Rhyacodrilus clio, Rodriguez, Pilar & Fend, Steven V., 2013

Rodriguez, Pilar & Fend, Steven V., 2013, New species of Rhyacodrilus (Annelida: Clitellata: Rhyacodrilinae) of North America, with re-description of R. sodalis (Eisen, 1879), Zootaxa 3664 (1), pp. 1-44 : 14-19

Rhyacodrilus clio sp. n.

( Figs 6–8 )

Holotype. USNM 1202056, dissected specimen stained in hematoxylin and mounted in Canada balsam.

Paratypes. USNM 1202057-61: 3 dissected specimens from type locality (17 July 2011), 2 whole mounts from Squaw Creek at Madrone Camp (18 July 2011). MNCN 16.03/3080: 2 whole mounts from type locality (17 July 2011).

Type locality. Squaw Creek at Chirpchatter Camp, Shasta Co., California N40.8606° W122.1205° (17 July 2011).

Other material. 7 mature whole mounts and 1 sagittally sectioned from Santa Clara Co., Coyote Creek, near Gilroy Hot Springs N37.11° W121.47° (22 July 2001, 17 April 2005, 26 March 2010, 16 April 2011). 5 dissected, and 3 whole mounts, stained with hematoxylin, from Shasta Co., Squaw Creek at Madrone Camp, N40.9276° W122.0972° (19 August 1999), 12 whole mounts (18 July 2011). 3 whole mounts, 9 dissected, 3 sagittally sectioned specimens from Squaw Creek at Chirpchatter Camp, N40.8606° W122.1205° (17 July 2011). 5 mature whole-mounts from Napa Co., Napa River drainage, Ritchey Creek, N38.5515° W122.5219° (25 April 2004), collected by R.W. Wisseman. 1 mature whole mount from Santa Cruz Co., San Lorenzo River, approx. N37.02° W122.06° (22 May 1998). 6 mature or nearly mature whole mounts from San Benito Co., Pinnacles National Monument, Chalone Creek near lower park boundary, N36.4598° W121.1549° (27 March 2004). All sites in California ( USA).

Etymology. Named after Clio (Greek Kleio), the Latin name of the muse of history, and thus also of natural history. "To thee, O Muse, has been vouchsafed the power to know the hearts of the gods and the ways by which things come to be" ( Valerius Flaccus, Argonautica 3, 1A.D. (trans. J.H. Mozley). Noun in apposition.

Description (from specimens of the type locality). Elongated, rounded prostomium (140–200 µm long) ( Fig. 6 A). Diameter of the body in segment VIII (whole-mounted specimens) 210–340 µm; maximum diameter at clitellum up to 390 μm. Length of preserved worms 8–15 mm, 56–73 segments. Epidermis non-glandular, 6–10 µm high in anterior segments. Clitellum from level of chaetae in X to XII and weaker in XIII, thickest dorsally and laterally, 16–26 µm high, usually with distinctly glandular epithelium ( Fig. 6 B).

Dorsal bundles composed of 1–3 hairs (commonly 2 in anterior segments, 1 in posterior segments) and 1–3 bifid chaetae. Hair chaetae smooth, usually longer than body diameter in anterior segments, the longest in each bundle 250–450 μm. Dorsal bifid (or pectinate) chaetae (70–86 µm long) in anterior segments (shorter in II), with very fine intermediate teeth (only visible at 1000x), lateral teeth equally long and lyre- or narrowly U-shaped; dorsal bifids shorter and teeth equal in posterior segments, without intermediate teeth ( Fig. 6 C, D). Ventral chaetae bifid; anterior ventral chaetae 5–6 per bundle, 70–79 µm long, shorter in II, with distal tooth slightly longer than proximal and about as thick; unmodified ventral chaetae in segment X; posterior ventral chaetae 3–6 per bundle (70–77 µm long) with distal tooth thinner and equal to or shorter than proximal ( Fig. 6 E, F). One pair spermathecal pores at the beginning of segment X, in line with ventral chaetae; a pair of transverse (crescent-shaped) shallow grooves (35–45 μm long) just anterior to spermathecal pores, the thicker ends extending mediad, nearly conjoined near the midline, forming a narrow, slightly raised (50–70 μm long, 12–24 μm high) anchorage bridge (Cuadrado & Martínez-Ansemil 2001) between spermathecal pores ( Fig. 7 A). One pair male pores in posterior part of segment XI, in line with ventral chaetae. Modified penial chaetae (76–94 µm long) in segment XI, usually 2 per bundle (sometimes with an additional, shorter replacement), although the number of penial chaetae varies among different populations ascribed to the species (see Table 2). Penial chaetae simple-pointed or faintly bifid, and nodulus at 0.2 from distal end.

