Endectyon (Hemectyon), Topsent, 1920

Sitjà, Cèlia & Maldonado, Manuel, 2014, New and rare sponges from the deep shelf of the Alboran Island (Alboran Sea, Western Mediterranean), Zootaxa 3760 (2), pp. 141-179 : 169-171

Subgenus Hemectyon Topsent, 1920

Diagnosis. Erect, probably undivided (see "Taxonomic Remarks"), growth form. Skeletal organization with recognizable axial, extra-axial and ectosomal regions. Axial skeleton of multispiculate-cored fibres densely reticulated. Extra-axial skeleton consisting of a more lax reticulum of pauci- to multispicular radiating primary tracts intercrossed by uni- to paucispicular secondary tracts. Spongin fibres and tracts of the axial and extra-axial regions are cored by smooth choanosomal styles; the radiating primary tracts of the extra-axial skeleton may be sparsely echinated by acanthostyles, particularly in their subectosomal regions. In the subectosomal region, the peripheral nodes of the extra-axial network serve as basis for small bouquets of longer (subectosomal) styles, which pierce the sponge ectosome to make a long, dense hispidation. At the point where each of these protruding bouquets of styles pierce the sponge ectosome, a surrounding brush consisting mostly of acanthostyles (but also incorporating some choanosomal styles) occurs, being this skeletal trait a distinct character for the subgenus Hemectyon (modified herein to accommodate the features of the new species).

Endectyon (Hemectyon) filiformis nov. sp.

( Figs. 11C–D , 13 ; Table 2)

Etymology. This species is named after its erect, undivided body shape.

Material examined. Holotype: Specimen MNCN-Sp69 BV21, from type locality Stn. 21 ( Table 1 , Fig. 1 ), a 93 to 101 m deep, gravel bottom on the deep shelf of the island.

Macroscopic description. Flexible, slender, thread-like sponge, measuring 54 mm in height and 3 mm in diameter, attached to a gravel piece. The surface is densely and markedly hispid ( Fig. 11C–D ), with no obvious oscules. The color in life is bright orange, turning into creamy white in ethanol.

Skeleton. Megascleres in 4 spicule categories: Subectosomal styles, choanosomal styles, occasional oxeas, and acanthostyles. The subectosomal styles are long and slender, slightly curved at the centre or near the round end, with a regular round end, and an acerate point that can be sometimes softly stepped or, in the thinner growth stages, hastate ( Fig. 13A ); they measure 713– 1465 x 3.2–20 µm. The choanosomal styles measure 187.4–272.5 x 6.4–9 µm, being irregularly curved once or twice, sometimes in a rhabdostyle fashion, with hastate or acerate points ( Fig. 13A–B ). These styles may show a slight swelling either near the round end or towards central positions. The oxeas are less common than the previous categories, typically curved at the middle, with sharp conical ends that can be slightly different ( Fig. 13A, C ), measuring 234–277 x 3–9 µm. The acanthostyles are nearly straight or slightly curved and show scarce, large, conical spines. Spines are usually sparse over the spicule length, mostly making a sort of verticillate cluster at the round end, producing a clavulate acanthostyle; the spines very rarely appear around the sharp end of the spicule. The number of spines varies from one to four at the round end and from one to ten over the shaft length, and they can be straight, curved toward the spicule points or in the opposite direction ( Fig. 13A, D ). The acanthostyles are far less abundant than the choanosomal styles and measure 114–150 x 6–7 µm.

Axial and extra-axial skeleton are poorly differentiated. The axial skeleton is a relatively more compact reticule of pauci- and multispicular tracts of choanosomal styles surrounded by moderate spongin ( Fig. 13F ). The reticule becomes progressively less compact towards the periphery (extra-axial region?) and is built with thinner tracts (pauci- and unispiculate) of choanosomal styles and occasional oxeas. From the periphery of this extra-axial network, groups of 2 to 10, long subectosomal styles project radially ( Fig. 13E ), piercing the surface and causing the long hispidation of the surface. At the point where one of these radiating tracts of long subectosomal styles pierces the sponge ectosome, a surrounding brush consisting mostly of acanthostyles (but also incorporating some oxea or choanosomal style) occurs ( Fig. 13E ); this skeletal trait is a diagnostic character for the subgenus Hemectyon .

Distribution and ecology notes. The only individual of Endectyon (Hemectyon) filiformis nov. sp. was collected from a 93 to 100 m deep, organogenic-gravel bottom.

