Olavius isomerus, Erséus, Christer & Bergfeldt, Ulrika, 2007

Erséus, Christer & Bergfeldt, Ulrika, 2007, Six new species of the gutless genus Olavius (Annelida: Clitellata: Tubificidae) from New Caledonia, Zootaxa 1400, pp. 45-58 : 50-52

Olavius isomerus sp. nov.

Figure 3

Material examined

Holotype: SMNH Type Coll. 6381, whole­mounted specimen.

Type locality: New Caledonia, N of Touho, intertidal (Station NC93­33).

Paratypes: SMNH Type Coll. 6382–6389, 8 specimens: 3 specimens from type locality, 4 from NC00­25, 1 from NC00­7.

Other material: SMNH Main Coll. 85081–85110, 30 specimens: 6 from type locality, 1 from each of NC93­24, NC93­53, NC93­61 and NC00­7, 2 from each of NC93­25, NC93­26, NC93­34 and NC93­55, 3 from each of NC93­31, NC93­32, NC93­50 and NC00­25.

Description

Length 4.6–7.2 mm, with 34–53 segments. Width at XI, 0.19–0.23 mm. Body cylindrical. Prostomium rounded. Pygidium variable, with rounded tip. Clitellum somewhat variable but generally extending over 1/ 2X–XII. Secondary annuli 4–5 per (postclitellar) segment. Somatic chaetae ( Fig. 3 A) bifid, with upper teeth thinner and shorter than lower, and each with conspicuous subdental ligament. These chaetae 41–53 m long, about 2 m thick, (2) 3 per bundle in anterior segments, 2 per bundle in postclitellar segments. Penial chaetae ( Figs. 3 B; 3C, pc) slender, 3–4 per bundle, straight and more or less parallel, 48–60 m long, about 1–1.5 m thick, with single­pointed and somewhat curved tips. Spermathecal pores paired, located in line with dorsal somatic chaetae, anteriorly in X. Male pores paired, located more or less in line with ventral chaetae, in posterior part of XI.

Male and female genitalia ( Fig. 3 C) paired. Vas deferens 7–10 m wide for most parts, somewhat muscular, longer than atrium, coiled, gradually widening into atrium, cilia not observed but probably present inside. Atrium C­shaped, 75–135 m long, 24–34 m wide, with thin indistinct muscular layer, but cilia not observed on densely granulated inner epithelium, lumen narrow. Two, somewhat lobed, prostate glands present, one located anterior to and attached to ental part of atrium, other located posterior and attached to ectal end of atrium by stalk. Atrium opening into inner end of a complex copulatory sac, at base of large papilla formed by fold of sac, with heavily folded wall; this sac communicating with exterior through small (male) pore (pore not shown in Fig. 3 C, as it is hidden under copulatory sac). Spermathecae variable, in postcopulatory specimens ( Figs. 3 C, s) with short ducts, and thin­walled, slender, up to about 100 m long ampullae, and latter containing somewhat bundled sperm; most specimens, however, precopulatory, i.e., with spermathecae only 57–95 m long, with short ducts and oval, 24–36 m wide, ampullae, latter empty, apparently not fully developed ( Fig. 3 D).

Remarks

This species is most closely related to Olavius propinquus Erséus, 1984 , originally described from Fiji ( Erséus 1984). However, it is separated from that species by (i) its more numerous somatic chaetae, which are (2)3 per bundle in anterior segments and 2 per bundle in postclitellar segments (the bifids of O. propinquus are consistently 2 per bundle); and (ii) its fewer secondary annuli on the body wall. A form reported as O. propinquus from Rottnest Island, Western Australia, by Erséus (1993), has penial chaetae that are not as straight as those of O. isomerus and the South Pacific O. propinquus . In the light of the variation now noted for these different forms, the Western Australian O. propinquus is likely to be a separate species, and it will be reassigned to a new taxon (Erséus in prep.). See Table 1 for a summary of this information, and Discussion below for further comments.

TABLE 1. Morphological comparison between three closely related, Indo­West Pacific, forms of Olavius .

Distribution and habitat

New Caledonia (Grande Terre and Loyalty Islands); common at Touho, but less so at Lifou. Lower intertidal and shallow subtidal, more or less heterogeneous sand, to at least 3 m depth.

Figures

FIGURE 3. Olavius isomerus sp. nov. A) free­hand drawing of somatic chaeta, B) free­hand drawing of penial chaeta, C) lateral view of (pre­copulatory) spermatheca and male genitalia in segments X – XI, D) spermatheca of another, postcopulatory specimen.