A New Species of Mictognathus (Acari: Halacaridae) from the Great Barrier Reef

Abstract

Mictognathus colemani Otto, n. sp., is described from the Great Barrier Reef. It is the third known species in its genus and the first species of Mictognathus known to occur in tropical waters. Distinguishing features are dorsal lamellae on the telofemora, membranous flaps on anterior and posterior dorsal plates, lack of distinct areolae or costae, relatively long median claws on all legs, and the lack of corneae. Some of these characters are similar to those of the mictognathine species Corallihalacarus chilcottensis, but it is unknown whether they indicate a close relationship. A key to species of Mictognathus is presented.

Mites of the Family Halacaridae are common but minute (0.2-2 mm) inhabitants of the marine benthos and occur from the intertidal zone to the abyss. Approximately 1000 species have been described to date, but new species are added frequently, suggesting that many, perhaps most, of the world's halacarid species are still unknown. A genus only rarely encountered during halacarid surveys is Mictognathus Newell, of which two species were known previously, M. werthelloides Newell, 1984, and M. secundus Bartsch, 1992. In this paper I describe a third species of Mictognathus, which was found in coral sand in the southern section of Australia's Great Barrier Reef Marine Park.

Materials And Methods

The holotype specimen, deposited in the Queensland Museum (QM), at the branch Museum of Tropical Queensland in Townsville, was extracted from a hand-collected and subsequently frozen sediment sample. After thawing, the sample was vigorously stirred in a bowl of water and the supernatant decanted through a 100-mm sieve. The specimen was cleared in lactic acid and mounted in PVA. Measurements and the illustrations were obtained from the slide-mounted, slightly compressed specimen. Abbreviations in the description are as follows: AD, anterior dorsal plate; AE, anterior epimeral plate; GA, genitoanal plate; GO, genital opening; OC, ocular plate; pas, parambulacral seta(e); PD, posterior dorsal plate; P-1 to P-4, palp segments designated in sequence from the proximal to the distal; I-IV, leg I to leg IV. Additional abbreviations used in the illustrations are explained in their captions.

Subfamily MICTOGNATHINAE Otto, 1999 Genus Mictognathus Newell, 1984

Mictognathus Newell, 1984:211; Bartsch, 1992:85 (type species: Mictognathus secundus Newell, 1984, by monotypy and original designation).

Mictognathus colemani Otto, n. sp. Figures 1, 2

Type Material:

Holotype: male, QMS105562, Great Barrier Reef, Turner Cay, NE, ca. 21° 43′S, 152° 330′E, 8 December 1998, G. Coleman coll., sand on reef flat.

Etymology:

Named in honor of Greg Coleman, who collected the only known specimen of this species.

Diagnosis:

Dorsal and ventral plates overlapping, closely abutting or fused (Figure 1A, B). AE dorsally fused, forming a collar. Anal opening visible in ventral view. Five pairs of dorsal setae (excluding seta on PE). Gnathosomal base about as long as wide. Rostrum triangular, not connected to idiosoma via a flexible neck; both pairs of maxillary setae on rostrum. Palps four-segmented (Figure 1C), attached laterally; P-2 with one dorsal seta; P-3 with a minute median seta or seta absent; P-4 very slender, at least as long as P-2 and P-3 combined, with a single basal seta. Trochanters III and IV with dorsal triangular process or lamella. Tibiae I-IV with two bipectinate ventral setae. Telofemora I and II with large ventral lamellae. Telofemora, genua, and tibiae with elaborate articular lamellae. Tarsus I with three dorsal setae, one or two eupathid ventral setae, and a pair of doubled pas. Tarsus II with three dorsal setae, one ventral seta, and either a pair of doubled pas or a pair of pas singlets. Tarsi III and IV with three dorsal setae and a pair of pas singlets. Solenidion on tarsus I in dorsomedial position, that on tarsus II dorsolateral. All tarsi with two paired claws and median claw, all without pecten.

Figure 1.

Mictognathus colemani, n. sp., male. A, Idiosoma, dorsal view; B, idiosoma and gnathosoma, ventral view; C, palp, dorsal view. AD, anterior dorsal plate; AE, anterior...