Hyalonema (Prionema), Lendenfeld, 1915

Reiswig, Henry M., 2000, The hexactinellid Leiobolidium Schmidt (Porifera) is a Hyalonema Gray, Zoosystema 22 (2), pp. 411-417 : 413-415

Subgenus Prionema Lendenfeld, 1915

TYPE SPECIES. — Hyalonema agujanum Lendenfeld, 1915 by susequent designation (Ijima 1927: 52).

DIAGNOSIS. — (from Ijima 1927). Dermal pinular ray varying in general shape from swollen and spindle-like to slender with tapering rachis. The largest or the second largest kind of amphidisc with umbel teeth which are finely serrated or fimbriated on their lateral edges.

Hyalonema (Prionema) repletum n. sp. ( Figs 1 A-F, 2: Table I)

MATERIAL EXAMINED. — Holotype ( MCZ # 8023m, old # 297), dry.

ETYMOLOGY. — From Latin replere, to fill up.

TYPE LOCALITY. — Lesser Antilles. 16 km, W-SW of the island of Bequia, USCSS Blake, stn 235, 12°57’10”N, 61°25’25”W, 2757 m, 21. II.1879, A. Agassiz.

DIAGNOSIS. — Hyalonematid with macramphidiscs bearing teeth with finely serrated edge: with uncinates; rhabdodiactins and macrohexactins as principalia; three distinct classes of amphidiscs and one class of microhexactins; body shape ovoid.

DESCRIPTION

Body

The single specimen, the holotype ( Fig. 1A, B ), is a nearly spherical ovoid in body form, slightly expanded in the middle, 11.2 mm tall by 12.7 mm wide. A small rounded apical cone projects slightly from a surrounding ring-like oscular aperture. The margins of the aperture are round- ed and bear a palisade of pinular diactine marginalia. Lateral surfaces are covered by a dense felt of pinular pentactins, supported by a rectangular lattice of hypodermal pentactins, 0.4 mm mesh size, easily visible to the naked eye ( Fig. 1A ) where the pinular feltwork has been partially abraded. Dermal pinules have no regular arrangement, are spaced at about 25 µm distances, with tangential rays profusely overlapping in all directions. An aperture with a peripheral expansion is present at the inferior pole ( Fig. 1A, B ). This is presumed to be the point of emergence of the root tuft, which is lacking and is inferred to have been torn out during collection. No acanthophores were found in an extensive search of this entire region. The ectosome, 0.6 mm in thickness, consists of a dense dermal surface supported by radial pillars outlining an extensive series of confluent subdermal spaces. The choanosome consists of a structureless pulp of spicules, with neither large cavities nor organized skeletal structures evident to the naked eye or at any level of magnification ( Fig. 1B ).

Spicules

Ten classes of spicules have been found in this species: their dimensions are presented in Table I.

Rhabdodiactin. ( Fig. 2A ) Parenchymal principalia (with macrohexactins); thin, evenly tapering to sharp tips; entirely smooth with central inflation; most occur singly but occasionally in poorly defined tracts two to six spicules wide.

Macropentactin. ( Fig. 2B ) Hypodermalia providing support for dermal pinules: tangential rays smooth, acute-tipped, slightly bent downwards, angle between proximal and tangential rays 79.8 ± 5.5° 50 (68.9-91.4); smaller pentactins common in mesh spaces of main hypodermal lattice.

Macrohexactin. ( Fig. 2C ) Parenchymal principalia (with rhabdodiactins); entirely smooth, acute-tipped, slightly unequal-rayed; occur

* total width including spines; ** rachis width.

randomly throughout choanosome with slight suggestion of rectangular organization in peripheral areas.

Pinular diactin. ( Fig. 2D ) Marginalia; occur only as a palisade around margin of oscular rim; pinular ray usually broken, so few available for measurement.

Pinular pentactin. ( Figs 1C ; 2E ) Dermalia (the only spicules present in dermal surface); spines of pinular ray long and sparse, inserted at fairly large angle to rachis, giving a ragged, bushy aspect; spines of lower quarter distinctly curved outwards: tangential rays straight, tapered, spined distally or throughout, always crossing perpendicularly.

