Family MYXILLIDAE Dendy, 1922

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Family MYXILLIDAE Dendy, 1922

Compiler and date details

2010 - John N.A. Hooper, Queensland Museum, Brisbane, Queensland, Australia; Felix Wiedenmayer (1994), Naturhistorisches Museum Basel, Basel, Switzerland; updated by John N.A. Hooper (1999)

Introduction

Myxillidae Dendy, 1922 are encrusting, massive, lobate, fan-shaped or branching sponges. They have a specialised ectosomal skeleton composed of diactinal tylotes tornotes (see Hooper & Wiedenmayer 1994: figs 6, 7), with smooth or apically spined bases, arranged as bouquets or lying paratangential or sometimes perpendicular to the surface. This is occasionally absent.

The choanosomal skeleton is typically composed of isotropic, anisotropic or plumoreticulate tracts of smooth or partially spined monactinal or
diactinal choanosomal megascleres (Hooper & Wiedenmayer 1994: figs 17–19), sometimes echinated by small acanthose styles (see Hooper & Wiedenmayer 1994: fig. 82). Hymedesmioid arrangement occurs in thinly encrusting forms. Spongin development is variable, usually consisting of light spongin cementing spicules together at their nodes, but sometimes with heavy fibres. Microscleres include anchorate and sometimes palmate isochelae (Hooper & Wiedenmayer 1994: figs 66, 68) in one or more size category and may include derivative chelae such as spatulate, unguiferous or birotulate isochelae, sometimes anisochelae (Hooper & Wiedenmayer 1994: fig. 73), occasionally polydentate), and one or two size categories of smooth sigmas (Hooper & Wiedenmayer 1994: figs 79, 80).

Members of this large family are widely distributed in the world's oceans from intertidal habitats to depths of at least 5000 m (Hartman 1982). Based on the most recent revision (Van Soest 2002), 31 nominal genera have been referred to this family at one time or another, but many are deemed synonyms of established taxa (although some of these are still very poorly known, requiring corroboration from independent data sets), with currently only eight genera recognised here, of which only three have published records for the Australian fauna.

Bergquist & Fromont (1988) emended the definition of Myxillidae (sensu Topsent, 1928) to include the microcionid genus Antho, based on its possession of an isodictyal reticulate skeletal architecture composed of spined spicules. This decision is not followed here (see also Hooper 1988), as we consider that the geometry and origin of the megascleres that make up the various sections of the skeleton are of greater importance than the skeletal structure (see remarks for Raspailiidae). Hence we retain here Van Soest's (1984) diagnosis of the Myxillidae which excludes isodictyal microcionids (e.g. Antho) and raspailiids (e.g. Amphinomia). This view implies that isodictyal architecture has arisen independently in several groups (Microcionidae, Myxillidae, Raspailiidae, Chalinidae; cf. Hooper 1990, 1991), and we suggest that it should not be treated as an isolated character, taken independently from other possibly more important features such as spicule geometry and localisation. Myxillidae is a sister family of Tedaniidae, in having an apomorphic, specialised ectosomal skeleton composed of diactinal tylotes or tornotes, often basally spined, but lacking the chelae microscleres found in that family (refer to remarks in Tedaniidae).

Reviews can be found in Brien et al. (1973), Bergquist (1978), Hartman (1982) and Van Soest (1984, definition and discussion), with a conceptual revision of the family provided by Hajdu et al. (1994). New Zealand species were revised by Bergquist & Fromont (1988). Recent revisions of some genera are given by Hooper & Lévi (1989), Wiedenmayer (1989), Desqueyroux-Faundex & Van Soest (1996, 1997).

Diagnosis

Encrusting, massive, lobate, fan-shaped or branching sponges. Specialised ectosomal skeleton composed of tornotes with smooth or apically spined bases, arranged as bouquets or lying paratangential or perpendicular to the surface. This is occasionally absent. Choanosomal skeleton composed of isotropic, anisotropic or plumoreticulate tracts of smooth or partially spined monactinal or diactinal choanosomal megascleres, sometimes echinated by small acanthose styles. Hymedesmioid arrangement occurs in thinly encrusting forms. Spongin development variable, usually consisting of light spongin cementing spicules together at their nodes, but sometimes with heavy fibres. Microscleres include one or more size and form categories of anchorate isochelae and/or derivatives (spatulate, unguiferous isochelae, sometimes anisochelate, occasionally polydentate), and one or two size categories of smooth sigmas.

ID Keys

KEY TO GENERA
(1) Choanosomal skeleton includes smooth or spined strongyles ----------------------------------------------------------- 2
Choanosomal skeleton consists of styles only --------------------------------------------------------------------------------- 4

(2) Strongyles large and thick; there are no zone II (cf. Fig. of Myxillina chapter) long styles------------------------- 3
Skeleton is plocamiid, i.e. there are long styles erect on a basal reticulation of strongyles --------- Plocamiancora

(3) Strongyles spined all over--------------------------------------------------------------------- Ectyonopsis
Strongyles smooth except the heads which may have light spination -------------------------------------- Damiriopsis

(4) Microscleres include sphaerancorae ---------------------------------------------------------------------- Melonanchora
No sphaerancorae ----------------------------------------------------------------------------------------------------------------- 5

(5) Chelae include polydentate chelae ------------------------------------------------------------------------------------------ 6
Chelae are spatulate or unguiferate with not more than 3 teeth -------------------------------------------------- Myxilla

(6) Skeleton hymedesmioid ----------------------------------------------------------------------------------- Hymenancora
Skeleton reticulate ---------------------------------------------------------------------------------------------------------------- 7

(7) Tornotes present next to the choanosomal styles -------------------------------------------------------- Stelodoryx
No tornotes, a single megasclere type or no megascleres at all ----------------------------------------- Psammochela