Family CHAPERIIDAE Jullien, 1888

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Family CHAPERIIDAE Jullien, 1888

Compiler and date details

July 2001 - Dr Philip Bock

Introduction

This family was established by Jullien (1888) for the Recent Chaperia Jullien (1881) and the fossil Marginaria Roemer, subsequently placed in a separate family. Uttley (1949) restricted Chaperia to species lacking both avicularia and ovicells, introducing Chaperiopsis for the preponderance of species in which both were present. Brown (1952) recognized only Chaperia but Gordon (1982) redefined both genera, and reviewed the family at length, recognizing eleven genera worldwide. Antarctic and subantarctic species of Chaperiopsis were described by Hayward & Thorpe (1988).

Most species develop encrusting, unilaminar colonies, frequently only loosely attached to the substratum, but erect, vinculariiform colonies occur in some genera, whereas others form uniserial runners. The unifying characteristic of the family is the presence of paired calcareous struts, termed occlusor laminae, within the cavity of the zooid. Considering the wide range of other characters seen in the species assigned to the family at present, the possibility exists that the presence of occlusor laminae is a homoplasy, and that the family grouping may be an artificial one.

The family has a predominantly cold temperate - polar distribution in the southern hemisphere. Chaperia, Chaperiopsis and Exostesia have been recorded from the eastern coasts of Australia, although taxonomy of the first two is confused (Hayward & Ryland 1995). Bock (1982) illustrated Chaperia cervicornis (Busk, 1854), which was referred to Chaperiopsis by Gordon (1982); this species is recorded from southern Australia, New Zealand, and South America, and may be a complex of similar species. Two additional species of Chaperiopsis, C. colensoi (Brown 1952) and C.rubida (Hincks 1881) are also known from southern Australia. Three species of Chaperia, C. acanthina (Lamouroux, 1825), C. albispina (MacGillivray, 1882) and C. setigera (Hincks, 1881), and Exostesia didomatia Brown (1948) are also recorded. The original material of C. acanthina was from southern Africa, and it is probable that the Australian material is of one or more different species. Gordon (1984, 1986) has described and illustrated an extensive New Zealand fauna of chaperiids, some of which may prove to occur off southern Australian coasts. Eight species of Chaperiopsis occur in Antarctic seas. In addition, two species of the genus Icelozoon, and one of the genus Exallozoon, none of which have avicularia, have been figured by Hayward (1995). Material identified with the Australian Tertiary species Chaperiopsis (Clipeochaperia) halli (MacGillivray, 1895) was figured by Wass & Yoo (1983) (as Hiantopora halli) from southern Australia.

Chaperiid colonies tend to be brittle, unilaminar sheets, often only loosely attached to the substratum. They encrust algae, shell and inorganic substrata, but many species appear adapted to encrust sponges and large hydroids. In these, the basal walls of the autozooids bear short spiniform projections. Many species have a deep ochreous coloration, however, others are white, with light pink larvae. Exostesia, occurring off New South Wales and Queensland develops erect, cellariiform colonies. The frontal membrane of the zooid is underlain by a broad border of granular cryptocyst, defining an oval opesia; the gymnocyst is usually reduced. Occlusor laminae are readily visible in cleaned zooids, each arising from the lateral walls of the zooid and converging distally at the terminal wall. Chaperia is characterized by a distal series of long, thin and usually numerous (10-20) oral spines, and in lacking both avicularia and ovicells. In Chaperiopsis the spines are usually fewer in number but are typically bifurcate or trifurcate, and often complexly clubbed. Most species of Chaperiopsis have a mid-distal, sessile, adventitious avicularium, and in a majority there is also a variety of columnar or distinctly pedunculate avicularia. In Clipeochaperia Uttley & Bullivant (1972), regarded as a subgenus of Chaperiopsis by Gordon (1982), and in some species of Chaperiopsis, a mid-proximal adventitious avicularium forms part of a spinous or platelike shield overarching part or all of the frontal membrane. In Chaperiopsis, the ovicell is hyperstomial, often globular, with a large fenestra in the ectooecium, banded by a thickened ridge. It is closed by the maternal operculum. Vertical walls of zooids bear large, multiporous septula.

Chaperiids have a wide ecological range: many are found encrusting algae in shallow subtidal depths, but others have been collected at slope depths greater than 1200 m.

The family is known from the Maastrichtian (Taylor 1993). Several Australian fossil species are known, including Catenariopsis morningtoniensis (Bock & Cook 1993).

Diagnosis

Colonies mainly as encrusting sheets, rarely as runners or erect rods. Zooids with little gymnocyst, and a narrow border of granular cryptocyst surrounding the opesia, expanding as a shelf on the proximal side in some species. A pair of calcareous plates, or occlusor laminae, are found in most forms. Spines are commonly present, either as a number of articulated spines on the distal margin of the zooid, or complexly branching spines arching over the frontal membrane (or both types). Avicularia absent, or adventitious avicularia of various types. Ovicells absent, or prominent hyperstomial or independent.