Uncinate. ( Figs 1F ; 2I ) Parenchymalia and comitalia to hypodermal pentactins; with low, sharp barbs all oriented in the same direction; very clear axial cross present centrally and occasionally associated with a slight central inflation.

Macramphidisc. ( Figs 1 C-E; 2F) Occur only ectosomal in linings of subdermal cavities: never dermal or choanosomal; long and narrow in form: usually eight teeth (four to eight) with finely serrated margins, ragged-toothed tips, and smooth rib support on inner side ( Fig. 1E ); shaft with a central whorl of long, cylindric knobs with rounded tips; elsewhere sparsely ornamented with scattered small, low, round-tipped knobs.

Mesamphidisc. ( Fig. 2G ) Occur sparsely in ectosome but mainly in choanosome with micramphidiscs in lines interpreted as residual membranes of major water channels, not randomly strewn; shape like macramphidisc; eight teeth, smooth-margined (not serrate); tips parabolic, rounded; shaft bearing eccentric-placed whorl of elongate knobs and dense covering of short rounded knobs.

Micramphidisc. ( Fig. 2H ) Distribution as mesamphidisc: 16 teeth; shaft bears only a few sharp spines.

Microhexactin. ( Fig. 2J ) Distributed randomly throughout choanosome; rays slightly curved, occasionally straight; finely rough.

REMARKS

Although the specimen lacks a root tuft and acanthophores, both presumed lost during collection, there is no doubt that it is a member of the genus Hyalonema ; taxonomic literature contains many similar situations and conclusions. Lévi’s (1964) suggestion that nine of the recognized subgenera of Hyalonema be raised to generic status, and five others be considered doubtful, has not been followed by authors of subsequent publications, but it may yet form the basis of a needed revision of the genus. Because the 12 subgenera of Hyalonema accepted by Ijima (1927) are not diagnosed with mutually exclusive characters, L. repletum could be assigned to either of two subgenera on the basis of Ijima’s diagnoses, Prionema Lendenfeld, 1915 , with serrated amphidisc teeth, or Onconema Ijima, 1927 , with uncinates. The former assignment has been selected on practical grounds, that is, macramphidiscs are easier to inspect and evaluate as autochthonous structures than are uncinates. This choice agrees with Lévi’s (1964) opinion that Prionema be considered an acceptable distinct taxon but that Onconema be considered a doubtful taxon. With its distinctive combination of serrated amphidisc teeth and uncinates, this species is not a close relative of any Hyalonema species so far described. Among the species presently assigned to the two pertinent subgenera, this species is most similar to H. (Prionema) spinosum Lendenfeld, 1915 , a form also with serration of macramphidisc teeth. The two differ in presence/absence of uncinates and shape of the dermal pinules, microhexactins, and body form. Ultimate resolution of the relationships between these groups of Hyalonema will depend upon more exclusive diagnosis of its subgenera and the importance accorded the uncommon occurrence of uncinates in this genus. For the present, H. repletum is comfortably contained within the subgenus Prionema , and Schmidt’s generic name, Leiobolidium , can be put to rest.

Figures

FIG. 1. — Hyalonema (Prionema) repletum n. sp.; A, external view of body; B, internal structure; C, macramphidisc and dermal pinule (SEM); D, serrated macramphidisc teeth (SEM); E, view of macramphidisc umbel with broken teeth in section (SEM); F, part of an uncinate (SEM). Scale bars: A, B, 1 cm; C-F, 10 µm.

FIG. 2. — Spicules of Hyalonema (Prionema) repletum n. sp.; A, rhabdodiactin; B, macropentactin; C, macrohexactin; D, pinular diactin; E, pinular pentactin; F, macramphidisc; G, mesamphidisc; H, micramphidisc; I, uncinate; J, microxyhexactin. Scale bars: A-D, 200 µm; E, F, I, 100 µm; G, H, J, 20 µm.