Dysponetus populonectens Pleijel, Aguado & Rouse, 2012, new species

Dysponetus populonectens, new species

Figs 1, 2

Dysponetus sp. Rouse & Pleijel 2007, fig. 4A.

Type material: Holotype (in two pieces) SIO-BIC A2583, paratypes SIO-BIC A2584, SIO-BIC A2585, SIO-BIC A2586, SIO-BIC A2587, SIO-BIC A2588, SIO-BIC A2589, SIO-BIC A2590, SIO-BIC A2591, SIO-BIC A2592, SIO-BIC A2593, SIO-BIC A2594.

Material examined: California. Holotype (SIO-BIC A2583), male, initially entire but broken during preservation, preserved in formaldehyde, La Jolla, off La Jolla Cove, 32°50.713’N, 117°17.058’W, 12 m depth, Macrocystis pyrifera holdfasts, SCUBA, colls FP and GWR 29 Aug 2007; 2 entire spms preserved in RNALater, same collection data, (in GWR collection); 2 entire spms preserved in osmium tetroxide for SEM, same collection data, destroyed; 1 entire spm preserved in ethanol, same collection data, destroyed for DNA sequencing, 1 paratype (SIO-BIC A2584), posteriorly incomplete female preserved in formaldehyde, same collection data; 2 paratypes (SIO-BIC A2585), entire spms preserved in formaldehyde (larger spm male), same collection data; 1 paratype (SIO-BIC A2586), entire female preserved in ethanol, La Jolla, Bird’s Rock, 32°48.367’N, 117°17.181’W, 18 m depth, Macrocystis pyrifera holdfast, coll. Eddie Kisfaludy 2 Feb 2010; 1 paratype (SIO-BIC A2587, SIO-BIC A2588), entire female, anterior end preserved in formaldehyde, posterior end preserved in ethanol, same collection data; 1 paratype (SIO-BIC A2589, SIO-BIC A2590), posteriorly incomplete male, anterior end preserved in formaldehyde, posterior part preserved in ethanol, same collection data; 2 paratypes (SIO-BIC A2591), 1 entire male and 1 entire female preserved in ethanol, 32°50.26’N, 117°17.11’W, 15 m depth, Macrocystis pyrifera holdfasts, SCUBA, colls GWR & Phil Zerofski 15 Oct 2010; 2 paratypes (SIO-BIC A2592), 1 entire male and 1 entire female preserved in ethanol, same collection data; 3 paratypes (SIO-BIC A2593), 2 entire males and 1 entire female preserved in ethanol, same collection data; 1 paratype (SIO-BIC A2594), entire female preserved in ethanol, same collection data.

Description: Up to 5.5 mm long for 36 segments. Live specimens transparent yellowish orange, males opaque white (Fig. 1 A), females with orange eggs (Fig. 1 B). Mid-dorsal blood vessel broad and distinct, red. Eyes bright red. Preserved specimens whitish. Body in dorsal view symmetrically tapering towards both ends (Fig. 1 A, B), venter flattened. Prostomium rounded quadrangular in dorsal view. Palps elongated cylindrical with tapering ends, palpophores absent (Fig. 2 A, B). Paired antennae as long as palps, with rounded basal parts and long, fine tapering ends (Fig. 2 A). Median antenna similar to paired antennae but with shorter tip, inserted frontally on prostomium (Fig. 2 A, B). Eyes large, rounded, anterior and posterior pairs of equal size. Nuchal organs not observed. Everted proboscis not observed, internally with single pair of lateral stylet-shaped jaws. Ventral mouth flap cone-shaped (Fig. 2 A, B). Segment 1 with dorsal and ventral cirri only, segment 2 with dorsal cirri, notopodial lobes with notochaetae and ventral cirri but no neuropdial lobes or neurochaetae; segment 3 with dorsal cirri, notopodial lobes with notochaetae, neuropodial lobes with neurochaetae, but no ventral cirri. Segment 4 similar to remaining segments. All anterior dorsal and ventral cirri of similar shape to following ones. Dorsal cirri of median segments inserted postero-ventrally to notochaetal bundle, with small cirrophores, with inflated basal part and long tapering tips (Fig. 2 D). Notopodial lobes with small, conical postchaetal extension. Notochaetae about 25 (Fig. 2 C), all curved with two rows of teeth, internally chambered, with distinct diaphragms but without visible longitudinal canals in LM. Neuropodial lobes conical. Neurochaetae all compounds except for single accessory simple chaeta (similar to notochaetae but smaller, positioned antero-dorsally in chaetal bundle), compounds about 25 (Fig. 2 D), shafts with distinct internal longitudinal canals and diaphragms, blades with well developed teeth and very fine, bidentate tips. Blades of median and dorsal compound chaetae about 2.5 times longer than those of ventral ones. Noto- and neuroaciculae single, internally with longitudinal canals but no distinct diaphragms. Ventral cirri with small cirrophores, inserted subdistally on underside of neuropodium, similar in shape to dorsal cirri but smaller (Fig. 2 E). Pygidium forming pointed cone, without cirri (Fig. 2 F). Egg size in mature females ca. 100 µm.