Taxonomic remarks. Members of the genus Endectyon are the only raspailiids having echinating acanthostyles with clavulate morphology and located outside the axial skeleton ( Hooper 1991; Hooper 2002b). Within the subgenus Hemectyon , only one species had been described to date: Endectyon (Hemectyon) hamatum ( Schmidt, 1870) . This species was originally reported from the Caribbean ( Schmidt 1870; Topsent 1920). It was subsequently cited from the East Africa (North Kenya) by Pulitzer-Finali (1993), but a revision of that specimen assignation would be advisable, as it contains abundant raphides and the brief skeletal description suggests it to be a raspailiid different from Endectyon spp.

The occurrence of acanthostyle brushes surrounding the groups of hispidating styles clearly indicates that the newly described Alboranian material belongs to the subgenus Hemectyon , making the second known species in this subgenus. The differences between E. (H.) hamatum and E. (H.) filifomis nov. sp. are clear: 1) the axial and extraaxial differentiation is less marked in the new species, as well as the differentiation between radiating primary tracts and secondary intercrossing tracts; 2) the primary radiating tracts are only very rarely echinated by the acanthostyles in the new species; 3) the acanthostyles do not have clavulate spines at the round end in E. (H.) hamatum , but they do have them in the new species; 4) The hispidating styles in E. (H.) hamatum are relatively small (220–275 x 2 µm) and shorter than those coring the choanosomal fibres and tracts (270–615 x 6–18 µm), whereas they are notably longer (up to 1465 x 20 µm) in the new species; and 5) the new species contains occasional oxeas, while they do not occur in E. (H.) hamatum . Indeed, oxeas are an uncommon spicule type in Endectyon spp. , although occasional modifications of styles into oxeas and strongyles have already been recorded in Endectyon (Endectyon) tenax ( Schmidt, 1870) from North Carolina by Wells et al. (1960) and Endectyon (Endectyon) multidentatum ( Burton, 1948) from Congo Coast ( Burton 1948).

To accommodate the skeletal features of this new species, it has been necessary to modify herein the last accepted diagnosis of subgenus Hemectyon , which was proposed by Hooper (2002b) on the basis of the only species available at that time. An additional reason to revise the subgenus diagnosis is the growth habit. Originally, Hemectyon was erected on a partial sponge fragment that was assumed to be part of a larger, branched individual ( Schmidt 1870; Topsent 1920). Ever since, the successive genus diagnoses have included terms such as "rameuse" ( Topsent 1920) or "arborescent" ( Hooper 2002b), a branching condition that has never been corroborated objectively. Given that the holotype of E. (H.) hamatum is an undivided cylindrical fragment (23mm x 3.5) and that the complete holotype of E. (H.) filiformis nov. sp. is also an undivided, digit-like growth form, there is no reason to support any longer that the sponges of the subgenus Hemectyon are arboresecent. Rather, they should be postulated as erect, branchless growth forms, at least until future collections of new material disprove it.

Figures

FIGURE 1. (A) Localization of the Alboran Island in the Mediterranean. (B) Distribution of the 25 studied sampling stations over the bathymetric map of the shelf of the Alboran Island.

FIGURE 11. (A–B) Neotype (MNCN-Sp23-BV14) of Rhabdobaris implicata Pulitzer-Finali, 1983 collected from the Alboran Island and photographed on its both sides. Note some ribs (r) on the lamina. (C–D) Holotype of Endectyon (Hemectyon) filiformis nov. sp. (MNCN-Sp69 BV21) attached on a small piece of gravel, photographed on its both sides.

FIGURE 13. Endectyon (Hemectyon) filiformis nov. sp.: (A) Line drawing summarizing the spicule complement of the holotype (MNCN-Sp69-BV21). There are subectosomal styles (a) with a round end and an acerate or hastate distal end (b) and choanosomal styles with a regular or swollen round end (d) and an acerate, hastate or polyaxonic distal end (e). There are also oxeas (f) with conical to hastate ends (g) and acanthostyles (h) with large spines that can be clavulate at the round end (i). (B) Light microscope view of choanosomal styles, with slight subterminal swelling (bs) or a subtle subtyle (sb). (C) Light microscope view of an oxea. (D) SEM micrographs of acanthostyles. (E) Line drawing sketching the organization of the ectosomal skeleton, which consists of the subectosomal styles (es) surrounded by an hispidating brush of acanthostyles (as). (F) Light microscope view of the choanosomal skeleton where spongin (s) can be observed embedding the choanosomal styles.