Parartemia longicaudata 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 : 3-9

Parartemia longicaudata Linder, 1941

( Figs. 1–4 )

Linder (1941) provides a brief description of males of this species, based on six poorly preserved specimens which have subsequently been lost from the WAM. Given that the female was unknown at the time of description, there are no types and that it is similar to one of the new species described below, P. longicaudata is herein redescribed and a neotype designated.

Neotype. one male, Pink Lake, Esperance, (33o 50’ 42”S, 121o 49’ 39”E), 7 October 2008, BVT, WAM 45203.

Topotypes. 1 female, same collecting data as neotype, WAM 45204; 2 males, 2 females, same collecting data as neotype, WAM 45205; 2 males, 2 females, some collecting data as neotype, AM P82971

Other material. 7 males, 6 females, small roadside salt lake southeast of Yarra Yarra Lake, 5 km W of Winchester, (29o 46’ 17”S, 115o 52’ 31”E), 14 September 2003, BVT, WAM 45206; 5 males, 3 females, small roadside salt lake 18 km S of Lake Grace, (33o 15’ 50”S, 118o 28’ 09”E), 28 July 2008, BVT, WAM 45207; 7 males, 3 females, Lake Carmody, southern end, (32o 32’ 48”S, 119o 21’ 50”E), 12 August 2008, BVT, WAM 45208; 10 males, 10 females, Esperance hinterland, North Speddingup Road, small lake 9 km E of railway, (33o 30’ 56”S, 121o 52’ 12”E), 2 August 2005; BVT, WAM 45209; 20 males, 20 females, Israelite Bay, Daringdella Lake, (33o 39’S, 123o 49’E), 31 January 2007, BVT, WAM 45210.

Description. Male. Length 24.6 mm (head plus thorax 10 mm, abdomen 14.6 mm).

First antenna ( Fig 1 A) filiform, almost twice as long as eye plus peduncle and subequal in length to basal antennomere of second antenna.

FIGURE 2. P. longicaudata . Male, 5th thoracopod. Length 3.2 mm (without setae). Main diagram shows posterior setae (PS) and subsidiary diagram of endites shows anterior setae ( AS). Some setae enlarged. Key: End = endite, Edp = endopodite, Exp = exopodite, Epp = epipodite, Pep = praeepipodite.

Second antenna. Basal antennomeres ( Fig 1 A) fused at about 45o to body axis. Ventral margin with paired ventral processes ( Fig 1 A) about 1.5 times longer than high. Distoventral corner of ventral processes broadly rounded and slightly protruding while medial edge thickened cylindrically and also protruded, but more expressed and narrowly rounded. Ventral process margin clothed in well spaced minute spines. Medial space between ventral processes a little narrower than their length and domed. Anterior process ( Fig 1 A) digitiform, small and subequal to ventral process depth. Distal antennomere almost twice as long as basal antennomere, somewhat curved medially, cylindrical and tapering to a sharp apex. Labrum lacking a spine.

Thoracic segments ( Fig 1 B) with small lateral lobes, increasing in size posteriorly and reaching a maximum on segment 11. Lateral bulge on first genital segment even greater than 11th lobe, so that maximum body width in genital segments. Eleven pairs of thoracopods, with first two reduced in size and last without an epipodite.

Fifth thoracopod (Fig. 2) with endite 1+2 and 3 evenly curved, the former about 3 times the size of the later. Endite 1 anterior seta about as two-thirds as long as adjacent posterior setae (shown enlarged in Fig. 2) and with few setae. Endite 2 anterior seta very short, about same length as base of anterior seta 1. Its spine even shorter and both weakly setose apically. Endite 3 anterior seta about four times length of anterior setae 2; both it and its subequal spine weakly setose apically. Endites 1 to 3 with posterior setae long and thin, clothed with numerous short setules and numbering about 60 on endite 1+2 and 15 on endite 3. Endites 4 to 6 asymmetrical (i.e. distal edge shorter than proximal edge) and with 2 anterior + 3 posterior setae, 2 + 2 and 1 + 2 respectively. Anterior setae of unequal lengths, but shorter and stouter than posterior setae, except basal seta of endite 4; this seta subequal in length to adjacent posterior setae. The five anterior setae of endites 4–6 with a double pectin of short setules except near their bases. All endites clothed basally with small spines generally grouped in 3–5s (not shown in Fig. 1 ). Endopodite broadly rounded and bearing about 36 posterior setae, all based with a coronet of numerous (>10) small spines. The first 8 of these setae (essentially those on the medial edge of the thoracopod) stouter and with a one-sided pectin on the distal half of setae, whereas the remaining setae thinner and closely feathered with short setules. Exopodite elongate oval and about twice length of endopod and bearing about 44 posterior setae similar to most on the endopodite. Epipodite oval shaped and praeepipodite elongated oval shaped, both unadorned.

