Newcomb's snail (Erinna newcombi) is a species of air-breathing freshwater snail, a gastropod mollusk in the family Lymnaeidae. This species is endemic to Hawaii, in the United States, and its natural habitat is rivers. It is threatened by habitat loss.
Erinna newcombi is the type species of the genus Erinna.
Taxonomy The scientific collection efforts of the United States Exploring Expedition of 1838 to 1842 obtained the first known specimens of Newcomb's snails. Historical documents indicate that the specimens were collected sometime between 25 October and 6 November 1840, at "Hanapēpē Falls," presumably what is now called Manuwaiopuna Falls, or possibly one of several other waterfalls located in the middle Hanapēpē watershed of southeast Kauaʻi. Individuals from this early collection made their way to the British Museum of Natural History and were used as the type specimens from which the species was later described in 1855.
As type locality is referred: "Heneta River, Kami, Sandwich Islands", which means Hanalei River, Kauai, Hawaii. English common name and also specific name is in honor of Dr. Wesley Newcomb, that collected them in Hawaii. Erinna newcombi is one of four species of Lymnaeidae snails are native to Hawaii. Three of these species inhabit two or more of the eight main islands. The fourth species, Newcomb's snail, is restricted to the island of Kauaʻi.
A Japanese lymnaeid exhibits a very similar reduced shell shape, but a study of chromosome numbers suggests that Newcomb's snail's evolutionary ties lie with the rest of the Hawaiian lymnaeids, all of which are derived from North American ancestors. Therefore, it appears that parallel evolution of similar shell morphology occurred between these two distinct lineages of lymnaeid snails.
At the present time, no completely accepted nomenclature exists for the genera of Hawaiian lymnaeids, although each of these snail species, including Newcomb's snail, is recognized as a valid species. Bengt Hubendick (1952) did not believe the distinctive shell form (described below) and reduced structures of the nervous system of Newcomb's snail warranted a genus (second species of the genus Erinna is considered extinct). In fact, Hubendick included all Hawaiian lymnaeids in the genus Lymnaea. Joseph Paul Eldred Morrison (1968) contradicted Hubendick and argued the distinctive shell characters of Newcomb's snail supported the generic name Erinna. John B. Burch (1968), Charlotte M. Patterson and Burch (1978), Dwight Willard Taylor (1988), and Robert H. Cowie et al. (1995) all followed Morrison and referred to Newcomb's snail as Erinna newcombi, which is the currently accepted scientific name.
Description
Newcomb's snail is unique among the Hawaiian lymnaeids in that the shell spire, typically associated with lymnaeids, is substantially reduced. The result is a nearly smooth, brown to black shell formed by a single, oval whorl, long and wide.
The shell is semi-globose, thin, horny, olivaceous, longitudinally finely striated. The spire is very short, obtuse. The apex is rather eroded. The last whorl is ventricose. The aperture is large and semi-ovate. The inner-lip is posteriorly ascending on the body whorl. The columella is straight, excavated, and with a curved, elevated, external ridge continued in front into the outer lip which is simple and acute.Adams H. & Adams A. (1858). The genera of recent Mollusca: arranged according to their organization. Volume 2. John Van Voorst, London. p. 644
The jaw is low, wide, slightly arcuate, ends pointed; a decided median projection to the cutting edge. The anterior surface of the jaw is smooth.
The radula is as usual in the Helicidae. The central tooth is long and narrow, small in proportion to the laterals, the reflected portion has one long median cusp, the side cusps being subobsolete. The lateral teeth are wide, broad as long, the reflected portion almost as large as the whole base of attachment, and tricuspid, the inner cusp very small, the median cusp large and bluntly truncated, the outer cusp smaller than the median and bluntly pointed. The marginal teeth are subquadrate, wider than high, the apex reflected, obliquely produced and bearing five or more blunt, short denticles, of which the inner two are the largest.
Distribution
Newcomb's snail is endemic and restricted to the island of Kauaʻi. A number of very large watersheds traverse the southeast quadrant of the Kauaʻi island, including Olokele Stream, Hanapēpē Stream and Waimea River, all of which have numerous tributaries. No recent surveys for Newcomb's snails have been undertaken in the Hanapēpē watershed, or in any of the large neighboring stream systems, because they are located on privately owned lands and are difficult to reach because of the rough terrain. It is possible that Newcomb's snail populations remain in that region of Kauaʻi.
Until about 1925, snails were collected from small sites located in Kalalau Stream, Hanakoa Stream, Hanakāpī`ai Stream, Wainiha River, and Keālia Stream. Three of these populations (Hanakoa Stream, Hanakāpī`ai Stream, Wainiha River) are now thought to be extirpated. Since about 1993, Federal and State agencies, academic researchers, and other interested parties have conducted opportunistic surveys at approximately 50 sites along numerous streams and their associated tributaries and springs on Kaua'i, and have located four previously unknown populations of Newcomb's snail. These recently discovered populations are located in Lumaha`i River, the Hanalei River, Makaleha Stream (a tributary to Kapa`a Stream), and the North Fork Wailua River. With the exception of the snails at Makaleha Springs, most of these populations have only been observed once or twice. Recently, two individual snails were reported from a single site in Limahuli Stream in the Hanalei District of Kauaʻi's north shore. However, if a viable population of Newcomb's snail exists in the Limahuli watershed, its location remains unknown, therefore Limahuli Stream is not considered to have a "population" of Newcomb's snails.
