Parartemia cylindrifera Linder 1941

Timms, Brian V, 2010, Six new species of the brine shrimp Parartemia Sayce 1903 (Crustacea: Anostraca: Artemiina) in Western Australia, Zootaxa 2715, pp. 1-35 : 9-11

Parartemia cylindrifera Linder 1941

(Fig. 5)

Linder 1941 described this species but did not mention the limb reduction in males, and only briefly reported on limb reduction in females. Given the widespread reduction of hind thoracic limbs in Parartemia , an analysis of hind limbs of both male and female P. cylindrifera follows.

Description. Male. Eleven pairs of thoracopods, last pair about a third normal size and with reduced components.

Thoracopod 10 (Fig 5A) also reduced with a small epipodite (about one third average size for thoracopods 3–9) and a flap like praeepipodite no wider than length of epipodite. Endites a little reduced, mainly in numbers of posterior setae (endite 1 with about 33, endite 3 with 9, other endites with normal 3+2+2). Endopodite and exopodite near normal in size and setation.

Thoracopod 11 (Fig. 5B) with endite 1+2 with anterior setae smallest of all setae and about 12 posterior setae. Endite 3 lobed like endites 4–6, with a small anterior seta (a little longer than anterior setae on endite 1) and 3 posterior setae. Endite 4 with a long (longest of all setae) and short anterior seta and 2 posterior setae, endite 5 with 2 anterior setae and no posterior setae, and endite 6 with just one seta, an anterior seta subequal in length to anterior seta of endite 3. Endopodite a rounded protrusion with just 9 posterior setae terminally. Exopodite rhomboidal with about 10 posterior setae on medial and terminal margin and a further 3 posterior setae on basal lateral margin. No epipodite or praeepipodite.

Female. Eleven pairs of thoracopods, with 9 and 10 about half size and reduced and 11th thoracopod a triangular stump.

Thoracopod 9 (Fig. 5C) only slightly reduced; endite 1+2 rounded as in normal limb but with only 22 posterior setae and anterior setae reduced in size to be smallest of all setae; endite 3 lobe like with a small anterior seta (just bigger than basal anterior of endite 1=2) and 10 posterior setae, endite 4 with two anterior setae, the basal one the longest of all setae and two posterior setae, endite 5 with two anterior and two posterior setae and endite 6 with one of each. Endopodite rounded and with about 15 posterior setae and epipodite lancoelate, protruding and with about 23 posterior setae. Epipodite small about one third average size of epipodites of thoracopods 2–8, and prae-epipodite an elongated flap protruding similarly to the epipodite.

Thoracopod 10 (Fig 5D) even more reduced with all anterior setae small, but basal seta of 4th endite the longest as usual. Endite 1+2 a rounded lobe with just 7 posterior seta, endites 3 to 6 lobular with just three anterior setae on endite 3 and none on endites 4–6. Endopodite a rounded protrusion with just 7 posterior setae and exopodite a rhomboidal flap with just 7 posterior setae all medial and terminal. No epipodite or praeepipodite.

FIGURE 5. Thoracopods of P. cylindrifera . A, male 10th; B, male 11th; C, female 9th; D, female 10th; E, female 11th. Lengths excluding setae and to the nearest 0.1 mm: A, 2.0 mm, B, 1.8 mm, C, 0.9 mm, D, 0.7 mm and E, 0.2 mm For further explanation see legend of Fig.3.

Thoracopod 11 (Fig 5E) a triangular stump with a small stout spine terminally and a bulge medially.

Remarks. P. cylindrifera is the only Parartemia with a significantly reduced male 11th thoracopod. It is similar to the 10th thoracopod of the female, with reduction of the endites, a small endopodite and exopodite and lacking an epipodite and praeepipodite. The slightly reduced 10th thoracopod of the male is similar to the 9th thoracopod of the female, but with a few more posterior setae. The 11th thoracopod of females is similar to that in many female Parartemia , though the presence of a small stout spine is unusual. It should be noted that the triangular stump is in line with the other thoracopod insertions, i.e. it is not lying medially as noted by Linder (1941).