Chondrocladia (Meliiderma) tasmaniensis, Vacelet, Jean, Kelly, Michelle & Schlacher-Hoenlinger, Monika, 2009

Vacelet, Jean, Kelly, Michelle & Schlacher-Hoenlinger, Monika, 2009, Two new species of Chondrocladia (Demospongiae: Cladorhizidae) with a new spicule type from the deep south Pacific, and a discussion of the genus Meliiderma, Zootaxa 2073, pp. 57-68 : 63-67

Chondrocladia (Meliiderma) tasmaniensis sp.nov. ( Fig. 4 )

Material examined. Type material. Holotype QM G326397: CSIRO Cruise-Station-Shot SS0207 Stn 33, Mini Matt seamount transect, SSW of Tasmania, -44.24473°, 146.16427°, 1120–1360 m, CSIRO, sled, 5 April 2007.

Paratypes QM G324724: T. Koslov Stn 47, Dory Hill seamount transect, S of Tasmania, -44.33333°, 147.11°, 1360–1656 m, demersal rock sled, 29 January 1997. QM G324735: T. Koslov Stn 62, Hill A1 Reserve seamount/ transect, S of Tasmania, -44.32833°, 147.26833°, 1399–2253 m, demersal rock sled, 30 Jan 1997; QM G 324745:T. Koslov Stn 47, Dory Hill seamount transect, S of Tasmania, -44.33333°, 147.11°, 1360–1656 m, demersal rock sled, 29 January 1997.

Type Locality. Mini Matt seamount transect, SSW of Tasmania, Australia.

Distribution. Mini Matt seamount south-southwest of Tasmania, and Dory Hill and Hill A1 Reserve seamount, south of Tasmania, Australia

Habitat. Attached to fragments of a scleractinian coral Solenosmilia variabilis rubble dredged from depth range of 1120–2253 m.

Description. Four stipitate specimens, consisting of a subspherical body supported by a cylindrical stalk. Stalk broken in specimens G 324724 and G 324735, attached by an enlarged base to a fragment of Solenosmilia variabilis in holotype and in paratype G 324745. Body 7.2 mm in diameter in the holotype, varying from 3.5 to 9 mm in the paratypes, stalk 12 x 1 mm in the holotype, 12–30 x 0.9–1.5 mm in the paratypes. Body more or less regular in shape, surface uneven with numerous foreign bodies included. Stalk generally curved, smooth, slightly thicker near the base. Color cream to clear brown in alcohol. No visible aquiferous system; living tissue poorly preserved.

Skeleton. Stalk made of an axis of tightly packed longitudinal mycalostyles and substrongyles, including a few isochelae and isolated trochirhabds. Stalk axis covered by a dense sheath of closely packed trochirhabds, individual spicules sitting perpendicular to the axis with the larger swelling upwardly directed. Body with a skeleton of radiating fascicles of mycalostyles, and numerous anchorate isochelae. Foreign spicules of hexactinellid and of an Asbestopluma sp. present in several specimens.

Spicules. Megascleres ( Table 2 , Fig. 4 ). Mycalostyles 1 of the stalk and spicular axis of the body, slightly flexuous or a little bent in the third near the head, feebly fusiform, often with a slight swelling near the head, with a short acerate point. Size in holotype: 350–950 x 10 –27.5 µm. Mean size smaller in the fixation base: 350–660 (481 ± 77) x 10–21 (15.4 ± 2.7) µm, larger in the body: 740–950 (872.4 ± 53.6) x 15 –27.5 (21.6 ± 2.9) µm, intermediate in the stalk: 470–950 (745.2 ± 148.5) x 11.5–26 (19.2 ± 3.7) µm (from measurements in the holotype). Size slightly larger in specimen QM G 324735. Microscleres ( Table 2 , Fig. 4 ). Anchorate isochelae, rare in the stalk, very abundant in the body, with narrow fimbriae and five lanceolate teeth measuring 4–18 x 3.6–3.7 µm. Size 67.5–90 µm, shaft approximately 5.5–5.6 µm thick; Trochirhabds, very abundant as a sheath on the stalk, arranged perpendicularly in a dense cover with the large cap outwardly directed. Rhabd straight, bearing on each end respectively a cap and a subspherical bulge, and a disc in the middle. Cap large, resembling a mushroom pileus, convex and bearing small blunt spines giving it a rugose aspect on the upper surface, flat and smooth on the underside. Subspherical bulge, rugose on the surface. Disc without indentation, with a few blunt small spines on the edge. Rhabd smooth, sometimes with a faint swelling between the cap and the disc. Size 32.5–50 µm.

