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Genus Utterbackia

Family Unionidae



Utterbackia imbecillis is an introduced species, widespread and successful throughout central and southern North America, and now present in the Northeast region. Metro populations are apparently confined to the lower Delaware River watershed in New Jersey. It reportedly uses a wide range of host species, but can reproduce without glochidial parasitism. U. imbecillis is not legally protected by the US or the states of the metro area.

Species Summary

Utterbackia imbecillis (Say, 1829)
paper pondell


size: 100mm
beak: compressed, below line of dorsal margin when viewed laterally, double looped with weak ridges
color patterns: brownish green to brown, occasional green rays; interior white to bluish white, iridescent posteriorly
shape: moderately elongate, sub-rectangular
shell features: thin and fragile, posterior pointed, hingeline straight; posterior ridge moderately angled
teeth: teeth lacking


abundance: widespread and common
status: U.S., NY, NJ, CT: not legally protected; also known as papershell or paper floater
conservation challenges: This species should be sought in other parts of the Delaware River watershed


N.A. distribution: Maryland to Wisconsin, south to Kansas, Oklahoma and Texas, and on the Atlantic slope from New York to northern Florida and Mexico
present metro distribution: NY: not present in metro area; NJ: tributaries of the lower Delaware River; CT: does not occur
other regional localities: NY: Great Lakes region; NJ: lower Delaware River tributaries;


Life History:

habitat: ponds, lakes, and muddy-bottomed pools in rivers and streams Habitat Photo
hosts: has more identified potential hosts than any other unionid, including many tropical aquarium fish and three amphibians; known fish hosts include: Ambloplites rupestris (Rafinesque, 1817) rock bass; Aplocheilus lineatus (Cuvier and Valenciennes, 1835) panehax killifish; Barbus semifasciolatus (Gunther, 1868) golden barb; Betta splendens (Ryan, 1809) Siamese fighting fish; Brachydonia kerri (Smith, 1931) blue danio; Colisa lalia (Hamilton, 1822) flame gourami; Etheostoma lepidum (Baird and Girard, 1853) greenthroat darter; Fundulus diaphanus (Lesueur, 1817) banded killifish; Gambusia affinus (Baird and Girard, 1853) mosquitofish; Haplochromis venustus (Boulenger, 1908) marbled cichlid; Hemmigrammus erythrozonus (Durbin, 1909) glowlight tetra; Lepomis cyanellus (Rafinesque, 1819) green sunfish; Lepomis gibbosus (Linnaeus, 1758) pumpkinseed; Lepomis gulosus (Cuvier, 1829) warmouth; Lepomis macrochirus (Rafinesque, 1819) bluegill; Lepomis marginatus (Holbrook, 1855) dollar sunfish; Lepomis megalotis (Rafinesque, 1820) longear sunfish; Melanotaenia maccullochi (Ogilby, 1915) Australian rainbowfish; Melynnis argenteus (Ahl, 1923) silver dollar; Micropterus salmoides (Lacepede, 1802) largemouth bass; Moenkhausia oligolepis (Gunther, 1864) redeye tetra; Pangio myers (Harry, 1949) black loach; Perca flavescens (Mitchill, 1814) yellow perch; Poecilia reticulata (Peters, 1859) guppy; Pomoxis nigromaculatus (Lesueur, 1829) black crappie; Pseudotropheus zebra (Boulenger, 1899) zebra Malawi cichlid; Rasbora einthovenii (Bleecker, 1851) brilliant rasbora; Semotrilus atromaculatus (Mitchill, 1818) creek chub; Trichogaster trichopterus (Pallas, 1770) lavender gourami; Xphophorus helleri (Heikel, 1848) painted sword
Amphibian Hosts: Ambystoma tigrinum (Green, 1825) tiger salamander; Rana catesbeiana (Shaw, 1802) bullfrog; Rana pipens (Schreber, 1782) northern leopard frog; Xenopus laevis (Daudin, 1852) African clawed frog


U. imbecillis

Left view

left view

Right view

right view

Dorsal view

dorsal view

Profile view

profile view


white to bluish, iridescent posteriorly

Interior view

interior view
no teeth

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