Martinidrilus arenosus, Fend, Steven V. & Lenat, David R., 2007

Fend, Steven V. & Lenat, David R., 2007, Two new genera of Lumbriculidae (Annelida, Clitellata) from North Carolina, USA, Zootaxa 1666, pp. 1-22 : 15-17

Martinidrilus arenosus n. sp.

Holotype: USNM 1107802. A whole-mounted specimen, stained in borax carmine, collected by S. Fend and D. Lenat, 15 March 2007.

Type locality: North Carolina: Richmond Co.: Drowning Creek at SR 1004, N35º 03’ 58.3”, W79º 32’ 58.4”. Collected in fine gravel, in relatively fast current.

Paratypes: USNM 1107803-1107805. From the type locality: 15 March 2007, 1 whole mount, stained with hematoxylin. 26 April 2007, collected by D. Lenat, 1 dissected on slide, stained with carmine. North Carolina, Carteret Co.: Pettiford Creek, N33º 44’ 50”, W77º 01’ 20”, 16 March 2007 collected by S. Fend and D. Lenat, 1 dissected on slide, stained with hematoxylin.

Other material: From the type locality: 15 March 2007, 2 dissected on slides. 26 April 2007, 1 partially mature whole mount.

Etymology: The specific epithet refers to its distribution in the Sand Hills region, North Carolina.

Description. Small worms, length of preserved specimens 20–26 mm; maximum diameter usually in clitellum, 0.35–0.57 mm; 76–88 segments. Prostomium rounded, slightly shorter than wide, separated from the peristomium by a distinct groove. Secondary segmentation consists of an anterior annulus in segments beginning with IV; the anterior annulus is 1/5 the segment length through about VI, 1/4 the segment length posteriorly, but annulation may be very faint in the clitellum or in segments that are extended ( Fig. 9 A). Chaetae paired, in 4 bundles in each segment, beginning in II. Chaetae slightly sigmoid, simple-pointed, with nodulus slightly ectal to the midpoint, 0.35–0.43 the distance from the tip. Chaetae in preclitellar segments near midsegment, but in postclitellar segments they are near the posterior third. Chaetal length about 80–100 Μm in clitellar region and anterior, 60–65 Μm posteriorly.

Epidermis in anterior segments 15–20 Μm thick; in clitellum to 35 Μm in one specimen. Anterior segments appear to have indistinct midventral glands ( Fig. 9 C), but no obvious external pores. Clitellum thin but glandular, from mid-IX to mid-XIII in one specimen. A distinct, dorsal pharyngeal pad as described for M. carolinensis . Pharyngeal glands IV or V–VII. Nephridia as described for M. carolinensis .

Main dorsal and ventral blood vessels prominent, without secondary longitudinal vessels. One pair of commissural blood vessels in II–X; prominent and convoluted in II–VII, but shorter and difficult to see in IX– X. Perivisceral sinus begins in about VIII; chloragogen begins in about VII. Dorsal vessel closely appressed to top of gut behind about XVI. Starting near XVII–XX, the dorsal vessel has 5 or more very short, blind blood vessels; by about XXXV up to 10–15 blind vessels, some 1/4 to 1/2 as long as the body width; some have 2–3 branches near the base ( Fig. 9 B). Blind vessels become shorter behind segment LV. Usually two short blood vessels join ventral vessel to perivisceral sinus in each segment.

Male pores paired in X, behind chaetae on or slightly lateral to ventral chaetal lines, may be conspicuous on low porophores about 80–115 μm wide, to about 30–40 μm high ( Fig. 9 A, 9G) Female pores small, paired, on chaetal line at intersegmental groove 11/12; female funnels simple, 110 μm high. Spermathecal pores are narrow vertical slits (12 μm long), but ends of spermathecal ducts may be prominent, to 30 μm across in external view; pores on dorsal chaetal lines behind dorsal chaetae in VII and VIII ( Figs. 9 A, 9C). Paired testes large on anterior septa in IX and X, extending to mid-segment or posteriorly. Ovaries paired in XI, extending to posterior septum. Sperm sacs do not extend anteriorly; posteriorly extend as far as XVI or XVII. Egg sacs extend as far as XXIII in one worm.

