Sunella

***Sunella*** is an extinct genus of Cambrian stem group arthropod. It was named by Huo Shicheng in 1965. It is the type genus of the family Sunellidae. It has 4 species, including its type, *S. grandis.*

## Classification 
When it was first found by Huo Shicheng in 1965, Sunella was thought to be an Ostracod-like arthropod; then, in later studies it was thought to be an arthropod of uncertain affinities; then it was interpreted as a bradoriid and then as again an arthropod of uncertain affinities; then as a species of *Isoxys* along with other Sunellids in Vannier & Chen 2000; in later studies such as Zhang and Shu, 2007 and Sun et. al. 2021 a relationship that was later disproved due to the fact that Silesicaris was reassigned to Thylacocephala and in 2022 Tuzoia was reassigned to Hymenocarina based on newly described soft parts showing that the similarities between the carapace shape between Isoxys and *Sunella* was only superficial;

 Lagerstätte  is pictured above.]]

### Species 
*Sunella grandis* (Huo, 1965) is the type species of *Sunella.* Possible sexual dimorphism (when individuals of a species of different sexes are differentiated) is known.

###### Synonyms 
* *Sunella nanchengensis* (Huo, 1965)
* *Luella* (Huo, 1965)
* *Chiella* (Huo, 1965)

#### *Sunella nanchengensis* 
*Sunella nanchengensis* (Huo, 1965) is a possible sexual dimorph of *S. grandis* and is now thought to be a synonym of *S. grandis.*

#### *Sunella shensiella* 
*Sunella shensiella* (Huo,1965) is the only species of *Sunella* apart from *S. grandis* that is not considered a synonym of *S. grandis* or has been moved to its own genus. Probable sexual dimorphism has been observed.

#### *Caudicaella (Sunella) bispinata* 
A species that used to belong to *Sunella*, *S. bispinata*, and was moved to a new genus, *Caudicaella* (Sun et al. 2021) as *Caudicaella bispinata* (Cui and Huo, 1990). *Isoxys* *sp.* (Sun et al. 2021) (for the specimens from the Heatherdale shale, not the Shuijingtuo formation) which was found not to be a species of  *Sunella* by Melnikova 1998 *Chiella* was later considered a separate species within *Sunella,* but after Huo & Shu, 1985 *Chiella* was considered a junior synonym of *Sunella*

## Distribution 
*Sunella* fossils have been found in the Chengjiang biota (exact locality cannot be determined; dated to no older than 518 Ma), the Shuijingtuo formation (dated to around 526.5 Ma), the Qingjiang biota (dated to ~518 ma), the Niutitang formation ( generally Meishucunian (Cambrian Stage 2) to Nangaoan (Cambrian Stage 3) but may be up to as old as the Fortunian in some sections) and the Guojiaba formation (tentatively assigned to Cambrian Stage 3), all of which are in China.

Usually the only part of *Sunella* that is found is the shell, but rarely (only twenty-two times in *Sunella cf. shensiella* and only six in the related *Combinivalvula chenjiangensis)* soft parts are also found. When this occurs, the carapace usually adopts a "butterfly" position, possibly due to the decay of the shell muscles that hold it together. Only the soft parts of *Sunella* cf. *shensiella* and the related *Combinivalvula chenjiangensis* (Hou, 1987) have been preserved.

*Sunella grandis* had a bivalved elongate roughly semicircular shell with an anterodorsal sulcus and short spines, a typical bodyplan for a Sunellid, while *S. cf. shensiella* had a more oval shaped shell, shorter cardinal spines and an anterodorsal sulcus pointing at a slightly lower angle. Jinningella differs from *Sunella* by the presence of anterodorsal nodes. The largest specimen is over 15&nbsp;mm (1.5&nbsp;cm)(the largest recorded for a sunellid), while *Combinivalvula* and *Jinningella* reached roughly 10&nbsp;mm (1&nbsp;cm) and *Caudicaella* typically reached 10–12&nbsp;mm (1-1.2&nbsp;cm) due to its long  spines compared to other sunellids. In comparison to other bivalved arthropods of the Cambrian, sunellids where medium sized, larger than the bradoriids, which rarely reached above 10&nbsp;mm (1&nbsp;cm) and smaller than the Isoxyida which where often at least a few centimeters long with the exception of the dwarf *I. carbonelli* which grew to 11&nbsp;mm (1.1&nbsp;cm) and Surusicaris which grew to 14&nbsp;mm (1.4&nbsp;cm).

#### Distinguishing from similar arthropods 
*Sunella* can be distinguished from *Isoxys* by the presence of an anterodorsal sulcus, shorter cardinal spines and different carapace shapes. *Sunella* be distinguished from the isoxyid Surusicaris by the lack of an anterodorsal sulcus and the lack of cardinal spines.Bradoriids, which share the possession of an anterodorsal sulcus (leading to the former assignment of *Sunella* to Bradoriida)*S. cf. shensiella* and the related *Combinivalvula chenjiangensis* preserve a possible median eye. Neither the cephalic appendages nor proximal portions of trunk limbs as found in the related Isoxyidae are known.]]