Description of a New Softshell Turtle

From the Southeastern United States

Amyda mutica (in part), Stejneger, Bull. Mus. Comp. Zool.,
94(1):23-24, 1944.

Amyda muticus (in part), Cook, Jour. Mississippi Acad. Sci.,
1941-1947, p. 185, 1946.

Trionyx muticus Anderson, Copeia, 3:211, August 28, 1958.

Holotype.—UI 31071, hatchling, sex undetermined, from the Pearl River,
Roses Bluff, 14 miles northeast Jackson, Rankin County, Mississippi; obtained
by William F. Childers on August 25, 1952 (Plate 1).

Paratypes.—A total of 20 alcoholic specimens: TU 17301, hatchling male
(Plate 2). TU 17302-.1, 16682, three hatchling females, and TU 13473,[Pg 520]
adult female, from the Escambia River, 2 miles east and 1 mile north of
Century, Escambia County, Florida; TU 17306, adult female, from the Pearl
River, 9 miles south of Monticello, Lawrence County, Mississippi; USNM
7655, hatchling, sex undetermined, and KU 47117-19, three adult males, from
the Pearl River, 1 mile south to 4 miles north of Monticello, Lawrence County,
Mississippi; TU 17303-.4, 17304-.3, five hatchling males and four hatchling
females, from the Pearl River, Varnado, Washington Parish, Louisiana; TU
17305, immature female, no data.

Diagnosis and definition.—A subspecies of softshell turtle most closely allied
to Trionyx muticus muticus but differing from that subspecies in having:
(1) a juvenal pattern of large, circular spots, (2) no stripes on dorsal surface
of snout, and (3) postocular stripe with thick, black borders immediately behind
eye in adult males. T. m. calvatus resembles T. m. muticus, and differs
from the several subspecies of Trionyx spinifer in having: (1) no enlarged
tubercles on anterior edge of carapace, (2) no ridge projecting from nasal
septum, and (3) a smooth dorsal surface on carapace in adult males.
T. m. calvatus and T. m. muticus resemble T. ferox in having a smooth dorsal
surface on carapace in adult males, but differ from T. ferox in having: (1) no
tubercles along anterior edge of carapace, and (2) no ridge projecting from
nasal septum.

Description of holotype.—Carapace circular, widest at region of bridge;
margin entire; dorsal surface smooth; anterior margin of carapace lacking
tubercles; blunt vertebral ridge evident anteriorly; maximum length, 53.1 mm;
greatest width, 46.3 mm; greatest depth, 11.5 mm.

Plastron small, extending slightly farther forward than carapace; anterior
lobe truncate with slight midventral indentation; posterior lobe rounded,
sides forming acute angle; certain features of bony elements of plastron visible
through overlying skin; width of bony bridge, 4.5 mm; maximum length of
plastron, 37.5 mm.

Head extended to level of eyes; head terminating in long, rounded, flexible
snout; nostrils rounded with no ridges projecting from nasal septum; jaws
closed, each covered by fleshy lips except anteriorly where horny portions of
jaws are exposed; iris with dark stripe through pupil.

Forefeet and hind feet well-webbed and with five digits each; each limb
with nails on first three digits; dorsal surface of each forelimb with four
cornified areas, three of which have a free edge; each hind limb with two
cornified areas, one smooth on posterodorsal surface and other with free edge
on posteroventral surface.

Tail terminating in flexible point and not extending beyond posterior edge
of carapace; anus to tip of tail, 2.6 mm; anus to posterior edge of carapace,
8.1 mm.

In preservative: Ground color of carapace dark tan having pattern of 49
brownish spots; 47 spots circular; two spots noticeably elongate, one representing
fusion of two circular spots; 17 spots on carapace not exceeding
2.0 mm in diameter, whereas 32 spots range from 2.5 to 4.0 mm in diameter;
periphery of carapace pale except anteriorly; maximum width of pale margin
(posteriorly), 3.3 mm; junction of pale margin and dorsal ground color formed
by rough-edged line composed of small, closely-set dots; pattern of fine
punctations and other marks on dorsal surface of forelimbs and hind limbs.

Ground color of underparts whitish, lacking markings; top of head and snout
gray, lacking markings; lower eyelids with small dark dots.

Description of paratypes.—Adult females (2 specimens). No striping on
dorsal surface of snout; pale postocular stripe not distinct, dark borders
obscure (head not extended in TU 13473); carapace circular, pale brown with
mottled pattern; carapace lacking pattern of large spots; dark marks present
in pale margin of carapace; dorsal surface of soft parts of body finely stippled,
larger marks on hind limbs and on anterior surface of forelimbs near their insertions;
plastron and ventral surface of soft parts of body without markings.
Maximal measurements, respectively, are: length of plastron, 172 and 180 mm;
length of carapace, 238 and 263 mm; width of carapace, 203 and 218 mm;
width of head, 28 and? mm.