Very abundant nucleated and granulated coelomocytes, diameter 12–25 µm ( Fig. 6 L). Pharynx short, in II. Pharyngeal glands dorsal and ventral to the gut in IV–V, ventral only in VI; sometimes inconspicuous. Chloragogen layer covering the gut from segment VI. Small clusters of glandular cells on either side of ventral nerve cord; 2–4 pairs per segment beginning at about IV, and continuing through a few post-atrial segments, with narrow cellular extensions through ventral body wall, but without obvious pores ( Fig. 6 M). First nephridia visible in VIII in some specimens, or only in postclitellar segments in others; nephridia occur irregularly in postclitellar segments; postseptale granular and usually elongate-narrow; efferent duct and nephropore small and inconspicuous. One pair testes in segment X and one pair ovaries in segment XI. Sperm sac forwards to segment IX and backwards as far as XVIII. Egg sac back to segment XIX.

Locality Body Hair Dorsal Ventral Penial Spermatheca Maleduct

diameter chaetae: bifids: chaetae: chaetae:

in VIII number number number number

(µm) (length) (length). (length) (length)

Pectinations

Squaw 210–340 1–3 (longest 1–3 (70– 86 3–6 (70–79 2 (76–94 µm) Short duct (26–55 µm long), Ampulla (50– 80 x 36–60 µm), a short neck

Creek to 250–450 µm). Fine µm) shorter One as long as wide (diameter 20–30 µm) and a long, inflated atrial

µm) intermediate in II specimen duct (70–100 x 55 –75 µm) teeth with 5 on one

side

Coyote 203–238 1–2 (150–375 1–3 (46– 65 3–6 (57–71 1 (58–69 µm) Short duct (51–66 µm long), Small globular ampulla (41– 57 x 35–51 µm), a

Creek µm) µm). No µm) shorter as long as wide short neck (diameter 22–24 µm) and a long, intermediate in II inflated atrial duct (78– 98 x 45–72 µm) teeth

Spermathecae with a short duct (26–55 µm long, 35–55 µm wide) with high columnar epithelial cells. Spermathecal ampulla large and elongate-sacciform (150–340 µm long, 100–150 μm wide); epithelium in unmated worms irregular, 10–25 μm high (thickest near duct), in mated worms thin (3–6 μm) and more uniform; ampulla usually confined to segment X ( Fig. 7 C). Sperm free in the lumen of spermathecal ampulla.

Paired sperm funnels open in the ventral part of septum 10/11, each leading to a ciliated vas deferens, which joins the atrium at the middle of the ampulla. Vas deferens longer than atrium, length about 200–290 µm, diameter 17–23 µm. Atrium consists of a small globular to ovate ampulla and a long inflated duct; a short neck (20–30 μm long by 30–45 μm wide) connects the ampulla to the atrial duct; this section has narrow columnar epithelium ( Fig. 7 B). Atrial ampulla 50–80 μm long by 36–60 μm wide; epithelium granular with large, irregular cells having basal nuclei, lumen narrow (6–7 μm), muscle layer very thin; ampulla covered by a diffuse layer of prostate cells, 20–35 µm high, usually a mix of small clusters and individual cells. The outer duct forms an eversible penis; entire duct 70–100 μm long by 55–75 μm wide when penis is retracted, with thick, granular epithelium (10–14 μm) having basal nuclei and a thin (1–2 μm) outer muscle layer. Everted penis short and broad, formed by lining cells from outer part of atrial duct extending through pore ( Figs 6 K, 7D, E). Penial chaetae terminate within a small tubercle at the inner margin of the male pore, with a small patch of glandular cells, and several muscle strands extending to dorsal body wall ( Fig. 7 B, C).

Distribution and habitat. Known from several localities in central and northern California. Sites were small to mid-sized, gravel-cobble bed streams in relatively undisturbed, foothill settings; worms were collected from riffle habitats with coarse sediments. Sites on Coyote and Chalone creeks are intermittent, typically losing surface flow in summer.

