Stylodrilus coreyi, Rodriguez, Pilar, Fend, Steven V. & Lenat, David R., 2014

Rodriguez, Pilar, Fend, Steven V. & Lenat, David R., 2014, Sylphellapuccoon gen. n., sp. n. and two additional new species of aquatic oligochaetes (Lumbriculidae, Clitellata) from poorly-known lotic habitats in North Carolina (USA), ZooKeys 451, pp. 1-32 : 11-14

Taxon classification Animalia Lumbriculida Lumbriculidae

Stylodrilus coreyi sp. n. Figs 6and 7

Holotype.

USNM 1251703: A whole-mounted specimen in Canada balsam (collected 19 Jan 2010).

Paratypes.

USNM 1251704-1251707: 17 Feb 2007, 1 whole mount; 19 Jan 2010, 2 whole mounts; 5 Apr 2010, 1 dissected. MNCN 16.03/3085: 19 Jan 2010, 1 dissected and 1 histologically sectioned; 5 Apr 2010, 1 whole mount, stained in borax carmine. CASIZ 197900: 16 Feb 2011, 2 dissected. All from the type locality.

Type locality.

Pettiford Creek at Millis Road, Carteret County, North Carolina, USA.

Etymology.

This species is named in honor of Jesse Edward (Ed) Corey III, an Inventory Biologist at the North Carolina Division of Parks and Recreation. We celebrate Ed’s unwavering interest in all animals and plants, including our beloved oligochaete worms.

Other material.

From the type locality: 17 Feb 2007, 1 dissected. 30 Sep 2009, 7 whole mounts, 1 dissected. 19 Jan 2010, 5 whole mounts, 2 dissected, 3 sectioned (2 sagittal, 1 transverse), 2 in alcohol. 5 Apr 2010, 6 whole mounts, 2 dissected. 16 Feb 2011, 1 whole mount, 10 in alcohol. Floodplain seeps in Drowning Creek floodplain at State Road 1004, Moore County, North Carolina: 31 Dec 2008, 2 whole mounts. 12 Jan 2009, 2 whole mounts, 5 dissected. 17 Feb 2011, 1 whole mount. All specimens (including the type series) collected by D.R. Lenat.

Description.

Number of segments 53-69. In 27 unmounted specimens, body length 11.7-14.2 mm, diameter of the body in segment VIII, 240-585 µm (mean 379 µm); maximum diameter in the clitellar region to 760 µm (mean 467 µm); midbody diameter 330-630 µm (mean 429 µm). Prostomium round or conical, 142-196 µm long (Figs 6A, 7A). Brain deeply lobed, back to septum 2/3. Clitellum saddle-shaped, formed by cells in distinct rows (Fig. 7C), extending from the anterior part of segment X (from the level of chaetae) to the end of segment XII. Epidermis 6-17 µm high in anterior segments, and up to 23-34 µm in the clitellum; 25-32 µm high in the prostomium. Secondary annulation (a narrow ring in anterior part of segment) usually in IV to IX.

Chaetae simple-pointed (Fig. 7B), nodulus at 0.3 (rarely at 0.4) from the ectal end, of similar size in dorsal and ventral bundles or slightly longer in ventral bundles; smaller in segment II (63-70 µm), length increasing in the anterior segments to segment VIII (73-116 µm), and usually smaller in the posterior part of the body (71-111 µm, down to 63 µm).

One pair spermathecal pores in segment IX and one pair male pores in segment X, in line with and behind the ventral bundles of chaetae (one specimen from Drowning Creek regenerating the anterior part of the body, with spermathecal pores in VII and male pores in VIII). One pair female pores in the intersegment 11/12.

Pharyngeal pad well-developed dorsally, usually extending through IV; pharyngeal glands from the posterior part of segment IV back to VIII, dorso-lateral and ventral to the gut in segments V to VIII (Fig. 6B). Chloragogen cells covering the gut from the posterior part of segment VI onwards. Nephridia with long efferent ducts observed in segment VII and in some postclitellar segments, tubular shaped, running ventrally through several segments (Fig. 7D); nephridiopores without vesicles, in front of ventral chaetae. Lateral blood vessels absent in posterior segments. Two pairs testes, in anterior part of segments IX and X, and one pair ovaries in segment XI. Sperm sacs back to segment XV or XVI (never observed extending forward), and egg sacs back to XVI or XVII.

