Family HARRIMANIIDAE

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Family HARRIMANIIDAE

Compiler and date details

C. Burdon-Jones, Queensland Museum, Brisbane, Queensland, Australia

Introduction

The Harrimaniidae Spengel, 1901 are considered to be the most primitive family in the class Enteropneusta. In Protoglossus and Saccoglossus species, the body is elongate and sinuous with a lengthy, gradually tapering, intestinal region. In Harrimania and Stereobalanus species, the length to width ratio is much lower, giving them a comparatively stocky appearance. They are readily recognised when mature by the appearance of the paired parallel genital ridges, which lie on each side of the mid-dorsal line and extend throughout the length of the branchial region. The branchiae open into the deep dorso-lateral furrows which lie between the paired ridges and may be obscured by them, especially in contracted or preserved specimens. In most Saccoglossus species the proboscis is cylindrical, tapered apically, grooved mid-dorsally and many times longer than the collar. The collar is sub-cylindrical, longer than broad in most species, as broad as long in some, but shorter in others, especially in preserved or contracted specimens. Adults vary in length from 50–450 mm.

In Saccoglossus species, the longitudinal musculature of the proboscis is often concentrically arranged; in Protoglossus, Harrimania and Stereobalanus it is mostly radially segmented. The crura of the proboscis skeleton extend up to or into the posterior half of the collar. Perihaemal spaces may be present, but peribuccal spaces are absent. The branchial region has a parallel series of simple oval, elliptical or slit-like branchial apertures, opening directly to the exterior and may or may not lie in shallow longitudinal grooves on either side of the mid-dorsal line. The skeletal structures which support the branchiae are devoid of synapticulae, so the tongue-bars hang freely in the apertures. The branchial part of the pharynx is not separated from the ventral food-conducting part as it is in the Ptychoderidae. In the genus Saccoglossus, the posterior oesophageal region is perforated by one or more pairs of pores which lie in shallow diverging grooves on each side of the mid-dorsal line. Oesophageal pores are absent in the other genera.

The hepatic region has no distinguishing external features like the hepatic sacculation of ptychoderids, but is recognised by its deep brown or green pigmentation and thick convoluted walls which are visible through the semi-transparent epidermis. The trunk coelom is devoid of lateral septa, and the body wall is devoid of any circular musculature.

When mature, the sexes of Australian species may be distinguished by the orange to orange red (female), grey (male) colour of the genital sacs which lie within longitudinal dorso-lateral ridges and may be confined to the branchial region in some genera, or overlap the entire or posterior branchial region and the anterior hepatic region in others.

Spawning in some saccoglossids is known to be seasonal, epidemic, and temperature and tide related. Fertilisation is external, the buoyant eggs being dispersed by tides. Development involves a planula-like lecithotrophic larva, with a short, partially planktonic, dispersal phase, then settlement and an exploratory benthic phase prior to assuming a burrowing habit (Bateson 1884, 1885, 1886; Davis 1908; Kirk 1938; Burdon-Jones 1951, 1952, 1956; Colwin & Colwin 1950, 1951, 1954). The mechanism of sperm penetration, surface membrane and cortical layer changes in the ovum, developmental capacities of early blastomeres, axes and planes of eggs, and larvae in Saccoglossus have been studied by Colwin & Colwin (1950, 1954 and Colwin et al. (1957). Although regeneration is common in this family, there is no evidence of asexual reproduction by deliberate fragmentation (Tweedell 1961). Xenopleura is the only genus known to be viviparous (Gilchrist 1925).

The family contains five genera: Protoglossus Van der Horst, Saccoglossus Wagner, Harrimania Ritter, Stereobalanus Spengel, Xenopleura Gilchrist, and 24 species. Of the three species of Saccoglossus found in Australia, two are endemic (Thomas 1956, 1972). Two more have been identified from the Queensland coast and await description—both were found in association with seagrass beds, one in Halifax Bay and the other at Coochiemudlo Is., Morton Bay, Queensland (see Fig. 2).

The genus Protoglossus is presently regarded as the most primitive in the family Harrimaniidae. Its placement has been unstable. Initially, Caullery & Mesnil (1900) recorded the discovery of Balanocephalus koehleri, later changing the name to Protobalanus (Caullery & Mesnil 1904), because the first name was preoccupied, and proposed a new family, the Protobalanidae. Subsequently, Van der Horst (1939) discovered that the second generic name was already applied to a fossil balanid. He proposed the name Protoglossus and placed the genus in the family Harrimaniidae because of its close affinity with the genus Saccoglossus. Later, Dawydoff (1948) reintroduced the family, renaming it the Protoglossidae. However, its rediscovery (Burdon-Jones 1950) enabled a more extensive study of adult and juvenile specimens, and led to the conclusion that while certain anatomical features merited the establishment of a new genus, they are not significant enough to warrant the establishment of a new family (Burdon-Jones 1956). The repositioning of the genus is endorsed in the accounts of Vogel (1987) on Protoglossus koehleri and by Giray & King (1996) on their new species, Protoglossus gravelosus.

References to Xenopleura have been omitted from comparisons because the original description lacks the necessary detail. Although its viviparity separates it from all the other genera, a re-examination of the type material and further specimens from the type locality is required so that its present generic and familial status can be defined more fully.

Although fossil casts, spiral burrows, and trails thought to be the outcome of enteropneust activity have been described (Van der Horst 1940; Bourne & Heezen 1965; Kazmierczak & Pszczulkowski 1969; Bulman 1970; Wetzel 1972), the most convincing evidence to date of a fossil harrimaniid is that of Megaderaion, recorded by Arduini et al. (1981) from the Sinemurian deposit of Osteno, Lombardy, Italy. It consists of an imprint of a small (20 mm long), soft-bodied invertebrate with a vermiform, trimeric outline reminiscent of the genus Stereobalanus Spengel.