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Phorbas Posidoni N.Sp. (Porifera: Poecilosclerida) from the Aegean Sea, with a Discussion of the Family Anchinoidae

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Phorbas Posidoni N.Sp. (Porifera: Poecilosclerida) from the Aegean Sea, with a Discussion of the Family Anchinoidae JOURNAL OF NATURAL HISTORY, 1991, 25, 827-836 Phorbas posidoni n.sp. (Porifera: Poecilosclerida) from the Aegean Sea, with a discussion of the family Anchinoidae ELENI VOULTSIADOU-KOUKOLIRAt and ROB W. M. VAN SOEST~ t Department of Zoology, University of Thessaloniki, 54006 Thessaloniki, Greece Institute of Taxonomic Zoology (Zoologisch Museum), University of Amsterdam, P.O. Box 4766, 1009 AT Amsterdam, The Netherlands (Accepted 8 March 1991) A new species of the genus Phorbas Duchassaing and Michelotti, 1864 (junior synonym Anchinoe Gray, 1867) is described from the Aegean Sea (Eastern Mediterranean). Phorbas posidoni n.sp. is distinguished from the known Mediter- ranean species of Phorbas primarily by its elaborate repent-ramose habit combined with an extensive, spongin-enforced, plumoreticulate skeleton of oxea-like tornotes and the usual echinating acanthostyles and arcuate chelae. As in most Phorbas the surface bears characteristic areolae. The only other elaborate Mediterranean species, P. mercator (Schmidt) differs clearly in spiculation, since it lacks micro- scleres and has strongyles as the main skeletal elements. Phorbas fictitius (Bowerbank), P. tenacior (Topsent) and P. paupertas sensu Topsent are all incrusting and differ in spicule form and sizes as well. Likewise, Phorbas species from the neighbouring East Atlantic each show clear differences with P. posidoni n.sp. The genus Phorbas is discussed and compared with Pronax Gray (1867) sensu Lrvi (1973). It is proposed to unite the two genera because the alleged sharp difference between the two (only oxea-like tornotes in the skeletal tracts in Phorbas, only acanthostyles in the skeletal tracts in Pronax) is compromised by a range of intermediate conditions in various species. KEYWORDS: Systematics, Porifera, Poecilosclerida, Aegean Sea, Eastern Mediterranean. Introduction During recent collecting in the Aegean Sea (Eastern Mediterranean) a species of the family Anchinoidae Topsent, 1928 (=Phorbasidae De Laubenfels, 1936) was dis- covered, which could not be assigned to any of the known species from the Mediterranean (for a list of these, see Pulitzer-Finali, 1983). The new species is unusual because of its elaborate repent-ramose habit, whereas most other Anchinoidae are massively incrusting. In addition to providing a description of the new species, this paper also intends to address the confused taxonomy of the family Anchinoidae, based on a critical survey of the literature and examination of the characters of the type species of most genera assigned to the family, notably Phorbas amaranthus, type of Phorbas Duchassaing and Michelotti (1864), and Pronax plumosa, type of Pronax Gray (1867). Based on the usually employed criteria in Mediterranean sponge taxonomy, see, for example, Topsent (1928), Vacelet (1969), Pulitzer-Finali (1983), the new species 002~2933/91 $5.00 © 1991 Taylor & Francis Ltd. 828 E. Voultsiadou-Koukoura and R. W. M. van Soest conforms to the genus Anchinoe Gray (1867). This genus is defined by most authors as having smooth diactinal spicules in the skeletal tracts and in the ectosomal region, with echinating acanthostyles only in echinating condition. Recently, Anchinoe was synonymized with Phorbas Duchassaing and Michelotti (1864) (Van Soest, 1984, and Discussion below) and this slowly gained wide acceptance (Bergquist, 1961; Van Soest, 1984; Bergquist and Fromont, 1988; Uriz and Rosell, 1989). Accordingly, the new Eastern Mediterranean species is assigned to Phorbas. Systematic description Order POECILOSCLERIDA Topsent, 1928 Family ANCHINOIDAE (Topsent, 1928 (emended) (junior synonym: Phorbasidae De Laubenfels, 1936; Van Soest, 1984; even though the genus Anchinoe is now considered a junior synonym of Phorbas the family group name Anchinoidae is valid according to the ICZN rules). Poecilosclerida with plumose or plumoreticulate skeletal tracts consisting of choanosomal styles and/or smooth diactinal spicules, echinated by styles; ectosomal skeleton consisting of grouped smooth diactinal spicules lying perpendicularly, paratangentially or tangentially to the surface. Microscleres: chelae (if present) are arcuate; sigmata may frequently be absent; toxa and rhaphides are absent. Genus Phorbas Duchassaing and Michelotti, 1864 Synonymy: Pronax Gray, 1867: 536; Anchinoe Gray, 1867; Suberotelites Schmidt, 1868; Plumohalichondria Carter, 1876; ?Clathrissa Von Lendenfeld, 1888; Stylostichon Topsent, 1892; Lissopocillon Ferrer Hernandez, 1916; Merriamium De Laubenfels, 1936. Definition (emended): Anchinoidae in which the styles composing the choanosomal tracts, if present, are heavily spined