Poecillastra compressa Bowerbank 1866

Poecillastra compressa (Bowerbank, 1866)

(Figure 11–13, Table 4)

Synonymy.

Ecionemia compressa Bowerbank, 1866: Bowerbank 1866, p. 55; Bowerbank 1874, p. 19.

Pachastrella compressa: von Lendenfeld 1903 p. 76; Babiç 1922, p. 284; Russ & Rützler 1959, p. 759; Sarà 1964, p. 304; Lévi 1967, p. 244.

Poecillastra compressa: Sollas, 1888 p. 98; Topsent 1890a, p. 203; Topsent 1894, p. 384; Topsent 1904, p. 89; Ferrer- Hernández 1912, p. 586; Topsent 1913a, p. 12; Stephens 1915, p. 14; Topsent 1928, p. 131; Burton 1930, p. 487; Burton 1931, p. 2; Burton 1932, p. 263; Lévi & Vacelet 1958, p. 229; Burton 1959b, p. 8; Burdon-Jones & Tambs-Lyche 1960, p. 6; Vacelet 1961, p. 23; Vacelet 1969, p. 167; Uriz 1981, p. 45; Pulitzer-Finali 1983, p. 471; Pansini 1987a, p. 157; Pansini 1987b, p. 43; Pansini & Musso 1991, Table 2; Maldonado 1992, p. 1133; Boury-Esnault et al. 1994, p. 47; Chombard et al. 1998, p. 355; Maldonado 2002, p. 154; Voultsiadou 2005, p. 57; Longo et al. 2005, p. 1343; van Soest et al. 2007, p. 129; Cárdenas et al. 2010, Table 1; Cárdenas et al. 2011, Table S1; Bo et al. 2012.

? Poecillastra compressa parvistellata Topsent, 1913b: Topsent 1913b, p. 611.

? Poecillastra compressa antarctica Koltun, 1964: Koltun 1964, p.18.

Poecillastra compressa compressa Koltun, 1966: Koltun 1966, p. 32.

Poecilastra compressa (misspelling): Könnecker 1973, p. 455, Table II.

Hymeniacidon placentula Bowerbank, 1874: Bowerbank 1874, pp. 185, 189, 353.

Normania crassa Bowerbank, 1874: Bowerbank 1874, p. 258; Bowerbank 1882, p. 29.

Stelletta scabra Schmidt, 1868: Schmidt 1868, p. 19.

Poecillastra scabra: Sollas 1888, p. 99.

? Normania crassiuscula Sollas, 1886: Sollas 1886, p. 185.

? Poecillastra crassiuscula: Sollas 1888, p. 83; Topsent 1892, p. 37.

? Poecillastra incrustans Sollas, 1888: Sollas 1888, p. 105; Topsent 1913b, p. 610.

Poecillastra fragilis Vosmaer, 1894: Vosmaer 1894, p. 285.

Poecillastra cumana Vosmaer, 1894: Vosmaer 1894, p. 286.

Pachastrella stylifera von Lendenfeld, 1897: von Lendenfeld 1897, p. 82.

Pachastrella tenuipilosa von Lendenfeld, 1907: von Lendenfeld 1907, p. 234.

Not Poecillastra compressa (Bowerbank, 1866): Boury-Esnault & van Beveren 1982, p. 19 = Poecillastra schulzei (Sollas, 1888) (this study).

Material. ZMBN 77932, Steinneset, Langenuen, western Norway, 59º53'N, 05º3'E, 175- 25 m, triangular dredge; ZMBN 87919, Sognesjøen, north of Jutevikneset, Western Norway, 61°05.8'N, 5°05'E, 240–243 m, shrimp trawl; NTNU-VM 54879, three specimens, Tømmerdalen, Trondheimsfjorden, western Norway, 63°36'46.8''N, 10°35'20.4''E, 200–250 m; ZMBN 85246, Røst Reef, northern Norway, 450 m, van Veen Grab; ZMBN 85247, Røst Reef, northern Norway, 252–299 m, manned-submersible; ZMBN 85248, Traenadjupet, northern Norway, 320 m, large box corer.

Comparative material examined.

