Kootenaia burkei, Leonard, William P., Chichester, Lyle, Baugh, Jim & Wilke, Thomas, 2003

Leonard, William P., Chichester, Lyle, Baugh, Jim & Wilke, Thomas, 2003, Kootenaia burkei, a new genus and species of slug from northern Idaho, United States (Gastropoda: Pulmonata: Arionidae), Zootaxa 355, pp. 1-16 : 7-12

Kootenaia burkei new species

Figs. 1 , 2

Types: The holotype (Carnegie Museum [CM] 66404), collected on 3 October 2002, and one paratype (CM 66247), collected on 10 April 2003, were taken by J. Baugh and W. Leonard on woody debris and among black cottonwood ( Populus trichocarpa Torrey & Gray, 1852 ) leaves in riparian forest along Little Bumblebee Creek, Panhandle National Forest, Shoshone County, Idaho at an elevation of 700 m above sea level (asl). Additional paratypes were collected by J. Baugh and W. Leonard in riparian forest along Trestle Creek, Kootenai County, Idaho (CM 63987, 66246) and Chatcolet Lake, Benewah County, Idaho (CM 64703).

Etymology: The specific name burkei honors naturalist Thomas E. Burke in recognition of over three decades of study of Pacific Northwest mollusks, and for teaching WL and JB most everything they know about land snails.

Distribution: All known sites are located in either the Lake Pend Oreille or Coeur d’Alene Lake watersheds in the “panhandle” of northern Idaho ( Fig. 1 ). Specimens are known from the following locations in addition to the type locality: 2) Trestle Creek, Panhandle National Forest, Bonner County, Idaho, elevation 700 m asl, 3) Beauty Creek, Idaho Panhandle National Forest, Kootenai County, Idaho, elevation 640 m asl, 4) Heyburn State Park, Chatcolet Lake, Benewah County, Idaho, elevation 650 m asl, and 5) East side of Harrison, Kootenai County, Idaho, elevation 700 m asl (for details see Appendix).

Description

Size: Very small slug, adults from 9 to 14 mm extended length while in movement.

External Features: Head extending relatively short distance beyond mantle. Mantle elliptical, approximately half as long as extended body length; surface with lumps or wrinkles oriented roughly perpendicular to longitudinal axis. Tail rounded dorsally with no trace of mid­dorsal keel; with series of shallow parallel, longitudinal and oblique grooves; without line of abscission; lacking caudal mucus pore. Pneumostome positioned slightly posterior to middle of right side of mantle. Sole undivided, moderately wide. Pedal groove present above foot margin. Foot fringe moderately wide.

Coloration: Mantle pale gray or tan, with pale blue flecking, with dark gray or brown spots, blotches ( Fig. 1 ). Tail light gray or tan with pale blue flecking and series of dark gray or brown, parallel, longitudinal stripes (centered on grooves); on dorsal surface two or more stripes converge approximately 1 mm prior to reaching posterior end of tail, then continue to pedal furrow; along sides stripes run transversely without merging. Sole light gray with whitish flecks. Mucus clear. Occasionally, specimens lack dark gray pigmentation on mantle, tail; other specimens with intense blue flecking covering both mantle, tail.

Internal features

Shell: Calcareous plate with slight anterior apex. Jaw: Ribbed, with as few as five to more than thirteen ribs.

Reproductive System: Ovotestis comprises small number of lobules (as few as five); ovotestis partially embedded in posterior digestive gland ( Fig. 2 ). Hermaphroditic duct long, straight, not convoluted. Albumen gland large, extending to posterior limit of body cavity. Common duct long, occupying much of body cavity in mature individuals. No free epiphallus or vas deferens. Male component of reproductive system reduced to penial loop. Penial retractor muscle originates at anterior edge of diaphragm, inserts at apex of the penial loop. Penial loop consists of slender ascending duct, joining, at apex, a broader descending duct, the penis. On one stained slide mount, penis extended well into atrium. Atrium relatively large, barrel shaped, thin walled except for thickenings at genital pore. Duct of seminal receptacle arises from common duct at same level as penial loop but on opposite side of common duct. Duct of seminal receptacle, seminal receptacle loosely adhere to common duct, can be difficult to see in young animals. Duct and seminal receptacle enlarged, easily seen in fully mature animals.

