Marstonia comalensis
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''Marstonia comalensis'' is a species of minute freshwater snail with a
gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
and an operculum, an aquatic gastropod
mollusk Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is e ...
or micromollusk in the family
Hydrobiidae Hydrobiidae, commonly known as mud snails, is a large cosmopolitan family of very small freshwater and brackish water snails with an operculum; they are in the order Littorinimorpha. Distribution Hydrobiidae are found in much of the world, ...
. It is found in south central
Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
, United States. ''Marstonia comalensis'' is large for this genus. It has an ovate-conic, openly umbilicate
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...
. The penis has a short filament and oblique, squarish lobe bearing a narrow gland along its distal edge. It is well differentiated morphologically from other congeners that have similar shells and penes, and is also genetically divergent relative to those congeners that have been sequenced ( mt COI divergence 3.0–8.5%). This species has often been confused with ''
Cincinnatia integra ''Cincinnatia'' is a genus of very small freshwater snails that have an Operculum (gastropod), operculum, aquatic animal, aquatic gastropod molluscs in the family Hydrobiidae, the mud snails. Species The genus ''Cincinnatia'' is currently Monoty ...
''.


Taxonomy

In 1906, Henry Augustus Pilsbry and James Ferriss described this species under the name ''Amnicola comalensis'' based on six shells from Comal Creek and the Guadalupe River near
New Braunfels New Braunfels ( ) is a city in Comal and Guadalupe counties in the U.S. state of Texas known for its German Texan heritage. It is the seat of Comal County. The city covers and had a population of 90,403 as of the 2020 Census. A suburb just north ...
, south-central
Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
. Pilsbry and Ferriss differentiated this species from '' Amnicola limosa'' (Say) and two nomina (''Amnicola cincinnatiensis'' nthony ''Amnicola peracuta'' Pilsbry & Walker) that are currently recognized as synonyms of ''
Cincinnatia integra ''Cincinnatia'' is a genus of very small freshwater snails that have an Operculum (gastropod), operculum, aquatic animal, aquatic gastropod molluscs in the family Hydrobiidae, the mud snails. Species The genus ''Cincinnatia'' is currently Monoty ...
'' (Say) by its much smaller size and noted that it further differed from the latter by its less shouldered
whorls A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...
. The genus ''
Amnicola ''Amnicola'' is a genus of very small freshwater snails which have an operculum. ''Amnicola'' species are aquatic prosobranch gastropod mollusks in the family Amnicolidae according to the taxonomy of the Gastropoda (Bouchet & Rocroi, 2005). ...
'' was used at that time as "a catch-all for most American amnicoloid species that could not conveniently be placed elsewhere on the basis of their shells". ''Amnicola comalensis'' was not further treated taxonomically until Taylor (1975) transferred it to '' Cincinnatia'' without comment in a bibliographic compilation; this allocation was widely followed in the subsequent literature. During the course of a revisionary study of ''Cincinnatia integra'', Hershler and Thompson (1996) examined several alcohol preserved collections of a snail that they identified as ''Amnicola comalensis'' and noted that it closely resembled species of '' Marstonia'' (which were then placed in ''
Pyrgulopsis ''Pyrgulopsis'' is a genus of freshwater snails with a gill and an operculum, aquatic gastropod mollusks in the family Hydrobiidae. Etymology The name ''Pyrgulopsis'' is composed from '' Pyrgula'', another genus of snail, and '' opsis'' = ...
''); ''Amnicola comalensis'' was subsequently transferred to ''Marstonia'' based on this unpublished work. Hershler et al. (2003) published a molecular
phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...
analysis of the North American nymphophilines that included a specimen of ''Marstonia comalensis'' from Old Faithful Spring in
Real County, Texas Real County is a county located on the Edwards Plateau in the U.S. state of Texas. As of the 2020 census, its population was 2,758. The county seat is Leakey. The county is named for Julius Real (1860–1944), a former member of the Texas ...
(ca. 180 km from the type locality), which was depicted as nested within the ''Marstonia'' clade. This was the only published record for ''Marstonia comalensis'' subsequent to its original description. Hershler & Liu (2011) redescribed ''Marstonia comalensis'' based on study of a large series of dry shell and alcohol-preserved material, most of which was collected by malacologists J. J. Landye and D. W. Taylor from 1971–1993, and provided anatomical evidence supporting its current generic allocation.


