The Life-cyle of Gorgocephalus yaaji (Digenea: Gorgocephalidae)

The complexity of trematode life-cycles was really what first drew me in and fueled my worm obsession.  Thus, I am pleased to say that I have a new paper hot off the press, in which my co-authors and I elucidate the first full life-cycle for a species of the family Gorgocephalidae.  I recommend that you read my paper immediately:

"Huston, D.C., S.C. Cutmore and T.H. Cribb. 2016. The life-cycle of Gorgocephalus yaaji Bray & Cribb, 2005 (Digenea: Gorgocephalidae) with a review of the first intermediate hosts for the superfamily Lepocreadioidea Odhner, 1905. Systematic Parasitology, 93: 653-665." have a quick read on Readcube or go straight to researchgate PDF

The three species that comprise the Gorgocephalidae are true to their namesake (relatively), with little tentacles sticking out of their oral sucker. I reckon they look quite a bit like Graboids from that awesome movie Tremors.  Tremors was one of those flicks which nurtured my love of cheesy monster movies.

The family Gorgocephalidae didn't start out as a family. It was first erected by the American trematodologist H.W. Manter in 1966 as a subfamily of the Lepocreadiidae. Manter called his new subfamily the "Gorgocephalinae" which he created to accommodate the type species, Gorgocephalus kyphosi.  Manter had recovered these odd little worms from the silver drummer Kyphosus sydneyanus which had been caught by Robert Piddington off Adelaide, South Australia.

Gorgocephalus kyphosi Manter, 1966.

Not much happened in regards to these strange worms for some time, though greater glory was destined. In 1971 the most influential trematode taxonomist of all time, Yamaguti, took a look at a couple of Manter's paratypes, and thought they were more unique than their pitiful subfamily designation suggested. The little tentacle mouthed worms finally got that family rank. And so began the Gorgocephalidae Manter, 1966.


Nearly twenty years passed before another gorgocephalid was discovered. In 1983, a second species was described by the Russian trematodologist E.V. Zhukov from Kyphosus sectatrix off of Cuba.  I have never been able to find much information on Zhukov, likely due to majority of his work being published in Russian.  Based on the dates of his Cuban publications however, It looks like Zhukov was in Cuba before the fall of the Soviet Union. However, regardless of the tensions between the USA and the Soviet Union, Zhukov named his new species Gorgocephalus manteri in honor of Manter's contributions to the field.

In 2005, Rod Bray and Tom Cribb described the third (and currently final) species of gorgocephalid from Kyphosus vaigiensis off of Lizard Island on the northern Great Barrier Reef.  They called this species Gorgocephalus yaaji. 

Another ten years passed.

Then, in 2015, something new happened.  During a study of the intramolluscan trematode fauna of the banded periwinkle Austrolittorina unifasciata (Littorinidae) from along the south coast of Australia, O'Dwyer et al. (2015) discovered and described the first known cercariae of the family Gorgocephalidae.  They were able to confirm that these intramolluscan stages belonged to a species of the family based on 28S rDNA sequence data.  While a previous sequence existed for Gorgocephalus kyphosi (Olson et al. 2003) from Lizard Island, O'Dwyer et al. determined that their cercaria most likely represented a separate species, based on differences in the sequence data.

Now, I had just read O'Dwyer et al. (2015) before my first trip to Lizard Island.  This was also my first trip to the Great Barrier Reef, and after my many years working in the freshwater systems of Texas, research in a coral reef ecosystem was exciting and unique.  My original goal for the trip was to study the intramolluscan trematode fauna from gastropods of the family Cerithiidae. However, I found cerithids quite difficult to find.  In fact, I was only able to collect one species in large numbers, Rhinoclavis vertagus.  I began to understand that the trematode fauna of Great Barrier Reef cerithids might be a rather difficult topic, so in frustration I turned my attention to some gastropods that were a bit more common in the area, littorinids.

To keep the narrative of my serendipitous discovery brief, I collected and examined some specimens of Echinolittorina austrotrochoides from the rocks along the beach. By placing these little snails into little cups of seawater, I was able to induce natural emergence of some cercariae, which just so happened to look just like those described by O'Dwyer et al. (2015)!

Larval stages of Gorgocephalus yaaji. A) Cercariae; B) Rediae; C) Metacercariae encysted on algae. From Huston et al. (2016).

It had previously been speculated that the metacercariae of gorgocephalids would be associated with algae due to the algivorous nature of the kyphosid host fishes.  I tested this by placing my cercariae in little cups of seawater with some algae.  They happily obliged, and encysted on the algae within a few hours.  The route of gorgocephalid recruitment into kyphosids was confirmed.

Back in the lab, I generated ITS2 and 28S rDNA molecular sequence data from the cercariae as well as from adult gorgocephalids we collected from Kyphosus cinerascens during the same trip. This allowed me to confirm that the larval stages did indeed belong to Gorgocephalus yaaji.  From there I wrote up a manuscript about the life-cycle, and included a review of the gastropod-trematode relationships for the superfamily Lepocreadioidea.  This review led to some fairly interesting insights, though a discussion on those insights is a bit beyond the scope of this post.  I'll write another post about the other half of the paper some time in the indeterminable future!

References

Bray, R. A., & Cribb, T. H. (2005). Gorgocephalus yaaji n. sp (Digenea: Gorgocephalidae) from the brassy chub Kyphosus vaigiensis (Perciformes: Kyphosidae) off Lizard Island, northern Great Barrier Reef and further records of G. kyphosi. Zootaxa, 1068, 39-46.

Olson, P., Cribb, T., Tkach, V., Bray, R., & Littlewood, D. (2003). Phylogeny and classification of the Digenea (Platyhelminthes: Trematoda). International Journal for Parasitology, 33, 733-755.

O’Dwyer, K., Faltýnková, A., Georgieva, S., & Kostadinova, A. (2015). An integrative taxonomic investigation of the diversity of digenean parasites infecting the intertidal snail Austrolittorina unifasciata Gray, 1826 (Gastropoda: Littorinidae) in Australia. Parasitology Research, 114, 2381-2397.

Manter, H. W. (1966). A peculiar trematode, Gorgocephalus kyphosi gen. et sp. n. (Lepocreadiidae: Gorgocephalinae subfam. n.), from a marine fish of South Australia. The Journal of Parasitology, 52, 347-350.

Yamaguti, S. (1971). Synopsis of digenetic trematodes of vertebrates. Keigaku Publishing Co. Tokyo, Vol I, 1074 pp. Vol II, 349 plates.

Zhukov, E. (1983). New representatives of the fauna of trematodes from the fishes of the Gulf of Mexico. Parazitologiia, 17, 112-117.