Etymology: “ populonectens ” is Latin for “connecting people”, the motto of Nokia USA, San Diego in acknowledgement of their support for the Scripps Institution of Oceanography Collection Endowment.

Habitat: Only known from holdfasts of Macrocystis pyrifera at 12–18 m depth.

Remarks: Mature specimens collected both in February, August and October, indicating that breeding may be continuous throughout the year. In the present material the mature males tend to be of larger size than the females.

There are nine species previously referred to Dysponetus (Dahlgren 1996). Among these, D. caecus (Langerhans, 1879) from Madeira, D. gracile Hartman, 1965 from off New England, D. paleophorus Hartmann- Schröder, 1974 from Skagerrak, and D. pygmaeus Levinsen, 1879 from Greenland, all differ from D. populonectens n. sp. in lacking eyes. Dysponetus hebes (Webster & Benedict, 1887) from Maine has a single pair of eyes, sphaerical palpostyles and double mouth appendages (Dahlgren 1996), D. bidentatus Day, 1954 from Tristan da Cunha lacks ventral cirri on both segment 2 and 3 (Dahlgren 1996), whereas these are present on segment 3 in D. populonectens n. sp., the Mediterranean D. bipapillatus Dahlgren, 1996 is very small and has few segments (maximum observed size 11.1 mm long for 13 segments, mature specimens), minute eyes and, probably, males with external genital organs on segment 8 (Dahlgren 1996), and D. macroculatus Dahlgren, 1996 from Papua New Guinea differs from D. populonectens n. sp. in having both noto- and neurochaetae on segment 2, whereas D. populonectens n. sp. only has notochaetae on this segment.

Morphologically D. populonectens n. sp. is closest to the south-west Australian D. bulbosus Hartmann- Schröder, 1982. The original description of D. bulbosus contained errors regarding the distribution of the cirri and chaetae on the anteriormost segments (Hartmann-Schröder 1982), but this was later corrected in a complementary description based on specimens from Adelaide (Hartmann-Schröder 1986). We examined Hartmann-Schröder’s specimens (holotype HZM P-16751 and 4 paratypes HZM P-16752), together with 11 newly collected specimens from Adelaide of which some also were studied with SEM, and conclude that both descriptions appear erroneous and confuse the anterior segments and their appendages. Dysponetus bulbosus is in full agreement with the description of D. populonectens above, with segment 1 provided with dorsal and ventral cirri only, segment 2 with dorsal and ventral cirri and notochaetae but no neuropodia or neurochaetae, and segment 3 with dorsal cirri, noto- and neurochaetae and neuropodial lobes but no ventral cirri.

This also means that Table 1 in Dahlgren (1996), describing morphological features of different species of Dysponetus, needs to be corrected for D. bulbosus. Both species are very similar, except that D. bulbosus appears to be smaller, with the largest observed specimen measuring 3 mm in length for 26 segments, whereas D. populonectens n. sp. has a maximum size above 5 mm in length. However, the COI data shows the two to be genetically well separated with the sequence for D. populonectens n. sp. (GenBank accession number JQ623495) showing an uncorrected pairwise distance of 21.3% from a sequence obtained for this study for Dysoponetus bulbosus (GenBank accession number JQ623501; voucher Swedish Museum of Natural History SMNH 83511).