First Record For Springsnails (Mollusca : Hydrobiidae : Pyrgulopsis) From The Northern Rocky Mountains

12 Pages·2001·4 MB·English

by  R Hershler

PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
114(l):297-308. 2001.
First record for springsnails (Mollusca: Hydrobiidae: Pyrgulopsis)
from the northern Rocky Mountains
Robert Hershler and Daniel L. Gustafson
(RH) Department of Invertebrate Zoology, National Museum of Natural History,
Smithsonian Institution, Washington, D.C. 20560-0118
(DLG) Department of Ecology, Montana State University, Bozeman, Montana 59717-0346
Abstract. Pyrgulopsis bedfordensis, new species, from southwestMontana,
differs from other congeners having an enlarged penial lobe by its unique
pattern of penial ornament, consisting of a transverse terminal gland and a
raised gland on the inner edge of the lobe. This species is locally endemic in
the headwater region of the Missouri River basin. Origin of this novelty is
attributed to vicariance associated with Neogene migration of the continental
divide.
Pyrgulopsis is the largest genus ofinland tional Museum of Natural History, Smith-
aquatic moUusks in North America, with sonian Institution (USNM). Terminology
123 described species in common usage. and methods of morphological analysis are
&
Although phylogenetic structure within of Hershler (1994, 1998) and Hershler
Pyrgulopsis has not been well established, Ponder (1998). Measurements of shells of
the genus is divisible into non-overlapping the holotype and a series of paratypes are
eastern and western subunits which arewell in Table 1.
differentiated morphologically (Hershler
1994). The large western fauna is restricted Pyrgulopsis bedfordensis, new species
to the region extending from the southern —
Great Plains to the Pacific Coast, and from Type material. The holotype (UF
mm
the Columbia Plateau to the Basin and 271731) is a dried shell (3.37 shell
Range of northern Mexico. The much length. Fig. 1) from Warm Springs Creek
smaller eastern fauna ranges from the Cen- (also known as Bedford Hot Spring), Town-
tral Lowlands to the Atlantic Coast. send Valley, Broadwater County, Montana,
Snails conforming morphologically to T 7N, R. IE, sections 14, 23, elevation
m
the western group have been collected east about 1,200 (46.3537°N, 111.564rW);
of the continental divide only in the Pecos- collected by D. L. Gustafson and M. M.
Rio Grande drainage of the southern Great Hooten, 26 Jan 1991. The location of the
Plains (e.g., Taylor 1987). One of us type locality is shown in Fig. 2. Paratypes
(DLG), however, recently discoveredapop- (USNM 854975, USNM 854976, USNM
ulation of Pyrgulopsis living in a thermal 892153, USNM 892154, UF 184057, UF
spring in the upper Missouri River drainage 184058, UF 193049, UF 193050) consist of
just east of the continental divide which several series of dry shells and alcohol-pre-
also conforms to the western group. Herein served specimens collected from the type
we describe this new species, which repre- locality at the same time. Two additional
sents the first record of Pyrgulopsis in the series (USNM 892151, USNM 892152),
Northern Rocky Mountains. which are not designated as paratypes, were
Specimens are deposited in the Florida collected at the type locality by D. L. Gus-
Museum of Natural History (UF), and Na- tafson during 1995 and 1999.
298 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
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Table I. Morphometric and meristic shell features Description. Shell (Fig. 3A-E) clear-
of holotype and ranges of values for 10 paratypes of white, trochiform to ovate-conic, width/
Pyrgulopsis bedfordensis, new species. Morphometric height, 58-70%; height (larger adults),
parameters are expressed in mm.
about 2.9-3.7 mm; width, 1.9-2.3 irmi;
Holotype Paratypes whorls about 5.0. Apex usually eroded in
adult specimens. Protoconch valvatiform,
Shell height 3.37 2.94-3.69
Shell width 2.10 1.99-2.30 whorls about 1.25, diameter about 260 |xm,
Body whorl height 2.42 2.22-2.70 earliest 0.5 whorl slightly wrinkled, surface
Body whorl width 1.91 1.71-2.10 otherwise smooth (Fig. 3F, G). Teleoconch
Aperture height 1.39 1.31-1.59 whorls of low to medium convexity, nar-
Aperture width 1.35 1.27-1.47
rowly shouldered. Aperture ovate to pyii-
Shell width/shell height 0.62 0.58-0.70
Number of whorls >5.0 >4.0-5.0 form, broadly adnate to slightly disjunct.
