Stelodoryx oxeata Lehnert, Stone & Heimler, 2006, sp. nov.

Stelodoryx oxeata sp. nov.

(Fig. 8 a–f, Fig. 9 a–b)

Material

Holotype: USNM 1084236 (51° 19.969' N, 179° 30.194' W, Amchitka Pass, 176 m depth, 0 3. 0 8. 2004); Paratypes: USNM 1084237 (51° 38.292' N, 179° 34.651' W, Amchitka Pass, 395 m depth, 0 5. 0 8. 2004). AB J 2104­11­1 a (51° 39.397' N, 179° 35.028' W, Amchitka Pass, 712 m depth); AB J 2103­16­1 (51° 50.946' N, 179° 50.855' E, Amchitka Pass, 586 m depth); AB J 2104­13­1 (51° 38.292' N, 179° 34.651' W, Amchitka Pass, 395 m depth).

Description

This species was observed to occur in two growth forms. One is a stalked conical with a ridged surface (Fig. 8 a), the other is a massively encrusting, lobate sponge with a smooth surface (Fig. 8 b). Generally the smaller specimens have the conical growth form while the larger specimens are more lobate. Both growth forms are greenish and of rather hard consistency and only slightly elastic due to the densely packed spicules in the ectosome.

Skeleton: Ectosomal very dense, tangential arrangement of tornotes, peculiar oxeas and microscleres. In the ectosome often groups of 4–7 oxeas are oriented parallel, individual groups facing in different directions. Abundant, black particles of volcanic sediment were observed in the choanosome. The choanosome consists in places of an irregular, almost halichondroid reticulation of single spicules or it consists of short spicule tracts, meshsize 90–425 µm, tracts 65–110 µm in diameter.

Spicules: Megascleres are oxeas (Fig.8 c), measuring 517–558 x 20–30 µm. Points of oxeas with ragged, dented outline (Fig. 8 e). Tornotes (Fig. 8 c) with acanthose ends (Fig. 8 d), 230–270 x 9–11 µm. Microscleres are large isochelae (Fig. 8 f), 54–110 µm, medium sized isochelae (Fig. 9 a), 23–32 µm, small anchorate isochelae (Fig. 9 b), 9–13 µm and thin centrotylote sigmas (Fig. 9 b), 8–12 µm.

Discussion

This species is assigned to Stelodoryx (Myxillidae) because it shares the ectosomal tornotes and polydentate anchorate isochelae. Stalked or encrusting growth forms are usual within the genus. However, to accommodate this species in the Myxillidae and consequently in the genus Stelodoryx we have to expand the diagnosis of the family to allow for oxeas with acanthose ends, a character which is not known for any other species of the Myxillidae. Van Soest (2002:602) narrowed the concept of Myxillidae down to “genera which combine the possession of anchorate chelae (or polydentate derivations) with diactinal ectosomal tornotes and choanosomal styles in a reticulate arrangement”. However, Van Soest (pers. comm.) suggested placement of the present species within the genus Stelodoryx for the reasons mentioned above. Stelodoryx oxeata differs from all known species of Stelodoryx in the presence of the peculiar oxeas with acanthose ends. There are thirteen species of Stelodoryx known worldwide, six have been recorded from the northern hemisphere and will be compared with our new species; S. pectinata (Topsent, 1892) from the Azores (N­Atlantic), S. pluridentata (Lundbeck, 1905), S. vitiazi (Koltun, 1955) from the N­Pacific, S. flabellata Burton, 1959 from Iceland, S. procera (Topsent, 1904) from the Azores and S. toporoki (Koltun, 1958). As mentioned above none of these species shares the acanthose oxeas; further differences are discussed below.

S. pectinata is a thinly encrusting species of yellowish color. It has acanthostyles (465 x 16 µm) and smooth tylotes (415 x 5 µm) as megascleres. Microscleres are abundant isochelae of two size categories (60 and 20 µm) and peculiar shape. S. pluridentata is a cushion­shaped sponge. It has smooth styles (320–500 x 9–19 µm), ectosomal strongyles to subtylotes (226–320 x 5–10 µm). Microscleres are polydentate, anchorate isochelae (71–97 µm). Thus it differs in growth form and in lacking the small and medium sized categories of isochelae and the sigmas. S. vitiazi is a grey, lumpy sponge. Spicules are ectosomal strongylotes with acanthose ends (190–291 x 4–7 µm), choanosomal acanthostyles (436–520 x 21–29 µm) and anchorate isochelae (26–46 µm). S. vitiazi differs in growth form and the lack of two categories of anchorate isochelae and the sigmas. S. flabellata was reported from Koltun (1959) from the Kara Sea from 2300 m depth. It is a funnel­shaped sponge with ectosomal tylotes (250–312 x 4–6 µm), choanosomal acanthostyles to acanthostrongyles (322–425 x 12–20 µm) and anchorate isochelae (56–72 µm). Again it differs in lacking two size­categories of isochelae and sigmas. S. procera is a stalked species with ectosomal tylotes (235–300 x 5 µm), choanosomal styles in two size­categories (350–400 x 12 µm) and longer ones (620–700 x 12 µm). Microscleres are anchorate isochelae (45 µm). S. toporoki is a stalked sponge with a funnel­shaped body. It has ectosomal tylotes with acanthose ends (218–300 x 8–10 µm), smooth choanosomal styles (509– 1140 x 21–31 µm) and anchorate isochelae in two size categories, large (119–157 µm) and small (31–40 µm). It differs in the shape of the body, in having larger choanosomal spicules, the large category of isochelae is larger, and a comparable third category of isochelae is missing as well as sigmas.

Chondrocladia alaskensis Lambe, 1894 was considered by Koltun (1959) as a Stelodoryx but Van Soest (2002:620) was confident that Lambe´s specimen is a member of Monanchora while he regarded Koltun´s specimen as a different species which then has to be referred to as Stelodoryx alaskensis Koltun, 1959. As a member of Stelodoryx we have to compare it with our new species. S. alaskensis is a stalked species with a dactylate or irregularly lobate body. Ectosomal spicules are strongylote to stylote (124–228 x 8–9 µm), the choanosomal styles (156–383 x 16–25 µm) are smooth and it has two categories of anchorate isochelae, large (65–108 µm) and small (29–44 µm). It differs from S. oxeata in growth form, in lacking one category of isochelae and sigmas. In summary it can be said that there is no other known species of Stelodoryx which has oxeas with acanthose ends and no species from the northern hemisphere with three categories of anchorate isochleae and with sigmas.

Distribution

Known only from the type locality.

Etymology

Named after the unusually shaped oxeas of the species.