ZO 591 Biology of Mollusca (Taylor)
0 Spring 1968
Kay to Major families of Morth American freshwater snails,
by external charastess of living animals
1f2). Hind end of foot bearing a horny operculum that closes aperture of shell. Head and foot sepasated by a deep cleft, in front of which is an elongate, transversely wrinkled, mobile rostrum snout)
Eyes lateral to, or on, long axis of tentacles. Tentacles tapering
and slender. Feces extruded as discrete pellets or as dorsally
grooved, ragged-ended ropes. Shell low-spired to high-spired,
almost always dextral. SUBCLASS PROSOBRANCHIA 2(1) Hind end of foot bearing no horny operculum that closes aperture of shell, Head and foot closely united, with no elongate ea um
(snout) in front of foot. Eyes between bases of tentacles.
Tentacles flat and triangular or tapering and slender. Feces
extruded as smooth, ragged-ended ropes. Shell limpet-like,
discoidal, or high-spired; sinistral or dextsal. SUBCLASS
EUTRYNEURA, ORDER BASOMMATOPHORA . 0 0 0 • 0 0 0 0 17 , 3(4) Operculum multisplral, consisting of numerous equall) wide
overlapping spiral bands. Eyes in the middle of the tentacular
bases, on long axis of the tentacle in dorsal view. A ctenidium with lamellae on both sides of a central blade 'isipectinate ctenidlum) projects anteriorly from the mantle cavity. A cili- ated pallIal tentacle projects from the upper right corner of
the aperture. Rostrum with parallel sides, slightly expanded
at the end; terminal pads not set off by a na-row groove. Widest
part of foot at the front, where two narrow, tapering lobes curve 2
laterally and then posteriorly. Widest part of foot behind
anterior lobes is clearly in the posterior half of the foot.
Anterior pedal groove wide, deep, and V-shaped, so that upper
edge of foot below rostrum is posterior to front edge of sole.
Feces extruded as dorsally grooved nagged-ended ropes. Shell
low-spired to moderately high-spired, less than 10 mm high.
Superorder ECTOBRANCHIA, family Valvatidae.
4(3) Operculom concentric; or consistfng of only 3 or 4 spiral tU7nS.
Eyes on cute:- bases of tentacles (or rarely on short peduacles
if tentacles are absent). Ctenidium Internal, not projecting
from mantle cavity, consisting of many triangular lamellae that
hang from the roof of the mantle cavity (monopectinate ctenidium.
No pallial tentacle projecting well outside the shell. Rostrum
tapering toward the front; terminal pads may or may not be ex-
panded beyond width of rost.-um, usually set off by a narrow
groove. Front corners of foot expanded into short lobes that
project laterally; these are no wider than the greater part of
the foot, or are only slightly wider. Most of the foot behind
anterior lobes of equal width. Anterior pedal groove narrow, of
equal width across the edge of the foot. Feces extruded as
ditcrete ovoid or spindle-shaped pellets. Shell discoidal to
high-spired, minute to large (1 mm to about 100 mm long in
adults). Superorder PECT1NI8RANCHIA, Order TAERIOALOSSA . . 5
56) External color pattern splotched, mottled, marbled or YO legated;
yellow or orange pigment gi-anules usually present. Shell 10-100
mm long in adults, globose, conical, or discoidal. Operculum 3 calcareous or corneous, concentric or spiral. Nuchai lobes acting as inhalant and exhalant siphons may be vesent. Male
may lack a penis; or have penis in the right tentacle, or in
the roof of the mantle cavity, or (rarely) on the floor of the
cavity. Reproduction ovoviviparous or oviparous; female may
have brood pouch on back of head, or oviducal groove on right
side of body.•.• —•.•.•.• 0 , 0 0 0 . . 7 6(5) External color absent, faint, uniform, or in simpie patterns; no fine networks or marbling or mottling; usually no pigment except
melanin. Shell less than 10 mm long in adults, tueriform, globose, conical or discoidal. Operculum corneous, spiral. No nuchal lobes. Male with copulatory organ (verge on the
floor of the mantle cavity. Reproduction ovoviviparous or
oviparous; female does not have brood pouch on back of head or
oviducal groove on right side of body. Super7amily RiSSOACEA 15 7(8) External color pattern splotched, from irregula clusters of yellow or orange pigment granules. Operculum calcareous or Corneous, concentric or concentric around a small spiral nucleus. Nuchal lobes acting as inhalant and exhalant siphons present.