Inner lip completed, slightly thickened, col-
— umellar lip strongly reflected in most adult
Diagnosis. A medium-sized species of specimens. Outer lip usually thin, orthoc-
Pyrgulopsis with trochiform to ovate-conic line or weakly prosocline, sometimes weak-
shell having an eroded apex and well-de- ly sinuate. Umbilicus narrowly perforate,
veloped columellar shelf. Penis large; fila- often obscured by columellar lip. Perios-
ment medium length, lobe long. Penial or- tracum brown or tan. Shells ofmales form-
nament of a curved gland along the distal ing distinctly smaller size class (about 2.5-
edge of the lobe (terminal gland) and a 2.6 mm) than those of females.
smaller unit (Dg3) borne on the distal edge Operculum (Fig. 3H-K) medium thick-
of a well-developed swelling on the inner ness, light amber with darkerred hue innu-
edge of the lobe. clear region, ovate, paucispiral, nucleus ec-
Fig 1. Holotype ofP. bedfordensis. new species, from Warm Springs Creek, BroadwaterCounty, Montana.
VOLUME 114, NUMBER 1 299
Fig. 2. Map showing location of Warm Springs Creek. Sampling sites are indicated by thick arrows, cd,
continental divide.
centric. Edges of whorls without frills on (Fig. 4C, D) with 2-3 cusps on inner side
outer surface (Fig. 3H); outer margin with- and 2-4 cusps on outer side, central cusp
out rim. Attachment scar margin thickened large, spoon-shaped; neck weakly flexed;
between inner edge and nucleus (Fig. 31- outer wing 135-145% width of tooth face.
K). Inner marginal teeth (Fig. 4D-F) with 23-
Buccal mass large; radular sac extending 31 cusps, often bearing noticeably enlarged
behind buccal mass as small loop. Radula cusp proximally (Fig. 4F). Outer marginal
about 885 X 142 (xm, with about 57 rows teeth (Fig. 4D-F) with 34-38 cusps. Style
of teeth. Central teeth (Fig. 4A-C) trape- sac about as long as remainder of stomach;
zoidal, 33-39 |xm wide, dorsal edge medi- stomach with very small posterior caecum.
um indented; lateral cusps 3-4; central cusp Cephalic tentacles grey, dark brown, or
medium width, narrowly pointed, consid- black, pigmented lighter around eyespots.
erably longer than lateral cusps; basal cusp Snout usually dark brown (rarely lighter),
1, large, arising from intersection of tooth distal lips often lightly pigmented. Footme-
face and lateral margin. Basal tongue of dium to dark brown. Opercular lobe brown
central teeth broad V-shaped or U-shaped, or black all around, central area pale. Neck
basal sockets medium depth. Lateral teeth with light to medium cover of grey gran-
300 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Fig. 3. Scanning electron micrographs of shell and opercula of P. hedfordensis, USNM 854976. A-E. Var-
iation in shell shape (shell height, 2.86, 3.10, 3.26, 3.69, 2.66 mm, respectively). F Shell apex, viewed from
side (bar = 100 ixm). G. Shell apex, viewed from above (bar = 100 |Jim). H. Outer surface ofoperculum (bai-
= 500 |jLm). I-K. Inner surface ofoperculum (bars = 500 |a,m).
VOLUME NUMBER
114, 1 301
Fig. 4. Scanning electron micrographs of radula of P. bedfordensis, USNM 854976. A, B. Central radular
teeth (bars = 17.6 |xm). C. Section of ribbon showing central and lateral radular teeth (bar = 38 |j,m). D, E.
Sections of ribbons showing lateral and marginal radular teeth (bars = 43, 30 (xm, respectively). E Marginal
radular teeth (bar = 27 [i.m).
302 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
ules. Pallial roof, visceral coil black on dor- ping posterior and part of anterior stomach
sal surfaces, lighter ventrally. Penial fila- chambers anteriorly. Seminal vesicle a
ment having dark melanin core. small mass of tight coils opening from and
Ctenidium with about 18 medium sized positioned alongside the anterior portion of
filaments (not extending to rectum); fila- testis. Prostate gland small, sub-globular,
ments with pleats, broadly triangular, apices pallial portion very short or absent, ovate
centrally positioned; ctenidium abutting in section (Fig. 5D). Pallial vas deferens
pericardium posteriorly. Osphradium small, curving on columellar muscle. Penis large
intermediate width, centrally positioned. relative to head, base rectangular, smooth;
Renal gland slightly oblique; kidney with filament about 67% length of base, taper-
small pallial bulge and simple opening. ing, distally pointed, narrow, longitudinalor
Rectum straight, slightly overlapping cap- oblique (Fig. 5E). Lobe about as long and
sule gland, abutting prostate gland. wide as base, rectangular, longitudinal. Ter-
Ovary a single yellow mass, weakly lo- minal gland transversely positioned along
bate dorsally, 0.5-0.75 whorl, filling slight- edge of lobe, narrow, curved, rarely split
ly less than 50% of digestive gland behind into two units. Dg3 borne on prominent
stomach, overlapping posterior stomach stalk arising from inner edge of lobe, stalk
chamber. Albumen gland clear-white, hav- often clearly demarcated from lobe; glan-
ing very short pallial component (Fig. 5A). dular unit shorter than terminal gland,
Capsule gland yellow, about as long as but slightly curved. Penial ductnarrow, curved,
narrower than capsule gland, divided into coursing from close to inner edge proxi-
two sub-equal tissue sections (anterior sec- mally to near—medial position distally.
