TN00182 SPINY RIVER SNAIL IO FLUVIALIS
Physical description: This is a large-sized, gill-breathing, freshwater snail, reaching a maximum length of about 50 mm in Virginia. Specimens are generally thick, solid, and vary in color from tan to dark brown or olive green. Shells are tapered at both ends, high-spired, and gradually taper toward the top of the shell. Six or seven whorls (coils) are prominent on the exterior of the shell along with wrinkling of the epidermal surface. Two phenotypes occur in the upper Tennessee River. Shell sculpute on the smooth form of theis species consists of folds or paallel ridges which are slightly nodulous, without pronounced spines. The sculpture of the spiny form is magnified into pronounced, well-armored spines numbering from one to twelve; specimens average about seven spines. The opening of the shell (aperature ) is elongated, roughly one half of the shell, and has a smooth inner margin which ends in a pointed, rounded canal at the anterior end. Deveklopment of the pronounced canal is typical of this species. The inside margin of the shell opening is whitish, changing interiorly from a dull reddish-brown to reddish-purple with brown bands varying in number from one to seven. The animals head is of a dark brown color or mottled orange and black, and the mouth is medium purple in color. The foot is flesh-colored and very muscular, with a large cuplike formation resembling a sucker. The inside of the sucker is bright pink, and the foot pad is light purple with a dark brown and well-defined operculum which which tightly seals when the animal retracts itself. Shells of males and females exhibit no known sexual dimorphism *9286*. Reproduction: Female spiny river snails lay their eggs in spring when water temperatures approach 60 degrees F. Eggs are typically laid on smooth rock, shell, or other solid surfaces and often on the inside of fresh-dead mussel shells. Females typically lay eggs in an uneven line, resembling a ribbon or in a spiral shape. Lutz reported that the female actually stamps the egg down on the rock surface. Pink eggs have been observed by the author when first laid, but within minutes, the eggs apparently water harden and turn slate gray in color. Dazo observed females laying eggs in April and May on the glass of laboratory aquaria at a water temperature of 72 degrees F. Females layed 179 to 282 eggs in seperate clusters described as ribbon-like, gelatinous, colorless and devoid of any sand grain covering. Individual eggs were whitish to grayish-white, measured approximately 0.35 mm in diameter, and hatched in 15 days *9286*. Behavior: The food of the spiny river snail consists of the slimy algal coating and entangled organic debris on rocks *9286*. Limiting factors: Impoundment of the Tennessee River system has been the major factor contributing to the decline of this species. Adams also reported hundreds of spiny river snails killed by floods in the South Fork Holston River as a result of deforestation. This species does not occur in small creeks or rivers whose drainage area does not include limestone outcrops *9286*. Population parameters: The greatest concentration of snails occured above Chattanooga, Tennessee, and includes almost all the major tributaries of the upper Tennesse River system *9286*. PHYSICAL DESCRIPTION: SHELL IS FUSIFORM IN OUTLINE WITH AN OLIVE- GREEN TO BROWNISH EPIDERMIS, THERE ARE SIX TO EIGHT WHORLS, BUT TYPICALLY SEVEN, THE SUTURES ARE NOT IMPRESSED, INSIDE OF BODY WHORL IN SOME FORMS IS MARKED BY PURPLISH BANDS, THE INSIDE OF THE APERTURE IS WHITE OR SALMON-COLORED, BODY WHORL IS SCULPTURED BY WRINKLED GROWTH ARREST LINES, APERTURE IS ELLIPTICAL OR PYRIFORM AND ABOUT ONE-HALF THE LENGTH OF THE SHELL, COLUMELLA AND LOWER PORTION OF THE BODY WHORL ARE TWISTED, FORMING A WELL- DEFINED SINUS AT THE BASE, THIS SPECIES COMPLEX VARIES IN SHAPE FROM THE SMOOTH HEADWATERS FORM OF FLUVIALIS TO THE MORE INFLATED AND SPINOSE BIG RIVER FORMS LIKE THOSE OF BREVIS AND TURRITA, THE SPINES VARY FROM UNDULATIONS IN THE MIDDLE OF THE WHORL TO TUBERCLES, SHORT THICK SPINES, TO LARGE SPINES WHICH ARE NOT HIGHER THAN WIDE, THE THICKNESS OF THE SHELL VARIES FROM RELATIVELY THIN IN THE HEADWATER FORMS TO QUITE HEAVY IN THE DOWNSTREAM FORMS *TN5587* REPRODUCTION: EGGLAYING BEHAVIOR OF IO HAS BEEN OBSERVED IN AN AQUARIUM, FEMALE LAID 2-6 CLUTCHES DURING LATE APRIL AND MAY WITH AN AVERAGE OF 4.5 CLUTCHES OR 182 EGGS, NUMBER OF EGGSCLUTCH VARIES FROM 16-100 WITH AN AVERAGE OF 39, EGGS WERE CONTAINED IN A TRANSPARENT GELATINOUS RIBBON WITHOUT A SAND-GRAIN COVERING, THEY WERE ARRANGED IN A DIAGONAL PATTERN WITH ROWS OF 1-5 EGGS, YOUNG BEGAN TO HATCH AFTER 15 DAYS *TN5587*
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9286, TN5587
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