Megaciella anisochela, Lehnert, Helmut, Stone, Robert & Heimler, Wolfgang, 2006

Lehnert, Helmut, Stone, Robert & Heimler, Wolfgang, 2006, New species of deep­sea demosponges (Porifera) from the Aleutian Islands (Alaska, USA), Zootaxa 1250, pp. 1-35 : 4-6

Megaciella anisochela sp. nov.

( Fig. 2 a–f, Fig. 3 a–b)

Description

The holotype is a stalked, fan­shaped sponge ( Fig. 2 a) and was growing on a small boulder. The species has also been observed growing on exposed bedrock. The dimensions of the short stalk are 2 x 0.5 cm and the fan­shaped body has an irregular outline measuring approximately 11 x 5.5 cm. It is beige colored in ethanol. The surface is finely hispid with no recognizable oscules. It has a soft and elastic consistency.

Skeleton: The ectosome is a thin translucent membrane with tangentially arranged tylotes, single or in small bundles, facing in all directions within the tangential plane. The ectosome contains very abundant isochelae and is supported by underlying styles. The choanosome is partly a unispicular reticulation and partly there are ascending paucispicular tracts of two to four spicules connected by single spicules. Ascending tracts of styles are the length of one choanosomal style apart, penetrate the ectosomal membrane and cause the hispidation.

Spicules: Megascleres are smooth choanosomal styles ( Fig. 2 b), 490–615 x 18–22 µm, and ectosomal tylotes ( Figs. 2 b, c) with acanthose heads ( Fig. 2 d), 245–380 x 4–9 µm. Microscleres are palmate isochelae ( Fig. 2 e) with narrow extensions, 13–17 µm, a small category of palmate isochelae ( Fig. 2 f), 6–8 µm and a small category of distorted anisochelae ( Fig. 3 a–b), 4–6 µm. These small anisochelae, though somewhat unusual for the genus, are abundant in the sponge and consistently with unequal ends.

Discussion

Assignment of the present species to the family Acarnidae is based on the following characteristics: 1) The occurrence of an ectosomal skeleton with tangentially arranged tylotes having spined bases; and 2) a choanosomal reticulate skeleton of styles and two size categories of palmate isochelae. We assign it to the genus Megaciella because it shares the microspined tylotes, the choanosomal styles and palmate isochelae with other congeners. Megaciella anisochela sp. nov. differs from all known Megaciella in the presence of a small category of anisochelae and in the absence of toxa. To accommodate this species in Megaciella we consequently have to expand the diagnosis of the genus to allow for the presence of anisochelae and the lack of toxa. We should note that we found some very rare toxa with acanthose ends in one spicule preparation and that all known members of Megaciella possess toxa. Since we could not isolate the toxa in subsequent preparations and as these were toxa with acanthose ends, most similar to toxa found in the genus Artemisina Vosmaer, 1885 (family: Microcionidae ) we are confident that these were indeed foreign. Megaciella and Artemisina share many characters and the similarities between these genera were already discussed by Van Soest (1984) and Van Soest et al. (1994). However, doubts remained about family placement of Megaciella .

Megaciella presently contains ten species. Four species of Megaciella occur sympatrically with the species described here. All four previously known North Pacific species were described as Myxichela by Koltun: Megaciella fragilis ( Koltun, 1955) , M. spirinae ( Koltun, 1958) , M. ochotensis ( Koltun, 1959) and M. zenkevitchi ( Koltun, 1958) . As already mentioned, all known species of Megaciella have smooth toxa and are lacking anisochelae. Additional differences between these roughly sympatric species are discussed in the following.

Megaciella fragilis ( Koltun, 1955) is the only sympatric congener which shares smooth styles with M. anisochela sp. nov. However, its styles (291–364 x 12–18 µm) are much shorter and thinner, and the terminally acanthose strongyles (176–228 x 6–8 µm) are likewise considerably shorter, and it lacks a second category of isochelae but has two categories of toxa. M. spirinae ( Koltun, 1958) has acanthostyles (166–213 x 10–13 µm) which are smaller compared to the smooth styles of M. anisochela . M. spirinae has terminally spined, ectosomal strongyles, tylotes or tornotes (166–208 x 3–4 µm) which are again smaller. Isochelae of M. spirinae (23–35 µm) are larger and they are described as being arcuate, although Koltun (1959:138) writes that they are “very similar to palmate chelae, even though they have been classified by us as arcuate chelae.” M. spirinae has toxa (136–200 µm). Megaciella ochotensis ( Koltun, 1959) again has much smaller acanthostyles (168–252 x 11–14 µm), smaller tornotes (151–220 x 5–10 µm), larger and arcuate isochelae (25–32 µm) and toxas (84–134 µm). Megaciella zenkevitchi ( Koltun, 1958) has smaller but thicker acanthostyles (405–478 x 33 –42 µm), larger palmate isochelae (21–25 µm) and it has two size categories of toxa (178–364 µm and 75–92 µm).

Distribution

Known only from the type locality.

Etymology

Named after the anisochelae which are not known from other Megaciella .

Figures

FIGURE 2. Megaciella anisochela sp. nov. a, Holotype. b, Category of thick styles among smaller tylotes and microscleres. c, Tylotes with acanthose ends. d, Close up of acanthose end of tylote. e, Large category of palmate isochela. f, Small category of palmate isochela.

FIGURE 3. Megaciella anisochela sp. nov. a, small distorted anisochela. b, small anisochela.