Family HALICHONDRIIDAE Gray, 1867

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Family HALICHONDRIIDAE Gray, 1867

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)

Diagnosis

Halichondrida with oxeotes and stylotes, i.e. spicules taking variously the shape of oxeas, strongyloxeas, oxeas with blunt ends, and true styles, occasionally with slightly expanded tyle near one of the endings or more central. Spicules invariably smooth, often elongate fusiform, but also equidiametrical over much of their length, pointed apices normally elongated and gradually narrowing to a sharp point, usually slightly curved, occasionally straight or rarely crooked or doubly angulated. Individual genera and species may be recognizable on possessing either exclusively distinct oxeas or styles, but there is a strong tendency for species and genera to have these extreme shapes intergraded with intermediate forms. Spicules are typically of a wide size range, with not infrequently distinct size categories without a clear overlap; if that is the case, then the smaller sizes are often concentrated at the surface. There is a distinct ectosomal skeletal differentiation with either a tangential crust of intercrossing spicules, which is often easily detached due to underlying subdermal spaces, or a confusedly paratangential or palisade-like arrangement, in which case the surface skeleton is not easily detached and comes off in 'flakes'. The choanosomal skeleton is characterized as confused, with many of the megascleres seemingly randomly strewn and often with remnants of main spicule tracts and vague interconnecting spicules or tracts. Binding spongin is rare. Choanosomal organic parts show a distinct lack of collagenous matter in many genera. Spicule density may be quite high, and in combination often with large sizes of the megascleres the consistency may become hard and brittle. However, Halichondriidae with smaller spicules are often quite compressible and easily damaged due to lack of skeletal organisation. Some genera are 'fleshy' due do relatively high collagen content and low spicule density. Halichondriidae contain 53 nominal genera, 14 of which are considered valid. In one genus, two valid subgenera are recognised.

ID Keys

KEY TO GENERA

(1) Trichodragmas (hair-like spicules packed in wispy bundles) present ---------------------------------- Epipolasis
No trichodragmas ------------------------------------------------------------------------------------------------------------- 2

(2) Shape a massive base from which rise long conical semitransparent fistules strengthened by an internal spicule axis and extra-axial spicule bundles at right angles to the surface -------------------------------------- Ciocalypta
Various shapes, may include short fistules or papilllae, but no large semitransparent conical fistules ------------ 3

(3) Shape a thin blade, with scattered small oscules ------------------------------------------------- Laminospongia
No thin blade ------------------------------------------------------------------------------------------------------------------- 4

(4) Finely conulose surface, no special surface skeleton, choanosome collagenous, spicule density relatively low ------------------------------------------------------------------------------------------------------------------------ Axinyssa
Surface smooth, surface strengthened by special tangential or paratangential skeleton, spongin not visibly present ----------------------------------------------------------------------------------------------------------------------------------- 5

(5) Spicules exclusively short styles (many with a subterminal swelling) ---------------------------- Hymeniacidon
Spicules oxeas, or a mixture of oxeas and (sub/tylo-)styles ------------------------------------------------------------ 6

(6) Surface skeleton easily detachable without taking away part of the choanosome ------------------------------- 7
Surface skeleton only detachable as flakes with part of the choanosome attached -------------------------------- 10

(7) Spicules exclusively oxeas in a wide size range ------------------------------------------------------- Halichondria
Spicules oxeas and (sub/tylo-)styles ---------------------------------------------------------------------------------------- 8

(8) Stylote spicules have a distinct tyle and are in fact (sub-)tylostyles ----------------------------------- Vosmaeria
True styles, without tyle ------------------------------------------------------------------------------------------------------- 9

(9) Styles only in a small size category (200–400) next to larger oxeas ------------------------------- Amorphinopsis
Styles only in a large size category (next to smaller and larger oxeas ------------------------------------- Ciocalapata

(10) Consistency stony hard, crumbly, surface rough to the touch, choanosome a dense mass of single spicules -------------------------------------------------------------------------------------------------------------------------- Topsentia
Consistency dense but compressible, surface smooth, choanosome with tracts of spicules; spicules often angular or doubly bent; most species show aerophobic reaction when collected ---------------------------------- Spongosorites

New genus added post 2002:
Johannesia Gerasimova, Erpenbeck & Plotkin, 2008