A new Philomycus mantleslug species from Texas and a key to US Philomycus species.
A new species of Philomycus mantleslug from eastern Texas, USA, is described. Philomycus texanus Taber and Fleenor is distinguished from the remaining eight currently recognized Nearctic Philomycus species by its internal reproductive anatomy and by its external coloration. It is currently known only from the relict Lost Pines loblolly forest, which is a post-ice age refugium for a variety of animal and plant species not expected to occur so far west of the southeastern United States. A key to the nine recognized species of the genus is provided.
Philomycus is a pulmonate slug genus with eight species previously recognized in the United States, where the natural distribution lies entirely in the eastern half of the country as far west as Nebraska, with several of these slugs apparently highly endemic (Branson 1968; Hubricht 1985). They are called "mantleslugs" because the mantle covers the dorsum to such an extent that the mantle was once thought to be absent (Sterki 1908). Confusion and disagreement regarding the taxonomic status of these molluscs is a conspicuous feature of the sparse literature (e.g., Sterki 1908; Hotopp and Smith 1995), and difficulties occur when efforts are made to identify living and preserved material using the standard means of external mantle coloration without reference to internal anatomy. Much progress toward a solution was made by a series of articles that compared the illustrated reproductive systems of all the currently known taxa except Philomycus flexuolaris Rafinesque, for which data without illustrations were supplied (Fairbanks 1986, 1989, 1993, 1998). Here a new species is presented from a relict pine forest in east-central Texas near the western limits of this mostly eastern genus.
Family Philomycidae Keferstein, 1866
Genus Philomycus Rafinesque, 1820
Philomycus texanus Taber and Fleenor new species
Mantle heavily mottled, the complex pattern obscuring a dorsal double row of black dashes or spots and one dorsal brown band suggesting the merging of two adjacent bands, as well as one lateral brownish band on each side also obscured by darker mottling; sole of foot not tripartite, foot fringe gray-brown to brown; fresh mucus clear or white or tinted with orange; penis at least slightly sinuate in outline, penial pouch absent; penis retractor notably thickened at junction with penis and vas deferens; vas deferens often markedly wider in diameter than penis at and near their junction; dart sac large.
External anatomy (Figures 1-4). Mantle ground color off-white to buff, heavily mottled with both light brown and blackish markings, one longitudinal dorsal band and one longitudinal lateral band on each side formed from the light brown coloration but all bands uneven and broken from the lighter ground color and small blackish markings, the dorsal band suggesting two broadly fused bands more so than the lateral bands, two longitudinal dorsal rows of black dashes or spots appearing as nearly paired markings, these rows situated along the left and right edges of the brown dorsal band and extending nearly the entire length of the animal with smaller blackish marks scattered over the mantle, especially laterally, obscuring the brown longitudinal hands. Foot gray-brown to brownish in life, immaculate, with wrinkled, tread-like appearance in preserved material, but some specimens, especially among preserved material, with off-white foot instead. Mucus secreted by crawling slugs clear but whitish in thicker accumulations when handled. Orange-tinted mucus observed in culture dishes. Total length from holotype and 6 paratypes as preserved in 80% ethanol: 57 mm (48, 45, 44, 43, 40, 40). Extended length of crawling specimens can exceed 100 mm.
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Reproductive anatomy (Figures 5-6). Genital atrium usually orange when freshly dissected but sometimes white, penis white with at least slightly sinuate outline, strongly reflexed, usually narrower than vas deferens at and near their junction, penis lacking internal penial pouch, average total penis length = 10.6 mm (n = 7, s.d. = 0.8 mm), average vas deferens length = 39.0 mm (n = 7, s.d. = 6.2 mm), average dart sac width = 3.0 mm (n=6, s.d. = 0.4 mm), average dart sac height = 3.2 mm (n = 6, s.d. = 0.6 mm), average spermathecal duct length =10.1 mm (n = 7, s.d. = 2.0 mm), dart length of large specimen == 3.6 mm, white, tapering apically with a constriction 0.5 mm before apex and a second constriction near apex to form a nippled tip.
Type Material. SVPT = Saginaw Valley Philomycus Texanus. Holotype: SVPT0; collected 31 May 2010 in oak leaf litter near loblolly pine logs at time between 2100 and 2130, on trail east of pond at Stengl Biological Station. Paratypes: SVPT1, collected 29 May 2010 on rotted loblolly pine log between 2100 and 2130, Texas, Bastrop County, Stengl Biological Station; SVPT2, collected 31 May 2010 in water oak log at time of 1500, Texas, Bastrop County, Bastrop State Park, Stewart-Hinkley Tract; SVPT3, collected 15 May 2010 in water oak log, Texas, Bastrop County, Bastrop State Park, Stewart-Hinkley Tract; SVPT4, same data as SVPT1; SVPT5, collected 26 June 2010 on rotted water oak log above Alum creek, west side, between 1550 and 1700, Texas, Bastrop County, Bastrop State Park, Stewart-Hinkley tract; SVPT6, collected 30 May 2010 on rotted loblolly pine log along trail east of pond, between 1700 and 1730, Texas, Bastrop County, Stengl Biological Station.
