# Annulitubus

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Not to be confused with [Annulatubus](/source/Annulatubus), a genus of [Ediacaran biota](/source/Ediacaran_biota).

***Annulitubus*** is an extinct genus of [annelid](/source/Annelid) from the [Middle Devonian](/source/Middle_Devonian) of [Brazil](/source/Brazil). It has been found in both the [Ponta Grossa Formation](/source/Ponta_Grossa_Formation) and the [Pimenteira Formation](/source/Pimenteira_Formation) of [South](/source/South_Region,_Brazil) and [Northeastern Brazil](/source/Northeast_Region,_Brazil) respectively.[1][2]

In life, it would probably have been an sedentary tube-dwelling [polychaete](/source/Polychaete), partially buried in substrate and subsisting by [suspension-feeding](/source/Filter_feeder).[2]

## Etymology

The name *Annulitubus* derives from the [Latin](/source/Latin) words 'annulus', meaning ring, and 'tubus', meaning tube. The type species, *A. mutveii*, is named in honour of [Harry Mutvei](/source/Harry_Mutvei) for his work on the skeletal anatomy of various taxa,[1] while *A. fernandesi* is named after [Antonio Carlos Sequeira Fernandes](/source/Antonio_Carlos_Sequeira_Fernandes), a paleontologist from the [Museu Nacional](/source/National_Museum_of_Brazil), for his works on Brazilian paleoinvertebrates.[2]

## Description

Fossils of *Annulitubus* are found in together, preserved in great numbers upwards of 170 individuals/meter². There are found preserved either in a horizontal pose, parallel to the bed forming pavements, or more rarely in a vertical pose, occurring just above the pavements and which would be how they would be orientated in life. The shape of their tubes are between straight and slightly curved with numerous disc-shaped rings along its side, the interspace between the discs being a smooth surface, between 0.69 and 1.1 mm in length, and without growth marks. In its life position, the preservation exhibits 25 rings per centimetre. Some specimens range from 12.66 to 13.80 mm in length.[2]

## Paleoecology

*Annulitubus* would have lived in dense populations, buried head-up halfway through the substrate. Individuals were sedentary and would subsist by [suspension-feeding](/source/Filter_feeder). Based on fossil preservation, living individuals would settle on the pavement of dead *Annulitubus*, possibly using them to fix themselves in the sediment. This behavior is interpreted as positive taphonomic feedback, where the presence of dead individuals helps the colonisation by newer ones.[2] In the [Paraná Basin](/source/Paran%C3%A1_Basin), *A. mutveii* was reported as living on offshore beds.[1]

The exact [taxonomic affinity](/source/Affinity_(taxonomy)) of *Annulitubus* is still up for debate. Becker-Kerber et al. (2021) propose that it would pertain to the [Maldanidae](/source/Maldanidae) family, which are head-down orientated conveyor-belt deposit feeders, eating of the substrate and ejecting waste upwards. However, given that the fossils are preserved head-up, this is improbable. Another family put forward was [Chaetopteridae](/source/Chaetopteridae), which more closely resembles this taxon.[2]

## References

1. Vinn, Olev (2016). ["Possible polychaete tubeworms from the Late Emsian (Early Devonian) of the Parana Basin, Brazil"](https://www.researchgate.net/publication/287799605). *[Acta Palaeontologica Polonica](/source/Acta_Palaeontologica_Polonica)*. **61** (3): 627–632. – via [ResearchGate](/source/ResearchGate)

1. Sandro Marcelo, Scheffler (2024). ["Annulitubus fernandesi sp. n. a new Devonian Annelida tube worm (Pimenteira Formation, Parnaíba Basin, Brazil)"](https://www.researchgate.net/publication/383155462). *[Historical Biology](/source/Historical_Biology)*. – via [ResearchGate](/source/ResearchGate)

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