Etymology: Named from the type locality, Tasmania

Remarks: This species differs from the two other species of Chondrocladia that have trochirhabds by the shape of these microscleres, which have a single ring, instead of two in C. occulta and three in C. turbiformis sp.nov. The trochirhabds are also peculiar in that they have an enlarged end resembling a convex mushroom pileus rather than a hemisphere as in the two other species. C. tasmaniensis sp.nov. also differs from C. turbiformis sp.nov. by the absence of substrongyles (although the fixation base, in which these spicules are generally localized in Cladorhizidae is present in two specimens), by the possible absence of small isochelae (which are localized in the embryos in C. turbiformis sp.nov.), and by the absence of sigma.

The large isochelae are remarkably similar, although with slightly longer and larger alae in C. tasmaniensis sp.nov. Two specimens are preserved with a fixation base attached to a fragment of scleractinian coral, showing that they were living on small hard substrates rather than anchored in mud by a rhizoid system as many other Chondrocladia spp.

The two new sponges display the typical morphology of Chondrocladia , which may be rather diverse, but most frequently consists of a subspherical body perched on a stalk with various lateral appendages. The spicule complement of mycalostyles and anchorate isochelae, with or without sigmas or sigmancistras, is also typical of the genus, although it does not allow their identification to a known species of Chondrocladia . The new species are separated from other Chondrocladia by the presence on the stalk of a sheath of special spicules that we here propose to name “trochirhabds”, a name derived from the ancient Greek troch or trochal, meaning disc-shaped. The spicules strongly resemble spinning-top toys, which bear a disc or discs on a shaft. These trochirhabds are similar to the ‘discorhabds’ described in Latrunculia occulta Lehnert et al., 2006 , a sponge which has been interpreted as an elusive epizoan on the stalk of Chondrocladia concrescens ( Schmidt, 1880) ( Lehnert et al. 2006) . Our interpretation of these spicules as proper to some Chondrocladia species radically differs from that given by these authors, and we propose to correct the name of this sponge to Chondrocladia occulta ( Lehnert et al., 2006) . This interpretation rests on several points:

(1) Although the trochirhabds resemble the discate microrhabds called acanthodiscorhabds that are diagnostic of the Latrunculiidae ( Samaai & Kelly 2002; Samaai et al. 2003), the resemblance is mostly due to the presence of two or three discs along a rhabd and does not indicate that they are homologous. In trochirhabds the rings derive from swellings of the shaft of the spicule rather than from coalescing spines as in Latrunculiidae , as evidenced by our observation of incompletely developed spicules, which we have also observed on the slides of “ Latrunculia occulta ”. Similarly, the terminal bulges have a different structure and origin than the apex and manubrium of discorhabds. Lehnert et al (2006) also pointed out these differences and admitted that the terminology of discorhabds does not apply to these spicules. Trochirhabds appear in fact to be another example of discorhabd-like microscleres that have been described in several groups of sponges taxonomically different from Latrunculiidae , such as Didiscus or Barbozia ( Samaai & Kelly 2002) .

