Enchytraeus sp. 1

Erséus, Christer, Klinth, Mårten J., Rota, Emilia, De Wit, Pierre, Gustafsson, Daniel R. & Martinsson, Svante, 2019, The popular model annelid Enchytraeus albidus is only one species in a complex of seashore white worms (Clitellata, Enchytraeidae), Organisms Diversity & Evolution (New York, N. Y.) 19 (2), pp. 105-133 : 129

Enchytraeus sp. 1

Material examined SMNH 172893-172894 ( CE4859 - CE4860 ), two half mature specimens from Skopelos Island , Aegean Sea , Greece. For information on voucher collection locality and GenBank accession numbers, see Table 1 . Skopelos, Perivouli beach, NE of Glossa, 39° 11.84′ N, 023° 36.90′ E, in high intertidal sand, leg. C. Erséus, 21 Aug 2008 .

External characters Color white. Length of first 28–45 segments> 4–8.4 mm (fixed, amputated specimens); first 12 segments (anterior end to clitellum) 1.6–2.2 mm long; width at clitellum 0.46–0.77 mm. Chaetae straight or slightly curved entally. Lateral and ventral bundles with three–four chaetae anterior to clitellum, three chaetae in postclitellar segments. Chaetae longest in preclitellar ventral bundles ( VIII – XI) measuring 125–135 by about 10 μm. Clitellum not developed. Head pore between prostomium and peristomium. Epidermis with transverse rows of gland cells.

Internal characters Coelomocytes about 15 μm long, round, oval or spindle-shaped, granulated and with distinct nucleus. Paired pharyngeal glands present in IV, V, and VI. All pairs converging dorsally, first pair small, second pair largest. Esophageal appendages (peptonephridia) extending from dorsal wall of esophagus in III. Dorsal vessel seemingly originating in XV. Nephridia difficult to discern but pores of nephridial efferent ducts possibly observed in 5/6–7/8, and 8/9 and in some postclitellar segments, shape uncertain. Brain longer than wide, posterior margin straight.

Male genitalia paired. Developing testes in XI, penial bulbs and ovaries in XII. Rudimentary spermathecae in V.

Remarks Although this Aegean Sea species is yet unidentified, and no details about its genital characters are known, the DNA-based phylogeny ( Fig. 2 ) suggests that it is likely to be part of the E. albidus complex, and more closely related to E. cf. krumbachi than to the other species included here. Geographically, the record of E. sp. 1 is closest to the type locality of E. krumbachi in the Adriatic Sea ( Čejka 1913).

According to the original description (op.cit.), E. krumbachi has lateral bundles with three chaetae and ventral bundles with four chaetae. Both our specimens of E. sp. 1 have three chaetae in all postclitellar bundles, both ventrally and laterally, but these differences may be due to the fact that our specimens are not mature.

Interestingly, the size of the chaetae in E. sp. 1 is the largest recorded in this study and recalls that of E. mediterraneus , described by Michaelsen (1926) from Posidonia detritus in Djerba (Southern Tunisia). E. mediterraneus is a very large worm (26 mm long, with 90 segments), with 3–4 chaetae in all bundles (each chaeta measuring 150 by 10 μm at midbody), pharyngeal glands dorsally fused and with large ventral lobes, dorsal vessel from XVIII, sperm funnels three times longer than wide, vas deferens reaching XXI and with diameter measuring 40–50 μm entally, 85 μm along the mid portion and 27 μm near the male apparatus, spermathecal ampulla onionshaped with some small indistinct ectal swellings, ectal duct as long as ampulla but much thinner, and completely devoid of glands. As our specimens are immature, most of these char- acters cannot be compared to the description of E. mediterraneus . We therefore prefer to keep this Aegean material unidentified until fresh material of E. mediterraneus can be examined and barcoded.

Distribution and habitat Known only from the high intertidal of a beach on the island of Skopelos, Greece. The sand at this site appeared poor in decaying organic material.

Figures

Fig. 2 Species tree for the E. albidus species complex (shaded), estimated using the multi-locus coalescent model. The number of included speci- mens for each species is given after the species name. Values above branches are posterior probability (PP) support values, values under terminal branches are mean PP from species delim- itation analyses in BPP, written as: mean analysis A/mean analysis B/ mean analysis C. Scale measures the branch lengths in proportion to total tree length