Olavius nivalis, 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 : 55-57

Olavius nivalis sp. nov.

Figure 6

Material examined

Holotype: SMNH Type Coll. 6400, whole­mounted specimen.

Type locality: New Caledonia, off Touho, S end of Grand Récif Mengalia, intertidal (Station NC93­13).

Paratypes: SMNH Type Coll. 6401–6409, 9 specimens: 7 from type locality, and 1 from each of NC93­9 and NC93­33.

Other material: SMNH Main Coll. 85125–85139, 15 specimens: 9 from type locality, and 3 from each of NC93­9 and NC93­33.

Description

Large species, 12–34 mm, with 67–168 segments. Width at XI, 0.36–0.58 mm. Body cylindrical. Prostomium rounded, in most specimens somewhat longer than wide. Pygidium variable, sometimes much longer then wide, tapering with rounded tip. Clitellum extending over 1/ 2X –2/ 3XII. Secondary annuli 3–4 per (postclitellar) segment. Somatic chaetae ( Fig. 6 A) bifid, with upper teeth thinner and shorter than lower, and each with conspicuous subdental ligament. These chaetae 60–85 m long, about 5 m thick, 2 per bundle throughout body. Penial chaetae ( Figs. 6 B; 6C, pc) 50–75 m long, about 2.5 m thick, 4–7 per bundle, straight and more or less parallel within bundle, with single­pointed and strongly curved tips. Spermathecal pores paired, located in line with dorsal somatic chaetae, anteriorly in X. Male pores paired, located in line with dorsal chaetae, in posterior part of XI.

Male and female genitalia ( Fig. 6 C) paired. Vas deferens not muscular, 12 m wide for most parts, longer than atrium, coiled, gradually narrowing into atrium, cilia not observed but probably present inside. Atrium curved, somewhat kidney­shaped, 85–165 m long, about 35–75 m wide, with thin indistinct muscular layer, but cilia not observed in inner epithelium. Two large, somewhat lobed, prostate glands present, one located anterior to and attached to ental part of atrium, other located posterior to and attached to ectal end of atrium by broad stalk. Atrium opening into inner end of complex copulatory sac with heavily folded wall; this sac communicating with exterior through small (male) pore (pore not shown in Fig. 6 C, as it is hidden under copulatory sac). Spermathecae ( Fig. 6 C, s) slender, thin­walled, totally 185–265 m long, with ampullae 22–36 m wide, and ducts only 24–36 m long, 14–22 m wide, shape of ampullae somewhat variable, but typically bipartite, with inner about two thirds separated from outer part by a constriction. Each spermatheca contains bundle of sperm.

Etymology

Named Olavius nivalis (Latin for “snow white”) due to its distinctly white colour.

Remarks

Olavius nivalis is one of the largest species of gutless Phallodrilinae known to date; otherwise is seems to be closely related to O. lifouensis sp. nov. (see above). Both species have few secondary annuli, stout somatic chaetae in bundles of two throughout the worm, multiple but rather short penial chaetae, dorsal spermathecal pores, deeply folded copulatory sacs (lacking particular papillae inside), and filiform spermathecae. In addition to the difference in general body dimensions, however, O. nivalis is distinguished from O. lifouensis by its lack of a narrow duct­like portion set­off from the main body of the atrium.

Distribution and habitat

New Caledonia (Grande Terre). Intertidal and and barely subtidal coarse sand.

Discussion

The South­west Pacific Ocean appears to be one of several hotspots for gutless Phallodrilinae in the world. Thirteen species had been reported from Queensland ( Australia), the Solomon Islands and Fiji ( Jamieson 1977; Erséus 1981, 1984) prior to the present work, one being a yet unnamed species closely related to Olavius avisceralis ( Erséus, 1981) (see Erséus 1997). With the addition of the six new Olavius species from New Caledonia, the total score is now 19 species (15 Olavius , 4 Inanidrilus ) from this area. Nevertheless, several other new taxa and range extensions in this part of the world are yet to be accounted for; e.g., the first author’s collections from New Caledonia contain a number of other gutless species, previously known only from Australia’s Great Barrier Reef, and these and other new records, from Lord Howe Island and the Great Barrier Reef, will be treated elsewhere (Erséus, in prep.).

Olavius is morphologically a more heterogeneous group of species than Inanidrilus , and as noted above, Inanidrilus appears to be phylogenetically nested within Olavius (Erséus et al. in prep.). While the species of Inanidrilus are numerous in the Caribbean area (Atlantic Ocean) (see Erséus 2003), those recognized as members of Olavius are more predominant in the Indo­West Pacific ( Erséus 1981, 1984, 1990b, 1993, 1997; present paper). It has proved difficult, however, to establish the sister group to Inanidrilus within Olavius (Erséus et al. in prep.), and a thorough revision of the whole complex, based on morphological as well as DNA data, is badly needed.

In the Olavius assemblage, certain subgroups are each composed of morphologically very similar species. One, here referred to as the “ albidus group”, contains a high number of Indo­West Pacific forms with similar appearance of the atrium/copulatory sac and the number and shape of penial chaetae (these chaetae about 3 per bundle and with characteristically hooked tips). The members of this group are O. albidus ( Jamieson, 1977) , O. propinquus , an unnamed form similar to propinquus from Western Australia (reported as O. propinquus by Erséus 1993; but see Remarks for O. isomerus sp. nov. above), O. albidoides Erséus, 1997 , O. capillus Erséus, 1997 , and O. isomerus sp. nov. Two of these species ( O. albidoides and O. capillus ) are partly sympatric (at Montebello Islands, Western Australia) and exhibit clear morphological differences. However, for two species pairs in particular, O. propinquus / O. isomerus sp. nov. and O. loisae / O. paraloisae sp. nov. (both pairs treated in respective Remarks above), the respective forms are allopatric but show very small differerences, which means that they could be interpreted as geographical variants of a single, widely distributed species. This can only be resolved by molecular systematic methods that can establish the genetic distance between the populations/forms, preferably in combination with morphological data. For the time being, a conservative, morphology­based approach has been chosen, assigning these geographical forms to separate taxa, regardless of whether they in a “biological” or other meaning are true species. It appears that the propinquus / isomerus complex, as well as the rest of the “ albidus group” may be a suitable object for a further genetic studies of speciation and radiative patterns in gutless phallodrilines.

Figures

FIGURE 6. Olavius nivalis sp. nov. A) somatic chaeta, B) bundle of penial chaetae, C) lateral view of spermatheca and male genitalia in segments X – XI.