Family HERMATOBATIDAE

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Family HERMATOBATIDAE

Introduction

The gerromorphan family Hermatobatidae contains a single genus, Hermatobates Carpenter, members of which are exclusively marine and commonly known as seabugs. The family is pantropical in distribution and comprises a single genus and eight species (Andersen 1982; Slater 1982; Zoological Record 1980–1994; Henry 2009).

Hermatobatids are clearly adapted for sea life, and their derived morphology includes large eyes for water vision and strong claws for clinging to rocks in tidal zones. Seabugs are elongate-oval in shape, body length from 2.7 to 4 mm, black to dark brown in colour. The body and appendages are clothed with short velvety hairs. The appendages are relatively short. The head is transverse and declivent. The pronotum is very short. The mesonotum and metanotum are fused and extend over the abdomen in males. The female mesonotum has lateral lobes. Metathoracic scent glands are obscured beneath the metasternal margin. All species are apterous. The forelegs are short and stout; male forelegs are incrassate and possibly adapted for grasping females. The claws are robust and arise subterminally on the forelegs and terminally on the other legs. The tarsal formula is 3:3:3, with the first segment very short. The abdomen is shortened with considerable fusion. The fourth abdominal tergite has a gland opening. The female ovipositor is very reduced in comparison to other gerromorphans. The male pygophore is globular and rotated, the opening is dorsal. The claspers are reduced and the endosoma is elongate (Andersen & Polhemus 1976; Cheng 1977; Andersen 1982; Slater 1982).

The biology of the hermatobatids has been summarised by Cheng (1977), Andersen (1982) and Foster (1989). Hermatobatids are mostly predaceous, although Cheng (1977) also reports facultative algal feeding. They are encountered near the shore in coral crevices, mostly in the intertidal zone (Polhemus 1982; Slater 1982). Phillips (1959) observed seabugs walking on corals at low tide. Walker (1893) and Esaki (1947) reported them from submerged coral reefs. Cheng (1977) claims that seabugs hide in crevices at high tide, enclosing themselves in air bubbles, or they rest and swim on the water surface. They have been observed in association with other gerromorphans, such as Halobates Eschscholtz and Halovelia Bergroth species, and staphylinids, mites and springtails.

Carpenter (1892) described Hermatobates and included the genus in the Gerridae. Most early workers followed this arrangement, although Courtière & Martin (1901) erected a new subfamily for the seabugs. Matsuda (1960) excluded them tentatively from the Gerridae on the basis of thoracic characters, the granular eyes and the abdominal scent gland opening. Poisson (1965) raised hermatobatids to family level, which has been supported by nearly all subsequent gerromorphan workers. China (1957) and Cheng (1966) described most of the species and provided modern taxonomic treatments of the group. Andersen (1982) provided a phylogeny of the gerromorphan families and concluded that the hermatobatids are derived from freshwater ancestors, and are the sister group of the Veliidae plus Gerridae.

The family is widely distributed, and species are known from the Indian, Pacific and Atlantic oceans, although most species are only known from their type locality. Species are usually found along continental coasts and about islands, particularly volcanic islands and atolls (Andersen 1982). Two species are known from the coastal regions of Australia.