Poecillastra compressa, ZMBN 86300, Rockall Bank, 55°26'40.6''N, 16°4'18.4''W, field # BX173-B 2005, 629 m; ZMAPOR 7290, Ilhéus do Rombo, Cape Verde, 580 m; ZMAPOR 6661, off Banc d'Arguin, Mauritania, 500 m; ZMAPOR 4457, Grand Bassam, Ivory Coast; MNHN-DCL682, slide, South Africa, 37°53.3'S, 17°30'E, 309 m.

Poecillastra schulzei, MNHN-DNBE1055, slide made from holotype BMNH-1889:1:1:34, 52°04’S, 71°22’E, near Heard Island on the Kerguelen Plateau; MNHN-DNBE1280–1300, slides, originally identified as P. compressa (Boury-Esnault & van Beveren 1982), Kerguelen Islands, 172– 315 m.

Outer morphology. ZMBN 77932 is a massive fan-shaped fragment 9 cm wide, 9 cm high and 1 cm thick (Fig. 11 A). External color and choanosome of specimen alive and in ethanol was grayish. Northern Norway specimens (Fig. 11 D) were white, whitish or yellowish, and either fan-shaped or massive encrusting on dead parts of the coral Lophelia pertusa. Specimens are compressible. Surface is regular and slightly hispid, northern Norway specimens were more hispid than the other specimens examined. There is no visible cortex. In ZMBN 77932, uniporal oscules (0.5–1.2 mm) with a conspicuous sphincter are found on the concave side of the plate and cribriporal pores on the other (each cribriporal area has a diameter of ca 2 mm). In ZMBN 85246, this arrangement is reversed: pores are on the concave side (Fig. 11 D).

Skeleton (Fig. 11 B). Very thin cortex (23–45 µm) that is barely visible to the naked eye: accumulation of spirasters/metasters reinforced by paratangential triaenes, oxeas and microxeas. The cortex is crossed by some oxeas I and II; they are responsible of the local hispidity. Ortho/dichotriaenes and deformed triaenes are present, more or less positioned radially with their cladomes tangential to the cortex. There are very few triaenes in the choanosome. Apart from bundles of oxeas mainly parallel to the surface, the arrangement of the spicules in the choanosome is confused. The position of microxeas is random. Streptasters are abundant and can be found in the whole choanosome. Oxeas II are absent in the choanosome.

Spicules (ZMBN 77932) (Fig. 12). (a) oxeas I, stout, most are curved, sometimes modified to styles, length: 409- 1068.4 -2256 µm; width: 7.0- 17.4 -33.0 µm. (b) oxeas II, thin and pointy, bent or straight, length: more than 1200 µm; width: 2.5- 2.7 -5.0 µm. (c) ortho- and dicho- short-shafted triaenes (= pseudocalthrops), often irregular with deformities such as additional clads, rhabdome length: 223- 297.3 -420 µm (N=16); rhabdome width: 16.0- 20.0 -25.0 µm (N=16); clad length: 146.0- 221.8 -297.0 µm (N=16). (d) microxeas, in high numbers, microspiny, straight or bent, rarely centrotylote, length: 141- 184.2 -211 µm; width: 2.5- 4.5 -6.0 µm. (e) spiraster (most abundant) to metaster, microspiny actines, length: 11.5- 16.3 -23.0 µm; width: 9.0- 12.6 -21.0 µm. (f) plesiaster, 4-8 actines, microspiny actines, diameter: 22.0- 36.9 -51.0 µm.

Distribution (Fig. 13). NEA: Iceland (Burton 1959b); Norway (Topsent 1913b; Burton 1930; 1931; Burdon- Jones & Tambs-Lyche 1960); Shetland and Hebrides Islands (Bowerbank 1866; 1874; von Lendenfeld 1907); Rockall bank (von Lendenfeld 1897); Porcupine Bank (van Soest et al. 2007); Ireland (Stephens 1915; Könnecker 1973); France (Topsent 1890a); Spain (Ferrer-Hernández 1912); Ibero-Moroccan Gulf (Boury-Esnault et al. 1994); Azores Islands (Topsent 1904; Topsent 1928; Lévi & Vacelet 1958); Canary Islands (Topsent 1928); Cape verde (Sollas 1888, as P. crassiuscula); Mauritania and Ivory Coast (this study).

