 500 m (1,640 feet). Side-gill Slugs are found worldwide in polar to tropical seas. At least six species from this family are found in Mexican waters.

Reproduction: Side-gill slugs are simultaneous hermaphrodites ( having both male and female reproductive organs). They reproduce sexually through internal cross-fertilization (both individuals exchange sperm and eggs). The eggs are laid in ribbon-like masses, which may be spiraled, coiled, or spaghetti-like. The eggs develop into veliger larvae before settling to the seafloor and metamorphosing into benthic juveniles.

Ecosystem Interactions: Side-gill Slugs are diurnal and they feed on ascidians, mollusks, sponges, and tunicates, and practice cannibalism at a minor level. Very little is known about their predators; their skin is able to excrete acidic compounds that deter most predators. Sea turtles have been observed consuming certain species.