Rhodopidae

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Rhodopidae
Rhodope veranii live.png
Live individual of Rhodope veranii
Helminthope psammobionta dorsal schematic.jpg
Helminthope psammobionta dorsal view schematic
Scientific classification OOjs UI icon edit-ltr.svg
Kingdom: Animalia
Phylum: Mollusca
Class: Gastropoda
Infraclass: Mesoneura
Superfamily: Rhodopoidea
Family: Rhodopidae
Ihering, 1876
Type genus
Rhodope
Kölliker, 1847
Genera

Rhodopidae is a family of sea slugs. Rhodopids are small, meiofaunal organisms with worm-like body plans that differ considerably from a typical gastropod body plan, to the point that Rhodope was at one point classified as a flatworm. They have no shell. [1] Two genera are currently recognized within the family, Rhodope and Helminthope . [2] Helminthope has been described as the most worm-like gastropod. [1]

Contents

Etymology

Rhodope, the type genus of the family, is named for Rhodope, a figure in Greek mythology. [3]

Description

Rhodopids have worm-like bodies with no appendages. They often have red, orange, or purple bands, in varying pattern depending on the species, though some species are entirely white. [4] The species range in length from 1.5 to 8 mm, although they are capable of considerably contracting themselves. [3] The length-to-width ratios of the body while extended to crawl is around 9 in Rhodope and 25 in Helminthope. [5] Their bodies contain spicules below the epidermis that may provide structural support for the animal. [4] The nervous system of rhodopids has accessory ganglia, as in several other lineages of interstitial gastropod. [6]

Ecology

Some rhodopid species are epibenthic, while others, particularly the genus Helminthope, are fully interstitial organisms. [7] They are found in temperate and warm oceans worldwide. [3]

Rhodopids are the only known predators of placozoans, which make up the primary component of their diet. [7] At least some species, such as Rhodope placozophagus, can subsist entirely on a diet of placozoans; they are apparently not harmed by the toxins present in placozoans. [4]

Evolution

Although their affinities were long unclear, it is now known that rhodopids belong to the basal heterobranch clade Mesoneura. They are not closely related to any other lineage of sea slugs; their closest living relatives are sea snails of the family Murchisonellidae, [8] [9] and sea snails of the families Tjaernoeiidae and Parvaplustridae are their next-closest living relatives. [9] Although rhodopids lack a fossil record themselves, murchisonellids have a fossil record dating back to the Triassic, suggesting that rhodopids also date back as far. They may be one of the oldest lineages of slugs. [1] A molecular clock analysis suggested that the stem group of rhodopids may have arisen in the late Paleozoic, with an average age estimate of 281 million years ago and 95% of their age estimates falling within a range of 339 and 217 million years ago. [9]

References

  1. 1 2 3 Brenzinger, Bastian; Haszprunar, Gerhard; Schrödl, Michael (2013). "At the limits of a successful body plan - 3D microanatomy, histology and evolution of Helminthope (Mollusca: Heterobranchia: Rhodopemorpha), the most worm-like gastropod". Frontiers in Zoology. 10 (1): 37. doi: 10.1186/1742-9994-10-37 . ISSN   1742-9994. PMC   3704743 . PMID   23809165.
  2. ↑ Bouchet, P. (2015). Rhodopidae Ihering, 1876. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=23111 on 2015-04-14
  3. 1 2 3 Haszprunar, Gerhard; Heß, Martin (2005-11-01). "A new Rhodope from the Roscoff area (Bretagne), with a review of Rhodope species (Gastropoda: Nudibranchia?)". Spixiana. 28 (3): 193–197. ISSN   0341-8391.
  4. 1 2 3 Cuervo-González, Rodrigo (2017). "Rhodope placozophagus (Heterobranchia) a new species of turbellarian-like Gastropoda that preys on placozoans". Zoologischer Anzeiger. 270: 43–48. doi:10.1016/j.jcz.2017.09.005. ISSN   0044-5231.
  5. ↑ Jörger, Katharina M.; Neusser, Timea P.; Brenzinger, Bastian; Schrödl, Michael (2014). "Exploring the diversity of mesopsammic gastropods: How to collect, identify, and delimitate small and elusive sea slugs?". American Malacological Bulletin. 32 (2): 290–307. doi:10.4003/006.032.0205. eISSN   2162-2698. ISSN   0740-2783.
  6. ↑ Haszprunar, Gerhard; Huber, Georg (1990). "On the central nervous system of Smeagolidae and Rhodopidae, two families questionably allied with the Gymnomorpha (Gastropoda: Euthyneura)". Journal of Zoology. 220 (2): 185–199. doi:10.1111/j.1469-7998.1990.tb04302.x. eISSN   1469-7998. ISSN   0952-8369.
  7. 1 2 Eitel, Michael; Osigus, Hans‐Jürgen; Brenzinger, Bastian; Wörheide, Gert (2024). "Beauty in the beast – Placozoan biodiversity explored through molluscan predator genomics". Ecology and Evolution. 14 (4). doi:10.1002/ece3.11220. ISSN   2045-7758. PMC   11007570 .
  8. ↑ Wilson, Nerida G; Jörger, Katharina M; Brenzinger, Bastian; Schrödl, Michael (2017-11-01). "Phylogenetic placement of the enigmatic worm-like Rhodopemorpha slugs as basal Heterobranchia". Journal of Molluscan Studies. 83 (4): 399–408. doi:10.1093/mollus/eyx031. eISSN   1464-3766. ISSN   0260-1230.
  9. 1 2 3 Brenzinger, Bastian; Schrödl, Michael; Kano, Yasunori (2021-10-25). "Origin and significance of two pairs of head tentacles in the radiation of euthyneuran sea slugs and land snails". Scientific Reports. 11 (1). doi:10.1038/s41598-021-99172-5. ISSN   2045-2322. PMC   8545979 .
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