Recent survey work conducted from 1994 to 2003 limits the known range of Newcomb's snail to small sites located in a total of six watersheds in north- and east-facing drainages on Kauaʻi. They are: Kalalau Stream, Lumaha`i River, Hanalei River (four subpopulations), Keālia Stream, Makaleha Stream (two subpopulations), and the North Fork Wailua River. The term "subpopulation" refers to a discreet group of individuals, separated from other discrete groups within a single watershed. Because of low mobility, no interaction between subpopulations exists. No historical information is available on the population sizes of Newcomb's snail. However, anecdotal reports indicate the Kalalau Stream and Lumaha`i River populations of Newcomb's snails are larger in comparison to the other four.
Ecology Newcomb's snail is an obligate freshwater species. The details of its ecology, such as life span, reproductive cycle, and number of eggs/young, are unknown.
Newcomb's snail is active during the day.(2009). Erinna newcombi – Adams and Adams, 1855. NatureServe Explorer. Data last updated 17 July 2009. Retrieved 3 November 2009.
Newcomb's snail probably shares life history similarities with other members of its family. Lymnaeid snails generally feed on algae and vegetation growing on submerged rocks. Snails attach eggs to submerged rocks or vegetation and larval stages do not disperse widely; the entire life cycle is tied to the stream system in which the adults live. Little is known about the biological or environmental factors affecting Newcomb's snail population size, however, important factors may include: annual, multi-year, or decadal changes in stream flows; severe weather, high flow, or channel-scouring events; and periods of prolonged drought. Snail dispersal both upstream and downstream within a stream system probably plays an important function in colonizing or recolonizing suitable habitat, particularly microhabitat protected from channel scour. Dispersal of Newcomb's snail between stream systems is likely infrequent because of their obligate freshwater habitat requirements; historic dispersal probably relied on long-term erosional events that captured adjacent stream systems. This life history differs greatly from the freshwater Hawaiian neritid snails (Neritina granosa, Neritina vespertina) that have marine larvae that migrate into and up streams following a period of oceanic dispersal. Most likely, the planktonic larvae of the neritid snails disperse across the oceanic expanses that separate the main Hawaiian Islands and can colonize streams on any or all of these islands. Newcomb's snail lacks this dispersal capacity.
Habitat On the basis of past and recent field observations, the specific habitat requirements of Newcomb's snail include fast-flowing perennial streams and associated springs, seeps, and vertical or overhanging waterfalls. Surveys of main stream channels of many of the perennial streams of Kaua`i indicate Newcomb's snail is only found in areas protected from high scouring flows within main stream channels. The limited occurrence of this snail in main stream channels is likely due to periodic channel scouring by sediment, rocks, and boulders that are moved downstream during high flow runoff events. Consequently, suitable habitat is generally restricted to protected, small, spring-fed tributaries, or to stream segments with overhanging waterfalls that have perennial flows supported by stable groundwater input. The common element among sites harboring snail populations is that the water source appears to be consistent and permanent, even during severe drought.
Limited to a relatively narrow zone of mid-elevation sites, populations of Newcomb's snail are found at an average elevation of , and range between .
It is suspected that the four species of introduced caddisflies Trichoptera are adversely impacting native aquatic invertebrate populations either through competition for space and resources, or because of its large body size and sheer abundance in Hawaiian streams. For example, a single caddisfly species accounted for 57% of all biota collected in the upper elevation Kauaʻi streams.
Predators
Predation by the non-native rosy glandina snail Euglandina rosea remains a serious threat to the survival of Newcomb's snail. This predatory snail, introduced into Hawai`i in 1955, has established populations throughout the main islands. The rosy glandina feeds on snails and slugs, and field studies document that it readily feeds on native snails found in Hawai`i. Furthermore, the rosy glandina snail exhibits remarkable hunting behaviors leading to capture and predation of submerged prey. Although terrestrial, the rosy glandina will fully immerse itself in water to locate and feed on aquatic molluscs such as Newcomb's snail. The rosy glandina has been observed on the wet, algae-covered rocks of the Makaleha Stream in close proximity to individual Newcomb's snails, and is believed to prey on them. The rosy glandina snail is responsible for the extirpation of many populations and even the extinction of numerous species of native snails throughout the Pacific Islands, and represents a significant threat to the survival of Newcomb's snail.
Predation on the eggs and adults of native Hawaiian lymnaeid snails by two non-native species of sciomyzid flies, marsh fly Sepedomerus macropus and Sepedon aenescens represents a significant threat to the survival of Newcomb's snail. They feed on lymnaeid snails and were introduced into Hawaii in 1958 and 1966, respectively. These predatory flies were intended to act as biological control agents for the non-native lymnaeid snail Galba viridis (=Fossaria viridis), (an intermediate host of the cattle liver fluke Fasciola gigantica). These biological control species may represent a significant threat to Newcomb's snail and other native lymnaeid snails.