Skeletons in confusion: a review of astrophorid sponges with (dicho-) calthrops as structural megascleres (Porifera, Demospongiae, Astrophorida) Author Van Soest, Rob W. M. Author Beglinger, Elly J. Author De Voogd, Nicole J. text ZooKeys 2010 68 1 88 http://dx.doi.org/10.3897/zookeys.68.729 journal article http://dx.doi.org/10.3897/zookeys.68.729 1313-2970-68-1 Calthropella Calthropella durissima Topsent, 1892 Figs 25 A-F Calthropella simplex var. durissima Topsent 1892 : 43, pl. V fig. 14, Pl. VIII fig. 9. Material examined. Specimen provided by Dr. Joana Xavier, as yet unregistered: EMEPC/G3/08.30, S of Azores, Atlantis Seamount, 33.916°N; 30.171°W, 1132 m, 30 October 2008. Holotype. Not examined. Dr. P. Cardenas (in litteris) reports the existence of a slide, MNHN DT 883. Description. White, massive lump (Fig. 25A), encrusting volcanic rock, with optically smooth surface and hard consistency. Size approx. 2 x1.5x 1 cm. Skeleton: largely confused interiorly, with a densely crowded outer layer of microscleres. Spicules: calthrops, two types of oxyasters, tuberculated asters, lumpy asters; some broken oxeas. Calthrops (Fig. 25 B-C ) variable in size and shape, possibly divisible in two broadly overlapping size categories; the largest are often 'tripods' ( three-claded calthrops) (Fig. 25 B-C ), among the smaller are five-claded modifications with one or more cladi shorter or vestigial, cladi 61 -327.3- 679 x 4 -44.2- 96 µm (cladomes 98-955 µm ), smaller with cladi in the range 61-198 µm are usually normal calthrops, larger with cladi in the range 297-697 µm are predominantly tripods. Oxeas (Fig. 25B), few in number and invariably broken, smallest / largest fragment 800-1450 x 9-13 µm . Oxyasters, occurring in two distinct types: small oxyasters (Fig. 25D) with small center and long conical but thin rays, diameter 11 -13.7- 18 µm ; larger spherasters (Fig. 25E) with conical smooth rays ending in a single spine, relatively rare, diameter 18-24 µm (N=5). Tuberculated asters (Fig. 25F) with short rays (almost entirely taken up by the tubercles), rare and grading into lumpy asters, diameter 7-30 µm (N=4). Lumpy , irregular aster-derived silica bodies (Fig. 25F), probably derived from tuberculated asters, but most become entirely irregularly rounded: 7 -21.5- 36 µm . These asters were named 'spherochiasters' by Topsent (1904) . Figure 25. Calthropella (Calthropella) durissima , specimen EMEPC/G3/08.30, from S of Azores, Atlantis Seamount A habit B 'tripod' and calthrops C overview of spicules D oxyaster E smooth spheroxyasters F tuberculated spheraster and various derived slica bodies. Habitat. Deep water, 450-1132 m. Distribution. W of Flores and seamounts S of the Azores. Remarks. Topsent's variety durissima (type specimen MNHN DT 833 from deep water off the Azores) is here raised to species rank because of the peculiar modification of the tuberculated asters into small irregular silica-balls, which are also larger than those of Calthropella (Calthropella) simplex and Calthropella (Calthropella) geodioides . Topsent's type material was more extensive (largest specimen had half the size of a fist) and the surface more elaborate ( 'rugueux' , oscules sometimes on a papilla). In 1904, Topsent retracted his variety durissima as he had become convinced that the lumpy asters were derived from the tuberculated asters and probably subject to considerable variation. Having examined the variation of these asters, we disagree with the retraction of durissima and Topsent's assignment of it to the variability of Calthropella (Calthropella) geodioides . The predominance of three-claded calthrops and the absence of dichocalthrops combined with the presence of the lumpy entirely spined 'spherochiasters' is sufficient evidence for specific distinction.