tion smaller and lighter), ovate in section, Etymology. An adjectival geographical
right lobe thickerthan left; rectal furrow ab- name referring to location of the type lo-
sent. Ventral channel moderately overlap- cality near the historical site of Bedford,
ping capsule gland; longitudinal fold well- Montana. Gender female. We propose the
developed. Genital aperture a terminal slit vernacular name, "Bedford springsnail,"
positioned slightly posterior to anus. Coiled for this species, also in reference to its sin-
oviduct of a single anterior-oblique loop; gle known localit—y.
gonopericardial duct not evident in dissec- Comparisons. This novelty conforms
tion. Oviduct and bursal duct joining just morphologically to the western fauna of
behind pallial wall. Bursa copulatrix small congeners, which share weak protoconch
relative to albumen gland, narrow to ovate, microstructure, surficial position of the fe-
longitudinal, extending slightly posterior to male bursal duct relative to the albumen
albumen gland, sometimes slightly over- gland, and connection of the bursal duct
lapped by albumen gland dosrally (Fig. and oviduct at the posterior pallial wall
5B). Bursal duct originating from anterior (Hershler 1994). Pyrgulopsis bedfordensis
edge at mid-line, considerably longer than has an unique pattern of penial ornament,
bursa copulatrix, medium to wide, usually which consists of a transverse terminal
broadening distally, surficial or slightly em- gland and well-developed gland on the in-
bedded in albumen gland proximally. Sem- ner edge of the lobe (Dg3). Although not
inal receptacle small relative to bursa co- closely similar to any other member of the
pulatrix, narrow or ovate, positioned near genus, this species uniquely shares with
ventral edge of albumen gland slightly to several other congeners living in western
well anterior to bursa copulatrix, duct thermal springs an elongate-rectangular pe-
slightly shorter than body (Fig. 5C). nial lobe that is much larger than the fila-
Testis 1.25 whorls, composed of numer- ment (e.g., P. isolata, P. nana; Hershler &
ous compound lobes, filling almost all of Sada 1987,—figs. 32, 38).
digestive gland behind stomach, overlap- Habitat. The type locality (Fig. 6A, B)
VOLUME NUMBER
114, 1 303
Dg3
Pvd
^^NM
bLssteutrfrmutscSatsruicrdeoeepss.uolfBRa.tpr'nBoxsu;ftraCst'ga'e,'cg"col'apapnu"^sdliu,al^t^sen.hx^go-l^aaw"nnm'dd^g;^U"Cis^on"v'sdeu,rcttci.ooinSlceoadflo8evv9aia2sds1ud5cie2ntf.;eArA.De.gnC3sL.:efSE.tem^sPiMen^neai^lsofr.Befca^eermps^atlaLecl2^ge5l0^aann.:dd,uml^Uasr/Adao^uvci:tld,uu^cStc:aal^nedatas,s^is^noc^AiaoDt,ed
apertt^re; Pd, penial duct; Pf, penial filament; PI, penial lobe; Pvd, pallial vas deferens Pw posterior wdloJ
304 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Fig. 6. Type locality of f bedji)iden.sis. A. Lower end of sampling area, with diversions structure used to
.
irrigate nearby fields. Riparian area badly trampled by livestock. B. Typicalreachofspringrun(abovediversion
structure). Photographs, 22 August 1999.
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VOLUME 114, NUMBER 1 305
is a large thermal spring which flows for sampled aquatic habitats throughout Mon-
about 2.0 km (dropping 56 m in elevation) tana and adjacent states (Fig. 7) without
before entering the western pond at the up- finding this snail elsewhere. This sampling
per end ofCanyon Ferry Reservoirjust east included 30 of the Montana warm springs
of Bedford. (There are three more ponds to listed by Sonderreger et al. (1981), includ-
the east.) This creek drained directly to the ing all five ofthe springs in close proximity
Missouri River prior to construction of the to Warm Springs Creek.
