Rhyacodrilus longichaeta Rodriguez & Fend, 2013, sp. n.

Rhyacodrilus longichaeta sp. n. (Figs 14–16) Holotype. USNM 1202070, mature worm with sperm in the spermathecae, stained in hematoxylin, dissected and slide-mounted in Canada balsam. Paratypes. USNM 1202071-74, 4 mature worms (2 with sperm in the spermathecae): 2 sagittally sectioned, 2 dissected and slide-mounted (23 June 2011); MNCN 16.03/3082: 1 whole mounted, unmated worm (15 May 1998), 1 dissected worm (6 April 2008). All from type locality. Type locality. Guadalupe Creek, above Guadalupe reservoir, N37.1822° W121.8725°, Santa Clara Co., California (23 June 2011). Other material. 18 partially mature specimens from the type locality: 2 mature unmated individuals, with sperm on male funnels, one sectioned (23 June 2011) and one dissected (20 June 2011). Other individuals with well-developed reproductive organs, with visible sperm sacs but sperm not fully developed: 2 whole mounts (15 May 1998); 5 dissected, (2 from 19 March 1999, and 2 from 9 April 2011); 8 whole mounts (25 April 2006). Additional unmounted worms from the type locality, all partially mature with visible sperm sacs: 6 in alcohol (19 March 1999), 14 in alcohol (25 April 2006). Immature specimens tentatively attributed to R. longichaeta: 7 immature whole mounts from Cooper River, above Cooper Lake, N47.4357° W121.1911°, Kittitas Co., Washington (1 November 1990); 3 immature whole mounts from the Merced River in Yosemite Valley, N37.7407° W119.5666°, Mariposa Co., California (6 October 1994 and 16 September 1995). Futher material studied (not included in the description). Type series of Edmondsonia montana Brinkhurst, 1965: Holotype USNM 32652 (1 slide), Paratype USNM 32653 (9 slides), all from Dog Lake, Yakima Co. Washington. An additional specimen attributed to this species, USNM 32980, from Sugar Island, Michigan. Etymology. The specific name, longichaeta, refers to the extraordinarily long hair chaetae in segment II. Description (from type locality specimens). Number of segments 48–95. Prostomium rounded to conical, 180–360 µm long (Fig. 14 A). Body diameter 0.42–0.74 mm in VIII. Secondary annulation usually absent in anterior segments, or a weak anterior ring in about IX–XI; variable in posterior segments, with 0–3 narrow rings. Mid-dorsal pores in intersegments (3/4) 4/5 to 6/7 (7/8). One pair spermathecal pores in the most anterior part of segment X, in line with ventral chaetae; two crescent-shaped grooves demarcate a median raised area between the pores, interpreted as a copulatory anchorage bridge. One pair male pores in the line of ventral chaetae in segment XI, usually opening on small round papillae; modified penial chaetae located closer to the body midline (Fig. 14 C). One pair female pores at intersegment 11/12, between lateral line and line of ventral chaetae. Faintly hispid hair chaetae 1–4 per bundle in anterior segments (170–540 µm long), in segment II 1.4 to 2 times (620–960 µm) longer than the longest hairs in other preclitellar segments (Figs 14 A, 15F); hair chaetae present in most postclitellar segments, 0–1 per bundle, length less than 200 µm. Lateral hairs of hispid chaetae difficult to see in specimens from Guadalupe Creek (1000x usually required), but clearly visible at 400x magnification in Cooper and Merced River populations (Fig. 15 P). In anterior segments, 3–5 pectinate chaetae per bundle (96–144 µm long), with 4–7 intermediate teeth shorter than lateral teeth; 2–3 per bundle in posterior segments, commonly with very fine pectinations visible only at 1000x (Fig. 15 E–H). Upper teeth of anterior pectinates are slightly longer and thinner than, or equal to lower, although this varies even within the same bundle (Fig. 15 E); differences in size between lateral teeth are not as marked as in other populations (e.g. Cooper and Merced Rivers), or as in the type series of R. montana (Fig. 15 O, 16A, D, E). Ventral chaetae bifid; in anterior bundles 4–6(8) (96–149 µm long), with distal tooth thick and 1.5–2.5 times longer than proximal (longest in the most lateral chaetae within each bundle); 3–5 ventral chaetae in posterior segments (110–115 µm long) with distal tooth as long as but thinner than proximal (Fig. 15 I–M). In mature worms with sperm on the male funnels, ventral chaetae in segment X reduced in number (2–3 per bundle) and slightly larger (150–185 µm long), 1.2–1.8 times longer than chaetae in IX; the shape is also slightly modified, with distal tooth up to 3 times longer than lower (Fig. 14 B, 15N). At the male pore, (2)3(4) penial chaetae arranged more or less fanwise, simple-pointed or bifid (Fig. 15 D), 150–176 µm long, and associated with 2 strong dorso-ventral muscular strands (Fig. 14 E). Pharynx with a well-developed dorsal muscular pad. Chloragogen cells start in segment VI and form a layer up to 27 µm high. Large coelomocytes (diameter 21–39 µm), nucleated and granulated (Fig. 15 A). Epidermis 11–18 µm high, circular muscle layer 5–8 µm thick and longitudinal muscles 10–30 µm thick. Clitellum 45–54 µm high dorsally, usually from about 1/ 2 X –XIII, may extend anteriad as far as