MOLLUSCS, VERMES AND HYDROZOA 



The interior has a chalky white margin and bluish-white nacre, overshot 

 with delicate shades of green. The mature mussel is 2^4 inches long, i ^ 

 inch broad and i inch thick at the umbones. It is not as generally dis- 

 tributed as the foregoing, but may be found in almost all the river systems 

 of the Eastern and Middle States, a Western species being M. truncata. 



General Remarks. What has been stated as to the colors of snail 

 shells also applies to mussels. The presence of metallic oxides in the 

 water affects the color and acidities erode the valves, principally on the 

 umbones, the older portion of the valves; and when this has progressed 

 to the extent of perforating the valves the mussel dies. 



Best Aquarium Mussels. Nearly all the mentioned species will 

 thrive in the aquarium, instances being known of remarkable longevity. 

 Sphaserium, Lampsilis and Margaritana will survive for years; some in the 

 author's household aquaria at this writing having done most effectual duty 

 as scavengers for three and a half years and are still active and of good 

 appearance. The introduction of one mussel into the aquarium for each 

 8 or lo gallons of water is to be recommended, but watch should be kept 

 until they become acclimated, after which an occasional tap on the valves 

 will give assurance that they are alive. They are the best means of eradi- 

 cating the objectionable Tubicolores worms. If they die, the decay is rapid 

 and will cause trouble in the aquarium. 



FRESHWATER VERMES AND HYDROZOA 



Tubicola and Hydra. In addition to the already described low 

 forms of animal life in the aquarium the freshwater Worms and Polyps 

 should be mentioned. The eggs, spores or young are introduced with 

 the water supply, in pond mud and on the aquatic plants. They may 

 increase to such numbers as to become objectionable, as the worms bring 

 the soil and humus to the surface of the pebbles, and by their constant 

 activity cause turbidities in the lower water levels; and the polyps become 

 active enemies to the spawn and young fishes. 



Freshwater Worms. These belong to the order Annelida. The 

 most usual forms are Pristina leidyi and Stylaria lacustris which live in the 

 soil and mud. Lumbriculus limosus, about 2 inches long, and Nais 

 rivulosa, about f^ to ^ inch long, live in the axils and under the leaves of 

 aquatic plants. Of the Tubicolous worms, the objectionable Trimnodrilus 

 is usually the only species present. As of these all but the last named 

 are eaten by the fishes, no further mention is necessary. 



Timnodrilus claparadii. Fig. 192, and T. montanus are not eaten by 

 goldfishes and may increase to such numbers that the whole bottom of the 



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