Cookidrilus pocosinus, 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 : 4-10

Taxon classification Animalia Lumbriculida Lumbriculidae

Cookidrilus pocosinus sp. n. Figs 4and 5

Holotype.

USNM 1251699: a dissected specimen, stained in Harris’ hematoxylin and mounted in Canada balsam (collected 4 March 2011).

Paratypes.

USNM 1251700-1251702: from the type locality, 22 Feb 2011, 1 dissected; 4 Mar 2011, 1 whole-mounted; Pettiford Creek, at Millis Road, Carteret County, North Carolina, USA, 15 Mar 2007, 1 whole mount. MNCN 16.03/3084: from the type locality, 22 February 2011, 1 dissected, stained in Harris’ hematoxylin and mounted in Canada balsam, and 1 histologically sectioned, stained with hematoxylin-eosin. CASIZ 197899: Pettiford Creek, 15 Mar 2007, 1 whole mount.

Type locality.

Lake Run, outlet stream draining Little Singletary Lake at SR 1325, in Bladen County, North Carolina, USA.

Etymology.

The specific name refers to pocosin, “swamp-on-a-hill” in the Algonquin Indian language. Most specimens were collected in two sites draining pocosin areas.

Other material.

From the type locality, 22 Feb 2011, 4 whole mounts, 1 dissected, 1 sagittally sectioned. Pettiford Creek, at Millis Road, Carteret County, North Carolina, USA, 22 Apr 2008, 1 whole mount; 5 Apr 2010, 2 dissected. Drowning Creek at State Road 1004, Moore County, North Carolina, 12 Jan 2009, 1 whole mount. Anderson Creek at SR 2031, Harnett County, North Carolina, 27 Jun 2011, 1 whole mount. All specimens (including the type series) collected by D.R. Lenat.

Description.

Number of segments 53-71. Diameter of the body 279-342 µm in segment VIII and 360-441 µm at the clitellum. Prostomium round, 120-154 µm long. Brain back to intersegment 2/3. Secondary annulation (narrow ring in anterior part of segment) well marked from segment VI to IX, not always visible in the postclitellar region, but evident in the caudal region of the body (Figs 4A, 5B). Epidermis in anterior segments 10-16 µm high. Clitellum from segment X to XII, with epithelium 16-34 µm high, formed by small glandular cells arranged in regular transverse rows (Fig. 5E). Chaetae sigmoid, simple-pointed (Fig. 5C), length about equal in dorsal and ventral bundles, shortest in segment II (56-62 µm), progressively longer to the middle of the body (68-82 µm long), and gradually shorter to the end of the body (down to 66 µm). A chaetal gland behind chaetal bundles, conspicuous in anterior segments, smaller posteriorly (Figs 4B, 5D). Nodulus at about 0.3-0.4 from the distal end. Pygidium normally formed (Fig. 5B). Male pores located behind and in line of ventral chaetae of segment X (Fig. 5F). Female pores open in the line of ventral chaetae, in intersegment 11/12. Spermathecal pores opening midway between ventral chaetae and anterior septum, in line with the ventral chaetae, in atrial and 2 postatrial segments. In most sexually mature, fixed individuals, the ventral region of clitellar region is concave with prominent lateral margins (saddle shaped clitellum).

Pharynx developed mainly dorsally, in segments II and III. Pharyngeal glands in last part of IV, and well developed in V and VI, dorsally and laterally. Chloragogenous tissue starting in the hind part of VI and well developed from VII backwards. Nephridia present on at least one side in VII in some specimens; most specimens have at least one nephridium in XIII, and in a few posterior segments. Nephridiopores inconspicuous, without vesicles; nephridial duct very thin and transparent. Sperm sac extends forward to VIII, and backward to XII–XV. Egg sac back to XIII–XVII.

Two pairs testes, in segments IX and X, and one pair ovaries in segment XI. Two vasa deferentia per atrium (semiprosoporous condition), originating in sperm funnels located in the septa of intersegment 9/10 and 10/11, respectively. Posterior vas deferens not entering segment XI. Vasa deferentia very narrow (8-14 µm diameter), joining the atrium in the ectal (or basal) part of the ampulla, and running through the atrial musculature to the apical part of the atrium, where they open to the atrial lumen (Figs 4B, C, 5H, J). Atrium tubular, with elongated ampulla (86-120 µm long, 26-36 µm diameter) and short duct (34-40 µm long, 24-26 µm diameter). Atrial muscle layer thin, 2-3 μm thick. The columnar inner epithelium of the atrial duct can extend beyond the male pore forming a short, protrusible penis (less than 40 µm long, when protruded) formed by the extension of lining cells of the atrial duct (Figs 4C, 5G, K), extended cells may appear vacuolated. Atrial ampulla with ciliated lumen, and covered by 8-10 well-separated prostate glands formed by clusters of cells, each of which tapers to form a narrow stalk before joining the ampulla (Figs 4C, 5I, J).

Female funnels large, attached to the septum and opening in intersegment 11/12 (Fig. 4B). Three pairs of spermathecae, the first in the atrial segment (X), and the next in the ovarian (XI) and post ovarian (XII) segments. The spermathecae are formed by a bottle-shaped duct (34-86 µm long, 22-38 µm maximum diameter) and an oval ampulla (54-120 µm maximum diameter and 34-90 µm minimum diameter), filled by loose sperm (Figs 4B, 5L). In several of the examined specimens, the ampullar epithelium appeared very much vacuolized, with some vacuoles containing resorbed sperm.