the line of chaetae in IX. Pharyngeal glands from IV to VI, VII or VIII, in one individual back to the anterior part of IX. Sperm funnel on septum 10/11. Vas deferens ciliated (ca. 390–750 µm long, 30–50 µm wide), narrowing (18– 30 µm) before subapical junction with atrium. Atrium club-shaped, total length 250–350 µm. Atrial ampulla elongate (length 110–168 µm, maximum diameter 54–74 µm), covered by a diffuse layer of prostate cells (up to 28 µm high), with thin musculature (ca. 3 µm thick). Atrial duct (96–192 µm long, 30–53 µm wide) not separated from ampulla by any constriction, although clearly distinguished by the absence of prostate cells, high columnar epithelium and prominent muscle strands that externally attach it to the ventral region around the male pores (Fig. 14 C, D, F). Sperm sac back to segments XVI–XXVII, egg sac back to XVI–XXVII. Spermatheca with a short duct (55–108 µm long, 62–73 µm wide) that opens at the beginning of segment X, in the line of ventral chaetae. Spermathecal ampulla 168–305 µm long, of irregular sac-like shape, with unordered sperm (Fig. 14 C). Anomalies. One individual from Guadalupe Creek had the genitalia shifted 3 segments forward (male pores in VIII) suggesting regeneration after fragmentation; one other specimen appeared to have a regenerating prostomium. Distribution and habitat. Within Guadalupe Creek, R. longichaeta was found only in gravel-cobble sediments in riffle habitats above the confluence with Rincon Creek. Rhyacodrilus alcyoneus sp. n. was found only in riffles below this confluence, and neither has been found in downstream Guadalupe Creek sites, below the major reservoir. A benthic macroinvertebrate survey of Santa Clara Valley streams (Carter & Fend 2000) did not produce any other records of these species. Remarks. Rhyacodrilus longichaeta sp. n. belongs to the group of Rhyacodrilus species with both hairs and pectinates, and also with several penial chaetae arranged fanwise and modified spermathecal chaetae. Within this group, R. svetlovi Sokolskaya, 1976 and R. alcyoneus sp. n. have a similar elongate, tubular atrium, with the atrial ampulla not separated from the duct by a constriction. The vas deferens of R. svetlovi is shorter than the atrium, and joins it apically. Differences from R. alcyoneus (described in the present paper) include the smaller size, the chaetal characteristics, the absence of ventral chaetal tubercula in IX and X, and the presence of hair chaetae in dorsal bundles of postclitellar segments. Both species have similar male ducts, with elongate-tubular atria and a weakly differentiated atrial duct; differences are not very pronounced, with the atrial duct less histologically differentiated in R. alcyoneus, and the simple male pore on a round papilla in R. longichaeta but opening within a fold in R. alcyoneus. Other Rhyacodrilus species with modified penial chaetae (but without spermathecal chaetae) and clubshaped to tubular atria are R. vasalatus and R. korjakovi, described by Semernoy (2004) from Lake Baikal. Of these two species, the male duct in R. longichaeta resembles that of R. vasalatus in having a vas deferens which narrows considerably before the atrial junction, and also in the high columnar epithelium of the atrial duct. However, R. vasalatus has only bifid chaetae, as does R. korjakovi when it is mature. The lateral position of the female pores is uncommon in oligochaetes, where they typically have a more ventral position, in line with the ventral chaetae. Interestingly, this character is shared with other western American Rhyacodrilus species described here, i.e. R. saelonae, R. clio and R. alcyoneus. Rhyacodrilus species with long hairs in II have generally been attributed to Rhyacodrilus (= Edmondsonia) montana (Brinkhurst, 1965), although elongate hairs in II were not mentioned in the original description. Furthermore, although diagnostic characters in Rhyacodrilus are largely based on details of the reproductive system, the original description of R. montana was based on immature worms, and only included characteristics such as the number and shape of chaetae and the abundance of coelomocytes (see Fig. 16). The type series was collected at three sites in western North America: two from the northern Cascades Range in Washington (Dog Lake and Lake Tipsoo) and a distant California site (a pool at the edge of the Kings River); the holotype and a large series of paratypes were from Dog Lake. The species was transferred from the invalidated genus Edmondsonia Brinkhurst, 1965 to Rhyacodrilus by Brinkhurst and Cook (1966), based on the study of several populations of the Great Lakes region (eastern North America), but in that publication there is no comparison of chaetal characteristics with the type series and only limited information on the male duct. Our examination of the R. montana holotype (USNM 32652) and all paratypes (USNM 3265

Récupéré en direct depuis OpenAlex et désinversé. Les résumés ne sont pas conservés dans cette base de données : les index inversés représentent 8,6 Go des 9,3 Go de texte de la base, et le serveur dispose de 13 Go libres.