Tethya hibernica, Heim, Isabel, Nickel, Michael, Picton, Bernard & Brümmer, Franz, 2007

Heim, Isabel, Nickel, Michael, Picton, Bernard & Brümmer, Franz, 2007, Description and molecular phylogeny of Tethya hibernica sp. nov. (Porifera, Demospongiae) from Northern Ireland with remarks on the European species of the genus Te t h y a *, Zootaxa 1595, pp. 1-15 : 3-8

Tethya hibernica new species

Diagnosis. Small Tethya of 0.5–2.5 cm in diameter; megasters of 31–60 µm in diameter, displaying an R/C of 0.40–0.78, frequently with slightly curved tips; interstitial megascleres (strongyloxeas) present, 365–820 µm in length, 7–14 µm in diameter.

Examined material. Holotype Mc3037 (Leg. B. Picton, 10.06.2005). Paratypes Mc2426 (Leg. B. Picton, 14.06.2005) and Mc2487 (Leg. Jen Jones, 14.06.2006). Type locality: Damicornis Bay, Rathlin Island, Northern Ireland ( Fig. 1 ), coordinates 55° 17.44’N 006° 15.19’W.

Etymology. Referring to ‘Hibernia’, the Latin denotation for the Island of Ireland.

Description. Morphology ( Fig. 2 ). Body spherical, diameter 0.5–2.5 cm, clearly divided into a cortex region and a choanosomal core. Colour in life is ochreous to yellow ( Fig. 2 A–C). Colour in alcohol white, with greyish core. Body contractile in life. Consistency compressible. Surface conulose (expanded state) to papilose (contracted state), frequently heavily loaded with sediment. Tubercles at the surface may produce filaments and stalked buds ( Fig. 2 C). Cortex compact, 0.8–1.4 mm in thickness (without tubercles), with relatively few lacunae.

Skeleton structure ( Fig. 3 ). The radiate bundles of styles (strongyloxeas) are dense and terminate in cortical tubercles, forming terminal fans. Groups of auxiliary megascleres are present in the choanosome inbetween the main bundles. The megasters (oxyspherasters) are evenly and densely scattered throughout the whole cortex. Micrasters form a discrete layer allocated to the exopinacoderm surface and the endopinacoderm of the lacunae. In addition, micrasters are evenly distributed throughout the whole cortex as well as the choanoderm.

Spicules ( Fig. 4 and 5 , Tab. 1 ). Main megascleres are strongyloxeas ( Fig. 4 ), 880–1250 µm in length, 8– 18 µm in diameter. Auxilary megascleres are strongyloxeas, too, 365–820 µm in length, 7–14 µm in diameter. Megasters are oxyspherasters ( Fig. 5 A), 31–60 µm in diameter, with 13–18 rays which often slightly curve towards the tip, R/C = 0.40–0.78 ( Tab. 1 ). Micrasters fall into three catgories: mainly oxyspherasters ( Fig. 5 B), 10–19 µm in diameter, with 10–13 rays; strongylasters ( Fig. 5 C) 8–18 µm in diameter, with 11–14 rays; few small tylasters ( Fig. 5 D), 8–10 µm in diameter, with 7–9 slightly spinulated rays.

Molecular characters. The partial cytochrome oxidase subunit I (COI) nucleotide and deduced amino acid sequences of T. hibernica are presented figure S1 and figure 6. These characters delimit T. hibernica well from the other European species (Tab. 2).

Reproduction. Asexual reproduction by external stalked bud formation is documented ( Fig. 2 C). Whether or not T. hibernica reproduces sexually is presently not known, however it is likely in the context of knowledge on related species like T. aurantium and T. citrina ( Corriero et al., 1996) .

Ecology. The type location at surrounding Rathlin Island represents infralitoral hard bottom habitats which are influenced by strong tidal changes, especially regular periods of strong currents. The more sheltered areas and bays where T. hibernica was found are exposed to a high sedimentation, partly of organic matter, pointing towards nutrition-rich situation. The contractility of the species ( Fig. 2 A, B) represents a well documented behaviour within the genus Tethya ( Marshall, 1885; Sarà et al., 2001; Nickel, 2004), which also relates to movement of some Tethya species ( Fishelson, 1981; Nickel, 2006). The latter has not yet been reported for T. hibernica and will have to be proven by field or aquarium studies. However, the contraction behaviour of T. hibernica might be an adaptation to strong changes of external water currents during tidal cycles.

Distribution. At present, T. hibernica has only been reported from its type localities around Rathlin Island, Northern Ireland. This island is of particular interest concerning its poriferan fauna. The high numbers of 128 sponge species have been reported, of which 29 represent new species and further 19 are candidates for new species (Picton & Goodwin, unpublished). Despite these numbers it is unlikely that T. hibernica is endemic to Rathlin Island. A rather high number of records for T. citrina and also T. norvegica are present in faunal databases for the coasts of Ireland and Great Britain. Reinvestigations of these records and careful determination of new findings of specimens of the genus Tethya will have to show whether T. hibernica can be found throughout the coastal waters of Britain and Ireland or if it is endemic to the region of Rathlin Island.

