Siriella Dana, 1850

Talbot, Suzette, 2009, A survey of Mysida from the Lizard Island area, Great Barrier Reef, Australia, Subfamily Siriellinae (Crustacea, Mysida, Mysidae), Zootaxa 2114, pp. 1-49 : 5-6

Siriella Dana, 1850

Ii (1964) divided Siriella into 6 groups, based on the structure of the male pleopods. Six of the Lizard Island species, S. affinis , S. gracilis , S. lacertilis , S. thompsonii , S. vincenti and S. vulgaris are members of his thompsonii -group, in which the 3rd and 4th male pleopods are similar in size and structure to the 2nd, with coiled pseudobranchiae and simple, unmodified setae. In S. inornata , sole representative of his inornata -group, the pseudobranchiae on the 2nd – 4th male pleopods are also coiled, but the 4th pleopods are modified and carry a terminal armature of enlarged setae. Two species, S. distinguenda and S. anomala have males with straight pseudobranchiae on the 2nd – 4th pleopods. The former belongs to Ii's aequiremis -group in which only the 4th pleopods have enlarged and modified terminal setae, while the latter is a member of his ' anomala ' group, in which both the 3rd and 4th pleopods terminate in specialized setae. Males with modified pleopods are usually readily identifiable, but females and juveniles may be difficult to distinguish.

Each member of the genus in the Lizard Island collection has been found to have a series of fine setae, extending vertically upward from the outer margin of the uropodal endopod towards the ventral surface of the telson. These vertical setae are usually located adjacent to the otolith and may extend along the entire length of the margin. Distally they tend to be inserted near the bases of the regularly spaced lateral setae that fringe the endopod. In species such as S. vulgaris , the vertical setae appear to be structurally modified ( Fig. 25 A). Their proximity to the gravity receptor and their alignment suggest that they could be involved in some aspect of orientation, possibly the perception of water movement over the surface of the endopod. Their presence has yet to be investigated in other members of the Mysidae .

Figures

FIGURE 25. Siriella vulgaris Hansen, 1910. A, endopod of left uropod, ventral view. B, telson and right uropod, dorsal view. C, telson. Scalebars = A – C: 0.2 mm.