Polymastia Bowerbank, 1864

Plotkin, Alexander S. & Janussen, Dorte, 2008, Polymastiidae and Suberitidae (Porifera: Demospongiae: Hadromerida) of the deep Weddell Sea, Antarctic *, Zootaxa 1866, pp. 95-135 : 102-110

Genus Polymastia Bowerbank, 1864

Diagnosis (emended from Boury­Esnault 2002): Thickly encrusting sponges of spherical, hemispherical or cushion shape, always with papillae. Choanosomal skeleton is composed by radial tracts of principal spicules between which free spicules are scattered. Cortical skeleton constituted by at least two layers, the superficial palisade of small tylostyles and the lower layer made of intermediary spicules, lying tangential to the surface. The principal spicules can be tylostyles, subtylostyles, styles, and strongyloxeas, intermediary spicules are most often tylostyles, and cortical spicules are always tylostyles.

Remarks to diagnosis: At the moment 73 from 117 accepted polymastiid species are placed in Polymastia (van Soest et al. 2005), and some of them demonstrate noticeable discrepancies with the currently accepted diagnosis of the genus (see, e.g. Kelly­Borges & Bergquist 1997), that calls for its considerable re­evaluation. Since we did not aim to revise Polymastia in the present study, the emendations of the diagnosis given in Systema Porifera ( Boury­Esnault 2002) are minimized. Meanwhile, two Antarctic species, P. invaginata Kirkpatrick, 1907 and P. zitteli ( Lendenfeld, 1888) , concerned below, bear the features which somehow contradict the accepted diagnosis of Polymastia , the contradiction has not been previously emphasized. The dissimilarities include a single­layered cortex of the former species and the reticulated choanosomal skeleton of the latter. However, as the species in question share some other diagnostic features of Polymastia , we retain them as is, until the revision of the whole genus can be completed.

Type species: Spongia mamillaris Müller, 1806 (by monotypy).

Polymastia invaginata Kirkpatrick, 1907 ( Figs. 4–5 , Tables 2–3 )

Synonymy

Polymastia invaginata — Kirkpatrick 1907: 271; 1908: pp. 15–16, pl. XII(1b), pl. XIV (5–15a); Burton 1929: 446; 1932: 338; Koltun 1964: 26, pl. IV(10–14); 1976: 168; Boury­Esnault and van Beveren 1982: 36 –37, pl. IV (13–14), figs. 9d, e, f.

Polymastia invaginata var. gaussi — Hentschel 1914: 49, Taf. V, Fig. 4 .

Material examined

SMF 10540–10541 (2 specimens): PS61/132­3; SMF 10542 (4 specimens): PS61/134­3; SMF 10543 (1 specimen): PS61/141­9; SMF 10544–10545 (2 specimens) and 10546 (19 specimens): PS61/143­2; SMF 10547 (1 specimen): PS67/057­2; SMF 10548–10551 (4 specimens): PS67/074­7; SMF 10552 (1 specimen): PS67/078­11; SMF 10553 (4 specimens) and 10554 (2 specimens): PS67/102­11; SMF 10555 (1 specimen) and 10556 (4 specimens): PS67/121­7.

Description

External morphology. Sponges are cushion­shaped or hemispherical, always attached to the substrata (figs. 4A–C). Their diameter may reach 3.7 cm and thickness is up to 2.9 cm. The surface is usually densely hispid, its colour varies from dark brown to dark grey due to the sediment particles incorporated between protruding spicules. The upper surface bears one or very rarely few papillae, light brown or grey coloured and measuring 2–13 mm in length and 2–8 mm in diameter. Papillae are usually slightly sunken below the surface hispidation, occasionally being located inside a small pit within which the surface is smooth and pale. Oscula are opened at the papillae summits and ostia are scattered over the walls of the papillae. No ostia can be seen on the surface. The cortex is pale grey to whitish, hardly detachable and rather resilient. The choanosome is grey to beige, heterogeneous in consistency.

Skeleton. The main choanosomal skeleton is constituted by the radial tracts of principal spicules running from the sponge base to the surface, entering the cortex and diverging into bouquets (figs. 4D, E). The additional choanosomal skeleton is composed of small spicules scattered between the main tracts. These small spicules lie singly or grouped in stellate bundles (fig. 4F). Concentration of the scattered spicules under the cortex is higher than in the lower choanosome. The cortex, measuring 600–1560 µm in thickness, consists of the palisade of small spicules overlapped by the bouquets of the main tracts (fig. 4G). The latter are reinforced by extra­long spicules making up a surface hispidation, the thickness of which is 100–2700 µm. In the cortical bouquets of some sponges we also observed a few remarkable sceptre­like spicules, which were probably modified tylostyles (fig. 4H).

