Siriella brevicaudata, Paulson, 1875

Daneliya, Mikhail, Price, W. Wayne & Heard, Richard W., 2018, Revision of the Siriella brevicaudata species group (Crustacea: Mysida: Mysidae) from the West Indo-Pacific, European Journal of Taxonomy 426, pp. 1-80 : 3-6

Siriella brevicaudata species group

Diagnosis

Anterodorsal margin of carapace rather short, not protruding beyond tip of subrostral process. Telson rather short, less than 1.1 times as long as last abdominal somite and less than 2.5 times as long as wide. Telson anterior part with more than three (up to six) lateral spiniform setae. Antennular peduncle segment 3 of female with one medial seta. Appendix masculina conical. Male antennule inner flagellum normal, not dilated or meandering in proximal part. Labrum with short anterior spine, less than 0.3 times as long as rest of labrum. Pereopodal endopods about equally long and rather strong; anterior endopods slightly stronger than posterior. Pseudobranchia of male pleopods 2–4 spirally coiled; pleopod setae not modified. Proximal segment of uropodal exopod armed only with small number (three to six, rarely eight) of distolateral spiniform setae. Medial spiniform setae of uropodal endopod about equally long or slightly increasing in length distally, not forming groups of short and long setae.

Comparison

The Siriella brevicauda group is distinguished from other groups of the genus Siriella by a shorter labrum spine, which is in certain species very small and barely visible, while in others is rather welldeveloped, but never longer than 0.3 of the rest of the labrum (0.37–1.0 in other Siriella species groups). Species of the group also have a shorter telson, which is as long as or typically slightly shorter than the last abdominal somite, while in some species it can be slightly longer (1.1) than the last abdominal somite (never shorter than the last abdominal somite in other groups; 1.0–1.8). The telson is also less than 2.0 times as long as wide in the majority of brevicaudata group species, while it can be slightly more in some species (up to 2.5 in S. bassi sp. nov.); this value is never less than 2.0 in other groups of the genus. The brevicaudata group is most similar to the brevirostris subgroup of Siriella thompsonii group, from which it differs, apart from the labrum anterior spine length, by (1) a larger number of telson anterolateral spiniform setae (three to six as opposed to one or two in the brevirostris subgroup) and (2) pereopodal endopods being rather strong and nearly similar in length (slender and with middle pereopodal endopods clearly longer than anterior and posterior ones in the brevirostris subgroup).

Distribution and habitat

West Indo-Pacific ( Figs 1–2 ). Shallow-water, not deeper than 100 m (upper sublittoral).

Remarks

We modified the original definition of the group given by Murano & Fukuoka (2008) after the inclusion of six more species into the group. In particular, we modified the description of the anterodorsal margin of the carapace, because in S. gibbosa , S. occulta sp. nov., S. bassi sp. nov., S. spinula , S. talbotae sp. nov. and S. vincenti it is angular, as opposed to broadly rounded in other species. The telson is not always less than twice as long as broad in the anterior part, sometimes being slightly more than twice as long as broad in S. bassi sp. nov., S. spinula , S. talbotae sp. nov. and S. vincenti , and quite variable in this characteristic between species. In most of the other groups of the genus Siriella , the spiniform setae of the uropodal endopod are different in length along the medial margin, forming groups of shorter and longer ones, which is not the case for the brevicaudata group. However, a simpler pattern of uropodal endopod armature is not unique for the brevicaudata group. Additional characters common for all species of the group include: telson anterior armature and antennular setation and shape of processus masculinus and flagellae, which have different states in some species from other Siriella groups.

Composition

The group currently consists of 12 species: S. bassi sp. nov., S. brevicaudata , S. gibbosa , S. hanseni , S. lacertilis Talbot, 2009 , S. lingvura , S. muranoi sp. nov., S. occulta sp. nov., S. spinula , S. tabaniocula sp. nov., S. talbotae sp. nov. and S. vincenti .

Figures

Fig. 1. Distribution of species in the Siriella brevicaudata species group. Question mark (?) indicates published record requires verification.

Fig. 2. Distribution of species in the Siriella brevicaudata species group along the southern Australian coast.