Branchinella simplex Linder

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 : 55-57

Branchinella simplex Linder

Figs. 1 H, 11.

Branchinella simplex Linder 1941 , pp 247–8, figs. 32a–33d; Geddes 1981 p 265, fig. 6; Timms 2002 p87, Fig 11 , tab 3.

Material examined. Northern Territory, unnamed lake 20 km W of Erldunda, 25o 14’ 36.5” S, 132o 59’ 40.3”E, 10 March 2011, collectors M. Schwentner & BVT, AM P88351; South Australia, unnamed lake 5 km S of William Ck, 28o 59’ 42.3”S, 136o 26’ 24.1”E, 12 March 2011, collectors M. Schwentner & BVT, AM P88352; South Australia, Kalamurina Station, 220 km N of Maree, Stoney Dam, 27o 48’ 13”S, 138o 19’ 28”E, 15 July 2000, SAM C7036; Western Australia, Lake Carey, 27.5 km SW of Laverton, 28o 51’ 10”S, 122o 17’ 05”E, 8 March 2011, J. Coughran and E. Thomas, WAM C49907.

Remarks. Branchinella simplex was described by Linder (1941) from material collected in 1937 by Dominic Serventy from Kofar Lake (= Kopai Lake, 30o 16’ 11”S, 121o 15’ 29”E, Timms, 2002) near Kalgoorlie, WA. Linder was so impressed with the male’s lack of a frontal appendage and simple structure of the second antenna that he named it ‘simplex’ to celebrate this fact. He also noted some peculiarities in the structure of the thoracopods: all thoracopods have a notch mid length on the praeepipodite, and the first thoracopod endites 3–5 have 2:3:5 or 2:4:4 anterior setae instead of the usual 2:2:1. Geddes (1981) also recorded these peculiarities in his review. Linder, however, also reported that the female had some unique features too: a long wide second antenna and short brood pouch. These features need further elaboration.

With maturity the wide band-like second antenna of the females assumes a bend mid length so that it becomes somewhat sabre-shaped ( Fig. 11 D). While a few species of Branchinella have wide second antenna the shape in B. simplex is distinctive for Branchinella . The brood pouch is generally bulbous in Branchinella with a long posteriorly directed tube reaching abdominal segment 3 or 4, or rarely 5. However in B. simplex , while somewhat bulbous the main dimension in transverse to the body axis and the tube leading to the gonopore is short ( Fig 11 E).

Two other features are described here for the first time. The gonopod ( Fig 11 C) with a single row of basally pointed triangular spines medially and a wide field of narrow spines laterally is of characteristic Branchinella type (Brendonck, 1995; Rogers, 2006). The medial surface of the basal antennomere is not as simple as Linder (1941) and Geddes (1981) show. Generally there is a small tumidity protruding at about one third the length of the medial surface and in the Lake Carey, WA population there is an elongated tumidity on the distal half of the medial surface. Males from the population from the lake 5 km south of William Creek, SA lacks this feature.

Differential diagnosis. Branchinella simplex is indeed different from all other known Branchinella species, structurally and physiologically. This is partially reflected in a cladogram of Branchinella species based on 16S Mt DNA region ( Pinceel et al, 2012), in which it is well separated from the other halophilic species of Branchinella which form their own clade. Most of these have females with wide band-like second antenna and male second antenna with no or small frontal appendages. However B. simplex is separable from these on many morphological grounds, including extremely simply structured second antenna, unusual thoracopods (see above) and in females a bent second antenna and a transverse brood chamber. On the other hand it is curiously aligned with B. halsei which displays many morphological differences from B. simplex , including having basal lobes on the medial base of the second antenna, a small frontal appendage, usual thoracopods and in females a typical bulbous brood chamber with an elongated tube reaching back a few abdominal segments. This close relationship in the cladogram ( Pinceel et al., 2012) is possibly erroneous, as it is based on just one short section of DNA and apparently in this case is not representative of the full molecular differentiation in DNA.

Distribution and ecology. Branchinella simplex was thought to be an endemic species of Western Australia found in the Goldfields ( Linder, 1941; Geddes, 1981; Timms, 2002), but these new records extend its distribution to central Australia and northern inland South Australia. Despite extensive collecting in the eastern inland its presence has not been recoded there ( Timms, 2007 and unpublished data).