First thoracopod (Fig 3A) less than half the size of thoracopods 4–10; 2nd, 3rd, and 11th also reduced in size. These four thoracopods essentially similar to thoracopod 5, but 1st with a stout endite 1 anterior setae and a large endite 5 basal anterior seta as well as the usual enlarged endite 4 basal anterior seta (Fig 3A). The 1st endite anterior seta with a double pectin of stout stunted spines (‘teeth’), better developed on one side than the other, and the other two large anterior seta with double pectin of thin spines. Anterior setae reduced in numbers on endopod (8 cf ca 36) and exopod (20 cf ca 45).

Thoracopod 11 lacks an epipodite.

Gonopods ( Fig 1 C) fused basally. Each free apical tube with a recurved spine basoventrally and a short digitiform process inserted ventrolaterally at about half the length of the tube.

FIGURE 3. P. longicaudata , some other thoracopods. A, male 1st thoracopod; B, female 1st thoracopod; C, female 10th thoracopod; D, female 11th thoracopod. Numbers on endites, endopodite and exopodite refer to the usual numbers of posterior setae on that part. Those of endites 4 to 6 almost always are invariable for the thoracopod concerned, but the higher numbers on other endites and the endopodite and exopodite can vary by up to about 10%. Not to scale, but most thoracopods are 0.5 to 1.5 mm long, with the 10th shorter than the 1st and 11th, if present, <0.5 mm in length.

Abdomen ( Fig 1 B) with segments increasing in length and decreasing in diameter sequentially 1 to 6, with sixth unusually long being a little more than twice the length (and half the diameter) of first segment. Cercopods about length of fifth abdominal segment and sixth abdominal segment unusually long, about 2.5 times length of first abdominal segment.

Female. Length 11 mm (head plus thorax 5.9 mm, abdomen 5.1 mm).

Head ( Fig 1 D) with first antenna filiform and a little longer than eye plus peduncle. Second antenna a little longer than twice length of pedunculate eye, somewhat flattened, and narrowing suddenly to a sharp apex. Labrum with a prominent recurved spine.

Thoracic segments ( Figs 1 E,F) 1–8 typical, but segment 9 with prominent lateral lobes and dorsally a large tumidity. Segment 10, and particularly 11, reduced, sclerotized and dorsum denticulate. Neither with lateral lobes. Anterior edge of genital segment crenulated and in life close to posterior edge of segment 9’s lateral lobe. Brood pouch extended laterally and posteriorly terminating in a posteriolateral extension.

Fifth thoracopod as in males (Fig. 2), but with exopodite less prominent and with all anterior setae shorter than posterior setae and tapering uniformally, i.e. no blade like portion on any anterior setae. Ninth thoracopod, although smaller than average, of normal proportions, but with the basal anterior seta of endite 4 longer than adjacent posterior setae. First and tenth thoracopods much smaller than usual and with different component proportions. First thoracopod (Fig. 3B) similar to that in males but with a few more anterior setae on endopodite and exopodite, and double pecten of stout blunt spines on first endite anterior setae more balanced. Tenth thoracopod (Fig. 3C) more reduced, with no praeepipodite or epipodite, reduced numbers of anterior setae on exopodite, endopodite and endites 1–6, and no anterior seta particularly enlarged. Eleventh thoracopod represented by a bulbous protrusion with a small spinous projection (Fig. 3D).

Abdominal segments typical for Parartemia , i.e. segments increase in length sequentially from segments 1 to 6. Surface coarsely denticulate.