Spicules. Altogether 1267 spicules from 16 specimens were measured. Frequency distribution of length revealed three main categories of monactins, corresponding to extra­long spicules of the hispidation, principal spicules of the main tracts, and small spicules forming the additional choanosomal skeleton and the cortical palisade (fig. 5A). The fourth category was constituted by the infrequent sceptre­like spicules. Summarizing results of spicule measurements are given in the main text below, indicating the total number of spicules measured for each category (n). Particular results of spicule measurements for each specimen (sceptre­like spicules excluded) are given in table 2.

Principal spicules vary from styles to tylostyles (fig. 5B). They are mainly straight, often fusiform and measure: length 1026­1568 ­2186, proximal diameter 5­10.5­18 µm, central maximal diameter 8­18.5­32 µm (n =264). Their tyles, if present, are spherical, terminally located and measure 8­14.5­24 µm in diameter (n =228).

Small spicules are usually straight or rarely slightly curved, stout and fusiform tylostyles with spherical, well­developed, terminally located tyles (fig. 5C). About 11% of these are subtylostyles and nearly 3% are styles. Altogether they measure: length 60­383­988 ìm, tyle diameter 2­9.4­22 µm, diameter of the shaft underneath the tyle 1­5.8­19 µm, maximal diameter of the shaft 2­9.4­30 µm (n =860).

Extra­long spicules vary from styles to tylostyles (figs. 5D, E). They are straight, very slender and sharply pointed. Their dimensions are: length 2200­2753 ­4771 µm, proximal diameter 2­11.8­24 µm, central maximal diameter 5­24.6­41 µm (n =135). The tyles of the extra­long spicules, if present, may be spherical or oval, terminally located and measure 4­14.5­26 µm in diameter (n =111).

Sceptre­like spicules are considerably stout and either nearly isodiametric or its diameter increases from the proximal to the distal end, the former bearing a tyle and the latter being rounded (fig. 5F). The spherical tyles may be well or weakly developed, terminally located or slightly displaced. Sceptre­like spicules measure: length 145­482­1080 µm, tyle diameter 30­ 47.0­94 µm, proximal diameter 23­42.3­91 µm, central diameter 27­59.0­97 µm, distal diameter 25­60.0­103 µm (n =8).

Type locality: Antarctic: Southern Ross Sea: near Winter Quarters, 18–55 m and off Erebus volcano, 910 m.

Distribution: Antarctic near­continent sectors ( Koltun 1964; Sarà et al. 1992): NN 2–5 including the Western Ross Sea and NN 8–9 including the Weddell Sea (present study as well) and the South Shetland Islands. Depth: 18–1080 m ( Koltun 1964); ca. 1050–4800 m in the Northern Weddell Sea (present study).

SW Atlantic: South Georgia and South Orkney Islands ( Koltun 1964; Sarà et al. 1992); South Sandwich Islands, ca. 750–2300 (present study).

SE Pacific: Magellan area of Chile ( Desqueyroux & Moyano 1987).

Southern Indian Ocean: Kerguelen, 245–346 m and Heard, 750 m (Boury­Esnault & van Beveren 1982).

Measurements are given in µm. Each measurement is given as minimum­mean­maximum. Upper row represents length.

Middle row represents tyle diameter / diameter of the shaft underneath the tyle. Lower row represents maximal diameter

of the shaft and the number of measured spicules (in brackets).

SMF 10546 429­575­943 1029­1579 ­2086 No extra­long spicules were observed

(specimen 1) 11­13.1­15 / 5­7.4­11 12­16.9­24 / 8­10.7­14

11­13.9­16 (n= 24) 14­19.4­27 (n= 36)

SMF 10547 140­429­988 1026­1259 ­2052 2470­2786 ­3724 3­9.5­17 / 2­5.4­13 11­13.7­19 / 6­8.4­13 5­6.8­16 / 2­4.2­11 3­9.6­18 (n= 59) 13­16.2­28 (n= 8) 5­11.7­30 (n= 13)

SMF 10548 135­374­943 1029­1505 ­2186 2200­2791 ­3400 3­7.3­16 / 1­6.3­15 9­13.1­19 / 8­12.2­18 15­17.1­19 / 14­16.3­19 3­8.6­27 (n= 60) 16­21.3­32 (n= 40) 27­34.9­41 (n= 20)

