Euplectella paratetractina, Tabachnick & Menschenina, 2008

Tabachnick, Konstantin R. & Menschenina, Dorte Janussen And Larisa L., 2008, New Australian Hexactinellida (Porifera) with a revision of Euplectella aspergillum *, Zootaxa 1866 (1), pp. 7-68 : 43-48

Euplectella paratetractina sp. nov. ( Fig. 20–23; Tab. 18)

Etymology. The name was given according to the outstanding abundance of paratetractins within the choanosomal spicules, which is unique to this species.

Material. Holotype — WAM Z 262 — RV Soela , sta. SO 2/82/ 49, 105 miles NW of Port Headland, 19 o 6’– 5’ S 117 o 17’ –19’E, depth 156 m.

Paratypes: WAM Z 648 (2 specimens) — RV Soela , sta. 29. N of Karratha, 18 o 44’S 116 o 59’E, depth 404– 406 m. WAM Z 548 (3 specimens) — RV Soela , sta. SO 2/82/ 21, 154 miles NW of Port Headland, 18 o 45’S 116 o 26.50’–22.50’E, depth 720– 724 m. WAM Z 604 — RV Soela , sta. SO 1/84/051 NNW of Lacepede Archipelago, 15 o 42.60’S 120 o 37.30’–34.60’E, depth 500– 504 m. WAM Z 547 — RV Soela , sta. SO 1/84/81 NW of York Sound, 12 o 54.40’–50.60’ S 123 o 0.20’ E, depth 452– 462 m. WAM Z 646 — RV Soela , sta. SO 2/82/35 18.5 miles W of Imperieuse Reef Rowley Shoals, 17 o 34’–31’ S 118 o 38’ –40’E, depth 492– 520 m. WAM Z 593 — RV Soela , sta. SO 2/82/42 119 miles NW of Port Headland, 18 o 44’S 117 o 20’–19’E, depth 326– 360 m. WAM Z 549 — RV Soela , sta. SO 2/82/47 113 miles NW of Port Headland, 19 o 4’–5’ S 117 o 6’ –5’E, depth 200– 202 m.

Description. Body: The body shape is typical for the genus: tubular with numerous lateral oscula, colander­like sieve­plate and a tuft of basalia. The parietal ledges have various degrees of expression in different specimens, from low (as in E. regalis or young specimens of E. imperialis ) to prominent, circular and oblique (as in E. aspergillum ). The lateral oscula are oval (1–1.8x 2.5 mm), thay are not regularly situated; some of them are enclosed by ridges so the oscula are situated partly in rows with an alternating position and partly in regular horizontal and vertical rows. The holotype is a tube 110 mm long and 40 mm in diameter; basalia are about 40 mm long. The parietal ledges are prominent, up to 8 mm in width, and especially the last circular ridge, the cuff, situated in the vicinity of the main osculum (covered by the colander­like sieve­plate) is well expressed. The numerous paratypes are tubes 55–300 mm long, 12–60 mm in diameter or usually oval in section with corresponding measures; they are often broken so only their upper parts are present. One specimen (WAM Z 547) is a fragment of the wall.

Spicules: Principalia (large choanosomal spicules) are stauractins with rays 3–15 mm long and some other rare spicules: hexactins, hexactins with a reduced proximal ray, hexactins with two reduced rays (proximal and distal), tauactins and diactins. Hexactins are very rare; they have short rays 1–2 mm long. The hexactins with two reduced rays have tangential rays 2–9 mm and reduced rays 0.2–0.5 mm long. The diactins are 2–2.5 mm long, and tauactins are of similar size. The hexactins with a reduced proximal ray have a smooth distal ray (in other species of Euplectella , which have spicules of this type, it is rough or tuberculated) 3–30 mm long with tangential rays 3–11 mm, the reduced ray is 0.1–0.3 mm long. These spicules have conically pointed outer ends; the diameter of their rays is 0.08–0.23 mm. Other choanosomal spicules are mostly tauactins and paratetractins, rarely diactins. These spicules have rays 0.2–4.5/ 0.009–0.04 mm with rounded rough, sometimes­smooth, outer ends. Comitalia (diactins) which are associated with the principalia, usually with the long distal ray of pentactins and hexactins, seem to be absent in this species.

Basalia are anchorate, rarely clavate spicules with spiny shafts 0.003–0.04 mm in diameter. The anchorate spicules have 6, rarely 4 teeth; their discs are 0.05–0.07 mm in diameter and 0.05–0.11 mm long. The 4­ toothed and clavate spicules have shafts of the smallest diameter; their spicule center is situated some distance (about 0.15 mm) from the anchorate or clavate head (this may also be observed in 6­toothed anchorate spicules); the clavate spicules have spherical outer ends about 0.03 mm in diameter and are slightly rough in the upper parts.

