Janulum imago Kelly

Kelly, Michelle, Erpenbeck, Dirk, Morrow, Christine & Soest, Rob Van, 2015, First record of a living species of the genus Janulum (Class Demospongiae) in the Southern Hemisphere, Zootaxa 3980 (2), pp. 255-266 : 263-264

Janulum imago Kelly & van Soest sp. nov.

( Fig. 1 , 3 B–F, Table 1)

Material examined. Holotype—NIWA 94196, Paratypes—NIWA 93421, 94185: TAN1402/31, Lot 224, Forde Guyot, Louisville Seamount Chain, International Waters, 35.317° S, 170.452° W, 1205–1600 m, 11 Feb 2014, collected by epibenthic sled from RV Tangaroa .

Type location. Forde Guyot, Louisville Seamount Chain.

Distribution. Known only from Forde Guyot, Louisville Seamount Chain.

Description. Thinly encrusting in the interstices of stony coral Solenosmilia variabilis ( Fig. 3 C), holotype, about 4 cm length, 2 cm wide and 1–2 mm thick. Surface follows undulations of coral substrate and is punctate with flush oscules 1 mm diameter. Larger, elongate openings are also present ( Fig. 3 D). Interior cavernous. Texture in life firm, crisp, but very delicate and friable. Colour in life is translucent pale blue ( Fig. 3 C).

Skeleton. Choanosome and ectosome a cavernous, extremely fragile isodictyal reticulation of megascleres ( Fig. 3 E, F). Ectosome undifferentiated from underlying choanosome, consisting of a tangential isodictyal reticulation with the ends of spicules visible occasionally, protruding from the surface membrane ( Fig. 3 D).

Spicules. Megascleres—Strongyles ( Fig. 3 B, F; Table 1), faintly to acutely curved at each end, ends are orientated towards the same side or opposite sides of the spicule. Perfectly straight spicules and those with an acute bend at only one end are less common. Some spicules are slightly sinuous. Lightly spined, concave spines project perpendicular to the shaft, aligned in short spiralling linear arrays, ends rounded and smooth, slightly enlarged. Spines appear to be hollow in some spicules, 278 (240–320) x 15 (10–18) µm.

Substrate, depth range and ecology. Encrusting the interstices of dead stony coral rubble of the species S. variabilis , a CITES protected species and important habitat former in deep water around New Zealand ( Tracey et al. 2011). Forde is an elongated guyot, a seamount with a flat top, oriented northwest-southeast with a summit plateau at 1000–1100 m deep with flanks that are deeply incised with gullies and ridges. The plateau edge and upper flanks are exposed bedrock with sand and intact stony coral (Clark et al. in press 2015).

Etymology. Named for the “echo” of the genus Janulum , first recorded from the Late Eocene in the region of Zealandia that formed the Oamaru Diatomite, now found living on the Louisville Seamount Chain ( imago , echo; L.).

Remarks. Janulum imago sp. nov. is a small, fragile sponge, inhabiting a similar deep-water dead coral habitat to the genus type J. spinispiculum in the Mediterranean ( Boury-Esnault et al. 1994; Calcinai et al. 2013). The spined strongyles are remarkably similar in their overall shape and ornamentation to those of J. spinispiculum (c. 200–240 µm), but those of J. imago sp. nov. are almost 100 µm longer and are double the thickness. The spicules of J. imago sp. nov. are also much longer than the spicule of J. princeps sp. nov. illustrated in Hinde & Holmes (1892: 160 µm long x 8 µm thick), clearly differentiating it from the fossil species.

Figures

FIGURE 1. Study area showing the collection locality for Janulum imago sp. nov., Forde Guyot, Louisville Seamount Chain in International Waters to the east of New Zealand, and location of the Oamaru Diatomite (Late Eocene) from which J. princeps sp. nov. was illustrated by Hinde & Holmes (1892); □ Janulum imago sp. nov.; ○ Janulum princeps sp. nov.

FIGURE 3. Morphology and megascleres of New Zealand Janulum species: A. Janulum princeps sp. nov., spined strongyle, length 160 µm, width 20 µm, reproduced from Hinde & Holmes (1892: Plate 7, Fig. 51); Janulum imago sp. nov., holotype NIWA 94196: B. spined strongyles showing a range of curvature of the ends of the spicules; C. preserved holotype encrusting the stony coral Solenosmilia variabilis; D. close-up of surface showing oscules and larger perforations; E. view through sponge surface showing choanosomal isodictyal reticulation and tangential reticulation lining two canals; F. close-up view of strongyles in isodictyal reticulation.