Buccal and Tentacular Retractor Muscles: Both buccal, tentacular retractors have origins widely separated at posterior margin of diaphragm. No retentor muscle present.

Digestive System: Buccal mass large but otherwise unremarkable. Slender esophagus emerges dorsally, posteriorly to join crop. Crop distinctive: cylindrical shape modified by several circumferential constrictions that partially divide crop lumen into series of tandem compartments. Because constrictions are not quite perpendicular to long axis of crop, effect is to produce a spiral pathway for crop contents moving toward the stomach. Inner lining of crop consists of myriad of small, uniformly sized, spindle­shaped, opaque tissue patches. Patches arranged to reflect the spiral nature of space they help enclose. Pattern of patches changes at posterior end of crop to become longitudinal one just before crop joins stomach. Stomach forms right angle with long axis of crop. Anterior and posterior digestive glands connected to stomach by pair of ducts. Stomach leads to intestine, a somewhat flattened tube of uniform width that makes three bends before arriving at anus in wall of pneumostome. Aside from partially embedded ovotestis and minor adhesions between posterior digestive gland and albumen gland, the digestive and reproductive systems not intimately intertwined. Fig. 2 shows major anatomical features revealed by dissection of holotype.

Natural history

All known sites are forested and adjacent to a perennial water body, which is probably necessary for maintaining high soil moisture and moderating ambient temperature. Vegetation at the sites was composed of western hemlock ( Tsuga heterophylla (Rafinesque, 1832)) forest, with scattered western redcedar ( Thuja plicata Donn, 1824 ), black cottonwood ( Populus trichocarpa Torrey & Gray, 1852 ), paper birch ( Betula papyrifera Marsh, 1785 ), chokecherry ( Prunus virginiana Linnaeus, 1753 ), and/or red alder ( Alnus rubra Bongard, 1832 ). Most specimens were collected on the forest floor, either on or under woody debris, mats of moss, or deciduous tree leaves; two specimens were collected approximately 0.2 m aboveground on a moss­covered tree trunk along the edge of a stream. In the field we have observed specimens resting on and, apparently, eating lichens that were growing on woody debris. Five specimens from Trestle Creek, maintained in captivity between 5 October 2002 and July 2003, ate carrot, lettuce, sweet potato, yam, dry dog food, and goldfish flakes; one of these specimens (9 mm extended length while in movement) laid 3 oval eggs on 17 July 2003. These eggs (ca. 1 x 1.8 mm) were all viable and near to hatching on 8 September 2003 ( Fig. 3 ).

Comparative anatomy

Kootenaia burkei differs from all other known arionids by lacking a free epiphallus or vas deferens; to our knowledge, no other arionid has such a drastically reduced male component of the reproductive system. The only character that it shares with all other arionids is a ribbed jaw. We place K. burkei in the Arionidae based on the presence of the ribbed jaw and the widely separated origins of the buccal and tentacular retractors, a condition found in several arionid genera including Prophysaon . It differs from Prophysaon in lacking a line of abscission and in possessing a penial retractor. It differs from Zacoleus in the widely separated attachments of the buccal and tentacular retractors, in possessing a penial retractor, and in having an undivided sole. It differs from Hemphillia in possessing a fully embedded, calcareous shell; in the widely separated attachments of the buccal and tentacular retractors; in lacking a retentor muscle and in having the visceral cavity extend to the tip of the tail (see Table 1 ). A maximum parsimony tree, based on 15 anatomical characters for taxa of Hemphillia , Kootenaia , Prophysaon , and Zacoleus (see Fig. 4A ), shows that our new taxon clusters distinctly apart from the four species of Prophysaon studied here. The individuals of Kootenaia also cluster apart from Z. idahoensis and Hemphillia spp.

Comparative molecular genetics

The average among­group divergence based on K2P­distances ranges from 0.184 0.012 (between Zacoleus and Hemphillia ) and 0.227±0.012 (between Prophysaon and Hemphillia ) (see Table 2 ). Kootenaia appears to be most similar to Zacoleus with an average divergence of 0.185±0.014, though the divergences with Prophysaon (0.204±0.013) and Hemphillia (0.206±0.012) are not significantly larger.

