Branchinecta constricta, Rogers, D. Christopher, 2006

Rogers, D. Christopher, 2006, Three new species of Branchinecta (Crustacea: Branchiopoda: Anostraca) from the Nearctic, Zootaxa 1126, pp. 35-51 : 42-45

Branchinecta constricta n. sp.

Figures 2 , 3 .

Types: Holotype, male, data: USA: WYOMING; Sweetwater Co.: Antelope Pocket Overlook Rock Pool (42º 40’26”N, 107º 54’39”W), 15 June 1989, G. D. Langstaff, deposited: National Museum of Natural History, Washington D.C. USNM 1014985. Paratypes: same data as holotype, 3 females, 4 males, deposited: National Museum of Natural History, Washington D.C. USNM 1014986.

Material Examined: USA. WYOMING: Albany County: Todd’s Rock Pool I, Laramie Range, Veedauwoo Area, 2597m elevation, 41º 09’44”N, 105º 22’32”W, 20 May 1989, G. D. Langstaff. Todd’s Rock Pool II, 30m northwest of Pool I, Veedauwoo Area, 2597m elevation, 41º 09’44”N, 105º 22’32”W, 20 May 1989, G. D. Langstaff. Todd’s Rock Pool III, 50m east­northeast of Pool I, Veedauwoo Area, 2597m elevation, 41º 09’44”N, 105º 22’32”W, 17 May 1992, G. D. Langstaff. Todd’s Rock Pool IV, 20m west of Pool I, Veedauwoo Area, 2597m elevation, 41º 09’44”N, 105º 22’32”W, 17 May 1992, G. D. Langstaff. Fremont County: Antelope Pocket Overlook Rock Pool, Western Granite Mountains, 2178 m elevation, 2 km southeast of Wildhorse Rock Pool, 42º 40’26”N, 107º 54’39”W, 15 June 1989, G. D. Langstaff. Antelope Pocket Overlook Rock Pool, 2178 m elevation, 42º 40’26”N, 107º 54’39”W, 8 May 1989, G. D. Langstaff. Antelope Pocket Overlook Rock Pool, 2178 m elevation, 42º 40’26”N, 107º 54’39”W, 19 August 1987, G. D. Langstaff. Lankin Dome Summit Pool #1, 42º 31’50”N, 107º 33’40”W, 2316 m elevation, 4 June 1990, G. D. Langstaff. Lankin Dome Summit Pool #2, 42º 31’50”N, 107º 33’40”W, 2316 m elevation, 4 June 1990, G. D. Langstaff. Dead Antelope Rock Pool, 2181 m elevation, 42º 39’26”N, 107º 53’30”W, 8 May 1992, G. D. Langstaff.

Type Locality. Antelope Pocket Overlook Rock Pool (42º 40’26”N, 107º 54’39”W) is in the Western Granite Mountains, on the south side of the Beaver Divide, at 2178 m elevation, in Fremont County, Wyoming. The pool is in Sagebrush steppe, is roughly 1.5 meters in length, and is only a few centimeters deep. The water is clear to slightly turbid.

Etymology. The specific epithet describes the characteristic constriction of the male and female second antennae. The gender is feminine.

Description. Male. Average length of preserved material 16 mm. Head smooth, anterior­lateral corners projecting over eye peduncles. First antenna 1.5 to 2 times as long as eye plus stalk. First antenna 0.25 to 0.5 times as long as second antenna proximal antennomere. Second antennae extending posteriorly to sixth or seventh thoracic segment.

Second antenna stout, 2–2.5 times as long as broad. Proximal antennomere subcylindrical, pulvillus present, and with an anteriolateral tubercle in the proximal fourth ( Figure 2 D). Apophyses absent. Proximal antennomere bearing a transverse groove just distad of the pulvillus, giving the segment a “constricted” appearance. Transverse groove diminishes with age. Pulvillus and lateral tubercle with large, cylindrical, evenly spaced spines that may continue across the anterior surface of the proximal segment, as well as distally into the transverse groove in older males. Medial surface bearing a stout tubercle covered with fine denticles.

Second antennal distal antennomere 0.75 times the length of the proximal antennomere; robust basally at point of articulation. Antennomere flattened laterally (twice as broad as thick), basal half arcuate medially and parallel sided; distal half straight, margins explanate, with widest point just prior to apex; apex bent medially 90°, directed anteriorly, sub­truncate distally ( Figure 2 A–C, 3).

Labrum smooth, distal lobe projecting ventrally, rounded posteriorly. Mandibles with molar surface covered with fine denticles, posterior spine reduced and blunt. Maxilla 1 and 2 typical for the genus.