(2) The body of the presumed epizoic Latrunculia was not seen by the authors. Lehnert et al recorded only ‘ a very thin encrustation with a thickness of only a unispicular layer ’ of spicules. Similarly, the stalk of our specimens does not display an encrustation which could correspond to an epizoic sponge, neither in macroscopic observations nor on sections, but only a thin unispicular layer of trochirhabds arranged perpendicularly to the surface of the axis in the best preserved individuals. In some specimens of C. turbiformis sp.nov., specimen NIWA21359 for instance, some trochirhabds are intimately mixed with the spicules of the stalk axis, or display at the surface a rosette-like arrangement which is unknown in Latrunculiidae . Furthermore, there are no other spicules which could be proper to a Latrunculia , such as straight styles or strongyles arranged in wispy tracts. This would mean that the Latrunculia has lost the megascleres in relation with its epizoic mode of life, which is unlikely. The substrongyles that are found in the basal part of the stalk in the two new species are rather unusual in Chondrocladia , although quite common in the basal part of the stalk of many Cladorhizidae . We have checked that they are well integrated in the spicular axis of the stalk, with some intermediaries with the normal styles. They are thus proper to the Chondrocladia , and cannot belong to an elusive Latrunculia .

(3) The characters of the three Chondrocladia spp. in which trochirhabds have been observed are consistent. The trochirhabds are distinctive between the three species, and these characters are well correlated with the specific characters of the normal spicules of Chondrocladia .

These special, non-meniscoid microscleres are very unusual in Chondrocladia and more generally in Cladorhizidae , which have a large variety of microscleres derived from sigmas ( Vacelet 2007). Their protorhabds appears to be straight, contrary to that of the spinorhabds of Podospongiidae , which originate from a sigmoid spicule. However, the juvenile trochirhabds closely resemble in shape, size and arrangement the “spear-like spicules” described by Ridley and Dendy, 1887 in Meliiderma stipitata , transferred to Chondrocladia by Hajdu & Vacelet, 2002. In this species, the fully grown spear-like spicules have only faintly marked swellings. They are ‘ densely packed in a single layer around the stalk ’ ( Ridley and Dendy, 1887). Remarkably, Ridley & Dendy first thought that these spicules belong to an epizoic sponge, an interpretation similar to that of Lehnert et al.(2006), but that they discarded on closer examination. A special skeleton occurring at the base of the shaft is rather frequent in carnivorous sponges. It could be a feltwork of spinose microstyles in Asbestopluma , a sheath of granulose tylostyles in some Chondrocladia ( Lundbeck 1905; Topsent 1930), or short and thick substrongyles sometimes evolving in desmas. It seems that in a small group of Chondrocladia these spicules are more specialized, and in the form of trochirhabds.

The Chondrocladia considered here, with such a spicule lining of the stalk, clearly differ by the characters of these spicules. They are subtrochirhabds, spear-like spicules showing only annular swellings in C. stipitata (Ridley & Dendy, 1886) from the subantarctic Indian Ocean (between Prince Edward and Crozet Islands). They are fully formed trochirhabds in the three other species, with three discs in C. turbiformis sp.nov. from New Zealand, two discs in C. occulta from the North Pacific, and a single disc with a bulge enlarged in a cap in C. tasmaniensis sp.nov. from South Australia. The four species have a rather similar shape and other spicule complement, with anchorate isochelae bearing five teeth similar in size. We have examined the slides of L. occulta mixed with a Chondrocladia identified as C. concrescens by Lehnert et al (2006). This Chondrocladia has, in addition to trochirhabds 42–54 µm long and bearing only two rings, a spiculation rather similar to that of the two new species, indicating that they are near relatives ( Table 3 ). The styles are feebly fusiform, with a short acerate point, sometimes a little flexuous, 1200–2100 x 30–38 µm. The anchorate isochelae, 75–98 µm, bear five teeth, with rather large fimbriae. The trochirhabds form a very coherent layer on the base of the sponge, similar to the feltwork of granulose styles frequently found in cladorhizids, but here very regularly arranged. This spiculation, however, differs from that of the two new species not only by the characters of the trochirhabds, but also by the absence of sigmas. The absence of the small size of isochelae, which could be localized in embryos, and of substrongyles, which are localized at the base of the stalk, are less significant. The characters of the “normal” spicules, without taking into account the trochirhabds, clearly differ from those of the Caribbean C. concrescens , which according to Schmidt’s description checked by Topsent ( Schmidt 1880; Topsent 1920) has large isochelae with 6 or 7 teeth measuring 71–120 µm or 110–130 µm, small isochelae 28–31 or 27–40 µm long displaying a distinctive shape with long teeth nearly in contact by their tip, and sigmancistras 69–97 µm long.

