Amphimedon anastomosa Calcinai, Bastari, Bertolino & Pansini

Calcinai, Barbara, Bastari, Azzurra, Bavestrello, Giorgio, Bertolino, Marco, Horcajadas, Santiago Bueno, Pansini, Maurizio, Makapedua, Daisy M. & Cerrano, Carlo, 2017, Demosponge diversity from North Sulawesi, with the description of six new species, ZooKeys 680, pp. 105-150 : 111-115

Amphimedon anastomosa Calcinai, Bastari, Bertolino & Pansini sp. n. Figure 7

Material examined.

Holotype: MSNG 60138, PH-58, 17/01/2005, Tiwoho (Bunaken Island), about 20 m depth.

Diagnosis.

Dark green, highly branched sponge with an irregular ectosomal skeleton of rectangular, paucispicular meshes and multispicular choanosomal fibres, forming an irregular reticulation. Oxeas are mucronate.

Description.

Highly branched sponge (Fig. 7A) with repent habit. Anastomosing branches are flattened, 4-8 mm in diameter, creeping over the substrate. Colour in situ is dark green to dark brown, greenish in alcohol or in the dried state. Consistence soft and brittle; the sponge easily crumbles when dried. Surface slightly rough, irregular; when the transparent membrane is preserved, it gives a smooth appearance at the macroscopic observation. Oscula not visible. Numerous barnacles are embedded in the sponge tissue, with only their openings free (Fig. 7B).

Skeleton. The ectosomal skeleton is an irregular reticulation of rectangular meshes 120-150 µm, up to 190-250 µm in diameter, formed by fibres 20-40 µm thick (Fig. 7B, C). Fibres are cored by 4-6 spicules. In the well-preserved parts of the sponge, a thin dermal membrane covers the surface. When the membrane is damaged, the sponge surface is microhispid due to protruding fibres. The choanosomal skeleton (Fig. 7D) is irregular, formed by primary multispicular (approximately 10 spicules) fibres, about 60 µm thick, directed towards the surface; secondary fibres are 20-35 µm in diameter. Secondary and primary fibres create an irregular reticulation of more or less circular meshes 170-300 µm across. Spongin is not abundant.

Spicules. Megascleres are oxeas slightly curved, with sharp tips (Fig. 7E, F), 97 - (111.6 ± 6.7) - 122.4 × 2.6 - (4.5 ± 1.2) - 5.2 µm.

Etymology.

The name refers to the habitus of the sponge, characterised by anastomosing branches.

Remarks.