SMF 10549 105­244­450 No principal spicules were 2318­2970 ­3534 observed

5­7.7­13 / 2­4.2­8 4­5.3­6 / 3­4.5­6 5­7.3­16 (n= 47) 8­10.3­11 (n= 20)

..... continued SMF 10556 111­345­914 No principal spicules were No extra­long spicules were observed

5­12.8­22 / 3­9.7­19 observed

5­15­30 (n= 59)

Remarks

The external and spicule morphology of P. i n v a g i n a t a varies greatly, that caused some discrepancy between the descriptions of different authors (table 3). Kirkpatrick (1907) noticed a sole exhalant papilla, completely invaginated in the thick surface hispidation, and a basal fleshy pad (the latter structure having never been mentioned by the following authors). A year later ( Kirkpatrick 1908) a sponge with two papillae was discovered. Kirkpatrick recognized two categories of spicules – principal styles, or strongyloxeas, of the main tracts, and small tylostyles including the slenderer ones of the stellate bundles in the choanosome and the fusiform ones making up the cortical palisade. In 1914 Hentschel established a new variety, P. invaginata var. gaussi , which he distinguished from Kirkpatrick’s sponges by the principal spicules being subtylostyles of smaller size. Koltun (1964) emphasized that the principal spicules could vary greatly in shape from styles to subtylostyles and in size. Both Hentschel (1914) and Koltun (1964) found no differences in shape between the choanosomal and cortical small tylostyles, though Koltun pointed out that the latter could be slightly larger. All authors mentioned above dealt with Antarctic sponges. Meanwhile Boury­Esnault and van Beveren (1982), who studied the material from the Southern Indian Ocean (Kerguelen and Heard), described the specimens with papillae being only partially sunk in the surface hispidation. These authors recognized three spicule categories – principal tylostyles of the main tracts being considerably smaller than those described by the previous authors, small tylostyles of the choanosomal stellate groups and the cortical palisade, and long, sharply pointed tylostyles reinforcing the cortical bouquets of principal spicules and making up the surface hispidation. The latter echinating tylostyles of Boury­Esnault and van Beveren had dimensions similar to those of the principal spicules described by the previous authors.

The sponges examined by us share most of the morphological features with P. invaginata described by other authors. The presence of up to four papillae in a few ANDEEP specimens is not surprising if keeping in mind the note of Kirkpatrick (1908). The minor invagination of papillae and the sufficient variety of principal spicules from tylostyles to styles might be also expected. In the meantime we observed the cortex reinforced by sharply pointed monactins morphologically similar to those described by Boury­Esnault and van Beveren (1982), but on average twice as long as any spicules previously registered in P. i n v a g i n a t a. The other feature distinguishing some of our sponges is the presence of cortical sceptre­like spicules. Principal spicules of our sponges fit well the dimension range given by Kirkpatrick (1907, 1908), Hentschel (1914) and Koltun (1964). Small spicules are also similar to the previous descriptions though their length maximum is relatively higher. This may be explained either by the insufficiently distinct discrimination between small and principal spicules or by the existence of intermediary size category being hidden because of insufficient sample size. We were unable to ascertain if there was any difference between the choanosomal and cortical small spicules.

All dimensions are given in µm as either a mean value or minimum­maximum or minimum­mean­maximum. In spicule dimensions the upper row represents length; the lower row represents central diameter of the shaft.

The considerable polymorphism of P. invaginata described above may be due to the environmental distinctions between different localities, e.g., between the Antarctic and Southern Indian Ocean. Nevertheless the existence of a species complex also cannot be excluded. In any case, all described specimens of P. invaginata share the possession of a single or at least very few exhalant papillae, a densely hispid surface and a single spicule layer in the cortex. P. hispidissima Koltun, 1966 from the NW Pacific and P. villosa Desqueyroux­Faúndez & van Soest, 1997 from the SE Pacific are also characterized by the single papilla and the thick surface hispidation formed by extra­long spicules. However, these two species differ from P. invaginata by two spicule layers in the cortex. Meanwhile, a single­layered cortex is shared by P. kurilensis Koltun, 1962 from the NW Pacific and P. atlanticus Samaai & Gibbons, 2005 from the SE Atlantic. The latter species also possesses the choanosomal clews of small spicules similar to the stellate bundles of P. i n v a g i n a t a. But other features of both P. atlanticus and P. kurilensis , including smooth surface, numerous wart­like papillae as well as spicule shape and size, distinguish them considerably from P. invaginata .