Praepipodites and epipodites typical for the genus. Thoracopod I with exopodite ovate, with apex slightly directed ventrally, and margined with fine setae. Endopodite margined with stout setae, subtriangular, with apex slightly directed ventrally. Endite 1 + 2 and 3 margined with long plumose setae. Endite 4 with stout anterior setae and stout posterior pectinate seta. Endite 5 with stout anterior and posterior. Endite six with stout posteriorly directed pectinate setae.

Thoracopod V with exopodite oval in outline, endopodite elongate triangular. ( Figure 2 G). Exopodite margined with fine plumose setae. Endopodite margined with stout setae, with distal most setae pectinate, becoming short and medially curved on the medioventral margin. Endite 1 + 2 and 3 margined with long filiform setae bearing short, fine setules. Endite 3, 4 and 5 with setae similar to endites 1 +2. Endite 6 with pectinate setae.

Thoracopod XI with exopodite rounded, blunt, and endopodite oval. Exopodite and endopodite margined with fine setae. Endites margined with sparse stout setae.

Penes extending to base of abdominal segment 2. Medial spur arcuate, 3 times as long as broad, bending posteriorly. Penes with distoapical “wart­like” mounds on lateral surface, directed posteriorly with 5 to 10 apical spines.

Female. Average length of preserved material 14 mm. Head smooth, without projections. Maxillary glands large, typically asymmetrical. First antenna twice as long as eye plus stalk, and half as long as second antenna. Second antenna 2.5–3 times as long as broad, apex sub­acute. Six percent of females with second antenna proximal­medial surface bearing a small, slender spine. Second antenna lateral surface with a small tubercle bearing fine spines. ( Figure 2 E, H).

Thoracic segments IV–XII with dorsal­lateral sub­conical projections, the largest on segments V–VIII. Endopodite ovate, exopodite falcate to ovate ( Figure 2 F). Thoracopod setal arrangement similar to male.

Ovaries extend anteriorly to the eighth or ninth thoracic segment, and posteriorly to abdominal segment 4 or 5. Brood pouch sub­cylindrical, extending to abdominal segment four or five.

Cercopods in less than 10% of females (64) may be extremely short; only one fourth or less the length of the telson. Otherwise the cercopods are as in the male.

Cyst. Approximately 320 µm in diameter and typical for the genus. Surface with shallow polygons 10 to 15 µm across bordered by low rounded ridges.

Differential diagnosis. Male B. constricta are separated from all other Branchinecta species by the second antennal proximal segmentís transverse invagination, appearing as a “constriction”. B. constricta most closely resembles B. coloradensis Packard, 1874 and B. packardi Pearse, 1912 (see Lynch, 1964). All three species share a bulge or projection on the second antennal medial surface; however in B. coloradensis the bulge is spinose, and in B. packardi the medial projection is directed anteriorly. In B. constricta the medial projection is blunt and directed medially. B. coloradensis and B. packardi are also both readily separated from B. constricta by the presence of proximal posteriomedial apophyses on the second antennae.

Female B. constricta can be separated from all other female Branchinecta species by the dorsal thoracic ornamentation. Female B. constricta are most similar to B. packardi females. Both taxa share the large maxillary glands, and have similar brood pouch morphology and similar dorsolateral projections. However, in B. packardi the projections are angular and directed posteriorly, and are present only on thoracic segments nine through twelve.

Distribution and Habitat. B. constricta is apparently endemic to Wyoming, but may occur in northern Colorado. To date all of the locations for this species have been small pools, under 2.5 meters across, and only a few centimeters deep. It is possible that this species is opportunistic, surviving in shallow peripheral pools. Nearby larger habitats are typically occupied by B. lateralis , B. readingi , or B. serrata .

IUCN Red List Status. This species is currently known only from eight locations in south­central and southeastern Wyoming. Therefore this species meets the International Union for the Conservation of Nature and Natural Resources (IUCN) red list criteria for designation as a VU D2 species (IUCN, 2000). That is to say, this taxon is vulnerable due to the population being very small and restricted, that may be prone to the effects of human activities or stochastic events within a short period of time.

Figures

FIGURE 2. Branchinecta constricta n. sp.; A – C) male left second antennal distal segment: A) lateral view; B) posterior view; C) medial view. D) Male, anterior view of left side of head; E) female, anterioventral view of left side of head; F) outline of exopodite and endopodite of female fifth thoracopod; G) outline of exopodite and endopodite of male fifth thoracopod; H) female, lateral view. Scale bar for: A – E = 0.3 mm, F and G = 1.0 mm, H = 5 mm.

FIGURE 3. Apex of male right second antennae, distal antennomere, ventral view: left Branchinecta lateralis; right, Branchinecta constricta. The anterior side of the antennomeres is to the right.