Hyalopomatus madreporae, Sanfilippo, 2009

Sanfilippo, Rossana, 2009, New species of Hyalopomatus Marenzeller, 1878 (Annelida, Polychaeta, Serpulidae) from Recent Mediterranean deep-water coral mounds and comments on some congeners, Zoosystema 31 (1), pp. 147-161 : 151-158

publication ID	https://doi.org/ 10.5252/z2009n1a8
persistent identifier	https://treatment.plazi.org/id/303C7715-FFA5-FFC7-FF48-5266552090DA
treatment provided by	Marcus
scientific name	Hyalopomatus madreporae
status	sp. nov.

Treatment

Hyalopomatus madreporae View in CoL n. sp. ( Figs 2-4 View FIG View FIG View FIG )

Hyalopomatus sp. 1 – Sanfilippo 2007: 387.

TYPE MATERIAL (see Table 1). — APLABES, stn AP01, 513 m, 1 complete tube on M. oculata , holotype (PMC. S4h. 15.06.2007).

Paratypes: APLABES, stn AP01, 513 m, 5 tubes on M. oculata , 1 tube on a bryozoan, 4 tubes on the serpulid F. annulata , 94 distal parts and fragments from sediment (PMC.S 4p. 15.06.2007); 1 tube on a chitinous epizoan on M. oculata ( MNHN TYPE 1494); 2 tubes on the serpulid F. annulata ( MNHN TYPE 1495); 8 distal parts and fragments from sediment ( MNHN TYPE 1496).

ETYMOLOGY. — Named after its preferred host, the colonial coral Madrepora oculata .

DIAGNOSIS. — Tube white with smooth shiny surface, circular in cross-section, extremely brittle. Diameter 310 (253-397) µm, length attaining 15 mm. Proximal part more or less curved only partially and feebly adhering to the substrate, suddenly upward bending at a right angle; distal part nearly straight, raised from the substrate at least ½ of its total length ( Fig. 3B View FIG ).

Tubes are segmented owing to some interruptions in calcium carbonate secretion ( Fig. 3 View FIG B-D). One interruption just next the angle between attached and distal erect parts ( Fig. 3C View FIG ). A chitinous inner layer, still preserved in some specimens, keeps joined the adjacent parts ( Fig. 3D View FIG ).

Very weak round thickenings are sporadically visible ( Fig. 4A View FIG ). Crystals and their arrangement are not visible, covered by a regular cryptocrystalline amorphous film ( Figs 2E View FIG ; 4B View FIG ) which occurs also on the edges of tube disruptions ( Fig. 4 View FIG C-E). Outer surface is smooth, very thin and discontinuous growth lines being hardly seen under high SEM magnification ( Fig. 4B View FIG ).

Tube wall 15 µm thick ( Fig. 4F, G View FIG ) consisting of a unique layer with prismatic small calcium carbonate crystals (3-5 µm long) criss-cross arranged, with homogeneous microcrystalline ultrastructure (sensu Hall 1980), or fine complex crossed lamellar structure (sensu Carter et al. 1990). Major axes of crystals are visible only in crosssection ( Fig. 4G View FIG ) giving a layering whatever noticeable in longitudinal section ( Fig. 4F View FIG ).

REMARKS

Description is presently based exclusively on empty tubes, living specimens being lacking. Since most tubes belong to recently dead specimens, which still contain their chitinous inner layer, it can be expected that further samplings will yield living material, to integrate species description.

The new species is quite different from H. variorugosus , easily recognisable thanks to its peculiar sculptured tube described in Ben Eliahu & Fiege (1996) and Sanfilippo (1998). It is by far distinguishable from H. biformis which possesses a triangular attached tube with a high dorsal keel (Hartmann 1960), and from H. langerhansi whose tube is flattened in its attached part, with slight lateral keels. Descriptions of other species point to less obvious tubes characters, allowing as before to distinguish their tubes from those of H. madreporae n. sp.: tube of H. cancerum is attached for most of its length and shows a thickened base increasing area of attachment (Knight-Jones et al. 1997); tube of H. mironovi possesses weakly visible growth rings and round thickenings ( Kupriyanova 1993); tube of H. sikorskii is circular or semicircular in cross-section and rough on its surface ( Kupriyanova 1993).

Tubes of the two species H. macintoshi and H. jirkovi are merely described as smooth. Detailed observations on more than 150 tubes of H. madreporae n. sp., did not show any ornamentation, thus keeping H. madreporae n. sp. apart from most of the known Hyalopomatus species. Moreover, the tube of the new species is distinguishable from likewise smooth tubes of H. macintoshi and H. jirkovi , by its remarkably smaller size. In fact, the mean tube diameter in these two latter species is invariably larger than 750-800 µm – as reported in literature descriptions or indirectly deduced from width of animals inside tubes, when any value is reported.

Only H. variorugosus exhibits a comparably sized tube but, as stressed above,this latter species is morphologically quite different from H. madreporae n. sp.

Finally, comparison of the H. madreporae n. sp. tube with those of H. claparedii ( Fig. 5 View FIG A-D) and H. marenzelleri ( Fig. 5 View FIG E-H) provides that tubes are reminiscent each other; they are always circular in cross-section not increasing in diameter, with proximal part scarcely encrusting substrate and distal part straight and rising from the substrate for a sizeable length. Under light microscopy magnification, tubes seem indistinctly smooth and can be discriminate only based on their sizes. The mean diameter measured for H. claparedii and H. marenzelleri is respectively 480 µm and 780 µm compared to 310 µm for H. madreporae n. sp. (compare Figures 3B View FIG and 5A, E View FIG ).