Polymastia zitteli ( Lendenfeld, 1888) ( Fig. 6 )

Synonymy

Sideroderma zitteli — Lendenfeld 1888: 211. Polymastia zitteli— Hallmann 1914: 400 –402, pl. XV (fig. 6).

Material examined

SMF 10557 (1 specimen): PS61/132­3.

Description

External morphology. Sponge is cushion­shaped, removed from substrate (fig. 6A). It measures approximately 33x27 x 5 mm. Surface is macroscopically smooth, grey coloured. The cortex is firm, transparent and easily detachable (fig. 6E). It is perforated by numerous small ostia which are not visible by a naked eye. There are several exhalant papillae of conical or tubular shape measuring 2–7 mm in length and 2–4 mm in diameter. The colour of papillae does not differ from that of the surface. Oscula measuring 0.5 mm in diameter are opened at the papillae summits. The choanosome is grey and rather friable.

Skeleton. The main choanosomal skeleton represents a very loose reticulation formed by the tracts of principal spicules, which branch and anastomose (fig. 6B). Freely scattered intermediary spicules make up the additional choanosomal skeleton. The cortex, measuring 250–540 µm in thickness, consists of two layers (figs. 6C, D). The external palisade is made of the bouquets of small spicules. Its internal area is overlapped by the layer of intermediary spicules regularly arranged tangentially to the surface.

Spicules. Three size categories of spicules are well distinguished. Thirty spicules of each category were measured.

Principal and intermediary spicules are usually straight and fusiform styles, rarely strongyloxeas or subtylostyles (fig. 6F). Principal spicules measure: length 812­908­1315 µm, proximal diameter 6­7.5­10 µm, central maximal diameter 13­16.0­21 µm. Intermediary spicules measure: length 340­395­598 µm, proximal diameter 6­8.3­10 µm, central maximal diameter 8­9.1­11 µm. Small spicules are subtylostyles with slightly subterminal tyles which are only feebly developed (fig. 6G). These subtylostyles are very slender, often slightly curved and measure: length 247­287­333 µm, proximal diameter 2­2.8­4 µm, central maximal diameter 3­4.0­4 µm.

Type locality: SW Pacific: Eastern Australian Coast: Port Jackson, depth unknown.

Distribution (other than type locality): Antarctic: NW Weddell Sea, ca. 2080 m (present data).

Remarks. This is the second finding of P. zitteli since Lendenfeld (1888) described it from Eastern Australia. Our sponge fits well the original description as well as the re­description by Hallmann (1914). The latter author clarified the misinterpretations made by Lendenfeld, namely so called trichites, making the cortical palisade, which were in fact very slender subtylostyles, chelae scattered within the palisade, which were evidently foreign, and oxeas found in the choanosomal tracts and in the internal cortical layer, which were obviously extremely fusiform styles or strongyloxeas. P. zitteli shares the reticulated choanosomal skeleton with two shallow­water species, P. boletiformis (Lamarck, 1813) from the North Atlantic and P. croceus Kelly­ Borges & Bergquist, 1997 from New Zealand. P. croceus and P. zitteli also share three spicule categories, which are typical of most other Polymastia spp., and the small cortical subtylostyles with faintly­developed tyles, which distinguish these species from other congeners. Conversely, P. boletiformis is distinguished by the absence of the intermediary spicule category, but its cortical tylostyles possess well­developed tyles, which are quite typical of the genus.

Figures

FIGURE 4. Polymastia invaginata: external morphology and skeleton architecture. A – specimen SMF 10543. B – a specimen from series SMF 10546. C – a specimen from series SMF 10554. D – histological section of SMF 10543, general view. E – histological section of SMF 10546, general view. F – histological section of SMF 10548, detail of choanosome with stellate bundles of small spicules. G – histological section of SMF 10547, detail of cortex. H – histological section of SMF 10543, detail of cortex with a sceptre­like spicule. Scale bars: A – C 10 mm; D – E 1 mm; F – H 0.1 mm.

FIGURE 5. Polymastia invaginata: spicules. A – frequency distribution of length (sceptre­like spicules excluded). B – principal spicules. C – small spicules. D – extra­long spicule, general view. E – the same as D, details of proximal and distal ends. F – sceptre­like spicules. Scale bars: B – C 0.1 mm; D 1 mm; E – F 0.1 mm.

FIGURE 6. Polymastia zitteli. A – specimen SMF 10557. B – histological section of idem, general view. C, D – the same as B, details of cortex. E – surface view of detached cortex of idem. F – principal and intermediary spicules. G – small spicules. Scale bars: A 10 mm; B 1 mm; C – E 0.2 mm; F – G 0.1 mm.