''Siphopteron quadrispinosum'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of small sea slug, a marine

opisthobranch Opisthobranchs () is a now 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. Euopistho ...

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

in the

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

Cephalaspidea The order Cephalaspidea, also known as the headshield slugs and bubble snails, is a major taxon of sea slugs and bubble snails, marine (ocean), marine gastropod mollusks within the larger clade Euopisthobranchia. Bubble shells is another commo ...

, 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 sa ...

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 Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

Description

''Siphopteron quadrispinosum'' is a relatively small species of sea slug, growing to a maximum length of . 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; : parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointed late ...

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 on sand beds, and among '' Halimeda kanaloana'', a species of

macroalgae Seaweed, or macroalgae, refers to thousands of species of Macroscopic scale, macroscopic, Multicellular organism, multicellular, ocean, marine algae. The term includes some types of ''Rhodophyta'' (red), ''Brown algae, Phaeophyta'' (brown) and ...

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