Immature female (1 specimen). Carapace circular having juvenal pattern
of large spots, some of which have borders darker than their centers and are
best described as ocelli; junction of pale margin and ground color of carapace
formed by ill-defined, ragged dark border; dorsal surface of forelimbs and
hind limbs finely streaked and dotted, larger marks occurring toward insertions
of forelimbs; lower border of pale postocular stripe in contact with
upper margin of postlabial pale stripe; no stripes on dorsal surface of snout;
fine markings on dorsal surface of neck. Maximal measurements are: length of
plastron, 56 mm; length of carapace, 82 mm; width of carapace, 77 mm;
depth of shell, 13 mm; width of head, 12 mm.

Adult males (3 specimens). No striping on dorsal surface of snout; pale
postocular stripe with thick, black borders immediately behind eye; width of
black borders equal to approximately one-half width of pale postocular stripe;
dorsal surface of soft parts of body with indistinct markings that are larger
on hind limbs; plastron and ventral surface of soft parts of body without
markings; small dark spots posteriorly along ventral edge of carapace; pale
margin of carapace lacking markings or having few small black spots; carapace
circular with or without pattern of large spots. Maximal measurements of
smallest and largest specimens, respectively, are: length of plastron, 108 and
118 mm; length of carapace, 160 and 177 mm; width of carapace, 142 and
152 mm; width of head, 21 mm.

Hatchlings (14 specimens). These paratypes resemble the holotype in
all features mentioned; markings on neck tend to form longitudinal streaks in
TU 17303 and 17304. There are no secondary sexual differences in hatchling
turtles.

There is some variation in hatchling turtles. Four from the Escambia River
have dorsal spots 3 mm or larger in greatest diameter and on three specimens
the dorsal spots number 27, 37 and 37 (total number not discernable in
TU 16682); none of the dorsal spots is ocellate. Maximal measurements of
these three hatchlings, respectively, are: length of plastron, 35, 36 and 37 mm;
length of carapace, 50, 50 and 52 mm; width of carapace, 44, 45 and 47 mm;
depth of shell, 11 mm; width of head, 9 mm. Nine hatchlings from the Pearl
River at Varnado have more (all small) dorsal spots, which may be ocellate.
The dorsal spots and ocelli do not exceed 2 mm in their greatest diameter
except that some of those of TU 17304 are 3 mm; the spots range in number
from 38 (TU 17303) to 63 (TU 17304). Maximal measurements of the
smallest and largest specimens, holotype excepted, are: length of plastron, 30[Pg 522]
and 33 mm; length of carapace, 42 and 46 mm; width of carapace, 37 and 43
mm; depth of shell, 9 and 10 mm; width of head, 9 and 10 mm. The holotype
resembles hatchlings from the Escambia River in having large, non-ocellate
dorsal spots 3 mm in greatest diameter, and larger measurements.

One other specimen (not designated as a paratype), consisting of a head
with a few attached cervical vertebrae, was obtained on a sand bank of the
Escambia River, Florida. The postocular stripe, bright yellow with black
borders, was especially vivid in this adult male (KU 47116).

Range.—Trionyx m. calvatus is known from the Pearl, Pascagoula and
Escambia river drainages and is to be expected in the Tombigbee-Alabama
river drainage (Fig. 1). Tinkle (1958:41, fig. 53, stippled) has indicated
the probable range of calvatus. This subspecies is unknown from the Mississippi
and Tennessee river drainages, which are inhabited by T. m. muticus. The[Pg 523]
western limit of distribution is the Pearl River drainage and probably those
streams of the Florida Parishes of Louisiana that drain into Lake Ponchartrain.
The most easterly record of occurrence for T. m. calvatus is in the Escambia
River drainage; the eastern extent of geographic range is not known.

I have seen three preserved young turtles having the characteristic spotted
pattern from the Pascagoula drainage in eastern Mississippi. These specimens
are uncatalogued and in the collections at Mississippi Southern College,
Hattiesburg, Mississippi.

There is a specimen of T. m. muticus labeled as from Mobile, Alabama
(MCZ 1596), for which I believe the locality datum is incorrect. It is a
young turtle having a well-defined pattern on the carapace and is without
doubt a representative of T. m. muticus. Mobile is in the large drainage basin,
of the Tombigbee, Black Warrior, Coosa and Alabama rivers, which is between
the Escambia and Pearl rivers.

Yarrow (1882:28) reported a specimen of Amyda mutica, USNM 11630,
from Gainesville, Florida. This record was questioned by Cahn (1937:179),
and has been disregarded by subsequent authors. Stejneger (1944:23) lists
this specimen number with uncertainty from Mt. Carmel, Illinois. The exact
geographic provenance of this specimen is seemingly unknown.

Habitat.—I have collected eggs of T. m. calvatus on sand banks of the
Escambia River, Florida. The Escambia River has a sand-gravel bottom,
extensive sandy banks, a moderately-rapid current, and is flanked by a thick
riparian forest. It is approximately 80 feet wide with fallen trees and brush
intermittently emergent along the shoreline. The sand bar-habitat along the
Pearl River has been mentioned by Anderson (1958:212). All records thus
far are from lotic habitats.

