''Siphopteron quadrispinosum'' is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of small sea slug, a

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

opisthobranch Opisthobranchs () is now an informal name for a large and diverse group of specialized complex gastropods which used to be united in the subclass Opisthobranchia. That taxon is no longer considered to represent a monophyletic grouping. Euopisth ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

in the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Cephalaspidea The order Cephalaspidea, also known as the headshield slugs and bubble snails, is a major taxon of sea slugs and bubble snails, marine gastropod mollusks within the larger clade Euopisthobranchia.Jörger K. M., Stöger I., Kano Y., Fukuda H., ...

, the headshield slugs. This slug is a

simultaneous hermaphrodite Simultaneous hermaphroditism is one of the two types of hermaphroditism, the other type being sequential hermaphroditism. In this form of hermaphroditism an individual has sex organs of both sexes and can produce both gamete types even in the sam ...

Distribution

This species was originally identified in Hawaii (Kihei, Maui) and Papua New Guinea, and has a wide distribution throughout the western and central

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

Description

''Siphopteron quadrispinosum'' is a relatively small species of sea slug, growing to a maximum length of 5 mm. The body is bright yellow, and the siphon is orange-red in colour. The

parapodia In invertebrates, the term parapodium ( Gr. ''para'', beyond or beside + ''podia'', feet; plural: parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed ...

and siphon differ between the Papua New Guinean and Haiwaiian populations. Papua New Guinean specimens have the colouration of the siphon continuing along the posterior shield. Also, the parapodia are entirely yellow. In Hawaiian populations, the parapodia have a white margin and the orange-red colouration along the posterior shield is absent. Eggs of this species are pale yellow and are laid in a flattened mass.

Habitat

''Siphopteron quadrispinosum'' lives at depths of 6 to 27 metres on sand beds, and among '' Halimeda kanaloana'', a species of

macroalgae Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of ''Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as k ...

Behaviour

This slug can swim, and will do so when disturbed. It is active during the daytime.

Mating

''Siphopteron quadrispinosum'' is a simultaneous hermaphrodite. During mating, each animal stabs the other with a penile stylet, a form of penile appendage, and injects prostate fluids.

References

External links

*
Precopulatory stabbing, hypodermic injections and unilateral copulations in a hermaphroditic sea slug
', Nils Anthes & Nico K. Michiels (This link shows detailed anatomical images)
Images
(The top image is a Haiwaiian specimen, and the bottom images is a Papua New Guinean specimen)
Image
{{Taxonbar, from=Q7525774 Gastropteridae Gastropods described in 1989