Variability. Absolute size of adult males ranges from 10 mm in Lake Daringdella to 27 mm in a small lake near Lake Yarra Yarra and of adult ovigerous females from 7 mm in Lake Daringdella to 14 mm in the lake near Lake Yarra. In some populations the frontal process is somewhat shorter than the ventral processes are deep, while in others genital segments may not be quite as swollen as the lateral lobe of the 11th thoracic segment, and in others the 6th abdominal segment may be 2.5 to 3 times the length of the first. In females the tumidity on segment 9 may be small and hardly noticeable, and in other populations the lateral lobe of segment 9 may be extended backwards, and in still others where females are large, the ventrolateral tumidity between thoracic segments 9 and 11 is large and bears a small projection posteriorly. In the Lake Carmody population, the brood pouch is slightly extended posteriolaterally in the form of an egg-free pocket.

Differential diagnosis. No other species, except Parartemia boomeranga sp. nov., has a wide area between the ventral processes without a medial process; in P. longicaudata this area is convexly domed, while in Parartemia boomeranga sp. nov. it is concave. Further, more subtle differences, between these two closely related species are given under Parartemia boomeranga sp. nov. The long abdomen and long 6th abdominal segment are unusual, but not unique as shown below.

Female Parartemia longicaudata are distinctive from all other Parartemia , except again Parartemia boomeranga sp. nov., by having a central dorsal tumidity on thoracomere 9, but the two species are separable by the relative development of thoracomeres 10 and 11; in P. longicaudata thoracomere 10> 11, but in Parartemia boomeranga sp. nov. the sizes are reversed. Other differences are given under Parartemia boomeranga sp. nov.

Remarks. I am confident Linder and I are dealing with the same species as the neotype and topotypes are from the original type locality and the two descriptions are essentially the same, but the present account is more detailed. It differs in the understanding of the 8th abdominal segment (now 6th as the genital segments are now regarded as modified thoracic segments ― Walossek, 1993). Linder claims it is ‘very long’ and the ‘boundary between it and the telson obscure.’ Certainly this segment is longer than usual (ratio of length of first abdominal segment to sixth is an average of 2.24 times in 10 specimens compared to somewhat less than 2 times in many other species of Parartemia , eg, 1.31 in 10 specimens of P. informis , another large species) Also the whole abdomen is relatively longer than in many other large species ― the ratio abdominal length to head plus thorax length is an average of 1.27 in 10 specimens of P. longicaudata compared with 1.09 in 10 specimens of P. informis Linder. However some other species have relatively long abdomens, eg. P. purpurea sp. nov. the average ratio is 1.78 (see below) and some small species also have relatively long abdomens e.g. the ratio in P. yarleensis Timms and Hudson 2009 , a species <18 mm, is 1.4. However it is true that among the species familiar to Linder, P. longicaudata has an unusually long abdomen.

The thoracopods of P. longicaudata are similar to those described for the genus ( Linder, 1941, though with different terminology), and for P. minuta ( Geddes, 1973) and P. acidiphila ( Timms and Hudson, 2009) . The greatest differences from many other Parartemia species include larger numbers of posterior setae on endites 1–3 and exopodite.

Distribution and ecology. P. longicaudata is common throughout the Western Australian Wheatbelt, particularly in a band through Lake Grace ― Lake King and also northeast of Perth ( Fig. 4 ). It extends easterly to lakes bordering Israelite Bay and northerly to around Morawa; there are no records in the central east e.g. north of Merredin, nor in the Goldfields (Timms et al., 2009). It can withstand high salinities to at least 240 g /L and in the Esperance hinterland lives in higher salinity alkaline lakes while other species live in lower salinity lakes and acid salinas ( Timms, 2009b).

Figures

FIGURE 4. Map of Western Australia showing many places mentioned in the text and position of the type localities for each species.

FIGURE 1. P. longicaudata. A, male head with antennae; B, dorsal view of male thorax and abdomen, C, male gonopods; D, female head; E dorsal view of female thorax and abdomen T 7 to A 1; F, lateral view female thorax and abdomen T 8 to A 2. Scale bars 0.5 mm