Floor of mantle cavity divided lengthwise by a vertical lamella
epitaenia). Male with penis, variously located. Female without oviducal groove; if ovoviviparous with young in the pal Hal ovi-
duct at the right side of the mantle cavity. Shell conical
giobose, or discoidal, 10-100 mm long in adults, plain-colored or spirally banded. Feces are ovoid OF apindle-shaped pellet with internal spiral structure. Superfamliy V ViPARACEA 0 If
8(7) External color pattern, mottled, marbled, or variegated.
Operculum corneous, spiral. No nuchal lobes or epitaenia.
Male lacks penis. In female a groove (oviducal groove) descends
right side of body stalk to sole, or there is a brood pouch con-
taining young on the back of the head. Shell turriform, may
exceed 15-25 mm in length, often banded, spirally or irregularly
splotched. Feces are spindle-shaped pellets, non-spiral in
structure. Superfamlly CERITHIACEA ...... 13
9(10) Operculum corneous. Shell plain-colored or with spiral bands,
20-100 mm long in adults. Eyes op short peduncles, lateral to
tentacles or fused with lateral aspect of tentacles, not in low
swellings on lateral bases of tentacles. Penis present in roles,
either in right tentacle or on roof of mantle cavity, not on
floor of mantle cavity. Feces are ovoid pellets voided as a
group ...... 11
10(9) Operculum calcareous, concentric. Shell without bands, 10-15 mm
long in adults, conical, dextral. Eyes In low swellings on
lateral bases of tentacles. Copulatory organ on floor of mantle
cavity to right of midline; it is a verge with single accessory
process (inclluding a duct) on the left side. Feces are spindle-
shaped pellets, of spiral construction, voided singly or in
series, not in a group. Reproduction oviparous; eggs laid in a
double row of adjacent capsules. Family Bithynildae.
11(12) Operculum corneous and concentric, or concentric around a small
spiral nucleus. Shell conical, usually dextral, rarely sinistral;
25-100 mm long in adults; plain-colored or with 3-4 spiral brown
bands separated by approximately equal interspaces. Rostrum 0
, , ..-, simple:, .:- i nf2: t. :crc.:1 tcnt ics. E ‘,. CS. C.;') •'' ..:":'''1. •.'C'..11: .:...::::-.TI
:ftsc.:.- '..,:it ftterc:A ,7s::cct. 0;.'- tclt,-,:c:Ics. Tentcics stit,
tacrinp; E's,,:;,. trie,171 in fi.alios; pcnis In rii.,t- tc.: ',-,D- o
is then thic a',-6 rc:curveC K:steriorly. re:c:uctif2,n. ,..:.v- ..:n/I-,.
viparous. W> lunzf. Fc,mily Vivilricl.ce..
12(1 .1). Opercuium corncous, concentric. Sell 0obose or disoia:,
.de:aral; about 50-75 mm icing In ceults; ploin-colored or ‘-'ith
1 0-15 spiral brown hands of vc:ricble width se2aated :),,' intcr-
spaces appro:timately equal to width of Wider bands. RostruIIl.
with a. labial tentacle on each side. Eyes on shut peduncles •
lateral to the bases of the tcntacles. Tentacles lorq, sl ner,
mobile; symmetrical. Penis on roof of mantle cavity. fle.-4-o-
duction oviparous; eggs laid out of waters as clusters rxf
calcareous soherules. Part of mantle cavity a ±Ailmonary :,,...c,
with a long siphon. Family Ampullariidae. l3(14) Border of mantle smooth. FCM410 with a groove 0:)vidua1 vor.ve.)
descending right side of body stzik toward sole. llost7..um not •
flattened, oval in crass-section. Shell plain. ;olorcd or ntn
spiral bands. Family Plcuroceridae.
