Ctenorhabdotus

• Burgess Shale, Canada

Ctenorhabdotus capulus is an extinct species of comb jellies ( Ctenophora ). It is known from the Canadian Burgess Shale and comes from the geological period of the middle Cambrian.

The species was described in 1996 by the paleontologist Simon Conway scientifically Morris and Desmond H. Collins. Your genus name derives from the Greek ctenos for " comb" and Rheophilous for " stripe" and refers to the special shape of the typical Ctenophora comb ribs; the Artepithet capulus for " capsule " refers to the left at the end remote from the mouth organ of equilibrium. Formally, genus and species of a family Ctenorhabdotidae be assigned.

Features

The up to seven inches large animals had a variable body shape, rather than the cube, can be described as more spherical with other in some individuals. In the former case, the animals are in the side view approximately square, that is, both the mouth - or oral as well as remote from the mouth or aboral side are flattened.

The most striking feature of the animals are the twenty-four comb ribs extending from the oral to the aboral end and unite there in eight groups of three. They are wider than the corresponding structures of the type also Cambrian Xanioascus canadensis and differ additionally in the fact that the middle row in each case being shorter than the outer two. From the point of union of three ribs continue to run eight longitudinal stripes that come together in a running round the mouth opposite end ring. Because they lack the characteristic ridge rib cross bars, probably represent the remains of the comb plate bearing pad cells are in longitudinal rows probably not comb fins themselves in modern comb jellies are found at a similar point eyelashes bands initiated from the equilibrium organ at the aboral end and the forward momentum to the comb ribs. Against such an interpretation but speaks to the low probability that such sensitive structures could have been preserved fossil; apart from the series are also too thick compared to modern eyelashes bands for such interpretation. The descriptor instead go on the assumption that it is. Both the longitudinal structures as well as the ring to which they open out to is part of the inner channel system of Ctenophora, which is called Gastrovaskulärsystem This system, which serves among other things to the distribution of nutrients in the body, have modern types in one channel below the comb rib, which is referred to as Meridionalkanal. In the longitudinal structures of Ctenorhabdotus capulus it could be analogue parts of the body.

Unlike Xenioascus canadensis can be at Ctenorhabdotus capulus at the mouth side facing away from a unique equilibrium organ, the statocyst, make up, which is included as in modern species in a capsule formed of eyelashes, which rises like a dome over the statocyst.

At the mouth side of a wide mouth can be seen is surrounded by a cloth -like, possibly muscular collar. Evidence of tentacles there is not it.

Lifestyle and associated finds

Like the other Cambrian ctenophores Ctenorhabdotus capulus was evidently an active swimmer and captured in this way his food. This is also the lack of passive trapping structures such as tentacles.

Together with the kind was as a companion find a diverse fauna found to among other sponges ( Porifera ) as Hazelia delicatula, Priapswürmer ( Priapulida ) as Ottoia prolifica or Selkirkia columbia and Arthropods ( Arthropoda ) as Leanchoilia superlata, Canadaspis perfecta or the trilobite species Peronopsis montis included.

Locality and age

All specimens come from the Burgess Shale in the Canadian province of British Columbia, specifically the known as Raymond Quarry and Walcott Quarry quarries of the Stephen Formation. The holotype of the species, so the copy that defines its properties, has already been found in the 1920s by the American palaeontologist Charles Walcott, seventeen additional specimens that were set as the parameter types are known to this day. The fossils preserved in shale come from all of the period of the middle Cambrian period about 510-515 million years ago.

The holotype is now in the Royal Ontario Museum in Canada.

Systematic position

It is considered relatively safe, that Ctenorhabdotus capulus one of the Ctenophora, though sporadic, it was assumed that it could have instead been a kind of cnidarians. Of the known Cambrian forms the species is but the one that most closely resembles morphologically modern ctenophores. So they had, at least if the interpretation of the fossil described above is correct, already an inner channel system with Meriodionalkanälen below the ridge ribs on which pervaded the body and supplied with nutrients. Also, the organ of balance, the statocyst, probably had the same structure as in today's Ctenophora species.

The most obvious difference can be ascertained in the number of comb fins is all modern species at eight. Since two other Cambrian forms, Xanioascus canadensis and fasciculus had vesanus significantly more than these eight comb fins, it can be said with great probability that the number has stabilized comb ribs late on their present value. A possible scenario of how this process could have taken place, a comparison with Xanioascus canadensis, a species which had as Ctenorhabdotus capulus twenty-four comb ribs but, as far as recognizable, all had the same length and down to the mouth end away from not combined in groups of three. Although it is unlikely that Xanioascus canadensis was a direct ancestor of Ctenorhabdotus capulus, the comparison demonstrates yet, as the latter type by the merger of three comb fins on the aboral end of the animal could have resulted from an ancestral species, the Xanioascus canadensis at least in the comb Number of ribs and arrangement resembled. The selection pressure required for this purpose may have been generated through better coordination and control available for locomotion. The shape of the modern types with their eight comb ribs would be achieved either by atrophy of the outer ribs of each triplet or by omission of the inner ridge rib and fusion of the two outer concluded. At the latest in Devon, from the two species, Paleoctenophora brasseli and Archaeocydippida hunsrueckiana are known, today's comb rib number was certainly achieved.

While these Devonian species already had tentacles, Ctenorhabdotus capulus as well as other Cambrian species was apparently tentakellos. Whether this means that the species already present Nuda belonged, which are characterized by precisely this feature, or whether what molecular genetic, embryological and morphological studies suggest that Nuda, caused by secondary tentacles loss of tentacled forms, the Tentaculata is uncertain.