Semiprosoporous male ducts, with one anterior vas deferens attached to the sperm funnel in intersegment 9/10, and the posterior one to the funnel in 10/11, the anterior being longer (280-480 µm) than the posterior (215-300 µm). Both funnels appear deflected backward, somewhat behind their respective septa when full of sperm. Vasa deferentia (15)20-28 µm in diameter, to 34 µm close to the sperm funnel. Posterior vas deferens does not enter postatrial segment (Figs 6D, 7G). Atrium elongate (176-390 µm total length, including the penis), with the ampulla (120-184 µm long, 43-70 µm maximum diameter) usually restricted to segment X, but in some individuals passing into segment XI. Several discrete clusters of prostatic cells (44-100 µm high) join the atrium by distinct stalks that traverse the atrial musculature (Fig. 7 E–I). Atrium length 0.45-0.70 (usually c. 0.50) times the body diameter at the clitellum. Short atrial duct not distinctly separated from the ampulla, narrowing to about 24 µm wide, the male pore on a short penis (25 µm long), in a shallow fold of the body wall. Several dorso-ventral muscular strands are associated with the male pore. Atrial epithelium very granulated, 14-19 µm high, and atrial lumen ciliated; atrial musculature thin (4-6 µm thick). Vasa deferentia join the atrium at about the basal one third, and run under the atrial musculature to the most apical part of the ampulla, where they open to the atrial lumen (Figs 6C, 7G).

One pair spermathecae, with ampullae typically located in segments IX and X, oval to nearly spherical (174-331 µm diameter, 205-348 µm long), containing a mass of loose sperm in the ectal part, sometimes together with amorphous material (Figs 6D, 7J). Ampulla with thin epithelium in ectal part (about 5-10 μm); epithelium with large, irregular cells (to over 50 μm), which may fill the lumen in ental part; no sorptive vacuoles were observed. Spermathecal duct long (150-247 µm) and relatively thin (22-31 µm diameter), slightly widening at ectal end up to 42 µm; with narrow, columnar cells and thin (<5 μm) muscle coat. One pair female funnels open ventrally in intersegment 11/12 (Figs 6D, 7L).

Worms from Downing Cr are generally larger than those from Pettiford Cr (see Table 4), but morphology is otherwise similar.

Taxonomic remarks.

Stylodrilus coreyi sp. n. conforms to the general diagnosis of the genus Stylodrilus Claparède, 1862 (see Rodriguez and Coates 1996), which includes most known lumbriculid species with 2 pairs of testes and one pair of ovaries, one pair of spermathecae in the first testicular segment, and one pair of semiprosoporous male ducts in the second testicular segment. According to Hrabě (1929, 1970), the genus Bythonomus Grube, 1880, which had the same arrangement of reproductive organs, was restricted to those species with all chaetae simple-pointed, 2 pairs of branched lateral blood vessels (sometimes only bifurcate or absent), tubular or oval atria, and vasa deferentia opening basally (ectally) to the atrium. Bythonomus was classified as junior synonym of Stylodrilus by Brinkhurst (1965), a decision that was refuted by Hrabě (1970), and still divides taxonomists in the present. For example, Giani and Martínez-Ansemil (1984) accepted the synonymy, and used the characters of Stylodrilus glandulosus as an example to invalidate Bythonomus as a genus; this view is actually supported by most authors (e.g., Rodriguez 1988, Timm 2009). However, Kaygorodova and Martin (2008), still supported a distinction between Bythonomus and Stylodrilus , based on the shape of chaetae. Until the taxonomic status of Stylodrilus is clarified by molecular analyses, we accept the synonymy, since several species of the Stylodrilus complex have a mixture of Bythonomus -like and Stylodrilus -like characters. In the present case, the new species has simple-pointed chaetae and tubular atria, but no posterior lateral blood vessels have been observed, and although the junction of vasa deferentia is basal, the opening to the atrial lumen is completely apical. The junction of the vasa deferentia to the atrium is not always easily defined as basal or apical in the " Bythonomus group", but rather it occurs in every possible position from basal to apical ( Brinkhurst and Wetzel 1984). Besides, the atrial shape can be difficult to categorize in species with long atrial ducts that gradually widen toward the ampulla.