14(13) Border of mantle with several elonozte papilicte. Femr::le ' th
a brood pouch containing live young on back of 'Telle. t: .t.-uli,
flattened dorso-ventrAly, long-eval in cross-sction. Eix:i
often with I rreF;:ularly spotched color pzittorn. 7;:rnfly
150 Eyes on sEcrt pcunelcs; no tentccies. Animei ,-7',Ir-c , -.
Shell conici71, iess nz::n 4 mm long, vnifc.rmiy 1:1 NOun, t.l o c...- -•
c.ercous port cif the .s ciii T.,E.', -c brcn-c..olcred. V,'2,1c 1,,t ,7
• biadc-Iii1;c coul.(ntovy 1,21- - n. (vere) in t:-:(1 i et: c ,-.:F:v.P,:y.. 6
usually just out of water, in s ring-bogs Of beside saline
pools. Family Assimineidae.
16(15) Eyes on low swellings on the outer bases of long tapering
tentacles. Animal pigmentless to lightly or darkly colored,
sometimes with yellow or white granules in addition to melanin.
Shell discoidal, conical, or turriform, 1-10 mm long in adults;
plain-colored, colorless, or (rarely) with spiral bands in the
periostracum; calcareous part of shell always colorless. Mole
with a copulatory organ verge) in the mantle cavity that may
be relatively large or small, simple or with bulky accessory
glands. Habitat almost always in water (fresh or brackish), rarely
Just out of water. Family Hydrobiidae.
17(18) Tentacles short, flattened, triangular in plan. No postvelar
flap at the posterior base of the tentacles. Posterio;- end of
foot rounded. Blood without evident color. Animals monoecious,
with genital openings on eight side of body (i.e., animal
dextral). the male opening beneath the hind end of the right
tentacle and usually hidden in the crease. Superfamily
LYMNAEACEA ...... 19
18(17) Tentacles long and narrow, rod-like. A narrow flap (postvelar
flap) extends posteriorly from the base of each tentacle and
encloses a groove on the lower side. Posterior end of foot
either rounded or acutely pointed. Blood red or without evident
color. Animals monoecious, with genital openings on left side
of body (i.e., animal sinistral); the male opening Just behind
the end of the postvelar flap ...... 0 . 0 . 21 19 '
ar anc.i cvities :
a sir:on. The srtall may air ftto ca7itv, r
ne cavity may be th1.jth wzter cr .a smoli hy Wc.
Family Lymnaeidae.
19) Shell limpet-like, generally ovcr 15 mril longtlhen
open furrow around the head anti foot contains no seconti.ary
or organs of any kind. I hypo lar ezvity or sip!ron. I D
'.ancidae.
2122) Posterior end of foot either reunCed or acutely ., -olnted. IOD
red or without evident color. Cifqes of mantle smoon, not
serrate. OpEning between hypopeplar and Fu/monary cavities
modified into a secondary gill Clseudoloranch); the animal
usually does not take air into the pulmonary cavity. Shell
discoidal, low-spired, or limpet-like; rarely 1; gn
Superfamily PLANORBACEA ...... 23
22(2)) Posterior end of foot acutely pointed. Blood without evlJeni:
color. Edges of man le usually serrate, sometimes smooth, the
mantle covering part of the heIl on the right side. € eri T Ç
bctwccn hyr,pepia,. and ;:ul:zonery cavities modified into Q
siphon with which the snail takes air into its 7,:Amr.-nccy
Shell high-spqred, p:;caring sinistral. Euper7(7mily
Physidae. 8
23(24) Posterio,' end of foot rounded. Blood without evident colo'.
Pseudobranch on left side of body does not protrude beyond
shell; it is a triangular flap with transverse lamellae. Shell
limpet-ilke, generally less than 5 mm long. Family Ancylidae.
24(23) Posterior end of foot either rounded or acutely pointed. Blood
red or without evident color. Tip end of pseudobranch protruding
from the shell on the left side is T-shaped In cross-section.
Shell discoidal or with a spl-e, appearing either dextral
sinistral, 2-30 mm in diameter in adults. Family Planorbidae.