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Gastropteridae, the bat-winged slugs, is a family of sea slugs, gastropod molluscs in the superfamily Philinoidea of the clade Cephalaspidea, the headshield slugs and bubble snails. It includes four genuses: Enotepteron, Gastropteron, Sagaminopteron, and Siphopteron containing 33 described species. The greatest diversity of these colourful small slugs is in the tropical and sub-tropical Indo-Pacific region.

Contents

1Description

2Anatomy and Morphology

3Distribution and Habitat

4Ecology

5Taxonomy

6References

7Further Reading

Anatomy and Morphology

Gastropteridae is a fairly diverse family containing four genera and thirty-three described species. Adults have an internal reduced shell or no shell at all. The body is fairly short, usually under 10 mm (0.4 in) in length, but exceptionally up to 35 mm (1.4 in). Compared to the closely related philinids and the aglajids, the mantle cavity is small, and the gills are located further forward, in an exposed position. In most species, the hind end of the headshield is narrowed, raised and curved forward, sometimes being further forward than the front edge of the head. The gonads are located near the cephalic region. There is an anterior simple tubular siphon in the posterior end of cephalic shield. A radula is present, but no jaws. These slugs are mostly brightly colored and distinctively patterned.

Gastropterids have parapodia (fleshy protrusions that are a lateral extension of the foot) and are used as an undulating fin for swimming, which has led to them being referred to as "bat-winged slugs". The nervous system is highly cephalized as far as cephalaspideans go[1], with a well-developed brain and these slugs exhibit various elaborate behavioral traits.

Several different views and positions of a gastropterid mollusk body form.

Distribution and Habitat

All gastopterids are benthic, even though they are frequently found swimming. Studies done in Japan on some species of Sagaminopteron and Siphopteron showed that most organisms are found in a particular area of the ecosystem. Further laboratory experiments suggest that substrate material is important for habitat selection in these species.[2]

Many gastropterids are found in the tropical and sub-tropical parts of the Indo-Pacific region or regions with a similar climate profile. However, not much is known about all of these species and distribution is thought to possibly be worldwide.[3] There has been record or Gastropteron found in a wide distribution; Florida, Gulf coast[4] and Atlantic coast[5]; Guade- loupe; Atlantic coast of Morocco; Southern coast of Portugal; Gulf of Gascony; and the Mediterranean Sea, including the Adriatic and Aegean Sea. Most species have been described since the middle of the twentieth century and there are many undescribed species. Gastropteron is the only genus with a presence in the Atlantic Ocean.

The coral triangle in the Indo-Pacific, specifically the Phillipines, has been documented to have the highest known diversity of heterobranch molluscs. Expeditions in 2014 and 2015 to the Verde Island Passage of the Phillipines resulted in the collection of several new species of Gastropteridae.

Ecology

The ecology of gastropterids has been little studied, but most Sagaminopteron species have been observed to feed on sponges that do not contain spicules.[6] At least some Siphopteron species are found on macroalgae and seagrasses. Other gastropterids have been recorded consuming animal substances and phytoplankton.[7][8]

Gastroperids are simultaneous hermaphrodites. They have a complex mating practice exhibiting traumatic insemination behaviors, with each of two slugs attempting to use spines for hypodermic insemination of the other one to inject prostate fluid into the other having stabbed it with a stylet. The male’s sex organ punctures and wounds the female’s protective outer layer, regardless of the costs to the receiver. The slugs begin mating by biting into their partners posterior visceral hump, followed by intertwining of their bodies. The two slugs circle clockwise around each other, each probing and attempting to pierce the underside of the other with the stylet while avoiding getting pierced itself. When one or both is successful, the penis is thrust into the other slug's gonopore, where further spines hold it in place, and mating takes place. Copulation may be reciprocal or only one slug may be successful reciprocal insertion of the penile bulb and injection of the prostate fluid.[9]

This is the case in Siphopteron quadrispinosum, only the gonopore is located next to the middle of the forehead. This means that the penis is forcefully inserted into the head of the slug. It is the first known instance of “cephalo-traumatic secretion transfer”[9].