A Bayesian phylogram of the combined COI/LSU rRNA data set reflecting the 50% majority­rule consensus of topologies sampled during the Bayesian search is shown in Fig. 4 B. The tree comprises the ‘outgroup’ taxa Z. idahoensis and three major clades: Prophysaon spp., Kootenaia sp., and Hemphillia spp.

Kootenaia clusters distinctly apart from all other taxa studied here and both the Prophysaon and the Kootenaia clades have posterior probabilities of 1.00. Within K. burkei , the two specimens for each of the two populations studied are homogeneous and the average divergence between the two populations is very low with a K2P­distance of 0.0044±0.002.

The new taxon deserves both new genus and new species designations on the basis of the absence of a free epiphallus alone. No other arionid even approaches this condition. Based upon the well­separated buccal and tentacular retractors and the general body appearance, Kootenaia appears to be more closely allied with Prophysaon than either Zacoleus or Hemphillia . In many Prophysaon species, the penis is reduced to a penial loop but none possesses a penial retractor muscle and all possess a well­developed epiphallus suggesting that the relationship between Kootenaia and Prophysaon is not especially close.

Zacoleus possesses converging retractors, a well­developed penis without a penial retractor, and a very large spermathecal duct. When these characteristics are considered together, they suggest that Zacoleus is even more distantly related to Kootenaia than Prophysaon . Even more distantly related is Hemphillia with its exposed horny shell, its visceral hump, its converging buccal and tentacular retractors, its retentor muscle and its well­developed penis. Pilsbry (1948) subdivided the Arionidae into four subfamilies. In this scheme, Kootenaia fits best in the subfamily Anadeninae.

The molecular analyses using two mitochondrial genes and the anatomical data produce congruent topologies. Our new taxon does not fit into any of the genera studied here but represents a distinct group. In fact, the two trees based on anatomical and molecular data presented in Fig. 4 show a very high degree of concordance, which is rarely seen in similar studies. However, as with the anatomical data, the molecular analyses cannot unambiguously solve the problem of sister group relationships. When using Zacoleus as outgroup, Bayesian inference suggests that the genus Prophysaon is the sister group of Kootenaia (see Fig. 4 B). But based on distance data, the genus Kootenaia would be more similar to Zacoleus ( Table 2 ). It appears as if future studies with more data and/or more taxa would be necessary to better address the problem of phylogenetic relationships among arionid taxa from the Pacific Northwest.

Figures

FIGURE 1: Relief map of Idaho showing the localities of Kootenaia burkei new species. 1) Little Bumblebee Creek, Shoshone County (type locality), 2) Trestle Creek, Bonner County, 3) Beauty Creek, Kootenai County, 4) Heyburn State Park, Benewah County, and 5) East side of Harrison, Kootenai County. For detailed locality information see the Appendix. The lower photograph shows paratype CM 66247.

FIGURE 2. Dissected holotype of Kootenaia burkei from Shoshone County, Idaho, showing the reproductive and digestive systems. Dorsal view of reproductive system on the left and ventral view of digestive system on the right. Total body length in alcohol = 10 mm.

FIGURE 3. Eggs of Kootenaia burkei photographed on 10 September 2003, 62 days after being laid in the laboratory.

FIGURE 4: A. Maximum parsimony tree for representatives of the genera Hemphillia, Kootenaia, Prophysaon, and Zacoleus based on 15 anatomical characters. Bootstrap values (10,000 replicates) are given at the nodes. The scale bar indicated the number of changes. B. Bayesian phylogram for the same species based on combined fragments of mitochondrial COI DNA and LSU rRNA showing the 50 % majority­rule consensus of topologies sampled during the Bayesian search. The scale bar indicates the substitution rate according to the model of sequence evolution applied. The numbers at the branches are the percentages that the clade occurs among all sampled trees; i. e. the posterior probability of that clade.

Tables

TABLE 2. Pairwise K 2 P­distances among the genera Kootenaia, Zacoleus, Prophysaon, and Hemphillia for the combined COI and LSU rRNA sequences. Standard errors (based on 1000 bootstrap replications) are given in parenthesis.

	Kootenaia	Zacoleus	Prophysaon	Hemphillia
Kootenaia	­
Zacoleus	0.185 (0.014)	­
Prophysaon	0.204 (0.013)	0.203 (0.013)	­
Hemphillia	0.206 (0.012)	0.184 (0.012)	0.227 (0.012)	­
Discussion