Securicauda hermani, Leonard, William P., Chichester, Lyle, Richart, Casey H. & Young, Tiffany A., 2011

Leonard, William P., Chichester, Lyle, Richart, Casey H. & Young, Tiffany A., 2011, Securicauda hermani and Carinacauda stormi, two new genera and species of slug from the Pacific Northwest of the United States (Gastropoda: Stylommatophora: Arionidae), with notes on Gliabates oregonius Webb 1959, Zootaxa 2746, pp. 43-56 : 46-49

Securicauda hermani new species

Fig. 2 , 3 , 4

Types. The holotype ( CM 104647 ) and one paratype ( CM 104661 ) were collected on 17 October 2009 by W. Leonard and C. Richart on down woody debris in the riparian zone of Hobo Creek at Hobo Cedar Grove, Idaho Panhandle National Forest, Shoshone County. Additional paratypes were collected by W. Leonard and C. Richart in the riparian zone of Mannering Creek, Benewah County, Idaho ( CM 103973 ) and along Merry Creek, Shoshone County, Idaho ( CM 104022 ).

Etymology. The specific epithet is in honor of Steven G. Herman, Ph.D. A professor at The Evergreen State College since 1971, Dr. Herman has influenced hundreds of students and naturalists for decades in the Pacific Northwest.

Distribution. This species is known from three localities at elevations ranging between 1060 and 1300 m asl in Shoshone and Benewah counties, Idaho ( Fig. 1 ).

Description. Size: Very small, mature adults from 8 to 10 mm extended length while in movement.

External features: Head extending a relatively short distance beyond the mantle; surface smooth with several fine, semi-parallel, longitudinal grooves. Mantle elliptical; covered with glandular lumps; with free flap anterior of pneumostome; posterior edge seated in a slight depression in body; 64 to 80% (mean=72%; SD=0.05; n=7) of length of extended body in movement and 62 to 81% (mean=75%; SD=0.07; n=15) of preserved individuals. Pneumostome slightly anterior to middle of right side of mantle. Sides of body smooth with a series of fine, semi-parallel grooves between edge of mantle and pedal groove. Tail 7 to 20% (mean=17%; SD=0.04; n=7) of length of the extended body in movement; with prominent mid-dorsal keel posterior to edge of mantle; with a series of parallel longitudinal ridges and furrows on sides beneath keel; without line of abscission; caudal mucus pore lacking. Sole undivided. Pedal groove present above foot margin. Foot fringe moderately wide.

Coloration: Head tan; tentacles dark-brown or gray. Neck semi-translucent; adults with distinct white patch on right side. Mantle tan or gray with fine pale-blue flecking and dark-brown or gray blotches; usually with relatively broad lateral stripe on each side. Sides below mantle gray or tan. Tail light-brown with light-blue flecking, with or without dark-brown markings coincident with furrows. Sole pale-gray to beige with scattered white flecks. Mucus clear.

Internal features. Shell: Dome-shaped, situated toward rear of mantle; with marginal horny layer and fingernail-shaped, calcareous central portion.

Jaw and radula: Jaw a slender palisade arc composed of about 50 transverse inscribed subdivisions. Radula of typical arionid type with tricuspid middle tooth and bicuspid laterals. Mesocones elongated and blade-like; ectocones much shorter and thorn-like, becoming increasingly shorter and blunter in lateral rows.

Reproductive system: Ovotestis situated just under the posterior margin of the diaphragm and partially buried in the digestive gland; consisting of 15 or more lobules ( Fig. 3 ). Hermaphroditic duct long and thick; leading to fertilization chamber; partially surrounded by very large albumen gland. Spermoviduct a bicolored coil that develops many digitate outgrowths in sexually mature individuals. Vagina a very broad, but shallow structure that leads directly to gonopore. Duct of the small ovoidal spermatheca very short, arising from the vagina near its junction with the spermoviduct. Vas deferens originating from spermoviduct just before spermoviduct-vagina junction; continuing over one face of the vagina and then ascending alongside of the penis to which it is loosely adherent. As the vas deferens approaches the top of penis it joins a very short U-shaped epiphallus that becomes partially buried in and wrapped around penis. Penis thick-walled. Penis retractor muscle especially robust, originating at the diaphragm; its muscle fibers insert in penis apex and continue internally into a large verge. Verge acorn-shaped with nipple-like projection at its free end. This projection serving as the opening for a duct that appears to connect with the buried portion of the epiphallus. Projection supported by very short rods that surround the duct opening. Fig. 4 shows the nipple-like tip and a portion of duct. Penis leading directly to the gonopore.

