Hajdu, van Soest and Hooper, 1994
Definition: Poecilosclerida with microscleres consisting of tridentate or polydentate chelae (arcuate chela, Myxilla incrustans chSEM); toxas are lacking. Ectosomal megascleres are diactinal, although aniso-terminations commonly occur. Choanosomal megascleres are styles.
Remarks: Myxillina are sponges of basically encrusting shape and soft consistency, although some are very thinly encrusting; occasionally they may be branching or of firm consistency. With Microcionina they share a distinction in separate ectosomal and choanosomal megascleres.
The ectosomal megascleres which are dubbed tornotes in this suborder are most frequently arranged as palisades or bouquets; their shape is basically diactinal (oxea-, strongyle- or tylote-like), but very frequently shape and ornamentation of both ends are slightly different, and they are then dubbed anisotornotes. In one family their shape is so nearly a subtylostyle that these are likely to be truly monactinal and their homology with other tornotes is doubtful; the use of the name “tornote” is here avoided. The tornote shafts are smooth; their endings may be variously sharply pointed, mucronate, blunt, swollen, microspined or bearing one or several larger spines. The extent to which the tornotes penetrate into the choanosomal skeleton varies considerably and in some groups they replace partly or wholly the choanosomal megascleres. In some groups the tornotes are grouped palisade-like around slightly raised rounded pore-fields dubbed areolae (in French: “cribles”).
The choanosomal megascleres are basically styles (although oxeas or strongyles occur occasionally), which may be smooth, lightly or more heavily spined on and around the head, or entirely spined. Like in many Microcionina they often occur in two categories: main and auxiliary, usually recognizable in size, ornamentation and position. Main megascleres tend to be smooth or lightly spined, and are usually longer and thicker; they form the basic skeletal reticulum or—in thinly encrusting forms—are perpendicular to the surface of the sponge, often penetrating it and causing a spined or hispid macroscopical aspect. The auxiliary meagscleres tend to be smaller and are usually entirely spined. They echinate the skeletal tracts, the nodes of the skeletal reticulum or—in thinly encrusting forms—are arranged in groups around a single main megasclere. In one family they simulate ectosomal spicules in forming a surface crust. The auxiliary megascleres are frequently lacking or not differentiated in shape from the main megascleres.
Several groups have their choanosomal skeleton partly or wholly replaced by a reticulation of sand grains and other foreign material.
The chelae differ from the usual palmate chelae of the remaining Poecilosclerida in having at least three clearly developed alae: a median fluke and two flanking alae. These “tridentate” chelae can be further differentiated in arcuate chelae, which have their flanking alae still partly attached to the shaft without visible development of further alae on the shaft, and anchorate chelae, which have incipient extra alae (dubbed fimbriae ). The alae of both arcuate and anchorate chelae are normally rounded blades (dubbed spatulate ) but may be occasionally pointed, looking like predator’s teeth and then they are dubbed unguiferate. Such unguiferate chelae often develop extra alae and are then called polydentate. In one family the species possess probable derivations of anchorate chelae in the shape of “double-umbrella” microscleres dubbed birotulates. Chelae may occasionally be absent in genera and species otherwise sharing convincing similarities with various Myxillina. One family lacks chelae entirely and its membership of Myxillina is tentative based on similarities of the tornotes.
sigmas (shared with Mycalina, but lacking in Microcionina) are of very frequent occurrence; often two size categories are evident. They are lacking in one family.
Toxas are absent.
Trichodragmas and single raphides are occasionally found.
One family has special raphide-like microspined microscleres dubbed onychaetes.
Families: Nine families are tentatively recognized in the Myxillina, but they still need further corroboration. Most Myxillina have arcuate chelae, but three families (Myxillidae, Desmacididae and Crambeidae) have exclusively anchorate chelae. Such restriction often results in—possibly artificial—separations of genera previously united in a single family Myxillidae (e.g. Lissodendoryx and Myxilla ). Birotulates are considered as homologous in all genera possessing them, and they are probably derived from anchorate chelae; genera bearing them are consequently assigned to a single family (Iotrochotidae n. fam.) sister to the Myxillidae and Desmacididae. Fistular or bladder-like growth form is considered as an adaptive, non-phylogenetic character and consequently Coelosphaeridae sensu Topsent (1928) are united with non-fistular genera with reticulate skeletons. Anchinoidae Topsent (1928) will very soon be merged with Hymedesmiidae as the ultimate consequence of discussions in the literature; hymedesmioid growth form and architecture is thought to grade into Anchinoid architecture; spiculation is largely similar in all members of these two former families to be named Hymedesmiidae s.l.; however, since this has not been published we will here retain Anchinoidae. Crellidae are closely related sharing the areolate porefields with many Hymedesmiidae. Phoriospongiidae remain of problematic status and affinity because of their reduced nature; they are united by having a single megasclere category. Crambeidae are exceptional in having subtylostyle-like ectosomal megascleres; they are included in Myxillina on the basis of their anchorate chelae. Tedaniidae are exceptional in lacking microscleres other than onychaetes, and lacking auxiliary acanthostyles; their assignment to Myxillina is based on similarities in tornote shape.
Source: Van Soest, unpublished.
Families represented in the area:
Family Anchinoidae: arcuate chelae; ectosomal tornotes; choanosomal bundles of tornotes echinated by acanthostyles.
Family Coelosphaeridae: arcuate chelae; ectosomal tornotes; isodictyal reticulation of predominantly smooth megascleres.
Family Crellidae : arcuate chelae; ectosomal crust of acanthoxeas or -styles; choanosomal plumose bundles of tornotes echinated by acanthostyles.
Family Desmacididae : anchorate chelae; only oxeas as megascleres in plumoreticulate arrangement.
Family Hymedesmiidae: arcuate chelae; ectosomal tornotes; hymedesmoid skeleton with large acanthostyles erect on substratum, echinated by acanthostyles.
Family Iotrochotidae: ectosomal tornotes; no chelae, with birotulates.
Family Myxillidae: anchorate chelae; ectosomal tornotes; choanosomal isodictyal reticulation of spined styles.
Family Phoriospongiidae : arcuate chelae; no differentiation in ectosomal and choanosomal megascleres; smooth strongyles in plumose arrangement.
Family Tedaniidae : no chelae; ectosomal tornotes; choanosomal isodictyal reticulation; with onychaetes.
Family not treated here:
Family Crambeidae: subtylostyle-like tornotes; anchorate chelae.