How Do Remipedes Disperse?

For those not in the know, remipedes are small, blind, saltwater cave-dwelling (pan)crustaceans remarkable for their 'primitive' polychaete-like body plan, possible close relation to insects, and discovery in 1979. Here's a video with lots of hot remipede action and commentary from the clade's initial descriptor, Jill Yager:

I'd recommend just going to YouTube.

Remipede biogeography has become quite the complex topic, and in retrospect my last post failed to give it any justice. 22 out of the 25 known remipede species* are present in the Caribbean, with 15 being found in the Bahamas alone; Caicos Bank has 4 species while San Salvador Island, Cuba, Hispaniola, and Yucatán all have a single indigenous species (Koenemann et al. 2009). The Bahamas remipedes exhibit remarkable sympatry, with up to 6 species from 3 genera inhabiting a single cave system (Koenemann et al. 2004). It has been speculated that the diversity of remipedes in the Caribbean, and particularly the Bahamas, is due to the complex geomorphology of the caves and changing sea elevation (and thus coastlines) throughout the Pleistocene (Koenemann et al. 2009). It should be cautioned that since remipedes were initially discovered from the Bahamas, sample bias may have exaggerated the disparity of diversity between the Bahamas and other Caribbean locales.

* Species count from Koenemann et al. (2009), which includes species with formal descriptions in preparation. Not included are unidentified and undescribed species, the number of which is ambiguous.


In the Bahamas and Caicos, individual remipede species are occasionally present on multiple islands, including G. robustus from Exuma Cays, Great Bahama Bank and North Caicos (Koenemann et al. 2009). Also notable is Speleonectes lucayensis, the first described remipede, which is present on Andros and Cat Island from the Great Bahama Bank as well as Grand Bahamas and Abaco from the Little Bahama Bank (Koenemann et al. 2009). Iliffe et al. (2010) took note of a pair of Godzilliognomus on either side of the Bahamas Banks, and speculated that dispersal may have occurred through open water, the deep sea, or cave colonization when the banks were forming during the Cretaceous. Very recently it was discovered that remipedes are not restricted to subterranean caves, but are present in sub-marine caves with similar properties located on shallow 'platforms', which apparently increases the potential range considerably and may explain occurrence on multiple islands (Daenekas et al. 2009). It is certainly an intriguing thought that islands which share remipede species have a contiguous, or nearly so, distribution of individuals in between. Since islands outside of the Bahamas and Caicos all have unique remipedes, it can be assumed this phenomenon has limited applicability for planetary-scale dispersal.

So what are those other Caribbean remipedes? All are members of the genus Speleonectes (Koenemann et al. (2009), and morphology-based phylogeny places S. epilimnius (San Salvador), S. gironensis (Cuba), and S. tulumensis (Yucatán) well within the genus (Koenemann et al. 2007). The Bahamas and Caicos are also home to several Speleonectes and other speleonectids (Koenemann et al. 2009), and I think it would be fascinated if all the divergent speleonectids were analyzed through molecular phylogeny to determine relations more certainly and calculate divergence times. If the Speleonectes from outside the Bahamas and Caicos are indeed closely related to those within, it would seem to suggest that colonization occurred very recently, presumably during or after the sea level changes of the Pleistocene.

Speleonectes are also present far outside of the Caribbean, as now two species are known from the Canary Islands. Both S. ondinae and S. atlantida were found in the Túnel de la Atlántida (apparently the world's largest lava tube), despite it being only 1,700 m (~ 1 mile) long, and much simpler in structure and more recently formed (~20,000) than the Bahamas locales which support remipede sympatry (Koenemann et al. 2009). Remipedes are also rarely seen in the tube despite ideal viewing conditions, and Koenemann et al. (2009) suggest they may be found outside the system, although this has not been confirmed. Morphological phylogeny tended to place S. ondinae around Caribbean Speleonectes (Koenemann et al. 2007) and limited examination of DNA demonstrated S. atlantida formed a clade outside S. ondinae, with a difference between the two being larger than a mean intraspecific distance for a few select species (Koenemann et al. 2009). It would be interesting to determine if the species are sister taxa, or if they managed to colonize the tube independently.

Incredibly, there is a species of remipede from Western Australia - and it isn't Speleonectes! Lasionectes exleyi is still a speleonectid and is currently classified as congeneric with L. entrichoma (Koenemann et al. 2009) however morphological phylogeny generally shows Lasionectes to be paraphyletic, and places both species basally in Speleonectidae (Koenemann et al. 2007). Unlike the other cases, this evidence could suggest a relatively ancient dispersal.


Remipede biogeography is still an emerging topic, and for all I know, there could be remipede colonies in between the Caribbean and disjunct locales, or even worldwide. As the Canary Islands species occur in a very recently-formed lave tube, it would suggest that remipedes can occasionally disperse through open waters and colonize ideal locales. It could be possible they haven't been detected yet due to being rare, although confusion with polychaetes is possible. Hermaphrodites would be ideal colonizers, and since it is now known remipedes can live in caves off the mainland, it would greatly increase the chances of dispersal. The exact extent of remipedes and sub-marine caves is intriguing, but it seems likely that contiguous populations between islands are only likely to occur in the Bahamas and Caicos. Why only Speleonectes are dispersed throughout the Caribbean and Canary Islands is curious, so presumably there's some aspect of their life history which aids dispersal.


Instead of having to write on this topic again every couple years, I'm considering setting up one of those fancy blog 'pages' to keep everything strait on remipedes. Then again, I have no idea what that may be getting me into.

References:

Daenekas, J., Iliffe, T., Yager, J., and Koenemann, S. (2009). Speleonectes kakuki, a new species of Remipedia (Crustacea) from anchialine and sub-seafloor caves on Andros and Cat Island, Bahamas. Zootaxa 2016, 51-66. Available.


Iliffe, T., Otten, T., and Koenemann, S. (2010). Godzilliognomus schrami, a new species of Remipedia (Crustacea) from Eleuthera, Bahamas. Zootaxa 2491, 61-68. Available.

Koenemann, S., Bloechl, A., Martinez, A., Iliffe, T., Hoenemann, M., and Oromi, P. (2009). A new, disjunct species of Speleonectes (Remipedia, Crustacea) from the Canary Islands. Marine Biodiversity 39, 215-225. Available.


Koenemann, S., Schram, F., Honemann, M., and Iliffe, T. (2007). Phylogenetic analysis of Remipedia (Crustacea). Organisms, Diversity & Evolution 7, 33–51. Available.

Koenemann S., Iliffe T., and Yager, J. (2004) Kaloketos pilosus, a new genus and species of Remipedia (Crustacea) from the Turks and Caicos Islands. Zootaxa 618, 1–12. Available.