Cyamon vickersii (Bowerbank 1864)

Contrary to most other authors referring to Cyamon vickersii, Van Soest et al. 2012 have demonstrated that this species does not occur in the Western Atlantic. The evidence for this is two-fold. (1) There is considerable uncertainty about the origin of the type specimen. Bowerbank (1862: 831), when he first drew attention to the polyactine spicule, described it as follows: Spiculated inequi-angulated triradiate, with cylindrical entirely spined radii (Plate XXXVI. fig. 15). – From a fragment of a sponge presented to me by Mr. Vickers of Dublin, who thinks it probably came from the West Indies. This spiculum is an external defensive one. The triradiate rays are imbedded immediately beneath the dermal membrane, and the spicular ray is projected through it at right angles to its plane; they are very numerous. The specimen was subsequently named Dictyocylindrus vickersii by Bowerbank (1864: 267) with the same sentence and figure repeated. Bowerbank’s slides of the type material in BMNH marked as Bk 1887 were labeled prudently “West Indies ?”, but first Gray (1867: 546) and later Carter (1879: 292) omitted the question mark. Carter did an extensive redescription of the Bowerbank material, which properly established the characters of the species. Shortly before that (Carter, 1876: 391) he alluded to a specimen with quadriradiate spicules obtained from Thomas Higgin from Grenada (Caribbean Sea), which he thought to belong to the same species. Higgin (1877: Pl. 14 Fig. 9) figured the spicule. However, both authors mentioned only long styles in addition to the polyactines, which is, as we know now, insufficient to characterize Cyamon species. As Van Soest et al. 2012 described, and was also clearly pictured by Carter himself (1879: Pl. 27 Fig. 6c), C. vickersii should possess undulated or crooked centrotylote thin styles or strongylostyles. Van Soest et al. 2012 demonstrate that none of the Western Atlantic specimens of Cyamon examined possess such spicules, in stead of which they have straight thin styles without centrotylote swelling or undulations. Nevertheless, from the time of Carter onwards it was assumed, that Bowerbank’s type came from the West Indies. Subsequent reports of Cyamon from Western Atlantic localities all employed the name C. vickersii, and ignored the peculiar shape of the short thin styles. (2) Dendy (1922) and Thomas (1973) reported Cyamon vickersii from the Seychelles. Their descriptions exactly match the properties of Bowerbank’s type specimen, including the undulating short thin centrotylote styles. They especially mention the spination on the pointed ends of many of the undulating styles, precisely as Van Soest et al. 2012 found in the type. De Laubenfels (1936: 80) also was of the opinion that the Seychelles material differed specifically from the Western Atlantic material. Because he believed that C. vickersii was West Indian, he proposed the name Cyamon dendyi for the Seychelles material. Van Soest et al. 2012 also describe and illustrate material they obtained from the Seychelles, in which they demonstrate beyond doubt that it belongs to Cyamon vickersii. To conclude: specimens identical or similar to the type of C. vickersii are reported from the Seychelles. Specimens recorded from the Western Atlantic are dissimilar to the type of C. vickersii, a.o. by lacking the characteristic undulating spicules. For the Atlantic representatives, the name Cyamon agnani (Boury-Esnault, 1973) is available (q.v.).