Distribution

The type locality is Comal Creek, near
New Braunfels New Braunfels ( ) is a city in Comal and Guadalupe counties in the U.S. state of Texas known for its German Texan heritage. It is the seat of Comal County. The city covers and had a population of 90,403 as of the 2020 Census. A suburb just north ...
, Comal County, Texas. The original collections of ''Marstonia comalensis'' are worn shells having the appearance of drift material. It is possible that ''Marstonia comalensis'' became extinct at Comal Springs when this water body temporarily dried in 1964; it is also possible that the shells of this species which have been found at this site were washed downflow from extant populations in the headwaters of the Guadalupe River. Records published by Hershler & Liu (2011) considerably expanded the geographic range of ''Marstinia comalensis'', which lives in springs and fluvial habitats spread among four river basins in south-central Texas. Almost all of these localities are on the
Edwards Plateau The Edwards Plateau is a geographic region at the crossroads of Central Texas, Central, South Texas, South, and West Texas. It is bounded by the Balcones Fault to the south and east, the Llano Uplift and the Llano Estacado to the north, and the ...
. Records indicate that ''Marstonia comalensis'' was historically distributed in the upper portions of the Brazos River, Colorado River (Texas),
Guadalupe River (Texas) The Guadalupe River (), () runs from Kerr County, Texas, to San Antonio Bay on the Gulf of Mexico, with an average temperature of . It is a popular destination for rafting, fly fishing, and canoeing. Larger cities along it include Kerrville, Ne ...
and
Nueces River The Nueces River is a river in the U.S. state of Texas, about long. It drains a region in central and southern Texas southeastward into the Gulf of Mexico. It is the southernmost major river in Texas northeast of the Rio Grande. ''Nueces'' ...
basins, south-central
Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...
. The species has been live collected at only 12 localities and only two of these have been re-visited since 1993. Hershler & Liu (2011) were unable to confirm a previous report by Cable & Isserhoff (1969)Cable R. M. & Isserhoff H. (1969). "A protandrous haploporid cercaria, probably the larva of ''Saccocoelioides sogandaresi'' Lumsden, 1963". '' Proceedings of the Helminthological Society of Washington'' 36: 131-135. of this species from a drainage canal near Galveston Bay. Hershler & Liu (2011) also analyzed previously published molecular data to evaluate the genetic divergence and phylogenetic relationships of ''Marstonia comalensis'', whose geographic range is broadly disjunct relative to other members of the genus.


Shell description

The
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses ** Thin-shell structure Science Biology * Seashell, a hard o ...
is ovate-conic with 4.5–5.5
whorls A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...
. The height of the shell is about 2.6–4.6 mm. Protoconch is near planispiral, slightly tilted, initial 0.75–1.0 whorl strongly wrinkled.
Teleoconch The gastropod shell is part of the body of a gastropod or snail, a kind of mollusc. The shell is an exoskeleton, which protects from predators, mechanical damage, and dehydration, but also serves for muscle attachment and calcium storage. Some ...
whorls are weakly convex, often narrowly shouldered, rarely having subsutural angulation. The
sculpture Sculpture is the branch of the visual arts that operates in three dimensions. Sculpture is the three-dimensional art work which is physically presented in the dimensions of height, width and depth. It is one of the plastic arts. Durable ...
of strong collabral growth lines, later whorls having numerous weak spiral striae. The
aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An ...
is pyriform or ovate. Inner lip complete across parietal wall in larger specimens, usually narrowly adnate, rarely slightly disjunct; usually thin, sometimes slightly thickened apically; columellar shelf absent or very narrow; outer lip thin or slightly thickened, orthocline or prosocline. Umbilicus is open but small. The operculum is thin,
amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In ...
, narrowly ovate, multispiral with eccentric nucleus. The last 0.25 whorl is sometimes frilled on outer side; inner side having well developed rim near outer edge. The attachment scar border is sometimes weakly thickened near the nucleus.