Related species. The closest related species seems to be T. norvegica , which shares general body characters (size, partly colour). However, T. hibernica can be clearly distinguished from T. norvegica firstly by the presence of auxiliary styles as well as the lack of bifurcated or spiny rays of the megasters. In addition the R/C values of the megasters differ between T. norvegica and T. hibernica ( Tab. 1 ). Tethya hibernica can be clearly distinguished from the other European species by size, colour, consistency and megastar R/C in case of T. aurantium and by body size, consistency and megastar diameter in case of T. citrina (compare key to the European species below).

The morphological differences between all the European species is confirmed by extensive nucleotide and amino acid exchanges within the molecular marker COI (Tab. 2).

TABLE 2. Amino acid exchanges (upper section) and base pair exchanges (lower section) of the COI between two different Tethya species. All specimens of T. hibernica analysed here displayed identical nucleotide and amino acid sequences, consequently they were treated as a single OTU. Two populations of T. citrina slightly differed in the nucleotide sequences, consequently they are presented separately. T. hibernica 1 = Mc 3037, T. hibernica 2 = Mc 2426, T. hibernica 3 = Mc 2486, T. citrina 4 = North-Ireland, T. citrina 5 = Croatia.

Figures

FIGURE 1. Geographic location of Rathlin Island (star in right map) within the British Isles between Northern Irleand and Mull of Kintyre (Scotland). The insert map (left) displays Rathlin Island with coordinates and the collection point of the type specimens of T. hibernica (filled circle).

FIGURE 2. In vivo images of T. hibernica types from the type location at Rathlin Island. Both specimens have been used for morphological description and DNA sequencing. A. Expanded holotype (Mc 3037) with open oscules (arrow heads). B. Contracted holotype (Mc 3037) with closed oscules, after contraction stimulation by extensive artificial water current. C. Paratype (Mc 2748), with external buds (arrow heads). Mind the colour variation from brownish to yellowish between the two specimens.

FIGURE 4. Megascleres (strongyloxeas) of T. hibernica. A. SEM image collage of a main megasclere, presenting typical geometry and diameters of both ends and a middle section. B. Size distribution of auxiliary megascleres (filled triangles; n = 70) and main megascleres (filled circles, n = 40), which form distinct groups of normal distributions (Kolmogorov-Smirnov test), significantly separated by spicule length (p <0.001; independent t-test).

FIGURE 5. SEM images of T. hibernica spicule morphology. A. Typical megasters. B. Acanthostrongylasters, which represent the major group of micrasters (> 95 %). C. Acanthotylasters (rarest group of micrasters). D. Oxyasters, which are slightly more frequent than tylasters.

FIGURE 3. A. Schematic overview on the skeletal arrangement in the cortex (light grey) and the choanoderm (dark grey) in a contracted specimen of T. hibernica. B. Micrograph of tissue slice preparations. Main megascleres form bundles, which fan near the surface. Auxiliary megascleres are present in-between bundles in the choanoderm. Megasters are mainly present throughout the whole cortex. Micrasters are present throughout the sponge, with a prominent layer supporting the outer and inner pinacoderm layers. The lacuna system of the ectoderm is not dominant due to the contracted state of the specimens investigated. For details on the spicules refer to Figures 4 and 5.

Tables

TABLE 1. Morphometric features of megasters of Tethya species distributed in the North East Atlantic (NEA). For comparison, the values from the Mediterranean Sea (MS) are provided for T. citrina. R / C values are calculated according to Sarà (2002).

Species	Location Average size [µm] (n)	Size range [µm]	Average R/C (n)	Reference
T. citrina	Marsala (MS) 80.48 ± 13.9 (1012)	38.83 – 126.55	0.85 ± 0.3 (1012)	Sarà et al. 1992
	Torbay (NEA) 60.34 ± 14.8 (992)	29.63 – 93.06	0.77 ± 0.2 (992)	Sarà et al. 1992
	Rathlin Island 67.25 ± 5.8 (206) (NEA)	40.00 – 80.79	0.82 ± 0.1 (88)	-
T. norvegica	Norway (NEA) 42.13 ± 8.7 (805)	16.17 – 59.50	0.70 ± 0.3 (805)	Sarà et al. 1992
	The Faroes (NEA) 41.99 ± 6.0 (503)	26.00 – 53.00	0.80 ± 0.3 (503)	Sarà et al. 1992
T. hibernica	Rathlin Island 44.76 ± 6.1 (403) (NEA)	31.73 – 65.02	0.60 ± 0.1 (102)	-