Gastropterids exhibit several different types of embryonic development. Some species exhibit indirect development and lay eggs that develop into veliger larvae, and others develop just as planktrophic veliger larvae. Additionally, some lay larger eggs that go through intracapsular metamorphosis that hatch as benthic juveniles.[10]

Taxonomy

Gastropteridae was established in the late 1800’s. From then until 1964, only 3 species had been described. In 1973, Carlson & Hoff described one new species of Sagaminopteron and three new species of Gastropteron that were transferred later to Siphopteron.[11] Following that, in 1984, Gosliner & Armes described three new species of Gastropteron, one from Florida[12], and two from South Africa[13]. These species were later transferred to Siphopteron. In 2001, the genus Enopteron was erected with Enotepteron heikae (Brodie, Klussmann-Kolb & Gosliner et al. 2001)[14].

A discovery of a new species of Enotepteron revealed the presence of a very large anal gland. This character was not previously recognized and has been a useful taxonomic and phylogenic characteristic.[15]

There continue to be many taxonomic shifts due to new discoveries and further understanding of the group.

The following genera are recognised by the World Register of Marine Species:

Enotepteron Minichev, 1967 Gastropteron Kosse, 1813 - synonym: Sarcopterus Rafinesque, 1814 Sagaminopteron Tokioka & Baba, 1964 Siphopteron Gosliner, 1989

Reference

Ong E, Hallas J, Gosliner T. 2016. Like a bat out of heaven: the phylogeny and diversity of the bat-winged slugs (Heterobranchia: Gastropteridae). Zoological Journal of the Linnean Society, 180: 755–789.

Tanamura D, Hirose E. 2017. Seasonal Occurrence of Gastropterids (Gastropoda: Cephalaspidea) and Their Habitat Selection in a Subtropical Back-reef on Okinawajima Island (Ryukyu Archipelago, Japan). Zoological Studies 56: 34.

Marcus E, Marcus E. 1960. Opisthobranchs from American Atlantic Warm Waters.Bulletin of Marine Science, 10(2): 129-203.

Abbot RT. 1955. American seashells. New York, D. Van Nostrand Co., XIV + 541pp., 40 pis.

Tomlin JR LE B. 1927. Report on the Mollusca (Amphineura, Gastropoda, Scaphopoda, Pelecypoda). The Zoological Society of London, 22(3): 291-320.

Gosliner TM, Behrens DW Valdés Á. 2008. Indo-Pacific nudibranchs and sea slugs: a field guide to the World’s most diverse fauna. Gig Harbor/San Francisco: Sea Challengers/ California Academy of Sciences.

Graham, Alastair. 1955. Molluscan diets. Proc. Malacol. Soc., 31; 144-159.

Vayssiere, Albert. 1879- 1880. Recherches anatomiques sur les mollusques de la famille des bullides. Ann. Sci. Nat. Zool. Ser. 6, 9: 1-123.

Lange R, Weminghausen J, Anthes N. 2014. Cephalo-traumatic secretion transfer in a hermaphrodite sea slug. Procedings of the Royal Society B 281.

Anthes N, Michiels N. 2007. Reproductive morphology, mating behavior, and spawning ecology of cephalaspid sea slugs (Aglajidae and Gastropteridae). Invertebrate Biology 126(4): 335–365.

Carlson CH, Hoff PJ. 1973. Two new species of Gastropteridae from Guam, Marianas Islands (Opisthobranchia: Cephalaspidea). Publications of the Seto Marine Biological Laboratory 21: 141–151.

Gosliner T, Armes P. 1984. A new species of Gastropteron from Florida (Gastropoda: Opisthobranchia). The Veliger 27: 54–64.

Gosliner T. 1984. Two new species of Gastropteron (Gastropoda: Opisthobranchia) from southern Africa. Publications of the Seto Marine Biological Laboratory 29: 231–247.

Brodie GA, Klussmann-Kolb A, Gosliner T. 2001. Anatomy and histology of a new species of Enotepteron (Cephalaspidea: Gastropteridae) from tropical northeastern Australia. The Veliger 44: 362–369.

Cunha C, Migotto A. 2016. Rediscovery of Gastropteron chacmol(Gastropoda: Gastropteridae) on the Brazilian coast. Marine Biodiversity 46: (1-2).