Further differences can be envisaged by SEM observations on micromorphology of the outer surfaces. In H. claparedii the cryptocrystalline cover is less homogeneous than in H. madreporae n. sp., locally determining areas of loosely-patched crystals along the tube surface ( Fig. 6A, B View FIG ). These areas seem recurrent in accord with growth phases ( Fig. 5D View FIG ). Additionally, tube micromorphology in H. marenzelleri is even more different from that described for H. madreporae n. sp., displaying an evident rough surface, especially on the distal part, and well visible traces of growth ( Fig. 5F, G View FIG ). At higher magnification such outer rough surface displays crystals, which are visible due to the absence of the cryptocrystalline film ( Fig. 6C View FIG ).

The interruptions along the tube have been observed in all specimens of the three compared species ( Figs 3D View FIG ; 5B, H View FIG ). Though not mentioned in descriptions of other Hyalopomatus species , these structures probably occur in at least some species; they seem associated to lightly flaring collar rings and peristomes reported by some authors for H. claparedii (Kupriyanova & Jrkov 1997) , H. marenzelleri ( Zibrowius 1969) and H. variorugosus (Ben Eliahu & Fiege 1996; Sanfilippo 1998). Such thought is supported by Ben Eliahu & Fiege (1996: 16, fig. 6B), where high magnification displays an interruption immediately behind a peristome between the attached and raised tube parts, a position recurrent also in the new species and two congeners.

Tube wall structure that is built up of crystal layers is scarcely visible in H. madreporae n. sp. and H. claparedii in contrast to H. marenzelleri , which in longitudinal sections shows more obviously layers overlaying each other during growth ( Fig. 6 View FIG D-F).

The homogeneous microcrystalline structure of the wall in the new species ( Fig. 4F, G View FIG ) resembles that of H. variorugosus ( Sanfilippo 1998) and H. claparedii ( Fig. 6D, E View FIG ), with crystals also having comparable sizes. Conversely, H. marenzelleri possesses more squat crystals ( Fig. 6F View FIG ).

TUBE MICROANALYSIS

Serpulid tubes are composed of a mixture of calcium carbonate crystals and an organic matrix ( Neff 1971). They are composed of magnesian calcite, aragonite or mixture of these two minerals ( Bornhold & Milliman 1973). The magnesium carbonate content within serpulid tubes was documented by Bornhold & Milliman (1973) who discussed its concentration in relation with temperature and mineralogy.

SEM-EDS microanalysis on H. madreporae n. sp. tubes confirmed calcium as a fundamental constituent (average 45 wt%) and magnesium in extremely subordinate percentage (average 0.2 wt%). The presence of slight strontium amounts (average 1.5 wt%) can be explained considering its tendency as vicariate of Ca.

X-ray microanalyses in H. madreporae n. sp. revealed that concentration of carbon was relatively high within the tube wall (average 22 wt%); it is even more higher along the outer and inner surfaces of the tube (average 26 wt%); here it is mixed with the cryptocrystalline carbonate coverings ( Fig. 4B, E View FIG ). The presence of abundant organic matrix is also noticeable in Figure 4G View FIG where crystals inside the tube wall are partially obliterate, embedded within the organic matrix.

The organic content in H. madreporae n. sp. resulted more abundant than in H. claparedii tubes. Microanalysis on this latter species gave mean weight percentages in carbon of 16wt% inside the tube wall and of 23 wt% along outer and inner surfaces. Strontium and magnesium have been also detected (average 1 wt% and 0.3 wt% respectively), values comparable to those of H. madreporae n. sp.

DISTRIBUTION AND ECOLOGY

Hyalopomatus madreporae n. sp. is a deep-water species found in the central Mediterranean (northern Ionian sea); the Santa Maria di Leuca finding is from 497 to 1146 m depth, and corresponds to bottom-water temperatures of 13.2-15.0°C, salinities of 38.66-38.89‰ and dissolved oxygen of 145-238 µM/l (Budillon et al. in press).

Hyalopomatus madreporae n. sp. lives attached to tissue-barren branches and calices of living or fresh looking Madrepora oculata , on mound rising from muddy bottoms (Mastrototaro et al. in press; Rosso et al. in press). It also colonises some coral epibionts, like branched bryozoans and hydroids which possess weakly calcified or not mineralised skeletons ( Figs 2A, C View FIG ; 3B View FIG ) and small-sized serpulids (raised distal ends of Filogranula annulata (O. G. Costa, 1861)).

Except for several distal ends that have been recorded from bottom sediments around bioconstructions, presumably detached and fallen down from coral branches, the new species was neither found on bottom substrates (firm- and hard-grounds) nor on other coral species sampled in the same area (Rosso et al. in press). This suggests a possibly preferential selection for the scleractinian Madrepora and its associated small-sized epizoans. A similar ecological selectivity was also observed for H. cancerum , epizoic exclusively on the spider-crab Encephaloides (Knight-Jones et al. 1997) .

The colonization of small-sized epizoans was also observed for H. mironovi , found on thin branches of the bryozoan Striatodoma dorothea Winston & Beaulieu, 1999 living in deep-water sponge stalk communities ( Beaulieu 2001).

It is noteworthy the co-occurrence of H. variorugosus on the Santa Maria di Leuca coral frames, where it is generally cryptic (within calices); unlike H. madreporae n. sp., it also colonises shells and crevices of hard-grounds interspaced in the neighbouring bottoms from the same area (Ben Eliahu & Fiege 1996; Rosso et al. in press) and from other Mediterranean bathyal localities (Ben Eliahu & Fiege 1996; Sanfilippo 1998).

Furthermore, the numerous findings of H. claparedii and H. marenzelleri , during the BIOICE cruise, correspond to a depth range of 838-1215 m, with bottom-water temperatures of 3.7-5.5°C. These new records extend to the Icelandic waters the geographical distribution of both species.