Biology:Sunellidae

Sunellidae is a family of bivalved arthropods known from the Cambrian period.

History of study

Sunellidae was originally made to include three genera: Sunella, Chiella &and Luella but later the latter two where synonymized with Sunella. Later two other genera, Jinningella &and Combinivalvula were described and the definition of Sunellidae was strictened by adding the additional defining feature, the possession of an anterodorsal sulcus. In 2021 one species of Sunella, S. bispinata was moved to the genus Caudicaella. It was assigned to Isoxyida in 2025.

Distribution

Sunellidae have been found in the Chengjiang biota (exact locality cannot be determined) (dated to no older than 518 Ma ), the Guojiaba formation ( tentatively assigned to Cambrian stage 3), the Qingjiang biota (dated to ~518 ma) and the Shuijingtuo Formation (dated to ~526.5 Ma) all of which are in China. Various more poorly documented formations also yield Sunellids. Caudicaella aff. bispinata specimens are also known from the Heatherdale Formation in Australia.

Preservation

Usually the soft anatomy of sunellids is not preserved but a few examples of soft part preservation (only twenty-two times in Sunella cf. shensiella and six in Combinivalvula chenjiangensis) have been recorded in Combinivalvula chenjiangensis and Sunella cf. shensiella.

Anatomy

Diagram of Sunella dimorphismus

Sunellids have a roughly semicircular carapace and have anterior and posterior carndinal spines. They are distinguished from other similar arthropods by the presence of an anterodorsal sulcus (a feature shared by the unrelated bradoriids). Probable sexual dimorphism has been observed in Sunella.

Phylogeny

After:

Panarthropoda

† "Lobopodia" 80 px 90 px 50 px (paraphyletic, ancestral to tardigrades, onychophorans and arthropods)   Total group Euarthropoda   †Megadictyon 80 px         †Kerygmachela 80 px       †Pambdelurion 80 px       †Opabiniidae 70 px       † Radiodonta (e.g Anomalocaris) 70 px   Deuteropoda   †Erratus 70 px       †Sunellidae (Sunella) 70px       †Isoxyidae 70px + "Great appendage bivalved forms" 70px         †Fengzhengia 80 px     †Kylinxia 70px         †Megacheira 80px     Pan-Chelicerata 70px 70px         †Kiisortoqia 70px     †Bushizheia 70px   Antennulata   †Artiopoda (including Trilobita) 70px   Mandibulata   †Fuxianhuiida 70px       †Hymenocarina 70px       Myriapoda 70px     Pancrustacea 70px 70px

References

Wikidata ☰ Q136364196 entry