acanthostyles; echinating styles are likewise heavily spined. Occasionally, the coring acanthostyles are completely replaced by the diactinal smooth spicules. For justification of the synonymy see below. FIG. 1. Holotype of Phorbas posidoni n.sp. Phorbas posidoni n.sp. (Porifera: Poecilosclerida) 829 Phorbas posidoni n.sp. HOLOTYPE,Zoological Museum of Amsterdam ZMA POR 8969, Gulf of Kavala, North Aegean Sea, 17 May 1977. Description. Form: the sponge is a ramose, bushy aggregate, more or less erect to sprawling, about 11 cm long, 9 cm high and 3 cm wide. The branches often anastomose and have a diameter of 0.5 to 1.5 cm and a height up to 5 cm; they are in most cases depressed and terminally thinned (Fig. 1). Colour: brown in formalin. Consistency: soft, elastic and compressible. Surface: it is smooth, with many tangential areolate pore fields. Oscules are numerous, irregularly distributed, up to 1 mm in diameter. The ectosome is fleshy and easily detachable. Skeleton: the ectosomal skeleton is made of abundant isochelae and hastate oxeas. Oxeas are arranged, at right angles to the surface, around areolate pore fields (Fig. 2). This vertical arrangement is not so strict in areas among the pore fields, where oxea-like tornotes can be found even tangentially laid in the ectosome. Isochelae are scattered without any pattern on the dermal membrane. The choanosomal skeleton is composed of well developed spongin fibres forming a more or less well organized network (Fig. 3). Oxea-like tornotes, identical to those found in the ectosome, are embedded in the spongin fibers, which are provided with echinating acanthostyles. No acanthostyles are found inside the fibres, thus having an accessory role in the skeleton. The spongin fibres have a diameter of l0 to 80 #m and they are in most areas totally cored with spicules, although in many of them only two-thirds of their width is cored. The spongin network is equally developed both in the base and near the surface of the sponge. Isochelae are present in the choanosome of the sponge but in lower abundance than in the ectosome. Spicules: megascleres. Diactinal spicules forming the main skeleton, are smooth oxea-like tornotes, measuring 265-310 x 3.5-6 #m. Acanthostyles, usually straight but sometimes slightly curved, covered with spines all along their length (Fig. 4). The spines, most of which are hooked become gradually smaller forward to the apex of the spicules. Acanthostyles measure 110-145 x 7#m. Microscleres: arcuate isochelae measuring 21.5~8.8 #m. Habitat. The sponge was dredged from a depth of about 30m. The substratum was sandy silt mixed with biogenic detritus. FIG. 2. Ectosomal skeleton of Phorbas posidoni n.sp. 830 E. Voultsiadou-Koukoura and R. W. M. van Soest FIG. 3. Choanosomal skeleton of Phorbas posidoni n.sp. F~G. 4. Spicules of Phorbas posidoni n.sp. a, hastate oxea; b, acanthostyle; c, isochelae. Etymology. The species is named after the Greek mythological God of the sea Posidon (Neptune). Discussion Comparison with related species from the Mediterranean The new species differs from the known Mediterranean species (cf. appendix in Pulitzer-Finali, 1983) assignable to Phorbas especially in the elaborate growth form and the development of discrete spongin-enforced spicule tracts forming a reticulation. In the elaborate growth form, it is approached perhaps only by Phorbas mercator Phorbas posidoni n.sp. (Porifera: Poecilosclerida) 831 (Schmidt, 1868 as Suberotelites, see also redescription of Topsent (1938) and Pulitzer- Finali, 1983), and P. dendyi (Ferrer Hernandez, 1916 as Lissopocillon). From the former species the new Phorbas differs clearly in its possession of chelae (absent in P. mercator) and oxea-like tornotes (tylostrongylotes in P. mercator). The latter species is described as a massive sponge, but the photo (Ferrer Hernandez, 1916, Fig. 9) shows short projections and elevations. It is described in a new genus on account of the occurrence of 'pocillos', modifications of the arcuate chelae not worthy of generic separation. A further difference with our new species is the possession of two distinct sizes of acanthostyles in P. dendyi sensu Ferrer Hernandez. Note that if the synonymization of Phorbas and Pronax/Stylostichon is accepted, the combination of Phorbas dendyi would be preoccupied by that of Topsent (1892). The other species of 'Anchinoe', namely A. tenacior Topsent 1925, A. paupertas sensu Topsent (1925) and A. fictitius (Bowerbank 1866), differ in being thinly or massively incrusting. Moreover, of these only A.fictitius is similar in spiculation to our new species, differing, however, in possessing the usual two size categories of acanthostyles. Both A. tenacior and A. paupertas have smooth strongyles instead of oxea-like tornotes. The Mediterranean species assigned to 'Pronax', namely P. dives Topsent (1891), P. flbulatum Topsent (1893) and P. lieberkuehni Burton (1930), all differ
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