Phorbas lieberkuehni (Burton, 1930a) is a massively encrusting red-brown sponge with smooth surface. It is only known from a few records from the Mediterranean and one from NW Spain. Its main distinguishing feature is the possession of two size categories of chelae in the absence of sigmas (microscopic examination necessary).
Colour: Bright red-brown.
Shape, size, surface and consistency: Thinly massive, encrusting. Surface smooth, without apparent apertures.
Spicules: Megascleres: Ectosomal tornotes smooth, straight but slightly asymmetrical: 180-270 x 4-5 µm; main acanthostyles slightly curved, with well-developed head, spined lightly especially in the upper half: 250-360 x 5-12 µm; echinating acanthostyles, curved, entirely spined: 75-220 x 5-6.5 µm.
Microscleres: Arcuate chelae in two size categories: 10-15 µm and 18-22 µm.
Skeleton: No data.
Ecology: Encrusting maerl between 10-32 m.
Distribution: NW Spain, Mediterranean.
Etymology: The species is named after N. Lieberkühn, one of the earliest authors to use spicules as characters of sponges.
Type specimen information: The type material consists of a spicule slide, BMNH 1867:3:11:91, made by Schmidt.
This species is can be distinguished from the related P. fictitius by the possession of two size categories of chelae as well as the absence of tornotes in the choansome. P. plumosus also has only a single size of chelae, but this is usually much thicker and orange in colour.
The nomenclatorial history of this species is complicated. The present name was given by Burton (1930) to replace one of Schmidt's (1862) specimens described under Myxilla fasciculata (Lieberkühn, 1859). Burton wrote:
"The species recorded by Schmidt as Myxilla fasciculata was supposed by that author to be the equivalent of Halichondria fasciculata Lieberkühn. Lieberkühn, in turn, had regarded the latter as the equivalent of Spongia fasciculata Pallas. But S. fasciculata has been shown by Topsent (1920b) to be an Ircinia, and Halichondria fasciculata Lieberkühn is obviously a Hymedesmia, so that the systematic position of Myxilla fasciculata Schmidt is a matter of doubt. Topsent (1920a) in reviewing the species says that the "type" is a typical specimen of Myxilla rosacea. Unfortunately he states in a later work (1920b) that it is a Lissodendoryx. To add to the confusion, Schmidt deposited a specimen at Graz, one at Strasbourg (which he erroneously called the "type"), one at Copenhagen, and a spicule preparation (BM 67:3:11:91) at the British Museum, all identified under the name Myxilla fasciculata. Of these four specimens the first two belong to M. rosacea, the third to Lissodendoryx (fide Topsent), and the last is a typical Hymedesmia. And as the last-named is identical with Halichondria fasciculata Lieberkühn, I propose a new species for their reception, Hymedesmia lieberkühni sp.n. (= Halichondria fasciculata Lieberkühn, 1859: 552, pl. XI fig. 7 = Myxilla fasciculata Schmidt, 1862: 71 (pars): nec Spongia fasciculata Pallas), with the spicule preparation BM 67:3:11:91 as holotype. The dimensions of the spicules of H. lieberkühni, here represented by text-fig. 6 are: -acanthostyli not differentiated into two categories, 0.075 by 0.006 to 0.27 by 0.012 mm; tornota, 0.18 by 0.005 mm; chelae arcuatae of two distinct sizes, 0.015 and 0.021 mm respectively."
Source: Burton (1930); Solórzano et al. (1991).