Lophenteropneusts and Beyond

Lophenteropneust - the worm that never was. From Pawson (2003).

My younger and more credulous self continuously pored over the Regional Checklist of Mystery Animals and one of the many cryptic entities which captured my imagination were lophenteropneusts, deep-sea chimerical invertebrates known only from photographs. This was during the informational Dark Age of the early 00’s and having that one scrap of information to go on made them all the more tantalizing. Revisiting the topic on a whim led to the shocking discovery that one ‘lophenteropneust’ was captured before the checklist was even composed and that the hypothetical worm was a gross distortion of an already fantastic group.

Unidentified acorn worm. From Wikipedia Commons.

‘Lophenteropneusts’ were initially interpreted as a transitional form between pterobranchs (sea angels) and enteropneusts (acorn worms) and used to argue that the latter had evolved into the former (Holland et al. 2005). Both the angels and the worms are hemichordates, deuterostomes with a three part (proboscis/collar/trunk) body plan and separate coelom in each region (Swalla and Smith 2008 – citing various). Hemichordata has been consistently recovered as the sister clade of echinoderms (e.g. Swalla and Smith 2008) and knowing what the ancestral hemichordate looked like could be very informative about the evolution of echinoderms and even more distant relatives such as vertebrates. The two hemichordate body plans are strikingly disparate as acorn worms are solitary, have numerous gill slits and a strait gut whereas sea angels are colonial tube dwellers, have reduced or absent gill slits, a u-shaped gut and feed with tentacles (Cannon et al. 2009). The ‘lophenteropneust’ looks like an acorn worm with sea angel tentacles glued on and was thus interpreted as a transitional form. Lacking the original source I’m puzzled why the hypothetical worm was interpreted as evidence of an acorn worm to sea angel transition and not vice versa. Despite the dubiousness of ‘lophenteropneusts’ the hypothetical relationship between the hemichordates has some merit.

The sea angel _Rhabdopleura normani_. From Wikipedia Commons.

Cameron et al. (2000) recovered pterobranchs as being within Enteropneusta in a molecular analysis and noted that pterobranchs share a number of traits with harrimaniid sea acorns such as small size, post-anal tail in harrimaniid juveniles, reduction in gill slits, filter feeding in some harrimaniids, and others. Cannon et al. (2009) reached a similar arrangement in their molecular phylogeny yet Osborn et al. (2011) did not. This hypothesis is still very much an open question – invertebrate biology seems to be full of these – and hopefully some sort of consensus will eventually be reached.

'Lophenteropneust'. From Thiel (1979).

After a few botched attempted at collection (Barnes 2004) in 2002 an acorn worm with a broader collar than any other described species was videotaped, collected and formally named Torquarator bullocki (Holland et al. 2005). Wide-collared acorn worms had been observed and photographed previously (but not captured) and in their review Holland et al. (2005) discovered that ‘lophenteropneusts’ showed a similarly wide collar area with no readily apparent tentacles. The Thiel photograph (above) is the highest quality ‘lophenteropneust’ picture (Holland et al. 2005) and it seems to have similar collar morphology to Tergivelum baldwinae (see Holland et al. 2009) with no indication of the looped and feathered tentacles imagined to be present. Holland et al. (2005) conclude that the ‘lophenteropneust’ concept was entirely based on misinterpreted low-quality photographs but that doesn’t mean that the worms behind them are at all boring.

Not concept art from Avatar 2 but an undescribed extra-wide-lipped acorn worm. From Holland et al. (2005).

Holland et al. (2005) found Torquarator bullocki unique enough to warrant its own family, Torquaratoridae, and while one analysis found a wide-collared species to fall within Ptychoderidae (Cannon et al. 2009) the clade was recently confirmed to be separate and monophyletic (Osborn et al. 2011). One issue is that extraction of genetic material from the type species and genus Torquarator bullocki has thus far failed however the family was also rediagnosed on morphology which the species displays (Osborn et al. 2011). Torquaratorids have a reduced to absent proboscis skeleton and an adult stomochord either absent or separated from the buccal cavity of the collar (Osborn et al. 2011). More remarkable traits displayed in Torquaratoridae include a deep sea habitat (acorn worms were previously regarded as primarily shallow water), no burrowing capabilities (the normal mode of life for acorn worms), controlled drifting (using gut contents as ballast, secreting mucous to increase drag in the water column) to travel between locations, the largest invertebrate eggs (outside of cephalopods) which may have something to do with the enigmatic planctosphaera larvae, far more morphological disparity than most acorn worms, and they are very specious with 13 species being added in one study compared to the prior total of 89 for all acorn worms (Osborn et al. 2011).

Going back to the impetus of this article, what does the discovery of torquaratorids mean for cryptozoology? The misinterpretation of ‘lophenteropneust’ pictures was used as a cautionary tale by Dubois and Nemésio (2007); the authors further discussed cryptozoological “problems” resulting from photographs being used to name species such as my old nemesis Cadborosaurus willsi. The sightings and photographs of ‘lophenteropneusts’ and other wide-collared acorn worms prior to 2002 (see Holland et al. 2005 for review) highlights an awkward period between initial observation and discovery which is surprisingly common. But is it cryptozoological? Since the earlier observations (and anecdote) of pre-discovery torquaratorids apparently did not lead to the discovery of Torquarator bullocki I would argue that no, it isn’t. This does not mean that photographs and even anecdotes are useless as tools for discovering new species (they’re not) but they must be treated with caution and restraint. I have a suspicion I’ll be discussing this extensively and excessively in the future.

References:

Barnes, R. S. K. 2004. Kingdom Animalia. IN: The Diversity of Living Organisms. Blackwell Publishing.

Cannon, J. T. et al. 2009. Molecular phylogeny of hemichordata, with updated status of deep-sea enteropneusts. Molecular Phylogenetics and Evolution 52, 17–24. Available.

Dubois, A. & Nemésio, A. 2007. Does nomenclatural availability of nomina of new species or subspecies require the deposition of vouchers in collections? Zootaxa 1409, 1–22. Available.

Holland, N. D. et al. 2009. A new deep-sea species of epibenthic acorn worm (Hemichordata, Enteropneusta). Zoosystema 31(2), 333-346. Available.

Holland, N. D. et al. 2005. ‘Lophenteropneust’ hypothesis refuted by collection and photos of new deep-sea hemichordate. Nature 434, 374-376. Available.

Osborn, K. J. et al. 2011. Diversification of acorn worms (Hemichordata, Enteropneusta) revealed in the deep sea. Proc. R. Soc. B doi: 10.1098/rspb.2011.1916

Pawson, D. 2003. Deep-sea dreams: diary of a mad lophenteropneust watcher. Deep-Sea Newsl. 32, 6–7. Available.

Swalla, B. J. & Smith, A. B. 2008. Deciphering deuterostome phylogeny: molecular, morphological and palaeontological perspectives. Phil. Trans. R. Soc. B 363, 1557–1568. Available.

Thiel, H. 1979. Structural Aspects of the Deep-Sea Benthos. Ambio Special Report 6, 25-31. Available.

One thought on “Lophenteropneusts and Beyond

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s