The similarity in shape and in spicule complement of these four Chondrocladia spp. with a spicule lining on the stalk indicates a close relationship, which could justify the distinction as a subgenus of Chondrocladia . We propose here to revive Meliiderma ( Ridley & Dendy 1887) as a subgenus of Chondrocladia for these species, with the diagnosis given above. The four known species have anchorate isochelae with five teeth, and substrongyles may be present in the basal part of the stalk in the species where the fixation base is known.

Another Chondrocladia (Meliiderma) species, with similar characters and probably new to science, has been discovered in 2005 during the ANDEEP III-Expedition in the deep Antarctic Weddel Sea, and is in the process of description (D. Janussen, personal communication).

Shape Mycalostyles Substrongyles Isochelae Sigmas Trochirhabds C. turbiformis Subglobular, 1000 –1700 x 260– 1288 x 12–30 68–95 & 32– 30–50 30–50, three sp.nov. stipitate 15–45 & 340– 50.5 with 5 rings

1400 x 4–15 alae

With the exception of a superficial resemblance to the discorhabds of Latrunculiidae , the trochirhabds have no known equivalent in Recent sponge spicules. However, and interestingly, they closely resemble the fossil spicules described by Möstler (1990) from sediment of the Early Jurassic of the Northern Calcareous Alps. The fossil spicules generally have two rings, as those of C. (M.) occulta , and exactly the same shape. Similar spicules, with three rings, have also been recorded from strata of deep-sea sediments dating back to the Miocene from the NE Atlantic near Iceland ( Bukry 1979). These spicules were termed ‘cricorhabds’ or ‘microcricorhabds’ by Möstler (1990), followed by Wiedenmayer (1994), a rather general term used by Rauff (1893) for monaxons provided with annular swellings. We prefer here to coin the new, more specific term ‘trochirhabd’ for these spicules. The fossil records suggest that Chondrocladia (Meliiderma) spp. with trochirhabds are very ancient, dating back at least from the Early Jurassic. The presence of Chondrocladia sp. at this period has been already suggested by Möstler (1990), based on the presence of anchorate isochelae, but these microscleres are more ubiquitous and less significant.

Figures

FIGURE 4. Chondrocladia (Meliiderma) tasmaniensis sp. nov. A. View of the type specimens; from left to right, holotype QM G 326397, paratypes 1, 2 and 3. B – E. Spicules of the holotype. B. Mycalostyles. C Head and tip of a mycalostyle. D. Anchorate isochelae. E. Trochirhabds.

Tables

TABLE 2. dimensions (µm) of Chondrocladia (Meliiderma) tasmaniensis sp. nov.

	Mycalostyles	Isochelae	Trochirhabds
QM G 326397	350–950 (699.5 ± 192.3) x 10–27.5 (18.5 ± 4.1)	72.5–90 (80 ± 4.6)	32.5–40 (37.1 ± 2.26)
QM G 324724	330–910 (567 ± 160) x 12.5–30 (19.5 ± 5.8)	75–90 (82 ± 4.6)	35–45 (38.5 ± 2.95)
QM G 324735	340–1062 (847.2 ± 215.3) x 15–50 (31.2 ± 11.26)	67.5–90 (80.8 ± 4.6)	35–50 (38.7 ± 3.13)
QM G 324745	343–985 (505 ± 195) x 11–27.5 (18 ± 4.76)	74–89 (80.8 ± 3.6)	35–45.5 (39.5 ± 2.42)
Discussion

TABLE 3. Characters of Chondrocladia spp. subgenus Meliiderma, spicule sizes in µm.

C. tasmaniensis Subglobular , 330–1062 x 10– sp.nov. stipitate 50	67.5–90, with 5 alae	32.5–50, one ring
C. occulta Subglobular, 1200 –2100 x Lehnert et al. stipitate 30–38	75–98, with 5 alae	42–54, two rings
C. stipitata Ridley Subglobular, Up to 2200 x 38 & Dendy stipitate	85, with 5 alae 55	Spear-like styles 62–100