Branchinella simplex is tolerant of salinity, as first noted by Geddes (1981) based on a salinity of 21 g /L in Lake Annean at the time of collection. Subsequent records ( Table 1 ) confirm its marked salinity tolerance, the greatest for any Branchinella species, commonly to about 30 g /L, rarely to 60 g /L (Timms, 2009). It is not known whether its body tissues are tolerant of these salinities as it is in two other species ( B. australiensis and B.

compacta ) with mild tolerance to salinity, or whether it hypo-osmoregulates as does Parartemia in similar situations. To be tolerant to such high salinities as 60 g /L would be remarkable, just as it would be remarkable for a species of Branchinella to hypo-osmoregulate.

Branchinella wellardi Milner, 1929 , pp. 29–31, plate 6; Linder, 1941, p269; Geddes, p. 281, Fig. 16f; Timms, 2002, p.87; Timms, 2008, pp 302–304, Fig. 9 .

Material examined. 5 males, 5 females, New South Wales, Muella Station, 125 km NE of Bourke, temporary lake on eastern boundary south of road, 29o 31’59”S, 145o 00’ 54”E, 19 February 2010, BVT. AM P88374.

Remarks. Since its discovery in the Murchison district, Western Australia, this species has been encountered only a few times, three times more in mid Western Australia (Timms, 2002, 2008), and in a few sites in the Paroo, northwestern New South Wales and southwestern Qld ( Timms and Sanders, 2002). Milner’s description and diagrams, together with those in Timms 2008 are adequate, except for the some detail of the frontal appendage and the thoracopods which are described in detail here.

Frontal appendage with a short trunk and two branches, each about four times longer than the trunk. A bilobed lamellar extension at the bifurcation almost as large as the main trunk. Each branch pseudosegmented and bearing 10 branches laterally and 9 medially, all except the basolateral branch in opposite pairs. Subbranches decreasing in length apically and knobbly with each knob bearing a narrow epidermal outgrowth on each side and terminally.

Fifth thoracopod with endite 1+2 and 3 evenly curved, the former about three times the size of the later. Anterior seta of endite 1 naked, and about half the length of adjacent posterior setae. Anterior seta of endite 2 about half the length of endite 1 anterior seta and bearing a strong pecten of spines and attended at its base by a small smooth spine. Endite 3 with an anterior setae similar in length to the first anterior seta, and bearing a strong pecten of spines and attended at its base by a short naked spine. Endites 4–6 asymmetrical and covered with small spines. Endites 4 and 5 with two anterior setae and endite 6 with one anterior seta, representing two types. The first on all three endites with a fine pecten most of their length and a few spinules basally; the seta on endite 6 a little longer than the other two. The second setal type on endites 4 and 5 only, comparatively short (half length of adjacent anterior setae) and almost naked except for a few widely spaced spinules. Posterior setae of all endites long and numbering about 60 on endites 1+2, 20 on endite 3, then 3,2,2 respectively on endites 4–6. Endopod squarish with a wide shallow notch apically. It bears 4 short feathered setae medioapically, each inserted on the mid dorsal surface of an elongated knob (the whole structure like a sledge hammer coupled to the endopod), another 3 more normally inserted before the broad apical notch and 13 more on small raised knobs on the remaining apical surface and lateral edge. Exopod with about 33 feathered setae, most about double the length of the endopod setae and each on a similar small raised basal knob. These small knobs with 1–4 spinules, but the large knobs on the medial endopod without any outgrowths. Epipod elongate oval and naked. Praeepipodite large (about equivalent to exopod + endopod) and with smooth edges.

The significant structures on this thoracopod are the knobs on the medial surface of the endopod. As far as is known they are unique to B. wellardi and they clearly differentiate it from a closely related species, B. herrodi sp.nov. (see above).

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 9. Male fifth thoracopods. A, B. herrodi sp. nov.; B, B. wellardi Milner. Scale bars 1 mm.

FIGURE 11. Branchinella simplex Linder. A, male head with second antenna, dorsal view, Lake Carey; B, male head with second antenna, dorsal view, William Ck; C, penis; D female head, normal and post mature; E, brood chamber, ventral view. Scale bars 1 mm.

Tables

TABLE 1. Salinity records for Branchinella simplex

Authors Locality	Salinity range	No. of records
Geddes, 1981 Kalgoorlie, WA	to 21 g/L	2
Timms et al., 2007 Lake Carey, WA	12.8 to 62 g/L	6
Outback Ecology, Lake Carey, WA pers.comm., 2011	15.3 to 34.7 g/L	4
Bindy Datson, pers.comm., 2011 Lake Carey, WA	12.5 to 28.6 g/L	7
Author, unpublished Central Australia	14 to 30 g/L	2
Branchinella wellardi Milner 1929 Figs. 1J, 9B, 12.