A NEW TYPE OF THE NAYAD-GENUS FUSCONAIA. GROUP OF F. BARNESIANA LEA.
Reading edition
BY A. E. ORTMANN.
During the study of the nayad-fauna of the upper Tennessee, the present writer found that there exists, in this region, a peculiar type of shells, belonging to the genus Fusconaia, the various forms of which have been described previously under a great number of specific names, which, however, seem to belong all to one species. In addition, among material received from L. S. Frierson from the Ozark Mountains, a form was discovered which presented the same structure.
The oldest name for the upper Tennessee form is Unio barnesianus Lea. A more detailed account of its various phases is to be given elsewhere, and it suffices here to mention only those 59forms which belong here. According to obesity, I distinguish three local, or ecological races:
1. Fusconaia barnesiana (Lea) 1838.
U. barnesianus Lea, ’38. U. meredithi Lea, ’58. U. pudicus Lea, ’60. U. Lyoni Lea, ’65. U. tellicoensis Lea, ’72. U. lenticularis Lea, ’72.
As the normal (most abundant) forms we may regard U. meredithi, pudicus and lenticularis, which differ from each other only in the development of the rays (topotypes examined). U. barnesianus is a slightly more elongated individual, with poorly developed rays. U. tellicoensis (topotypes examined) is a lenticularis slightly more swollen; and U. Lyoni forms the transition toward var. tumescens, having a little more elevated beaks, greater obesity, and rather distinct rays.
2. Fusconaia barnesiana bigbyensis (Lea) 1841.
U. bigbyensis Lea, ’41. U. estabrookianus Lea, ’45. U. fassinans Lea, ’68. Pleurobema fassinans rhomboidea Simpson, ’00.
The most frequent form is fassinans rhomboidea (topotypes examined), with rays poorly developed. U. bigbyensis has more distinct rays; U. estabrookianus (topotypes examined) is an old, overgrown form, without rays; U. fassinans is founded upon an individual (type examined, also topotypes), which is exceptionally elongated, without rays.
3. Fusconaia barnesiana tumescens (Lea) 1845.
U. tumescens Lea, ’45. U. crudus Lea, ’71. U. radiosus Lea, ’71.
U. tumescens is the most typical form, greatly swollen, with more or less developed rays; U. radiosus (type and topotypes examined) is less swollen, but for the rest like tumescens; U. crudus (topotypes examined) lacks rays, and has much eroded beaks, but stands close to radiosus.
The mutual relations of these forms may be understood by the help of the following key. Only the three largest divisions are to be regarded as varieties, in the other forms the characters are merely individual, although specimens representing only 60one (or a few) of these “forms” often prevail at a given locality.
a1. Flat, compressed, dia. of shell less than 40 per cent of the length (var. bigbyensis).
b1. No rays, or rays obscure, color of epidermis brown, dark.
c1. Rhomboid in shape.
d1. Large. Estabrookianus.
d2. Smaller. Fassinans rhomboidea.
c2. More ovate, tapering behind. Fassinans.
b2. Rays distinct, well developed over most of the disk. Ground color of epidermis lighter. Bigbyensis.
a2. Moderately convex, dia. 40‒49 per cent of length. Barnesiana typica.
b1. Beaks not elevated, shape trapezoidal, rhomboid, or subovate.
c1. Dia. about 41 or 42 per cent; size small.
d1. Shape somewhat elongate (trapezoidal); rays obscure. Barnesianus.
d2. Shape shorter (rhomboidal).
e1. Rays obscure. Lenticularis.
e2. Rays present, color of epidermis lighter.
f1. Rays few. Meredithi.
f2. Rays numerous. Pudicus.
c2. Dia. about 45 per cent; larger. Shape subovate. Rays obscure. Tellicoensis.
b2. Beaks more elevated, shape subtriangular. Dia. 46 per cent, with rather distinct rays. Lyoni.
a3. Much swollen, dia. over 50 per cent. Beaks elevated. (var. Tumescens).
b1. Without rays. Dia. 51 per cent. Beaks much eroded. Crudus.
b2. With rays. Dia. about 56 per cent or more.
c1. Dia. about 56 per cent. Radiosus.
c2. Dia. about 64 per cent. Tumescens.
As to the geographical distribution, it should be briefly stated that the swollen forms (a3) inhabit the largest rivers; the compressed forms (a1) are found in the headwaters, and the intermediate 61forms (a2) belong to the streams of moderate size. Intergrades are frequent.
Anatomy.[7]
All these shells have the same, and an extremely characteristic and unique structure of the soft parts, so that there is not the slightest question that they belong together. I have examined the soft parts of some 200 specimens in the field, and over three dozens have been preserved in alcohol, and have been examined at leisure in the laboratory. They include representatives of the three main varieties, and of practically all of the individual variations.
Gravid females have been found on the following dates: May 11, ’13; May 15, ’13; May 16, ’13; May 20, ’13; May 20, ’14; May 22, ’14; May 25, ’14; July 5, ’13; July 9, ’13; July 10, ’13; July 13, ’13; July 14, ’13. Glochidia have been observed on May 20, ’14 (immature), and July 14, ’13. Thus this species evidently is a summer breeder (tachytictic).
The soft parts are those of the genus Fusconaia: the supraanal is separated from the anal by a very short mantle-connection, which is absent (or torn?) in rare cases. Inner lamina of inner gills free from abdominal sac. All four gills are marsupial. Placentae well developed and subcylindrical.