Taxonomic remarks.

Cookidrilus pocosinus sp. n. has been ascribed to the genus Cookidrilus Rodriguez & Giani, 1987 based on the main diagnostic characters of the genus: 2 pair testes and one pair ovaries, two (anterior and posterior) vasa deferentia joining each atrium, one pair spermathecae in the atrial segment, and subsequent pairs of spermathecae in postatrial segments ( Rodriguez and Giani 1987). The groundwater lumbriculid genus Cookidrilus was originally described from the Labouiche Cave in southern France. Since then, another species has been described from the hyporheos of Lachein Creek, a karstic stream in the same geographic region ( Route et al. 2004). In the present study, a third species is described from coastal plain habitats of North Carolina (USA), mostly from acidic swamp streams.

In Table 3, we have summarised the main morphological features that distinguish the three species of the genus Cookidrilus . The new species is closer to the type species of the genus, Cookidrilus speluncaeus Rodriguez & Giani, 1987, based on the presence of three pairs of spermathecae instead of only two pairs in Cookidrilus ruffoi Giani et al., 2004 (in Route et al. 2004). However, it resembles Cookidrilus ruffoi in the structure of the prostatic cell layer, which is organised in well-separated clusters that join the atrial ampulla by distinct stalks. The new Nearctic species Cookidrilus pocosinus is distinguished from both European species by the singular position of the spermathecal pores in front of the ventral chaetae, instead of behind the chaetae (the most common position in lumbriculids). The genus Cookidrilus , previously amended by Route et al. (2004), is now further amended to include some additional diagnostic features.

In the original description of the genus, Rodriguez and Giani (1987) discussed the taxonomic relationships of Cookidrilus with other lumbriculids ( Kincaidiana Altman, 1936 and Guestphalinus Michaelsen, 1933) having a pair of spermathecae in the atrial segment. Kincaidiana hexatheca Altman, 1936 is endemic to North America where there are also representatives of the genus Guestphalinus (S. Fend, unpublished data). However, although the former has a similar arrangement of spermathecae to Cookidrilus speluncaeus , a combination of characters clearly distinguishes it from Cookidrilus : a proboscis, a forward shift of reproductive organs, a single pair of testes, and one prosoporous vas deferens per atrium ( Fend 2009). In addition, morphology of the atria, spermathecae, and chaetae does not resemble that of the known Cookidrilus species. Guestphalinus is semiprosoporous, but has only one pair of spermathecae, and like Kincaidiana , has a proboscis. Guestphalinus also has a forward shift in reproductive organs relative to the position in Cookidrilus .

The presence of penis may be a common generic character in Cookidrilus , since it is only absent in the type species, Cookidrilus speluncaeus . On the other hand, Cookidrilus ruffoi differs in the number of spermathecae. The analysis of lumbriculid genera performed by Brinkhurst (1989) stated that characters related to number and placement of the spermathecae (characters 7 and 9 in that analysis) were subject to changes/reversals in the resulting phylogenetic tree, and such variations are probably not highly significant. Thus, variation in number of spermathecal segments within Cookidrilus (3 in two species, versus 2 in Cookidrilus ruffoi ) is not extraordinary, as similar variation occurs in other lumbriculid genera such as Trichodrilus and Rhynchelmis Hoffmeister, 1843 (see Cook 1971).

The position of spermathecal pores in front of the ventral chaetae is an unusual feature of the new Cookidrilus species. Spermathecal pores in lumbriculids are usually placed behind the chaetae of the corresponding segment, and in the other 2 species of Cookidrilus , even the first spermatheca opens in the narrow space between the ventral chaetae and the male pores. This character is shared with several Nearctic lumbriculids: Kincaidiana hexatheca (for the first pair of spermathecae), some Rhynchelmis species (in Fend and Brinkhurst 2000), and Eclipidrilus pacificus Fend, 2005.

Ecological remarks.

Cookidrilus pocosinus sp. n. appears to have a life cycle adapted to seasonal drying of surface flow. This is the first record of Cookidrilus in North America, and it is also the first report of the genus in a non-subterranean habitat. This species has been found so far in four North Carolina streams, but almost all specimens were from Lake Run and Pettiford Creek. These streams are both located in the southern Coastal Plain, in relatively undisturbed watersheds, and drain pocosin areas with peat soils. Both streams have extremely low pH values (often less than 4.0), very low conductivity, and dry up completely during summer droughts. In Lake Run, most specimens were found in shaded sections, in midstream areas with both good flow and a fine sand substrate. In Pettiford Creek, the substrate consisted of fine sand covered by a layer of organic debris. These data indicate that Cookidrilus pocosinus is usually associated with very low pH, although single specimens were collected from a seasonally inundated side channel of Drowning Creek, and from the main channel of Anderson Creek. Both of those streams have average pH values near 5.5.

Diagnosis of the genus

(amended by Route et al. 2004, and modified here with additions in italics): Type species. Cookidrilus speluncaeus Rodriguez & Giani, 1987.

Chaetae sigmoid, simple-pointed. One pair male pores in segment X (the second testis-bearing segment), behind and in line with the ventral chaetae. Two or three pairs spermathecae; first pair in the atrial segment, anterior to male pores, and one pair in the first, or in the first and second postatrial segments. Two pair testes, in IX and X. One pair atria in the second testicular segment. Semiprosoporous male duct, two vasa deferentia per atrium. Prostatic cells either in a simple diffuse layer or forming discrete clusters. One pair ovaries located in the first postatrial segment (XI).