Spicules of the sieve­plate are large diactins and tauactins, as well as small hexactins and pentactins. The diactins are 0.46–8/ 0.008–0.13 mm; they are usually curved; the small ones have a widening in the middle or four rudimentary tubercles; their outer ends are rounded or conically pointed, smooth or rough. Tauactins are less common than diactins; their unpaired ray is smaller than the two others. Hexactins and pentactins have rays 0.04–0.2/ 0.008 –0.023 mm, spiny with conically pointed or rarely rounded outer ends. The spicules do not undergo notable fusion, however this process differs between specimens: considerable fusion was observed in the sieve­plate of the holotype and in some of the spicules in the basal part of the body, whereas the fusions in other specimens are very limited.

Dermalia are hexactins with a rough distal ray, the other rays are smooth, conically pointed. The distal ray of dermal hexactins is 0.041 –0.189 mm long, tangential rays are 0.061–0.23 mm, the proximal ray is 0.144 – 1.071 mm, their diameter is 0.004 –0.015 mm. Atrialia are pentactins with rounded rough or sometimes conically pointed, smooth outer ends, the proximal ray is entirely absent or may be represented by a tuberculated rudiment. The tangential rays of atrial pentactins are 0.015–0.23 mm, the distal ray 0.245 –0.969 mm long, diameter is 0.004 –0.008 mm.

Spicules situated in the vicinity of lateral oscula (oscularia) are mainly pentactins (28 %) and stauractins (28 %), some paratetractins (15 %), triactins (15 %) and diactins (11 %), and hexactins are rare (3%) (this spicule counting was done for the holotype, n=74). These spicules have smooth rays, 0.026–0.3 mm (avg=0.133; std=0.072; n=25) long and 0.007–0.05 mm in diameter, their outer ends are usually rounded. Often these spicules have tuberculated rudiments of reduced rays with variable lengths, which makes attribution of such spicules to any class very difficult. At some distance from the lateral oscula similar regular hexactins and some pentactins are found, which have rays conically pointed, smooth or slightly rough in the holotype and paratype WAM Z 549 , but which are notably spiny in other specimens. Their rays are 0.056–0.49/ 0.01­0.02 mm .

Microscleres are floricomes, oxyhexasters, graphiocomes and sigmatocomes in some specimens. The floricomes are 0.074 –0.113 mm in diameter with the primary rosette 0.007 –0.021 mm in diameter. The oxyhexasters with 2–4 secondary rays are 0.055 –0.097 mm in diameter with the primary rosette 0.007 –0.017 mm in diameter. The sigmatocomes (probably young floricomes) are numerous in the paratype fr792, but they were not found in the holotype, they are 0.04–0.063 mm in diameter with the primary rosette 0.011 –0.019 mm in diameter. The graphiocomes are present in various specimens in variable amounts (they are sometimes numerous, but not everywhere), the size of these fragile spicules, mostly destroyed in preparations, can be reconstructed as 0.24–0.385 mm in total diameter; their primary rosette is 0.013 –0.023 mm in diameter.

Remarks. The new species E. paratetractina is defined on the basis of a specific combination of ‘principalia’ (large choanosomal spicules) which are represented by numerous stauractins, hexactins, including hexactins with one or two (proximal and distal) reduced rays, tauactins and diactins. The extraordinary variability of large principal spicules building the choanosomal skeleton is characteristic of the genus Euplectella . These spicules are represented by stauractins in E. marshalli Ijima, 1895 , E. oweni Herklots and Marshall, 1868 , E. curvistelata Ijima, 1901 , E. simplex Schulze, 1895 , E. imperialis Ijima, 1894 , E. regalis Schulze, 1900 , E. aspergillum Owen, 1841 , E. timorensis Ijima, 1927 , E. nobilis Schulze, 1904 and E. gibbsae Tabachnick and Collins, 2008 . Mainly hexactins with a reduced proximal ray and additional stauractins are found in E. aspera Schulze, 1895 , E. crassistellata Schulze, 1886 and E. plumosum Tabachnick and Levi, 2004 . Pentactins and, sometimes in some species, hexactins are present in E. jovis Schmidt, 1880 , E. nodosa Schulze, 1886 , E. suberea Thomson, 1876 and E. cucumer Owen, 1857 . In E. paratetractina sp. nov., the most numerous choanosomal spicules are tauactins and paratetractins, whereas in other species of the genus, paratetractins, if reported at all, are rare spicules, e.g. in E. oweni , E. marshalli , and probably in E. curvistellata . The microsclere composition and proportions of thick­rayed spicules (mainly pentactins) situated in the vicinity of the lateral oscula are similar to those of E. aspergillum , E. timorensis and E. regalis . The fusion of spicules is not prominent – only a few of the large choanosomal spicules show traces of secondary silica deposition.

Basal spicules with their spicule centre situated not in the anchorate head were described before from one genus Holascella Lendenfeld, 1915 , whose definition was based on this feature only. Later it was synonymized with Holascus ( Tabachnick 2002b) ; the finding of the same feature in a related genus, Euplectella , provides further support for this action.

It is very difficult to compare oscularia with the small hexactins and pentactins situated some distance from them. Thus it is uncertain if these two types are a special category, or if they should be regarded as belonging to the general category of dermal­atrial spicules. It seems that this situation is unique for Euplectella , and needs to be re­examined in most species of the genus.