Branchinella compacta, Linder, 1941

Timms, Brian V, 2012, Further studies on the fairy shrimp genus Branchinella (Crustacea: Anostraca: Thamnocephalidae) in Australia, with descriptions of five new species, Zootaxa 3595, pp. 35-60 : 41

B. compacta Linder, 1941

Figs. 1 D, 4, 5A

Branchinella compacta Linder, 1941 , pp.245–7, fig. 31; Geddes, 1981, pp. 261–262, fig. 4; Timms, 2008, pp.291–292, Fig. 2

Material. Victoria, Lake Ondit, 38o 14’S, 143o 35’E, 14 October 1971, M.C. Geddes, AM P19235, 3males, 9 females; New South Wales, Monaro Tablelands, 43 km S of Cooma, Avon Lake, 36o 37’ 06”S, 149o 02’ 50”E, 10 December, 1989, BVT, AM P74344, 6 males, 4 females; same locality, 14 March 2010, BVT, AM P88372, 4 males, 12 females; New South Wales, Monaro Tablelands, 23 km SW of Cooma, Salt Lake, 36o 21’ 52”S, 148o 57’ 11”E, 14 March 2010, BVT, AM P88373, 2 males, 1female.

Remarks. Branchinella compacta occurs in southern Victoria, and now in southeast New South Wales, but not in southwestern Western Australia as the later specimens are described below as a new species. The following can be added to the description by Linder (1941) and Geddes (1981). While both authors note the absence of a frontal appendage in Victorian material, that from the Monaro, NSW, has a very small forked appendage. The medial surface of the basal antennomere bears minute spinules in some specimens which probably have a sensory function. There is also a very minor tumidity somewhere along this medial surface, apically ( Fig 4 of Geddes, 1981), but about midway in Lake Ondit and Lake Avon specimens studied.

The male fifth thoracopod is similar to that reported by Linder (1941) and Geddes (1981), but there are some important features of the anterior setae that need documenting. Endite 1 anterior seta is the longest of all 10 setae and is smooth. Endite 2 main anterior seta is half the length of anterior seta 1, has a pecten of spinules and is attended basally by a very short spiniform seta. Endite 3’s two anterior setae are like those of endite 2, but about 50% longer. Endites 4 and 5 have two anterior setae each, a longer one subequal in length to the main anterior seta of endite 2, with a pectin of spinules and a basal array of spinules. The shorter seta is about a quarter the length of the longer seta and naked. Endite 6 has just one anterior seta which is similar to the longer one of endites 4 and 5. The structure of these last five setae is unique to this species and serves to differentiate it from its sibling species described below.

Unlike most other species of Branchinella , B. compacta has outgrowths/tumidities on the genital segments. Linder (1941) noted a pair of stout spine-like outgrowths dorsally and two tumidities on the first genital segment, which Geddes (1891) reported also. The present specimens from Lake Ondit have a similar pair of spines but just one lateral tumidity and the Avon Lake specimens have a much larger pair of dorsal outgrowths directed posteriorly and terminating in a spine, but no apparent tumidities. It would seem then there is some variability in the expression of these outgrowths; this is accepted as normal for tumidites, given their variation, often associated with preservation, in Parartemia ( Timms, 2012) . In all mature specimens examined there is a bulbous tumidity ventrally on the brood chamber and in the Avon Lake specimens this has a posteriorly directed hook.

Figures

FIGURE 1. Resting eggs of selected species of Branchinella. A, B. affinis; B, B. clandestina n. syn.; C, B. anatinorhyncha; D, B. compacta; E, B. erosa sp. nov.; D, B. compacta; F, B. hearnii sp. nov.; G, B. herrodi sp. nov.; H, B. simplex; J, B. wellardi. Scale bars 50 µm. Images modified from Timms and Lindsay, 2011.

FIGURE 2. Branchinella anatinorhyncha sp. nov. A, male second antenna, dorsal view; B, frontal appendage; C male head and anterior thorax, lateral view; D, male gonopods; E, male penis; F, female head anterior view; G female genital segments and associated abdominal segments. Scale bars 1 mm.

FIGURE 4. Branchinella compacta Linder. A, male head, dorsal view, Ondit Lake, Victoria; B, male head, dorsal view, Avon Lake, NSW; C, female genital segments and brood pouch, Ondit Lake; D, female genital segments and brood pouch, Avon Lake. Scale bars 1 mm.