Stylodrilus coreyi sp. n. belongs to a group of Stylodrilus species with simple-pointed chaetae, elongate atrium, and posterior vas deferens not forming a loop in the postatrial segment (Table 5). Within this group, Stylodrilus coreyi is distinguished by several features of the male duct: atrium length about half (0.5-0.7) times the diameter of the body at the clitellum; a very short, barely differentiated atrial duct forming a short penis within a fold of the body wall; the atrial ampulla covered by large clusters of discrete prostatic glands, entering the atrium through narrow passages; vasa deferentia joining the atrium in the basal third of its length, and opening to the atrial lumen at the apical end.

Among this group of species, Stylodrilus wahkeenensis Rodriguez & Coates, 1996 can be distinguished from Stylodrilus coreyi not only by the remarkable shape of the chaetae (proximal nodulus, hair-like in dorsal bundles, and enlarged, hook-shaped in ventral bundles of segment II), but also by the position and structure of the atrium (in segment IX, small and covered by a simple, diffuse layer of prostatic cells, with no duct or penis observed). Of the other species in that group, Stylodrilus glandulosus Giani & Martínez-Ansemil, 1984 and Stylodrilus curvithecus Collado et al., 1993 are separated from congeners by clear apomorphies, such as a muscular, bulbous penial sac with associated glandular complex, and a long atrial duct. Stylodrilus beattiei Cook, 1975 and Stylodrilus tschaunensis Morev, 1982 also have simple-pointed chaetae and vas deferens not penetrating the postatrial segment, but they are well distinguished from this species group by the distinctly petiolate atrium with oval or pyriform ampulla, short atrial duct, and absence of a penis. Other species of the genus in which the posterior vas deferens does not penetrate the post-atrial segment are Stylodrilus cernosvitovi Hrabě, 1950, Stylodrilus mirandus ( Hrabě, 1982), and Stylodrilus aclotudi Kaygorodova & Martin, 2008, but they all have bifid chaetae.

Stylodrilus species with simple chaetae and an elongate to tubular atrium with short atrial duct include Stylodrilus absoloni ( Hrabě, 1970), Stylodrilus lemani and Stylodrilus chukotensis Sokolskaya, 1975, but in these species, the vas deferens penetrates the post-atrial segment, forming a loop. Another species in this group is Stylodrilus sulci ( Hrabě, 1934), distinguished from Stylodrilus coreyi by the median junction of vasa deferentia to the atrium, the entrance of the posterior vas deferens into the postatrial segment, and the absence of a penis.

In North America, there are only five Stylodrilus species known so far, one of which is cosmopolitan ( Stylodrilus heringianus Claparède, 1862). Stylodrilus beattiei (Cook, 1975) was the first Nearctic Stylodrilus species described, from a cave in West Virginia. Subsequently, Stylodrilus sovaliki (Holmquist, 1976) was described from lakes in Alaska. Later, Stylodrilus californianus Rodriguez, 1996 was discovered in subterranean waters in eastern California, and Stylodrilus wahkeenensis Rodriguez & Coates, 1996, was described from hyporheic waters and small streams associated with subterranean waters of Oregon and southeastern USA.

The low number of Stylodrilus species in North America may be related in part to the tendency of researchers in this area to erect new genera for those taxa with very distinct apomorphies (e.g., Spelaedrilus Cook, 1975, Phagodrilus McKey-Fender & Fender, 1988, Tenagodrilus Eckroth & Brinkhurst, 1996), despite a general arrangement of the reproductive system that fits the Stylodrilus pattern. This situation indicates the need for a sound revision of the genus, since some Stylodrilus species can in fact be closer to other genera.

Ecological remarks.

Stylodrilus coreyi sp. n. has been collected from seeps and pools in humic coastal plain streams (Drowning and Pettiford Creeks), most commonly outside of the main channel. These habitats have a temporary flow regime, with seasonal drying during summer months. Stylodrilus coreyi was mostly collected in detritus over a layer of fine sand. Both streams have very high water quality ( NCDENR 2007, 2011), but pH values are higher in Drowning Creek (usually about 5.5) than in Pettiford Creek (<4.3). This suggests that Stylodrilus coreyi tolerates extremely low pH values, but does not require such conditions. Interestingly, lumbriculids found in this kind of habitat have also congeneric relatives in groundwaters (three of five described Stylodrilus species in the Nearctic region are subterranean; see also Cookidrilus pocosinus remarks, above).