Anatomy

The cephalic
tentacles In zoology, a tentacle is a flexible, mobile, and elongated organ present in some species of animals, most of them invertebrates. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work mainl ...
are pale, except for black eyespots. Snout is brown, distal lips are pale and foot is pale. Pallial roof has black pigment bands along edges of ctenidium and dorsal edge of genital duct; visceral coil pale except for black pigment on testis. Ctenidium is positioned a little in front of pericardium. There are 24-25 ctenidial filaments, that are broadly triangular with lateral surfaces ridged.
Osphradium The osphradium is a pigmented chemosensory epithelium patch in the mantle cavity present in six of the eight extant classes of molluscs (it is absent in the scaphopoda and monoplacophora; among cephalopoda, only the nautilus has what appears to be ...
is narrow, positioned slightly posterior to middle of ctenidium. Radula has about 36 well-formed rows of teeth. Central teeth are about 38 μm wide with convex cutting edge. There are 3-8 lateral cusps. Central cusp are pointed or hoe-shaped, parallel-sided proximally or tapering throughout. There are 1-3 small basal cusps. Basal tongue is U- or V-shaped, about as long as lateral margins. Lateral tooth face is rectangular. Central cusp is pointed or hoe-shaped. There are 2-5 lateral cusps (inner) and 3-7 (outer). Outer wing is broad, flexed, with about 140% length of cutting edge. Basal tongue weakly is developed. Inner and outer marginal teeth both have 14-21 cusps and basally positioned rectangular wing.
Hypobranchial gland The hypobranchial gland is a glandular structure which is part of the anatomy of many mollusks, including several different families of gastropods, and also many protobranch bivalves. This gland produces mucus as well as biologically active compo ...
is large, overlapping rectum and part of genital duct, thickened alongside kidney. Style sac is longer than remaining portion of stomach, posterior stomach have small caecal appendix.
Reproductive system The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are als ...
: Testis is large (1.75 whorls), composed of compound lobes, broadly overlapping stomach anteriorly. Seminal vesicle is opening near anterior edge of testis, composed of a few thickened coils, positioned along ventral side of anterior 33% of testis. Prostate gland is small, pea-shaped, with about 50% of length in pallial roof. Anterior vas deferens opening from antero-ventral edge of prostate gland, section of duct on columellar muscle straight. Penis is large, base rectangular, inner edge without folds. Penial filament is short, narrow, tapering, oblique. Lobe is rather medium-sized, squarish, oblique. Terminal gland is narrow, usually transversely positioned along outer edge of lobe, less frequently horizontal, sometimes borne on short stalk. Penial duct is narrow, near outer edge, almost straight. Penial filament has black internal pigment core along most of length. Ovary is small (0.75 whorl), composed of simple, stalked lobes. It is slightly overlapping stomach anteriorly. Female glandular oviduct and associated structures are as follows: Coiled oviduct is narrow, vertical. Bursa copulatrix is small, ovate, horizontal, about 50% overlapped by albumen gland. Bursal duct is longer than bursa, narrow, opening from distal edge, partly embedded in albumen gland proximally, entirely embedded distally, junction with common duct well in front of posterior wall of pallial cavity. Seminal receptacle is small, pouch-like, positioned near ventral edge of albumen gland slightly anterior to bursa copulatrix. Albumen gland is largely visceral. Capsule gland composed of two distinct tissue sections. Genital aperture a terminal slit.


Similar species

''Marstonia comalensis'' has a closely similar shell and penis to some of its congeners, but can be differentiated from them in these ways: It can be distinguished from '' Marstonia gaddisorum'' by its less convex shell whorls, distinctive pallial roof pigmentation, larger number of cusps on the inner side of the lateral teeth and on the outer marginal teeth, larger penial lobe, narrower terminal gland, and smaller overlap of the bursa copulatrix by the albumen gland. If differs from '' Marstonia lustrica'' by its smaller prostate gland, smaller penial lobe, narrower penial filament, straight anterior vas deferens, partly imbedded (in albumen gland) bursal duct, and larger seminal receptacle. It differs from '' Marstonia ogmorhaphe'' by its smaller size, broader shell, smaller prostate gland, straight anterior vas deferens, and smaller bursa copulatrix.


Habitat

''Marstonia comalensis'' lives in cold water springs near their sources, and slack water riverine habitats. It has been most commonly found on mud, aquatic vegetation and dead leaves.


Conservation

This species was included in a recent federal listing petition (2007) based on its
critically imperiled The NatureServe conservation status system, maintained and presented by NatureServe in cooperation with the Natural Heritage Network, was developed in the United States in the 1980s by The Nature Conservancy (TNC) as a means for ranking or categ ...
(G1)
NatureServe NatureServe, Inc. is a non-profit organization based in Arlington County, Virginia, US, that provides proprietary wildlife conservation-related data, tools, and services to private and government clients, partner organizations, and the public. Nat ...
(2009) ranking, but found not to warrant listing owing to insufficient information. The data by Hershler & Liu (2011) suggest that the conservation status of this snail needs to be re-assessed.


References

This article incorporates CC-BY-3.0 text from the referenceHershler R. & Liu H.-P. (2011). "Redescription of ''Marstonia comalensis'' (Pilsbry & Ferriss, 1906), a poorly known and possibly threatened freshwater gastropod from the Edwards Plateau region (Texas)". ''
ZooKeys ''ZooKeys'' is a peer-reviewed open access scientific journal covering zoological taxonomy, phylogeny, and biogeography. It was established in 2008 and the editor-in-chief is Terry Erwin (Smithsonian Institution). It is published by Pensoft P ...
'' 77: 1-16. .


External links

* {{DEFAULTSORT:Marstonia comalensis Hydrobiidae