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Type Locality. Texas, Bastrop County, Stengl Biological Station, N 30[degrees]5'11.7", W 97[degrees]10'23.6", elevation between 142 m and 122 m. Paratype collection localities from water oak logs on the Stewart-Hinkley Tract are N 30[degrees]6'48.0", W 97[degrees]13'25.0" (134 m) and N 30[degrees]6'41.4", W 97[degrees]13'21.5" (127 m;both on west bank above Alum Creek), and N 30[degrees]6'42.7", W 97[degrees]13'24.5" (122 m) and N 30[degrees]6'43.2", W 97[degrees]13'24.7" (121 m; both above a seepage wetland draining to Alum Creek).
Remarks. The new species was discovered in the Lost Pines forest, an aptly-named, island-like ecosystem where the Austroriparian faunal zone of the southeastern United States meets the much smaller Texan faunal zone in the piney woods and palmetto swamps of eastern Texas (Pilsbry 1948; Burch 1962). New insect species were discovered here as well, along with other insects that were previously known no farther west than the Mississippi River (Taber and Fleenor 2003, 2005). Such findings are expected in relict refugia formed after the last ice age ended. In both publications a specimen is pictured of what was identified at the time as Philomycus carolinianus (Bosc). It now appears that the specimens were instead the new species described here.
The dart of P. texanus is very much like that illustrated for P. carolinianus (Tompa 1980). It was photographed immediately after dissection in PVA (polyvinyl alcohol) mounting medium but within two days the specimen had dissolved on the slide and so this is not a suitable substance for preservation. The dart sac of P. texanus may be compared to those illustrated for P. carolinianus and P. flexuolaris Rafinesque (Pilsbry 1948, 752, 759). The dart sac of P. flexuolaris is shown in three separate drawings, the dart sac of P. carolinianus is shown twice, and the former's size is markedly smaller in comparison to the penis than the latter's, which in its greater proportion is more like the dart sac of P. texanus. The smaller dart sac of P. flexuolaris was confirmed in writing by a second authority on the genus (Hubricht 1951), and shortly thereafter the large size of the P. carolinianus dart sac was shown in an additional illustration (Webb 1953). However, an initial inspection of the external mantle pattern and the internal anatomy by a contemporary authority who examined our material suggested P. flexuolaris as a possible but not definite identification with no indication of P. carolinianus as a possible alternative (H. Lee Fairbanks, personal communication).
The penis is at least slightly sinuate in outline rather than simply-tapering and this feature does demonstrate a greater similarity to P. flexuolaris than to P. carolinianus. The paired, or mostly paired, black dots or dashes on the mantle dorsum of P. texanus, however, are expected of P. carolinianus rather than P. flexuolaris (Huhricht 1952), though they are not expected to be so obscured by other colors of the mantle. Especially remarkable is the penis retractor that bears a thickened base unlike those illustrated for P. carolinianus and P. flexuolaris (Pilsbry 1948; Webb 1953; Fairbanks 1986, 1993, 1998), and its width is approximately equal to the combined widths of the penis and vas deferens at the confluence of all three. This feature, which did not vary, is different from all of the published non-sketchy illustrations for P. carolinianus, for which the retractor is about the same width as either of the tubes but not as wide as both tubes combined. The vas deferens of P. texanus is often notably thick compared to the penis in the area of their confluence. All of the living specimens of P. texanus have a brown to gray-brown foot fringe, a condition never published for either P. flexuolaris or P. carolinianus, which are reported to have white or cream-colored foot fringes instead, and the new species is more similar in this trait to Philomycus hisdosus Branson. However, photographs of specimens provided by Megan Paustian and believed to be photos of P. carolinianus with light brownish foot fringes suggest that the reported white or cream color might not always be the condition of that species. Selected external and internal characters for comparison among all nine species are provided in Table 1. The internal anatomy of freshly preserved specimens was found to be similar to that of freshly dead and unpreserved specimens.
TABLE 1. Selected character data compared to Philomycas texanus. +=condition like P. texanus, - = condition unlike P. texanus, +/- = condition between + and-or variable, ? = unknown or not clearly reported. Philamycus species epithets: C = carolinianu V=flexuolaris TQ = togatus, BA = batch, BI = bisdasus, S = sellatus, VE = venustus, VI = virginicus. Character scoring for previously recognized species follows illustrations and text as summarized from the literature (Branson 1968, 1969; Burch 1962; Fairbanks 1986, 1989,1993, 1998; Hotopp and Smith 1995; Hubricht 1951, 1952, 1953, 1972; Orstan 2007; Pilsbry 1948; Stange et al. 1999; Sterki 1908; Tampa 1980; Webb 1953), but scoring for P. texanus is original. Philamycus species Character P. texans C F TO BA BI S VE character states Paired present + - - - - +/- - black spots on dorsum Foot gray-brown +/- - - - +/- ? - fringe color Mucus white (or +/- ? - ? - ? ? color * clear) Penis sinuate or - + + - + - - shape with bulge near middle (not simply tapering) Penis thick at - - - + - ? - retractor junction of width penis and vas deferens Dart sac large + - + + - + - size Character VI Paired - black spots on dorsum Foot ? fringe color Mucus ? color * Penis +/- shape Penis - retractor width Dart sac - size * P. texanus secretes clear mucus when handled which is sometimes whitish when accumulated on the mantle but orange-tinted mucus was noticed in culture dishes.