Mediterranean Sea: Spain (Topsent 1894; Uriz 1981); Alboran Islands (Pansini 1987a; Maldonado 1992); France (Vacelet 1969); Corsica (Vacelet 1961); Italy (Russ & Rützler 1959; Sarà 1964; Pulitzer-Finali 1983; Pansini & Musso 1991; Longo et al. 2005); Adriatic Sea (Babiç 1922; Pansini 1987b; Bo et al. in press); Aegean Sea (Voultsiadou 2005); Algeria (Schmidt, 1868, as Stelletta scabra).

South Atlantic: Gough Island (Topsent 1913b, as P. compressa var. parvistella, as P. incrustans), Tristan da Cunha (Sollas 1888, as P. incrustans; Burton 1932), South Africa (Lévi 1967).

Depth. 0 (in a cave, Gulf of Naples)– 1740 m (Topsent 1928; Sára 1964).

Discussion. Spicules of ZMBN 77932 are identical to those of the holotype, illustrated by Maldonado (2002). The occasional presence of styles in this species had already been noticed (von Lendenfeld 1897; Topsent 1928). There is however, one important difference: the presence of a second category of oxeas in ZMBN 77932. These are not characteristic of the Norwegian population since we found similar ectosomal oxeas II in the specimen from Mauritania (ZMAPOR 06661). According to Maldonado (2002), the main difference between P. schulzei from the southern Indian Ocean and P. compressa is a second category of oxea in P. schulzei: isodiametric ectosomal oxeas. Since we found those in P. compressa from Norway, this difference does not stand anymore. However, we suggest here a new difference to discriminate both species: when we examined spicule slides of P. s c h u l z e i (including the holotype), we noted that microxeas were often sharply bent or even toxa-like; this was never observed in P. compressa. Therefore, the holotype of P. s c h u l z e i should be carefully reexamined for such new specific characters, as well as its possible synonyms from the Indo-Pacific: Poecillastra laminaris (Sollas, 1886) and Poecillastra eccentrica Dendy & Burton, 1926 (Maldonado 2002). Oxeas II are easy to overlook because they are only found at the surface, and may be easily scraped off during collection. Molecular data suggest that Vulcanella spp. and P. compressa are sister-groups (Cárdenas et al. 2011). We can therefore argue that these oxeas II are homologous to the atrial oxeas of Vulcanella, since they share a similar morphology and position. Indeed, these thin and long oxeas are often found around the oscule area of Poecillastra species (e.i. on the fringe of the plate specimens); this is especially striking in young specimens which can have long fringes around a few oscules (Rockall Bank specimen), making them look like Vulcanella gracilis (Sollas, 1888). Following this, we can suggest that the atrial area of Vulcanella is homologous to the oscule side of Poecillastra.

The colors of the Norwegian specimens are whitish, grayish to light yellowish, but in Scotland (Fig. 11 E, F) and in some parts of the Mediterranean, yellow or orange specimens are common (Topsent 1894; Uriz 1981; Bo et al. 2012). This does not seem to be due to light since orange specimens were found deeper than 100 m in the Mediterranean. Since white and orange P. compressa were observed living next to each other (J. Vacelet, pers. comm.) and that bi-colored specimens exist (Fig. 11 F), they are in our opinion probably just color varieties.

P. compressa, like P. monilifera, has been considered to be a single cosmopolitan species. It shares similar environments (hard-bottoms, deep-sea coral reefs and fjords), same depth ranges and a similar distribution in the Eastern Atlantic, but unlike P. monilifera, hardly any morphological variations were observed between the Norwegian and Mediterranean/southern specimens, by us or previous authors (Table 4). Specimens of P. compressa from the English Channel, the Mediterranean Sea and the Azores have identical spicules and vary only slightly in the relative sizes of these (Topsent 1928). Sollas (1888) could not see any difference of specific value with P. compressa in a specimen from Queen Charlotte Islands (western Canada). However, one noticeable difference concerned pore morphology. We observed like Topsent (1913a) that the mesh size of the cribriporal pores is smaller in the Norwegian specimens than in the specimens from the Azores, Cape Verde or Ivory Coast (Fig. 11 C– D). Additional data is needed to confirm the taxonomical relevance of this character. As for P. monilifera, genetic data is greatly needed to enlighten the status of this potential species complex.