Branchial opening with well developed papillae, anal with distinct, but small papillae. Palpi subfalciform, posterior margins connected at base only.
While thus the Fusconaia structure is typically developed, this species is quite unique in its color. This concerns chiefly the color of the gonads, eggs, and placentae.
The soft parts are often uniformly pale, whitish, but may shade to orange, and the orange is most prominent on foot, adductors, and mantle-margin; but the paler tints prevail, and often the orange is replaced by yellowish or brown. The gills 62are pale, but are generally suffused with blackish. The gonads are brown to red, mostly of a peculiar dull lavender color in the female, and the latter color, or purplish brown, is the prevailing color of the eggs and placentae. The charged gills become thus rather dark purple, or purple-brown, shading sometimes to dull red or blackish, in other cases to brownish, brownish pink, brick-red, or even pale brown. These are very peculiar tints, by which this species is easily recognized in the field: four marsupial gills of this blackish-purple color are not known in any other Nayad.
Glochidia have been found only in specimens belonging to the headwaters variety (barnesiana bigbyensis). They are subelliptical, slightly higher than long, L. 0.15, H. 0.16 mm.
Although a true Fusconaia, this species (or group of forms) stands isolated within the genus, in characters of the shell as well as in the soft parts. It differs from the species of the subrotunda-group (ind. ebena, pilaris etc.) very markedly by its smaller size and by the very shallow beak cavities. The forms of the undulata-group (incl. flava, and the cuneolus- and corforms) have generally also somewhat deeper beak cavities, and the shell has a more or less distinct posterior ridge, with a flattening or a shallow groove in front of it, characters which are missing in the barnesiana-group. As has been pointed out, in the latter group, the color of eggs and placentae is remarkable: in all other forms of Fusconaia, this varies from white to bright red.
I introduce here another species, in order to show that the barnesiana-type is also represented outside of the Cumberland-Tennessee drainage, namely in the Ozarks.
Fusconaia ozarkensis (Call) 1887.
F. ozarkensis Call, Pr. U. S. Mus. 10, ’87, p. 499, pl. 27. Tr. St. Louis Ac. 7, ’95, p. 33, pl. 18. Lampsilis ozarkensis Meek & Clark, Bur. Fisher. Doc. no. 759, ’12, p. 18. Pleurobema utterbacki Frierson, in: Utterback, Naiad. Missouri (Amer. Midland Natural 4, 1916, p. 86, pl. 5, pl. 20, f. 63).
I have specimens from James River, Galena Stone Co., Mo., and White River, Cotter and Norfolk, Baxter Co., Ark., donated 63by L. S. Frierson and collected by A. A. Hinkley on July 30 and Aug. 2 and 5, ’14, A number of specimens (8) were preserved in alcohol, coll. July 30 and Aug 2, which all were gravid females, and one of each date had glochidia. This marks probably the end of the breeding season, and the species is tachytictic.
There is some confusion with regard to this species. After the first description by Call, it has not again been recorded, except by Meek and Clark, and I believe, the identification of these authors (supported by B. Walker) is correct. But I think that other authors have seen this form, but have not recognized it, and, for instance, Simpson’s pannosus and subellipticus (regarded as varieties of Pleurobema argenteum and breve respectively) are also this. Frierson’s utterbacki is surely this, since my specimens were thus labeled by Frierson.
Walker, Frierson, and Simpson (in part) believe this to be a Pleurobema, and not a Lampsilis (see also Simpson, ’00, p. 557, and ’14, p. 131), and this comes nearest to the truth, in fact, it is the most plausible assumption to be made from the study of the shell alone. The shell “resembles a very elongated Quadrula coccinea,” according to Meek and Clark, and the comparison with Pleurobema argenteum and breve (which, by the way, are synonyms), made by Simpson, is significant. We must keep in mind that Call’s fig. 4 represents the normal shape of the shell, while his fig. 1 is rather abnormal, and possibly does not belong here at all. These two figures by no means represent the female and male, as Call believes.
The investigation of the soft parts has shown that this actually is a Fusconaia. Corresponding, both in soft parts and shell, to the barnesiana-type of the upper Tennessee region. F. ozarkensis differs from barnesiana by the more elongated (subtrapezoidal) outline of the shell, more anterior beaks, and the weak development of the rays, which are faint at the best, and often entirely absent. A swollen form of it is not known to me, but specimens from White River are slightly more convex than those from James River (farther up). Also Utterback’s quotation of Frierson (p. 87, footnote) make it probable that there are differences in obesity.
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Anatomy.
Supraanal opening probably separated from the anal by a short mantle-connection, but in all my specimens this is torn by rough handling. Inner lamina of inner gills free from abdominal sac. All four gills marsupial in the female. Placentae well developed and subcylindrical.
Anal opening with small papillae, branchial opening with well developed papillae. Palpi as usual, their posterior margins connected for about one third of their length or less.
As to the color of the soft parts, which is so characteristic in barnesiana, not much can be said, since my material has been too long in alcohol. But in most of my specimens the gills are yet distinctly suffused with black. The placentae have been rendered whitish, but here and there traces of a dark stain are preserved (which is disappearing gradually). It is quite possible that the color of the placentae originally was similar to that of barnesiana.
The glochidia are subelliptical, slightly higher than long; L. O. 15, B. O. 18, thus agreeing with those of F. barnesiana.