Etymology. The new mantleslug species is named for the state of Texas in which it was discovered.
KEY TO PHILOMYCUS SPECIES OCCURRING IN THE UNITED STATES
The following key relies mostly upon external characters for speed and convenience but is best used with living material. Internal anatomy should be inspected whenever feasible, as in distinguishing between the two species in the final couplet, and the cited sources should be consulted for comparison.
1. a. mantle brown or with brown oblique bands but lacking black spots or black dashes or any conspicuous black coloration 7
1. b. mantle with conspicuous black markings of paired spots, paired dashes, bands, or more extensive black coloration 2
2. a. dorsum with a series of paired black spots or dashes 3
2. b. dorsum lacking a series of paired black spots or dashes 5
3. a. dorsum with black transverse band just anterior to midpoint P. sellatus Hubricht; Alabama, Tennessee, and presumably Georgia. Illustrations: Hubricht 1972; Fairbanks 1993.
3. b. dorsum lacking black transverse band just anterior to midpoint 4
4. a. dorsal series of paired black spots or dashes conspicuous and not largely obscured by dark mottling surrounding these markings P. carolinianus (Bosc); eastern United States. Illustrations: Burch 1962; Fairbanks 1986, 1998; Stange et al. 1999; Orstan 2007.
4. b. dorsal series of paired black spots or dashes largely obscured by dark mottling surrounding these markings P. texanus Taber and Fleenor; Lost Pines forest of Texas. Illustrations herein.
5. a. foot margin and mucus orange or of similar reddish color P. togatus (Gould); from New England to Alabama and Mississippi and presumably Louisiana. Illustrations: Fairbanks 1986.
5. b. foot margin not of an orange or reddish color 6
6. a.. mantle nearly entirely black P. batchi Branson; Kentucky. Illustrations: Branson 1968; Fairbanks 1998.
6. b. mantle with some blackish markings but also with brownish longitudinal dorsal and lateral bands P. flexuolaris Rafinesque; from New England to Georgia and possibly much more widespread. Illustrations: Pilsbry 1948; Hotopp and Smith 1995.
7. a. mantle brown with no transverse or oblique bands, and foot margin is gray P. bisdostts Branson; Virginia and Kentucky. Illustrations: Branson 1968; Fairbanks 1989.
7. b. mantle with lateral and/or dorsal brown transverse or oblique bands 8
8. a. a series of regular brownish diagonal stripes extends in a row along each side of the mantle and one broad dorsal band is also present and internal structure of penis with circular pustulose ridge at atrial end P. virginicus Hubricht; Tennessee, Virginia, West Virginia, and presumably North Carolina. Illustrations: Hubricht 1953; Fairbanks 1993.
8. b. mantle with a series of oblique brown dorsal stripes that might each be broken into a series of spots and two dorsal bands are present and internal structure of penis lacking circular pustulose ridge at atrial end P. venustus Huhricht; from West Virginia to Tennessee and South Carolina. Illustrations: Hubricht 1953; Fairbanks 1989.
Note: for confirmation of identification, internal anatomy should be inspected using Pilsbry (1948), Branson (1968, 1969), and especially the series of articles by Fairbanks (1986, 1989, 1993, 1998). The related slug genus Megapallifera Hubricht is outwardly similar to Philomycus but lacks the calcareous dart, which can be easily extracted by dissection from the dart sac of all Philomycus species.
We thank H. Lee Fairbanks and Kenneth P. Hotopp for aiding in the identification of mantleslugs, Timothy A. Pearce and Megan Paustian for constructive comments during review, Steven Gibson of the Stengl "Lost Pines" Biological Station for providing GPS and elevation data, David Riskind and Park Superintendent Todd McClanahan for permission to collect in Bastrop State Park, and Dean Deborah Huntley of SVSU for subsidizing the cost of publication.
Branson, B. BRANSON, B.A. 1968. Two new slugs (Pulmonata: Philomycidae: Philomycus) from Kentucky and Virginia. The Nautilus 81 (4): 127-133.
----. 1969. Genital differences in Philomycus virginicus Hubricht and P. bisdosus Branson. The Nautilus 82 (2): 74.
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----. 2005. Invertebrates of Central Texas Wetlands. Lubbock: Texas Tech University Press.
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STEPHEN W. TABER Saginaw Valley State University
SCOTT B. FLEENOR University of Texas at Austin
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|Author:||Taber, Stephen W.; Fleenor, Scott B.|
|Date:||Mar 22, 2011|
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