Spermathecal ducts 60–90 μm long. A conical ental section about 30–45 μm wide tapers to a narrow neck; the ectal section widens to about 30–35 μm ( Figs. 9 D). Spermathecal ampullae in VIII long and sacciform, remaining in VIII or entering XI; length 420–600 μm and diameter to 120 μm in the two mated worms. Spermathecal ampullae in VII ovate, 210–230 μm long by 120–140 μm wide. Spermathecae in VIII are also larger than those in VII in unmated worms. Lining cells not differentiated in different parts of the ampulla; all cuboidal, thickness variable (12–25 μm) but relatively uniform within an individual. Sperm loosely packed and uniform throughout.

Male funnels paired, simple and directed forward; posterior lips 60–120 μm high on 9/10 and 10/11; funnels on 9/10 slightly smaller than those on 10/11. Anterior vas deferens 320–590 μm long; the posterior 330– 450 long, forming a short loop into XI ( Figs. 9 C, 9E). Both vasa deferentia up to 25–29 μm thick, but narrow to 20 μm or less as they join a short, narrow common duct (length 40–55 μm, width 17–19 μm); the common duct approaches the atrial ampulla from the posterior-median side, joining it apically or subapically.

Atria irregularly ovate to pyriform, not differentiated into a distinct ampulla and duct ( Figs. 9 F–G). The main portion 70–85 μm long; widest entally, to 46–65 μm. Atrial muscle layer very thin, about 2 μm thick; epithelium about 12–20 μm thick, surrounding a narrow lumen (7–18 μm wide). The atrium is loosely covered by up to about 20 irregular, petiolate prostate glands; prostates 40–100 μm long. Prostate cells usually very granular; up to about 30 cells in the larger prostate glands. Ectally, the atrium narrows and terminates within a pad of slightly elongated epidermal cells; the pad may be slightly produced as a low porophore.

Remarks. Martinidrilus arenosus is similar to M. carolinensis , but is easily distinguished by the number and position of the spermathecae. These are located in VII–VIII (instead of only in VI), and the pores are positioned more dorsally within the segment, on the dorsal chaetal line, instead of on the lateral line. The atria are generally shorter, lack a distinct ectal duct, and have a thinner muscle layer. Based on limited material, the male pores may be on low, indistinct mounds (porophores) instead of on distinct papillae within shallow pits. Although the posterior blood vessels are slightly different from those of M. carolinensis , the presence of multiple blind vessels in posterior segments seems to be a good synapomorphy. Other synapomorphies include the general form of the atria, the common duct joining the paired vasa deferentia to each atrium, and the anterior and dorsolaterally-placed spermathecae.

Martinidrilus arenosus has only been collected at two sites, and few specimens were obtained. At Drowning Creek, the only site where it occurred sympatrically with carolinensis , there was no overlap in distinguishing characters: all mature and partially-mature worms had spermathecal pores either midlateral on VI ( carolinensis ), or dorsolateral on both VII and VIII ( arenosus ).

Figures

FIGURE 9. Martinidrilus arenosus. A. Dorsolateral view of a whole worm (note worm was cleared, so ventral chaetae are underneath). B. Short lateral vessels branching off the dorsal vessel in two posterior segments. C. Reproductive segments (gonads not shown). D. Spermathecae in VII (left) and VIII. E. Male ducts and atrium. F. Atrium and male pore of an unmated worm, Drowning Creek. G. Atrium and male pore of a mated worm from Pettiford Creek. Scale bars: A 1 mm; B 50 μm; C 400 μm; D, E 200 μm; F, G 100 μm.