Comparisons.—Trionyx m. calvatus is most closely related to Trionyx m.
muticus. Both subspecies have the following characteristics: (1) no enlarged
tubercles on the anterior edge of the carapace, (2) no ridge projecting
from the nasal septum, and (3) a smooth carapace in adult males. These
characters distinguish these two subspecies from the several subspecies of
T. spinifer, and, except for the smooth carapace in adult males, from T. ferox.
Another feature of T. m. calvatus and T. m. muticus, not known to be definitive
or diagnostic but noticed on occasion, is the pale orange cast, in life, of the
dorsal surface of the carapace and soft parts of the body in young of these
turtles.

The spotted pattern of juveniles of calvatus is easily distinguished from
the pattern of muticus (small dots, streaks and dashes) figured by Agassiz
(1857, vol. 2, pt. 3, pl. 6, fig. 6), Smith (1950:154, fig. 104), Conant (1938:192,
pl. 21, fig. 1; 1958, pl. 11, opposite p. 94), and Cahn (1937:177, pl. 24C).

Unfortunately, the distinctive dorsal spotting in young calvatus becomes
obscure or absent in some adults of both sexes. Spotting in large males is
not so well-defined as in juveniles; it may be absent (TU 17306.3), or indicated
by two obscure spots (KU 17117), but is usually evident, at least
posteriorly. The spotted pattern is absent in large females, which have a pale,
mottled and blotched pattern of lichen-like figures; dorsal spots are obscure
in TU 17305 (length of plastron, 56 mm).

Two additional features are, so far as known, universal in calvatus; these
are: (1) the absence of striping on the dorsal surface of the snout, and (2)[Pg 524]
the presence of thick, black borders of the postocular stripe in adult males.
These features have also been observed in some specimens of muticus; their
presence in muticus cannot be properly evaluated at this time, and is seemingly
not due to individual variation. These two characters, however, coupled
with the distinctive juvenile pattern of spots, serve, in combination, to distinguish
calvatus from muticus.

Specimens examined.—All the localities listed below are plotted on the
distribution map (Fig. 1). Only those specimens of T. muticus muticus are
listed that serve to delimit the range of T. m. calvatus. Fortunately, the
identification of the specimens of muticus is certain as all show the characteristic
juvenile pattern, except the large female, TU 7543, from southeastern
Louisiana. USNM 95133-34 (carapaces and plastrons only) and TU 17236
are females, which lack the diagnostic spotted pattern of calvatus; the former
are referred to this subspecies on geographic grounds (Pearl River at Columbia,
Mississippi). TU 17236, from the Amite River, is dubiously relegated to
calvatus on the supposition that this river and others in the Lake Ponchartrain
drainage will yield the characteristic juveniles.

Trionyx m. calvatus (33 specimens): TU 13473, 16682, 17301, 17302-.1,
KU 47116 (skull only), Escambia River, 2 miles east, 1 mile north Century,
Escambia Co., Florida; TU 17303-.4, 17304-.3, Pearl River, Varnado, Washington
Par., Louisiana; TU 17306-.3, Pearl River, 9 miles south Monticello,
Lawrence Co., Mississippi; TU 16956, KU 47117-19, USNM 7655, Pearl
River, vicinity of Monticello, Lawrence Co., Mississippi; TU 17236?, Amite
River, near Baton Rouge, Louisiana; TU 13795, Bogue Chitto River, Enon,
Washington Par., Louisiana; TU 17305, no data, Louisiana; USNM 95133-34,
Pearl River, Columbia, Marion Co., Mississippi; UI 31071, Pearl River, 14
miles northeast Jackson, Rankin Co., Mississippi; Uncatalogued, see page
523, Leaf River, 3 miles southeast New Augusta, Perry Co., Mississippi.

Trionyx m. muticus (6 specimens): TU 5989, Ouachita River, Monroe,
Ouachita Par., Louisiana; TU 7543, Vacherie, St. James Par., Louisiana;
CNHM 7845, Gayles, Caddo Par., Louisiana; USNM 92605, Greenville, Washington
Co., Mississippi; USNM 113228, Jonesville, Catahoula Par., Louisiana;
USNM 118167, Wheeler Reservoir, Tennessee River, Alabama.

Records in the Literature.—USNM 113228, referred to above as Trionyx m.
muticus is listed by Stejneger (1944:56) as Amyda s. spinifera; four of the
specimens listed above (USNM 7655, 92605, 95133-34) are recorded by
Stejneger (op. cit.:23-34) as Amyda mutica. Cook (1946:185) records seven
specimens of the muticus group from Mississippi as follows: 1, no data;
1, Vicksburg, Warren Co.; 3, Forrest Co.; 1, Crawford Bridge, Jones Co.;
1, Lake Park, Columbus, Lowndes Co. I have not seen these specimens;[Pg 525]
they are plotted on the distribution map—the one from Vicksburg as muticus
and the others as calvatus on geographic grounds. The hatchlings of
Trionyx muticus referred to by Anderson (loc. cit.) include the nine paratypes
from Varnado, Louisiana.