Hyalopomatus dieteri Kupriyanova & Ippolitov, 2015, sp. nov.

Hyalopomatus dieteri sp. nov.

Figures 1 F, 11, 12

Material examined. R/V CORIOLIS, cruise BIOGEOCAL, 1987, East of New Caledonia, St. CP260: 17.4.1987, 21°00.00'S, 167°58.34'E, 1820–1980 m (holotype MNHN POLY TYPE 1564, 1 tube fragment prepared for SEM and X-ray diffraction analysis PIN 5485/16).

R/V JEAN CHARCOT, cruise BIOCAL, 1985, approximately 100 km South of New Caledonia, St. CP27, 29.8.1985, 23°05.52'S, 166°26.41'E, 1900 m (1 paratype without radioles AM W.46386, partly prepared for SEM).

Description. Tube: white opaque, ostensibly free, with shiny surface, straight, thick-walled, mostly quadrangular in cross-section, edges rounded and never denticulate. Juvenile tubes with sharper keels, becoming rounded in adults. Tubes slightly twisted, growth stops accompanied by sudden turns of tube around growth axis. Sides usually slightly convex, sometimes slightly concave.

Tube ultrastructure: wall unilayered with irregularly oriented prismatic (IOP) structure, in inner wall part transforming into semi-ordered irregularly oriented prismatic (SOIOP). Tube wall not clearly subdivided into layers, in longitudinal section revealing only larger isometric to slightly elongated crystals with size up to 5 µm long (Fig. 11 A–D). Crystal size smallest near lumen (Fig. 11 D), increasing in middle (Fig. 11 C), and becoming largest in outer part of the wall (Fig. 11 B). Cross-section showing distinct zone in inner wall part consisting of highly ordered cigar-shaped crystals (5–6 µm in length, 1–1.5 µm in diameter, Fig. 11 J) with long axes oriented parallel to tube surface (Fig. 11 E, J) resulting in SOIOP ultrastructure; in longitudinal sections this structure is unrecognizable. Transition from IOP to SOIOP structure gradual (Fig. 11 J). Parabolic growth lamellae (Fig. 11 A, C) present in all studied sections, axis of parabolae located in wall centre.

Tube mineralogy: 97–100% aragonite (I arag=69), doubtful calcite content.

Radiolar crown: with 7 pairs of radioles in holotype (radioles mostly missing in paratype), arranged pectinately, easily detachable from short radiolar lobes. Inter-radiolar membrane and stylodes absent. Terminal filaments of radioles thin, spirally twisted. Radiolar eyes and mouth palps not observed.

Peduncle: smooth, cylindrical, thin (approximately same thickness as radioles), distal wings absent; inserted conspicuously outside radiolar crown proper, between base of 1st and 2nd radioles (Fig. 12 B).

Collar and thoracic membranes: collar covering radiolar lobes, thin; trilobed, with ventral lobe slightly higher than the lateral ones (Fig. 12 B). Collar continuous with short thoracic membranes ending at 2nd chaetiger.

Operculum: soft membranous, semi-transparent, mostly globular, but with flattened top, slightly differentiated from the basal part; conspicuous constriction and additional small vesicular ampulla between operculum and peduncle (Fig. 12 A). Pseudoperculum absent.

Thorax: with 6 chaetigerous segments, 5 of which uncinigerous. Small bundle of collar chaetae, of two types: simple limbate and fin-and-blade with the distal blade separated from the basal fin by a short gap (Fig. 12 C, D). Subsequent chaetae limbate, of two sizes, Apomatus -chaetae absent (Fig. 12 E). Uncini along entire thorax raspshaped, with 20–25 small teeth in profile view, with 6–8 teeth in the row above flat anterior peg made of 3–4 rounded lobes, dental formula P:8:7:7:7:6:6:6:6:6:6:6:6:?:?:?:?:?:?:? (Fig. 12 F, G). Pair of prostomial eyes absent. Triangular depression absent, thoracic tori almost parallel to mid-ventral line of the thorax.

Abdomen: with up to 60 segments. Chaetae long, nearly capillary with only narrow geniculate tip clearly made of two rows of pointed teeth (Fig. 12 I). Capillary chaetae present in posterior chaetigers. Uncini rasp-shaped with over 20 teeth in profile and up to 9 rows of teeth (Fig. 12 J, K) above anterior peg flat divided into 3–5 rounded lobes (crenulated). Dental formula P:9:7:5:4:3:4:3:2:?:? or P:8:5:5:5:4:4:4:?:?. Achaetous anterior abdominal zone long.

Size: total body length up to 15 mm, including up to 9 mm long radioles, width of thorax up to 0.5 mm. Tubes incomplete and broken into fragments, maximum total length of fragments (in paratype) 40 mm. External tube diameter up to 1.3 mm, corresponding lumen diameter 0.9 mm. Thickness of tube wall in between the angular margins about 1/3–1/4th of outer diameter, and up to 1/2 when measured across keels.

Etymology. The species is named after Dr. Dieter Fiege (SMF) in recognition of his important contributions to taxonomy of Serpulidae.

Distribution. Coral Sea off New Caledonia, 1820–1980 m.

Remarks. The new species from New Caledonia resembles H. macintoshi (Gravier, 1911) in having a globular transparent, only slightly differentiated operculum. However, the tube of H. dieteri sp. nov. is distinct in being polygonal (quadrangular).

Four other Hyalopomatus spp. with known tube ultrastructures are H. variorugosus Ben-Eliahu & Fiege, 1996 (see Sanfilippo 1998a; Vinn et al. 2008), H. claparedii Marenzeller, 1878, H. marenzelleri Langerhans, 1884 and H. madreporae Sanfilippo, 2009 (see Sanfilippo 2009). Ultrastructural type and shape of crystals of H. variorugosus are very similar to those of H. dieteri sp. nov., despite chaotic orientation of crystals without defined SOIOP ultrastructure in the former. H. marenzelleri demonstrates squat prismatic crystal shapes, but the ultrastructure type is still the same (IOP). The closest to H. dieteri sp. nov. is H. claparedii that has a well-defined SOIOP ultrastructure near the lumen (Sanfilippo 2009, fig. 6E) with a gradual transition to IOP ultrastructure in the outer part of the tube wall. The tube of H. madreporae also shows a similar pattern, but its SOIOP zone (Sanfilippo 2009, fig. 4G) seems to be relatively wider than those in both H. dieteri sp. nov. and H. claparedii. All Hyalopomatus spp. studied to date have very similar tube ultrastructures supporting the generic placement of the new species described herein.