Cyclestheria hislopi ( Baird, 1859 )

Martin, Joel W. & Boyce, Sarah L., 2003, New Records Of Cyclestheria Hislopi (Baird, 1859) (Crustacea: Branchiopoda: Diplostraca: Cyclestherida) In Southeast Asia, Raffles Bulletin of Zoology 51 (2), pp. 215-218 : 216-217

Cyclestheria hislopi ( Baird, 1859)

Material Examined. – Malaysia. – LACM CR 2001 - 011.1 . Kepong, Kuala Lumpur. From a tin mine lake (under the management of the Perbadanan Kemajuan Negeri Selangor [ PKNS] local council in the suburb of Kelana Jaya) near the center of the city and infested with water hyacinths. Collected 17 Aug.2001 by Melissa Chin (Monash University). Gift to LACM (Natural History Museum of Los Angeles County) from Catherine Yule ( Monash University Sunway Campus ). Approximately 64 specimens, all apparently female, of which 26 were either ovigerous or had developing eggs visible through the thin cuticle of the trunk somites. The size range was from 1.3 mm (small individuals that could not be sexed) to 3.1 mm for a large female carrying welldeveloped embryos ( Fig. 1 ). Ovigerous females ranged from those carrying spherical eggs dorsally to those carrying well-developed embryos beneath the dorsal confines of the valves; larger individuals carried embryos that were more fully developed. The smallest brooding individual measured 2.4 mm in carapace length. Additional collections, not seen by us, have since come from two other lakes, one in the suburb of Ampang (approximately 30 km from the PKNS lake) that yielded more than 500 specimens, and one across the road from the PKNS lake (C. Yule, personal communication) .

Cambodia. – Approximately 75 individuals were collected in August and September, 2000, by Drs. Akifumi Ohtaka (Hirosaki University) and Haruo Katakura (Hokkaido University) near the northeastern part of Lake Tonle Sap, and near Phnom Penh. Qualitative collections were made with 0.1 mm- and 0.5 mm-mesh hand-nets. All specimens were fixed in formalin and later transferred to ethanol.

St. 2. Among aquatic vegetation ( Utricularia sp.) around tea vendor’s boat, Chongkneas, Lake Tonle Sap , near Siem Reap, Cambodia, coll. A. Ohtaka and H. Katakura, 30 Aug.2000. Four specimens of 1.2 - 2.7 mm in carapace length .

St. 3. Several littoral sites with aquatic vegetation along shore of Lake Tonle Sap on both sides of causeway leading to Phnom Krom, near Siem Reap, Cambodia, coll. A. Ohtaka and H. Katakura, 31 Aug.2000 and 1 Sep.2000. About 70 individuals of 0.9 - 3.5 mm in carapace length. Of the 35 specimens that were examined in detail, 15 with brood of spherical eggs, developed embryos, or bivalved young ready to be released; smallest brooding specimen 2.3 mm in carapace length .

St. 8. Paddy field at Pich Nil near Kompong Speu, near Phnom Penh, coll. A. Ohtaka and H. Katakura, 7 Sep.2000. One specimen of 1.2 mm in carapace length.

Most of the above-mentioned material has been deposited in the Lake Biwa Museum (Shiga Prefecture, Japan), but voucher specimens comprising approximately one third of the most abundant lot (St. 3) have been deposited in the Division of Biological Sciences, Graduate School of Science, Hokkaido University (Sapporo) .

Java. – Lake Bojongsari , Bogor, Java, Indonesia, coll. A. Ohtaka and Y. Sudarso, 3 Mar.2001. Forty-four individuals of 0.9 – 3.6 mm in carapace length. Of 29 specimens examined in detail, 5 brooding spherical eggs, 2 brooding developed embryos; smallest brooding specimen 2.4 mm in carapace length. The sample is to be divided between the Lake Biwa Museum (29 specimens), the Museum Zoologicum Bogoriense (Bogor, Indonesia; 10 specimens), and Dr. Ohtaka’s personal collection at Hirosaki University (Hirosaki, Japan; 5 specimens) .

Morphology and Identification. – The distinctive morphology of Cyclestheria hislopi ( Fig. 1 ) makes identification of this species relatively easy throughout its range. The nearly circular carapace (carapace height 85 – 88% of length in Cambodian and Javan specimens of brooding size), serrated anterodorsal border of the rostrum, lack of a fornix on the rostrum, simple tubular antennule, and spinose telson, when considered together, are characters unique among the bivalved branchiopods. Additionally, it is the only clam shrimp that completes its embryonic development within the confines of the carapace valves ( Fig. 1 ). In contrast, the young of other members of the group hatch from eggs at a nauplius stage. Cyclestheria hislopi also passes through a series of larval stages, some of which are perhaps the equivalent of a naupliar stage, but these stages occur within the confines of the egg membrane prior to eclosion at “larval stage V ” (see Olesen, 1999). Although only about 40% (26 of 64) of the Malaysian specimens were in some stage of ovigery (i.e., with eggs or embryos carried beneath the carapace or with developing eggs visible through the trunk cuticle), nearly all of the specimens that appeared mature enough to bear eggs were doing so. Most specimens without any sign of eggs were very small. Larger specimens, such as the one depicted in Fig. 1 , had larger and more fully developed embryos, and indeed some of the individuals counted by us as “nonovigerous” were probably just recently hatched. As has been the case with nearly all previous collections of this species, no males were found (for an exception see Olesen et al., 1996).

Cyclestheria hislopi has no close relatives. It is probably the only representative of its family, the Cyclestheriidae . A second species described in that family, Paracyclestheria sinensis Shen & Dai, 1987 , from China, was possibly based on juvenile stages of C. hislopi , according to Olesen et al. (1996). The relationship of the family Cyclestheriidae to other groups of branchiopods remains unclear; the family has been placed in the Spinicaudata (among the former Conchostraca ) or placed in its own suborder Cyclestherida (see discussions in Martin & Davis, 2001; Spears & Abele, 2000; Braband et al., 2002).

Distribution. – In their description of the male of Cyclestheria hislopi, Olesen et al. (1996) listed all known occurrences of the species worldwide. Cyclestheria hislopi has a circumtropical distribution, occurring from approximately 30 o N to 35 o S latitude. In Southeast Asia, Olesen et al. (1996) mapped it in Thailand (based on the record of Junk, 1977) and in Sumatra, Java, and Sulawesi (based on Brehm, 1939). Based on the known distribution of C. hislopi , our new records of the species in Malaysia, Java, and Cambodia are not surprising.

Figures

Fig. 1. One of the largest individuals (3.1 mm at widest point across the carapace) of Cyclestheria hislopi from the Malaysia specimens (LACM CR 2001-011.1) reported herein. Large arrows indicate areas enlarged to show detail while the smaller arrows highlight characters unique to the species, such as the serrated anterior rostral border, tubular first antenna, and heavily spinose posterior region. Note also the nearly circular carapace valves and developing embryos within the valves, both of which are also characteristic of Cyclestheria.