The species described here may be attributed to the genus Amphimedon due to its skeleton characteristics. Out of the 54 species of Amphimedon hitherto described ( van Soest et al. 2016), only two ( A. denhartogi de Voodg, 2003 and A. elastica (Kieschnick, 1898) are present in Indonesia, whereas 30 have been recorded in the Indo-Pacific region. Amphimedon denhartogi and A. elastica differ from A. anastomosa sp. n. in their skeletal organisation and general morphological characters. The species A. denhartogi is green in life, like A. anastomosa sp. n., but it has an erect, flabellate shape and star-shaped oscula; moreover, it has strongyles as spicules. In contrast, A. elastica is a single-tube yellow-brownish sponge with a wide apical osculum (11 mm in diameter) and smooth surface; spicules are oxeas of 90-100 µm. Also, the other Indo-Pacific species show significant differences with A. anastomosa sp. n.; A. aculeata Pulitzer-Finali, 1982 is a vase-shaped sponge with conical projections on the surface and strongyles as spicules, whereas A. aitsuensis (Hoshino, 1981), described from Japan, is a massive sponge, grey in colour and with oxeas of two distinct size categories (thick oxeas of 132-148 × 7-9 µm and thin oxeas of 115-135 × 4-6 µm). Amphimedon alata Pulitzer-Finali, 1996 has oxeas of 100-130 × 7-11.5 µm and peculiar, small, wing-shaped toxas (11-50 µm); A. brevispiculifera (Dendy, 1905) is an erect sponge light-brown in the dry state; it is digitate or flabellate, with evident large oscula; it differs from A. anastomosa sp. n. also for its stout primary fibres 164 µm thick. The two species A. chinensis and A. flexa have been described by Pulitzer-Finali (1982) from Hong Kong; A. chinensis differs from the new species for the orange colour, the pres ence of oscula arranged in a single row and the larger oxeas (125-145 × 8-9.5 µm), while A. flexa is plurilobate with oscula on top of the lobes; its primary fibres, slightly thicker than those of the new species, create larger meshes from 300 to 900 µm across. The species A. chloros Ilan et al., 2004 is green, like A. anastomosa sp. n., but cushion-shaped, with oxeas that usually become strongyloxeas. In contrast, A. conferta Pulitzer-Finali, 1996 is sub-cylindrical, brown in life, cream in the dry state, with ectosomal tracts 75 µm in diameter; spicules are oxeas longer and thicker (140-160 × 7-9 µm) than those of A. anastomosa sp. n., with frequent stylote modifications. Amphimedon cristata Pulitzer-Finali, 1996 is sub-cylindrical, violet in colour and rigid, with an apical osculum; it has large oxeas (230-370 × 11-18 µm) with blunt extremities. Other three species of Amphimedon have been described by Helmy and van Soest (2005) from the Red Sea: A. dinae , A. jalae , A. hamadai . Amphimedon dinae is a brown, massive sponge with oscula 2-4 mm wide and very thin and short oxeas (52-61 × 1-1.5 μm); A. jalae is massive, cushion-shaped, with large oxeas (100-170 × 4-6 μm) and choanosomal rounded meshes of 600-800 μm. Amphimedon hamadai is brown, irregularly lobated, with very short oxeas (48-60 × 2-3 μm), while A. delicatula (Dendy, 1889) is erect, bushy, yellow in colour and with stout fibres 126 µm thick and very slender, slightly curved oxeas (98 by 3.5 µm). Amphimedon lamellata Fromont, 1993 is a lamellate, erect sponge, pale pink in colour; with a reticular choanosomal skeleton and two types of oxeas differing in thickness (111-130 × 2.5-4.4 µm and 105-126 × 1.3-2.3 µm); A. massalis (Carter, 1886) is massive, yellow in the basal portion, dark brown-red on the surface, with vents "on monticular elevations" and oxeas measuring 155 × 6 µm. Amphimedon navalis , A. rubida , A. rubiginosa and A. spinosa have been described by Pulitzer-Finali (1993) from Kenya. Amphimedon navalis is a cushion-shaped sponge, dark blue and violet in colour, with blunt oxeas (160-210 × 11-15 µm); A. rubida is cylindrical, red brownish, with meshes of 220-360 µm across and oxeas measuring 185-230 × 11.5-18 µm. Amphimedon rubiginosa has a massive shape with elevated oscula and a skeletal organisation with ill-defined plurispicular tracts. Amphimedon spinosa has a tubular shape and fibres cored by single spicules, while A. paraviridis Fromont, 1993 is encrusting or ramose, green-olive in life, with primary fibres of 50-160 µm and secondary of 20-50 µm, thicker than those of the new species. Moreover, abundant oxeas (133-151 × 3.9-8.0 µm) are scattered in between the fibre reticulation (absent in A. anastomosa sp. n.). Amphimedon queenslandica Hooper & van Soest, 2006 is a blue-grey and green sponge with an encrusting base from which lobate or digitate portions rise. Unlike the new species, it has unispicular fibres. A. robusta (Carter, 1885) is a branching-digitate, orange sponge with oscula located on one side; A. rudis Pulitzer-Finali, 1996 is violet-brownish, with blunt and very stout oxeas (360-420 × 10-12.5 µm). Amphimedon strongylata Pulitzer-Finali, 1996 is sub-cylindrical, grey in colour, with strongyloxeas as megascleres; A. subcylindrica (Dendy, 1905) is a cylindrical sponge with reptant habit; it has a smooth surface and oscula with prominent rims; its fibres are cored by a high number of spicules (slightly longer (140 × 8 µm) oxeas), without visible spongin. Amphimedon sulcata Fromont, 1993 is a small, globular sponge with oxeas of 122-153 × 3.0-5.3 µm and C-shaped sigmas as microscleres. Finally, A. zamboangae ( Lévi, 1961), which is green in colour, has a velvety surface, thick fibres (130 µm) and two types of oxeas (120-150 × 4-6 µm and 120-130 × 3 µm).

" Amphimedon differ from other Niphatidae in having an optically smooth, but microscopically microtuberculate fibrous superficial skeleton, usually with abundant spongin, and lacking microscleres" ( Hooper and van Soest 2006). Because of the slight differences between Amphimedon and Niphates ( Desqueyroux-Fáundez & Valentine 2002), all the Indo-Pacific species of the latter genus were also checked. All these species of Niphates differ from the new species in shape, colour and skeletal organisation. The most similar species, in terms of the branched shape, is N. aga (de Laubenfelds, 1954), but it has a confused ectosomal skeleton and longer oxeas (175-180 µm). Amphimedon anastomosa sp. n. is well characterised by its growth form and colour. Since no species in this vast geographic area matches with our specimen, we are justified to erect a new species.