Buccal and tentacular retractor muscles: Paired buccal retractor muscles joining close to rear margin of buccal mass. The resulting broad retractor originates at rear middle of diaphragm very close to the ovotestis and a loop of the intestine. Optical tentacle retractors originating at lateral margins of diaphragm. Right-hand retractor passing between vagina and penis.

Digestive system: Esophagus leading to the very long, thin-walled crop that extends nearly to the rear limit of body cavity. Crop connecting to short stomach that turns toward left side where it gives rise to the short intestine that curves up and back to right side and toward the pneumostome. Paired ducts at crop-stomach junction lead to a pair of digestive glands.

Natural history. This species’ range apparently is limited to areas of high winter snowfall in the Western Hemlock Zone of northern Idaho. Western Redcedar ( Thuja plicata ) is a dominant tree species at the three known collection sites. All specimens were collected either on the underside of woody debris, especially long slender stems of Western Redcedar, or in moss. During the early spring this species has been found in upland forest up to 30 m from streams; however once the habitat conditions dried, detections were limited exclusively to mossy seeps, wetlands and stream margins. On several occasions we have found slugs on small woody debris that prior to its removal by us had been embedded up to several centimeters in the needle-duff layer. It appears that this species’ diminutive size enables it to move through spaces in the needle-litter layer, which is likely important in helping to modulate ambient temperature and moisture. Research is needed on the natural history and distribution of this species.

Comparative anatomy. We place Securicauda hermani in the Arionidae on the basis of its ribbed jaw, which is the only characteristic its shares with all other arionids. It differs from Carinacauda stormi in that it lacks an atrium and paired atrial accessory structures and has a very short epiphallus, partially buried in the penis. It differs from Kootenaia and Prophysaon by virtue of its keeled tail and from all other genera in Table 1 by its divergent buccal and tentacular retractors.

Additional comments. We suggest the common name Rocky Mountain Axetail in recognition of the geographic area from which the species is known and to reflect the hypothesized close relationship between Securicauda and Carinacauda . The name axetail was first applied to C. stormi by John Applegarth of Eugene, Oregon due to the presence of a sharp mid-dorsal keel that, when the slug is contracted, protrudes upward suggesting the head of an axe.

Figures

FIGURE 1. Relief map of the Pacific Northwest United States showing the localities of Securicauda hermani n. sp. (●) and Carinacauda stormi n. sp. (․); the open symbols containing an " X " represent the type localities. Solid pyramid (˔) = type locality for Gliabates oregonius.

FIGURE 2. Photographs of paratypes of Securicauda hermani n. sp. A. Mannering Creek, Benwah County, Idaho; 10 mm extended length in movement (CM 103973). B. Hobo Cedar Grove, Idaho Panhandle National Forest, Shoshone County, Idaho; 10 mm extended length in movement (CM 104661).

FIGURE 3. Photographs of the genitalia of three specimens (C and D are different views of the same individual) of Securicauda hermani n. sp. from Hobo Cedar Grove, Shoshone County, Idaho (CM 104661). AG = albumen gland; BW = body wall; E = epiphallus; FC = fertilization chamber; HD = hermaphroditic duct; OT = ovotestis; P = penis; PR = penial retractor muscle; SO = spermoviduct; SP = spermatheca; SPD = spermatheca duct; TR = tentacular retractor muscle; V = vagina; VD = vas deferens.

FIGURE 4. The penis of Securicauda hermani n. sp. from Hobo Cedar Grove, Shoshone County, Idaho stained and mounted on a slide (CM 104661). E = epiphallus; N = nipple-like tip of verge; P = penis; PR = penial retractor muscle; SP = spermatheca; V = verge.