Family PLAKINIDAE Schulze, 1880

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Introduction

Plakinidae Schulze, 1880 have encrusting growth forms. The body structure is simple, with the aquiferous system varying from simple asconoid construction to more complex folding and elaborate canal systems. The mineral skeleton consists of di-, tri- or tetractinal spicules (Hooper & Wiedenmayer 1994: figs 29–31), often with branched ends (lophotetractines; Hooper & Wiedenmayer 1994: figs 32, 33); Embryos are incubated and the larvae are amphiblastulae.

Ten nominal genera are known in this family, of which probably only five are valid, and four of which described so far for Australia. Species in this family are known from the Mediterranean, West Indian and Indo-Pacific regions (Hartman 1982).

Plakinidae Schulze, 1880 includes in synonymy Corticiidae Vosmaer, 1885, following Solé-Cava et al. (1992) and Maldonado (1993), and reviewed in Lendenfeld (1903), Brien et al. (1973), Bergquist (1978), and Hartman (1982). Revisions of the family have also been made by Diaz & Van Soest (1994)and Muricy & Diaz (2002), with recent additions to the Australian fauna by Muricy (2011).

Diagnosis

Thin to massive-encrusting Homoscleromorpha, with few species presenting tubular growth forms; surface usually smooth, sometimes wrinkled or convoluted. Skeleton, when present, is usually formed by a combination of small calthrops and/or derivatives through reduction (diods and triods), with rays of calthrops, diods, or triods multiple or complex branching. (lophodiods, lophotriods, and lophocalthrops). Two types of tetralophose calthrops are distinguished, those with all rays having a similar branching pattern (homolophose calthrops, typical but not exclusive of Plakina spp), and those in which one ray's branching pattern is different from the other three (heterolophose calthrops or candelabra, exclusive of Corticium spp). Spicules occur in one (most species) or two or more size classes (Plakinastrella and Placinolopha), and are generally arranged uniformly in the sponge body, surrounding the aquiferous system in a regular or more confusedly dispersed arrangement. Minute diactinal microscleres (Plakortis), and small lophocalthrops (Corticium, Plakina), may be found either dispersed on the sponge body, or concentrated at the surface.

ID Keys

KEY TO GENERA (of families Plakinidae and Oscarellidae)
(1) With inorganic (spicular) skeletal complement ----------------------------------------------------------------------------- 2
–. Without inorganic (spicular) skeletal complement --------------------------------------------------------------------------- 6

(2) Skeleton mainly composed of diods, triods, and/or calthrops in one size class ------------------------------ 3
–. Skeleton mainly composed of diods, triods and/or calthrops with a large size variation ------------------------ 5

(3) Lophose diods, triods, or calthrops complement the main skeleton of non-lophose spicules ----------------------- 4
–. Lophose spicules absent, diactinal "microscleres" (microrhabs) present in some species--------Plakortis

(4) Heterolophose calthrops (candelabra) complement the main skeleton of non-lophose spicules, which might be absent or rare; choanocyte chambers usually aphodal-------------------Corticium
–. Lophocalthrops with one to four homogeneously ramified actines complement the main skeleton of non-lophose spicules; candelabra absent; choanocyte chambers usually eurypylous -----Plakina

(5) Skeleton composed of non-lophose diods, triods and/or calthrops in three size classes --Plakinastrella
–. Skeleton formed by diods, triods, and/or calthrops with large size variation; the larger spicular category presents terminally-branching rays----------------------------------------------Placinolopha

(6) With sylleibid-like aquiferous system and eurypylous choanocyte chambers; ectosome thin, proportion of mesohyl to chambers ------------------------------------------------------- Oscarella
–. With leuconoid aquiferous system and diplodal choanocyte chambers; ectosome thick, proportion of mesohyl to chambers -----------------------------------------------------Pseudocorticium

Diagnosis References

Muricy, G. & Diaz, M. C. 2002. Order Homosclerophorida Dendy, 1905. Family Plakinidae Schulze, 1880. pp. 71-82 in Hooper, J.N.A. & van Soest, R.W.M. (eds). Systema Porifera: A guide to the classification of sponges. New York : Kluwer Academic/Plenum Publishers Vol. 1. [71]

General References

Bergquist, P.R. 1978. Sponges. London : Hutchinson 268 pp. 12 pls 81 figs 15 tables.

Brien, P., Lévi, C., Sarà, M., Tuzet, O. & Vacelet, J. 1973. Spongiaires. pp. 1-716 485 figs in Grassé, P.P. (ed.). Traité de Zoologie. Anatomie, Systématique, Biologie. Paris : Masson et Cie Vol. 3(1).

Diaz, M.C. & van Soest, R.W.M. 1994. The Plakinidae: a systematic review. pp. 93-109 in van Soest, R.W.M., van Kempen, T.M.G. & Braekman, J.-C. (eds). Sponges in Time and Space. Rotterdam : Balkema.

Hartman, W.D. 1982. Porifera. pp. 640-666 in Parker, S.P. (ed.). Synopsis and Classification of Living Organisms. New York : McGraw-Hill Vol. 1.

Lage, A., Muricy, G., Ruiz, C. & Pérez, T. 2018. New sciaphilic plakinids (Porifera, Homoscleromorpha) from the Central-Western Pacific. Zootaxa 4466(1): 8-38

Lendenfeld, R. von 1903. Tetraxonia. In Schulze, F.E. (ed.) Das Tierreich. Berlin : Friedländer Lf 19 168 pp. 44 figs.

Maldonado, M. 1993. The taxonomic significance of the short-shafted mesotriaene reviewed by parsimony analysis: validation of Pachastrella ovisternata Lendf. (Demospongiae: Astrophorida). Bijdragen tot de Dierkunde 63(3): 129-148

Muricy, G. 2011. Diversity of Indo-Australian Plakortis (Demospongiae: Plakinidae), with description of four new species. Journal of the Marine Biological Association of the United Kingdom 91(2): 303–319 [Date published 2011: dated 2010] [303]

Muricy, G. & Diaz, M. C. 2002. Order Homosclerophorida Dendy, 1905. Family Plakinidae Schulze, 1880. pp. 71-82 in Hooper, J.N.A. & van Soest, R.W.M. (eds). Systema Porifera: A guide to the classification of sponges. New York : Kluwer Academic/Plenum Publishers Vol. 1.

Solé-Cava, A.M., Boury-Esnault, N., Vacelet, J. & Thorpe, J.P. 1992. Biochemical genetic divergence and systematics in sponges of the genera Corticium and Oscarella (Demospongiae: Homoscleromorpha) in the Mediterranean Sea. Marine Biology, Berlin 113: 299-304

Vosmaer, G.C.J. 1887. Porifera. In Bronn, H.G. Die Klassen und Ordnungen des Thierreichs 2: i-xii 1-496 pls 1-34

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