Cornulum antarcticum Göcke & Janussen, 2013, sp. nov.

Cornulum antarcticum sp. nov.

(Figs. 5–6, Tab. 3)

Material. 18 specimens from station 048-1 (holotype: SMF 11770, paratypes: 11794–11797, 11803, 11804, 11843, 11844, 11851, 11852, 11758), 602.1 m, 70° 23.94' S, 8° 19.14' W, 12.01.2008. Material examined for comparison: Cornulum textile Carter, 1876: BMNH 1882.7.28.76 (holotype), NE Atlantic, det. Carter, wet specimen and slides; BMNH 1910.1.1.1363 (schizotype) & BMNH 1910.1.1.1364 (schizotype), Canon Norman’s Collection of British Sponges, slides.

Diagnosis: Tubular sponges of conical shape and erect growth, fixed to hard substrate. Tough outer layer of regularly arranged strongyles, fluffy inner tissue with tracts of strongyles, tylotes and rarely small styles. Microscleres palmate isochelae. The top side closed by a distinct cap-like plate structure. Outer surface shows growth rings.

Description. Tubular sponges of conical shape (Fig. 5 A–B) with erect growth. Body up to about 100 mm high and 10 mm wide, basal diameter 1 to 2 mm. At the top, tube closed by a firm cap (Fig. 5 B). Surface with distinct, regular rings, probably growth rings. Tube mostly hollow. Basis attached to hard substrate. Several tubes may originate from one basis, they can be counted as one individual (holotype, Fig 3). One of the tubes of the type detached during preparation, still preserved as part of the holotype specimen. On the firm surface, a rich fauna of epibionts found, including bryozoans, hydrozoans, sponges and polychaete tubes.

Skeleton: The epidermis, constituting the outer tube wall, very tough, with a tight layer of strongyles in rather regular orientation parallel to one another (Fig. 5 C). Rarely, spots can be found, where a more loosely packed second layer of strongyles is attached. Chelae also occur in the epidermis, but rarely. Epidermal spicules wrapped in a firm layer of spongin. Inside of the tubes coated by a fluffy soft choanosome (Fig. 5 D) including plumose or plumoreticulate spicule tracts, connected by rectangularly running tracts. These quasi-reticulations wide-meshed. Tracts, which run in parallel orientation to the epidermis, made up of strongyles, tylotes and rarely styles. Numerous palmate chelae occur as free spicules within the tissue. Inside of tubes mostly hollow, tissue usually covering only the inner surface of the epidermis, not filling the entire inner space.

Spiculation (Tab. 3): Main spicules relatively thick strongyles, usually curved with a distinct kink towards one end (Fig. 6 A, B), 330–470 (mean 415.7) µm long and 25–33.75 (mean 29.7) µm wide. Other prominent spicules are tylotes, long, relatively thin, diactinal spicules, usually with swollen endings. In some cases, swellings very weak or even absent, so that one end shows a strongyle-like shape. Endings of these spicules usually bear tiny spines, all oriented in distal direction (Fig. 6 E). In some cases, spines reduced to only one central spine (Fig. 6 F), thus giving the spicule a tornote-like shape. Contrary to tornotes, these tylotes are not epidermal, but choanosomal spicules. Tylotes show a wide size variance, with mean length of 320–590 (mean 443) µm and diameter about 6.25–15 (mean 12.3) µm. Very rare are styles (Fig. 6 G), 360–580 (mean 421.7) x 3.75–15 (mean 8) µm, which seem to be reduced tylotes, occasionally with spines at the rounded end. One specimen (SMF 11804) analyzed without styles. Microscleres palmate isochelae of usual shape, about 11–18 (mean 15.9) µm long (Fig. 6 C–D).

Etymology. The species is named after its type locality; it is the first Antarctic record of this genus.

Remarks. The genus Cornulum currently comprises nine valid species, none of which are known from the Antarctic (van Soest et al. 2012a). Of these, three show a growth form very similar to our new species. These are Cornulum enteromorphoides Fristedt, 1887, Cornulum textile Carter, 1876, the genotype, and Cornulum tubiforme Burton, 1935. Cornulum enteromorphoides in contrast to our species possesses acanthostyles and additional large chelae (about 70 µm), but no strongyles (Fristedt 1887). Cornulum tubiformes differs from C. antarcticum sp. nov. by the lack of strongyles. Instead, it has styles with a strong spine at the thicker end (called “oxeote tornota” by Burton) of 280 µm length (Burton 1935). Cornulum textile, the type species of the genus, shows a good deal of overlap with C. antarcticum sp. nov., so that the assignment of the new species to the genus is clear. Still, some differences occur. The holotype is shaped much like that of our new species, it is conical, with the smaller end attached to the substrate. As in the new species, the epidermis is very tough with a dense layer of spicules, while the inner tissue is quite soft with reticulate spicule tracts running parallel to the epidermis towards the upper end (Carter 1867). The holotype also shows distinct growth rings. However, in contrast to our new species, the holotype of C. textile widens much more towards the top end. Lundbeck (1910) portrayed two specimens of C. textile, which are even more similar to the new species in outer shape. These are more slender, not widening much towards the top. One specimen has the top preserved, showing a cap-structure, much like the ones in our new species. This specimen is overgrown by epibionts, which seems to be typical for the genus, as its surface is tough and the tube rises significantly above the ground, therefore providing a good substrate for other animals. The spiculation of C. textile and C. antarcticum sp. nov. shows significant similarities (compare Carter 1876; Hooper 2002a). Cornulum textile has tylotes with spiny ends, 290–370 x 8–22 µm, and thick styles, which can occasionally occur as anisostrongyles, 390–480 x 15–22 µm). Palmate chelae are of the usual type, as in C. antarcticum sp. nov., 11–15 µm. Also smaller, somewhat bow-shaped monaxons occur, which Hooper (2002a) refers to as “toxas”. Especially in the figures of Carter (1876), these spicules look much like the small styles described above for the new species. But unlike in the new species, in C. textile, they are very numerous and measure 190–310 x 1–3 µm. (all measurements taken from the re-description of the holotype by Hooper 2002a).

Another species that is similar in shape to our new Cornulum is Tedania (Tedaniopsis) tantula (Kirkpatrick, 1907), which is also very common in the Antarctic. Tedania (T.) tantula shows a very similar habit as C. antarcticum sp. nov. (especially good figures of the habitus of several specimens can be found in Ríos 2006). It has a tubular shape and grows erect on the substrate. However, the spiculation of T. (T.) tantula is very different from that of Cornulum. Tedania (T.) tantula has no chelae, but acanthose onychaetes. Other megascleres are thick strongyles, sometimes style-like with a pointed end, and tylote tornotes (Kirkpatrick 1908). The epidermis is not as tough as that of Cornulum, because the spicule layers are not as dense as in the latter. For detailed descriptions and measurements of the SYSTCO I T. (T.) tantula see below.

As the species occurred in quite a large quantity on the lower shelf in a quite well-studied area, it seems highly likely, that specimens of this species have been found before, but were mistakenly classified as the well-known T. (T.) tantula, because of the very similar shape. This may be a special problem when working with ROVs, as pictures of the two species will have no recognizable differences.