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Sunellidae was originally made to include three genera: Sunella, Chiella &and Luella but later the latter two where synonymized with Sunella.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" (paraphyletic, ancestral to tardigrades, onychophorans and arthropods) Total group Euarthropoda †Megadictyon †Kerygmachela †Pambdelurion †Opabiniidae † Radiodonta (e.g Anomalocaris) Deuteropoda †Erratus †Sunellidae (Sunella) †Isoxyidae + "Great appendage bivalved forms" †Fengzhengia †Kylinxia †Megacheira Pan-Chelicerata †Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
† "Lobopodia" (paraphyletic, ancestral to tardigrades, onychophorans and arthropods)
Total group Euarthropoda†Megadictyon †Kerygmachela †Pambdelurion †Opabiniidae † Radiodonta (e.g Anomalocaris) Deuteropoda †Erratus †Sunellidae (Sunella) †Isoxyidae + "Great appendage bivalved forms" †Fengzhengia †Kylinxia †Megacheira Pan-Chelicerata †Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Megadictyon
†Kerygmachela †Pambdelurion †Opabiniidae † Radiodonta (e.g Anomalocaris) Deuteropoda †Erratus †Sunellidae (Sunella) †Isoxyidae + "Great appendage bivalved forms" †Fengzhengia †Kylinxia †Megacheira Pan-Chelicerata †Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Kerygmachela †Pambdelurion †Opabiniidae † Radiodonta (e.g Anomalocaris) Deuteropoda †Erratus †Sunellidae (Sunella) †Isoxyidae + "Great appendage bivalved forms" †Fengzhengia †Kylinxia †Megacheira Pan-Chelicerata †Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Kerygmachela
†Pambdelurion †Opabiniidae † Radiodonta (e.g Anomalocaris) Deuteropoda †Erratus †Sunellidae (Sunella) †Isoxyidae + "Great appendage bivalved forms" †Fengzhengia †Kylinxia †Megacheira Pan-Chelicerata †Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Pambdelurion
†Opabiniidae † Radiodonta (e.g Anomalocaris) Deuteropoda †Erratus †Sunellidae (Sunella) †Isoxyidae + "Great appendage bivalved forms" †Fengzhengia †Kylinxia †Megacheira Pan-Chelicerata †Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Opabiniidae
† Radiodonta (e.g Anomalocaris) Deuteropoda †Erratus †Sunellidae (Sunella) †Isoxyidae + "Great appendage bivalved forms" †Fengzhengia †Kylinxia †Megacheira Pan-Chelicerata †Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
† Radiodonta (e.g Anomalocaris)
Deuteropoda†Erratus †Sunellidae (Sunella) †Isoxyidae + "Great appendage bivalved forms" †Fengzhengia †Kylinxia †Megacheira Pan-Chelicerata †Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Erratus
†Sunellidae (Sunella) †Isoxyidae + "Great appendage bivalved forms" †Fengzhengia †Kylinxia †Megacheira Pan-Chelicerata †Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Sunellidae (Sunella)
†Isoxyidae + "Great appendage bivalved forms" †Fengzhengia †Kylinxia †Megacheira Pan-Chelicerata †Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Isoxyidae + "Great appendage bivalved forms"
†Fengzhengia †Kylinxia †Megacheira Pan-Chelicerata †Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Fengzhengia †Kylinxia
†Fengzhengia
†Kylinxia
†Megacheira Pan-Chelicerata
†Megacheira
Pan-Chelicerata
†Kiisortoqia †Bushizheia Antennulata †Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Kiisortoqia
†Bushizheia
Antennulata†Artiopoda (including Trilobita) Mandibulata †Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Artiopoda (including Trilobita)
Mandibulata†Fuxianhuiida †Hymenocarina Myriapoda Pancrustacea
†Fuxianhuiida
†Hymenocarina Myriapoda Pancrustacea
†Hymenocarina
Myriapoda Pancrustacea
Myriapoda
Pancrustacea