Vosmaeropsis grisea Tanita, 1939

Figures 66a–e, 67a–e

Leuconia capillata sensu Burton, 1930: 5 (not: Poléjaeff, 1883: 55, pl. II fig. 1 as Leuconia multiformis var. capillata) Vosmaeropsis griseus Tanita, 1939: 319, figs 1–2 (mandatory correction to V. grisea, cf. ICZN article 31.2).

Material examined. ZMA Por. 00147, Indonesia, Maluku, Banda anchorage, 4.5398°S 129.9084°E, depth 9–45 m, trawled, coll. Siboga Expedition stat. 240; BMNH 1928.6.18.19a, two slides from Siboga material.

Examined for comparison: Vosmaeropsis macera, slides from the Dendy collection from South Australia, BMNH 1897.7.12.62a.

Description. A group of five Sycon -like individuals (Fig. 66a) attached to a dead gastropod shell. Surface shaggy with prominent oscular fringe (Fig. 66b). Size up to 2.5 cm high, 1 cm in diameter. Consistency firm. Color pale greyish brown (alcohol).

Histology. Due to bad preservation, choanocyte chambers could not be made visible, but the overall skeletal structure leaves little doubt that it is certainly not syconoid, very likely leuconoid, although a sylleibid arrangement cannot be excluded.

Skeleton. (Figs 66c–e) The cortex (Fig. 66e) consists of regular triactines (although tending to be slightly sagittal), scattered trichoxeas, and the shorter paired actines of pseudosagittal triactines, pierced by giant diactines at sharp angles (Fig. 66c). The choanosomal skeleton is dominated by perpendicular or more often sharp-angled giant diactines and scattered pseudosagittal triactines (Fig. 66c). Atrial skeleton (Fig. 66d) consisting of several layers of sagittal triactines and regular tetractines. The oscular fringe (Fig. 66b) is long and consists of a thick mass of long thin diactines.

Spicules. (Figs 67a–e) Giant diactines, equiangular triactines, pseudosagittal triactines, sagittal triactines, equiangular tetractines, trichoxeas.

Giant diactines (Fig. 67a), fusiform, 500– 1316.6 – 1760 x 20 – 44.3 –54 µm (predominantly in the size range of 1000–1500 µm).

Cortical equiangular triactines (Fig. 67b), 141– 176.0 –219 x 8– 10.1 –12 µm.

Pseudosagittal triactines (Fig. 67c), all actines of different length, and at variable angles, longest paired actines 168– 275.6 –361 x 9– 15.6 –21 µm, shortest paired actines 96– 194.1 –329 x 9– 15.5 –21 µm, unpaired actines 155– 233.5 –390 x 8– 15.8 –21 µm.

Sagittal triactines (Fig. 67d), with unpaired actines 111– 174.0 –249 x 4– 8.6 –12 µm, paired actines 78– 130.8 – 204 x 4 – 8.3 –12 µm.

Equiangular tetractines (Fig. 67e), with unpaired actines 126– 166.3 –192 x 9– 11.5 –15 µm, paired actines 117– 164.2–261 x 11– 13.2 –16 µm, and apical actines 18– 36.2 –54 x 4– 6.5 –11 µm.

Trichoxeas, invariably broken, pieces vary in size, 150– 242.6 –390 x 1–3 µm.

Diactines of the oscular fringe 1170– 1980 x 2–4 µm.

Ecology. Deeper water in sandy reef environment.

Distribution. Indonesia, Japan.

Remarks. Burton assigned this material to the Philippine species Leuconia capillata Poléjaeff, 1883 (as Leuconia multiformis var. capillata), but there are large differences with Poléjaeff’s description. The most important difference is that the subcortical triactines in the present specimen are distinctly pseudosagittal, not regular or subregular as in L. capillata. Measurements of all the spicules differ significantly from Poléjaeff’s description, e.g. the giant diactines in L. capillata are up to 6 mm against a maximum of 1.76 mm in the present material.

Assignment of this material to Vosmaeropsis is based on the combination of pseudosagittal triactines, a rather confused choanosomal skeleton, and presumed leuconoid aquiferous system. Recent descriptions of two Vosmaeropsis species from Brazil (Cavalcanti et al. 2015) appear to be similar in most aspects to our specimens, so we are confident that they are congeneric. Some doubts about the present classification was raised by a comparison with the type species of Vosmaeropsis, V. macera (Carter, 1886) (as Heteropia). That species has a sylleibid aquiferous system and, more importantly, an inarticulate skeleton (cf. Dendy, 1893: fig. 19), unlike our specimens. We were able to confirm this by examination of two slides of the type made by Dendy (1893), BMNH 1897.7.12.62a, borrowed from the Natural History Museum, London.

Of the described species of Vosmaeropsis, V. grisea Tanita, 1939 appears the most similar, in shape as well as spicular measurements. The only difference of possible significance is the shape of the subgastral sagittal triadiates, the majority of which have their unpaired actines shorter than their paired actines in Tanita’s description.

Vosmaeropsis dendyi Row & Hôzawa, 1931 from Western Australia has the pseudosagittal triactines distinctly smaller than our species, and there are cortical tetractines in addition to several spicule categories distinguished by Row & Hôzawa (1931), which have not been found in our specimen. Burton (1963) assigned V. dendyi to the synonymy of V. macera, but this differs strongly in habitus from V. dendyi and from our species. A similar species is Vosmaeropsis mackinnoni Dendy & Frederick, 1924, which was also synonymized with V. macera by Burton (1963). It has much larger cortical triactines than our species.