original Canyon Ferry Dam in 1901. The
water temperature was 21°C near the source Discussion
on 26 January 1991 (when the air temper-
ature was well below zero) and 23°C on 22 Origin of Pyrgulopsis bedfordensis is
August 1999. (Mean annual air temperature conjectural given the poorly resolved phy-
at nearby Townsend is 6.74°C.) Sondereg- logenetic relationships within the genus,
ger et al. (1981) indicated a temperature of and the incompletely known history of
23.6°C for this spring, along with pH, 7.2; drainage in the northern Rocky Mountanre-
specific conductivity, 467 |xmho/cm; and gion. An origin associated with upstream
350 mg/L TDS. penetration of the Missouri River basin ap-
Pyrgulopsis bedfordensis was abundant pears unlikely given the distinctiveness of
throughout the sampled section of spring the eastern and western faunas of Pyrgu-
run and snail shells made up a large com- lopsis (see above). The well documented
ponent of substrate in many areas. Snails Pleistocene rerouting of the ancestral Mis-
were collected by sweeping a fine aerial in- souri River, which coursed north to the
sect net underneath riparian vegetation Hudson Bay prior to blockage by the Lau-
which lined the stream margins. (Snails re- rentide ice sheet and assumption of the
leased from the vegetation withthe slightest modem path to the Mississippi River(How-
disturbance.) Snails were also found on all ard 1958, Lemke et al. 1965), probably had
other available substrates; mud, rocks, no bearing on this issue as P. bedfordensis
wood, mosses, aquatic and submerged vas- represents the northernmost record for the
cular plants, and filamentous algae. This genus (living and fossil) in the West. We
new species was collected along with an- instead attribute origin to vicariance of an
other gastropod snail {Fossaria sp.) and 31 earlier paleodrainage implied by the close
other invertebrates, most of which have geographical proximity of this species of
broad geographic distributions. The other poorly dispersing snail to fauna living
invertebrates include various species com- across the continental divide in the upper
monly found in thermal waters; e.g., Libel- Snake River basin (e.g., P. robusta; Her-
lula saturata Uhler andArgia vivida Hagen shler 1994). Note that Pyrgulopsis has not
(Odonata), Ambrysus mormon Montandon been found in the upper Colorado Riverba-
(Hemiptera), Chimarra utahensis Ross and sin (Green River drainage), which also is in
Protoptila erotica (Trichoptera), andMicro- close proximity to the Missouri headwaters.
cylloepus sp. (Coleoptera). Three species of Extensional faulting responsible for de-
fishes were collected Rhinichthys catar- velopment of the basin and range of south-
actae (Valenciennes), Gambusia affinis west Montana began during the middle
(Baird and Gi—rard), and Xiphophorus var- Miocene and profoundly disrupted an an-
iatus (Meek) the latter two of which are cestral landscape that consisted of broader,
introduced in M—ontana. shallower basins (Reynolds 1979, Fields et
Distribution. This species is thus far al. 1985, Boronsky et al. 1993, Sears &
known only from the type locality. Local Fritz 1998). (The Townsend pull-apart gra-
endemism is likely given that over the past ben, to which P. bedfordensis is endemic,
18 years one of us (DLG) has extensively lies along the boundary between this zone
306 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Fig. 7. Map showing location ofsampling sites in Montanaand adjacent states. The shadedareadepictsthe
regional distribution ofPyrgulopsis. with the disjunctoccurrence ofP. bedfordensis indicatedbythe arrow. CD,
continental divide.
of deformation and more stable crust to the (1989, 1993; also see Kreps et al. 1992) re-
north [Reynolds 1977].) The continental di- cently proposed that during the early mid-
vide probably had a complex history in this dle Miocene, the portion of southwestern
region (Fields et al. 1985) and the modem Montana now comprising the upper Mis-
north-trending Missouri headwaterdrainage souri River basin drained south to the pre-
may not have been assembled until the sent site ofthe Snake River Plain, with tec-
&
Quaternary (Robinson 1963, Fritz Sears tonic break-up of this landscape and rever-
1993). Anderson (1947) presented physical sal offlow direction occurring about 6.5 Ma
evidence that the continental divide shifted in association with local passage ofthe hot-
about 161 km to the east during the late spot. While some of the stratigraphic inter-
Tertiary, with associated severence of a pa- pretations of this proposal have been chal-
leodrainage that integrated southwest Mon- lenged, the hypothesized drainage reversal
tana and southeast Idaho (also see Ruppel has been accepted (Cheney et al. 1994, Fritz
1967). The development and migration of & Sears 1994).
volcanic centers and a topographic swell in The western fossil record ofPyrgulopsis
&
association with passage of the North dating to the late Miocene (Hershler Sada
American plate across the Yellowstone Hot 2001) is congruent with the above time
Spot (beginning ca. 16 Ma) has provided a frame of physical events contributing to vi-
cogent explanation for such an eastward cariance ofa postulated Missouri-Snake pa-
shift of the divide (Pierce & Morgan 1992, leodrainage. This hypothesis is also consis-
& &
1999; Smith Braile 1994). Fritz Sears tent with other organismal distributions