The Stylet - Diversity and Systematics of Acoela and Nemertodermatida

The classification of Acoela down to the “family level” was recently revised based on a phylogenetic study (U. Jondelius, A. Wallberg, M. Hooge, and O. I. Raikova, “How the Worm Got its Pharynx: Phylogeny, Classification and Bayesian assessment of Character Evolution in Acoela,” Systematic Biology, 2011.doi:10.1093/sysbio/syr073 )

Here is an overview of the current, i.e. new, acoel classification with diagnostic features of higher taxa in brackets and some comments regarding synonymizations. The suprafamilial clade names (without author and year) are informal, i.e. not part of a linnean classification.

• Acoela (digestive parenchyma, biflagellate spermatozoa)
  • Diopisthoporidae Westblad, 1940
  • Bitesticulata (Paired or follicular testes, ventral gonopore. The most inclusive clade that contains Paratomella rubra and Symsagittifera roscoffensis but not Diopisthoporus longitubus)
    • Paratomellidae Dörjes, 1966
    • Bursalia (Copulatory bursa often present. The most inclusive clade that contains Oligofilomorpha interstitiophilum and Childia groenlandica but not Paratomella rubra)
      • Prosopharyngida (Muscular pharynx in anterior part of body. The most inclusive clade that contains Hofstenia miamia and Oligofilomorpha interstitiophilum but not Haploposthia rubra)
        • Hallangidae Westblad, 1946
        • Hofsteniidae Papi, 1957
        • Solenofilomorphidae Dörjes, 1968
      • Crucimusculata (Ventral crossover muscle fibres). The most inclusive clade that contains Actinoposthia beklemischevi and Childia groenlandica but not Haploposthia rubra)
        • Dakuidae Hooge 2003
        • Isodiametridae Hooge & Tyler 2005
        • Otocelididae Westblad, 1948
        • Proporidae Graff, 1882
        • Aberrantospermata       (Spermatozoa with 9+0 or 9+1 axonemes. The most inclusive clade that contains Neochildia fusca and Childia                   groenlandica but not Actinoposthia beklemischevi)
          • Convolutidae Graff, 1905  This family now includes species formerly classified in Anaperidae and Sagittiferidae, which have both been synonymized with Convolutidae
          • Mecynostomidae Dörjes, 1968 This family now includes the species formerly classified in Childiidae as that taxon was synonymized with Mecynostomidae

1. • Acoela Incertae cedis, no phylogenetic hypothesis available
     • Actinoposthiidae (poorly sampled in the phylogenetic study, indications that this may be a polyphyletic assemblage)
     • Anthroposthiidae (single species)
     • Antigonariidae (single species)
     • Nadinidae (single species)
     • Tauridiidae (single species)

Field trip to Chile

There are very few acoels known from Chile. Through the ASSEMBLE programme we had the opportunity to go to the Estación Costera de Investigaciones Marinas (ECIM) in Las Cruces west of Santiago. The coast is exposed to impressive Pacific waves and it is a mixture of rocky shores and sandy beaches with a moderate tide of about 1.5 m amplitude.

Here is a photo of the ECIM

Randy Finke here at ECIM has helped us by SCUBA diving for samples, and so far we have found seven species that are new to science - and we found all of them in good numbers. Here is a photo of a new Isodiametra species from samples that we took at the beautiful Matanzas beach.

Collecting in Halland

While the acoel fauna around Kristineberg on the Swedish west coast is reasonably well known, the fauna on the southern part of the coast is virtually unstudied. On this trip we are collecting on the sandy shores of Halland. Our colleagues at Halmstad University have kindly lent us lab space.

On this trip sampling is shore based, and the water is really shallow...

We have to use simple methods for collecting sediment.

The acoels that dominate our samples in these shallow waters are members of Mecynostomidae. 

The first fieldtrip of the summer 2011 goes to Helgoland. We are all very excited to collect at the type localities from Dörjes descriptions. Here we will share some pictures and such for anyone who might be intrested in these little creatures.

Here on Helgoland we have sampled mainly sandy sediments from the boat Aade or from the shore. Below is a photo that shows sampling using a "slurp gun" at the low water line on the nearby islet Düne.

Here is one of the worms we found at Düne.

We found the anterior half of a Paratomella rubra swimming around in a petri dish with worms that we extracted from a sand sample. It seemed quite happy although it was missing the part that we are mostly interested in, i.e. the genitalia, which are often required for species identification. With Paratomella rubra identification is easy: the long slender and ruby coloured body are characteristic. Here is a photo:

Below is a close up of the head. You can actually see the nerve cords to the left and below the statocyst (the "pearl" in the upper part of the photo).

 Proconvoluta primitiva turned out to be an extremely common species around here, and we could collect hundreds of specimens of this large (up to 5 mm!) and translucent species. One of them, from the same sample as our P. rubra, a suspciously reddish colour to its  digestive parenchyma....

We have already made several trips with the R/V Aade to bring in sand from various acoel type localities near the lab.

Collecting!!

The crew at Aade operating the grabber.

Nice view from the lab.

We have mostly worked with acoels from sand samples on this trip. The species that live in the spaces between sand grains are often long and narrow like the specimen of Oligofilomorpha interstitiophilum below.

Sampling at low tide