Remarks. Rhyacodrilus clio sp. n. has been ascribed to the genus Rhyacodrilus based on the diffuse prostate layer covering the atrial ampulla, the vas deferens, which is longer than the atrium and joins it subapically, and the presence of modified penial chaetae. The new species is well-separated from other Rhyacodrilus species by the structure of the atrium, with a small ampulla and a large inflated duct that can be partially everted, with the inner epithelial cells of the duct extending beyond the male pore. Different populations that have been ascribed to R. clio show different numbers of penial chaetae and some variations in the range of measurements of chaetae and atrium (see Table 2). However, the general structure of male duct and spermatheca are consistent ( Fig. 8 ). The individuals from Ritchey Creek were collected in alcohol, and thus poorly preserved; they have been provisionally ascribed to this species based on shape of chaetae, the short atrial ampulla, and the short, everted penes.

Rhyacodrilus clio sp. n. appears to be related to the European groundwater species Rhyacodrilus subterraneus Hrabë, 1963 b, with which it shares the presence of hair and pectinate chaetae in dorsal bundles and penial chaetae but no spermathecal chaetae. As in R. clio sp. n., the atrium of R. subterraneus is composed of a small ampulla covered by diffuse prostate glands and a long duct; although the duct is thinner, it has been described as having cubic epithelium, and appears to be devoid of a penis. The shape of both dorsal and ventral anterior chaetae also distinguishes both species: R. clio has lyre or U-shaped pectinates, with teeth of equal length, while R. subterraneus has unequal V-shaped pectinates, and anterior ventral chaetae with upper tooth much longer than lower.

Rhyacodrilus subterraneus has been reported in several parts of Europe (Giani & Martínez-Ansemil 1981, Timm et al. 1996, Martin et al. 2009, Schenková et al. 2010), although some of these records may need to be reconsidered. A re-examination of the specimen reported by Giani and Martínez-Ansemil (1981) from a NW Spanish locality revealed the typical chaetal morphology of R. subterraneus ( Fig. 9 K, L). However, this specimen is probably a different species, as the atrium has a large ampulla relative to the short, narrow atrial duct. Timm et al. (1996) reported R. subterraneus from several locations in the Scandinavian Peninsula, but the studied specimens may be uncompletely mature since the spermathecal ampulla is drawn empty, and the atrium does not show an internal lumen nor a penis. Rhyacodrilus subterraneus has also been reported from several localities in eastern and central United States (Strayer & O'Donnell 1988, Strayer 2001, Wetzel & Taylor 2001, Wetzel & Morgan 2007), but these records must also be interpreted with caution, as they are based on chaetal characters of immature specimens (see also remarks for R. propiporus sp. n. below).

Figures

FIGURE 6. Rhyacodrilus clio sp. n. A. Prostomium and anterior body region. B. Clitellum in segments X to XII. C – F. Chaetae from Squaw Creek population: dorsal chaetae in segment VII (C), posterior dorsal (D), ventral chaetae in III (E), postclitellar ventral chaetae (F). G – J. Chaetae from Coyote Creek population: anterior dorsal chaetae (G), posterior dorsal chaetae (H), anterior ventral (I), posterior ventral chaetae (J). K. Penis everted (histological section). L. Coelomocytes. M. Detail of one ventral gland in V (histological section).

FIGURE 7. Rhyacodrilus clio sp. n. Schematic drawings of reproductive organs in Squaw Creek population. A. Position of spermathecal and male pores in segments X and XI. B. Male duct. C. Reproductive organs. D. Atria in different orientation and various degrees of extrusion of the penis. E. 3 consecutive histological sections of atrium.

FIGURE 8. Rhyacodrilus clio sp. n. A – B. Coyote Creek population. A. Reproductive organs. B. Atria in different orientations and with varying degree of extrusion of the penis. C. Reproductive organs in specimens from Chalone Creek population. Drawings schematic.

FIGURE 9. Rhyacodrilus propiporus sp. n. (A – J, M – N) and Rhyacodrilus subterraneus Hrabë, 1963 (K – L). A – J. Rhyacodrilus propiporus sp. n. A. Prostomium with coelomocytes. B – E. Dorsal chaetae of segment II (B), V (C), IX (D), and postclitellar (E). F – I. Ventral chaetae of segment V (F), VII (G), postclitellar (H) and very posterior (I). J. Dorsal chaetae of very posterior segments. K – L. Chaetae of Rhyacodrilus subterraneus (Martínez-Ansemil's collection, see text). K. Anterior pectinates. L. Ventrals. M – N. Rhyacodrilus propiporus sp. n. Ventral view of the body, whole mount. M. Spermathecal pores and male pores. N. Atrium opening in a porophore.