Qu e k e tt J o wrnal of M icr o s cop y, 2Q 1,2, 4 7, 67 9 -69 4 679 An introduction to the branchiopod crustaceans PHILIP M. GREAVES (Third Presidential Address delivered 15 May 2a12) Summary For a full account of the Branchiopoda, the reader is directed to the work of Dumont and The Branchiopods are a diverse and ancient class Negrea [2]. of crustaceans occurring in freshwaters, marine and (some genera) in hyper-saline environments. Classification They include the Cladocera (or water fleas), fairy and brine shrimps, tadpole shrimps and The classification of the Branchiopoda has a clam shrimps. Morphologically heterogeneous, long and mixed history. The term Branchiopoda they are united by the structure of thoracic was established by Latreille in 1817. Three sub- limbs which have flattened structures associated orders were recognised by Sars tn 1867; the with respiration and swimming. An overview of Phyllopoda (the 'large' branchiopods), the class is provided, including both extant and Cladocera (the 'water fleas') and Apistodostraca extinct orders, together with notes on their (= Branchiura, no longer considered economic importance and the British fauna. Branchiopods). Sars later modified this scheme one that contains most of the extant Introduction lt"H:],r. The Branchiopods are an ancient and diverse Suborder Phyllocarida (now classified with class of the Crustacea characterised by flattened the Malacostracan crustaceans) and foliaceous thoracic appendages (thoracopods); these structures have Suborder Phyllopoda ^ Notostraca (tadpole shrimps) respiratory (as well as other) function hence the - Conchostraca (clam or seed shrimps) name branchio- (breathing) poda (legs). The - Anostraca (fairy shrimps) Class includes the Cladocera ('water fleas') and - the 'phyllopod' orders; tadpole shrimps, fairy Suborder Cladocera (water fleas) shrimps and clam shrimps, and has around 1,200 - Calyptomera living species in 30 classes; a recent study has - Ctenopoda determined that there may actually be over - Anompoda twice this number of species [1]. The majority of - Gymnomera species live in freshwaters varying from stagnant - Onychopoda ephemeral pools to lakes and weakly-running - Haplopoda. waters. A number of species occur in saline Revision the classification branchiopods waters, including inland hyper-saline lakes and of of continued throughout the late 19'h and 2O'h world oceans. Most species are filter feeders, modern basis for although the tadpole shrimps are benthic centuries until the classification was developed Fryer 1982 who omnivores, several species are predators and by in [3], dispensed supra-ordinal hierarchic one, Ancbistropws emarginatws is an ectoparasite, with the levels and proposed eight extant and two fossil feeding on the ectodermof Hydra. Many species orders: of the Cladocera are small to microscopic and are amongst the smallest crustaceans known Order Anostraca (Alonella nana for example, typically has an Order Lipostraca (extinct) adult body length of less than 0.2 mm) whilst Order Spinicaudata the 'phyllopod' species are macroscopic, and Order Laevicardata can grow up to 70 mm (e.g. Triops cancriformis) Order Anomopoda or 100 mm in the case of the fairy shrimp Order Ctenopoda Branchinecta gigas. Order Onychopoda Order Haplopoda PHrrrp M. GnnevBs Order Notostraca in Leptodora. The majority are planktonic or Order Kazacharthra (extinct). benthic in freshwater habitats, ranging from temporary puddles and ditches to continental Since Fryer's publication, further studies have lakes; other habitats include wet mosses on the been performed using DNA analysis e.g. for [4] floor of cloud forests and tree trunks. extant orders, and cladistics analysis for both Approximately 2a% of species are now known living and extinct orders. One of the most recent to occur in ground-waters (possibly retreating phylogenies is Olssen who performed by [5] there during adverse conditions) and a few cladistics analysis 19 living and 6 fossil on species are stygbiotic (cave-dwe11ing). However, species, scoring each against 80 morphological the 'typical' habitats for Cladocera are large, features. No doubt there wiil continue to be permanent lakes where all habitats are exploited minor revision phylogeny the to the of including the pelagic, the littoral, the benthos branchiopods but is generally accepted that it and water-p1ant zones. the la:ry shrimps (Anostraca) are afl ancient sister group to the other seven branchiopod Most species reproduce parthogenetically orders (Fig.1). most of the time. Embryo development begins and is usuaily completed in the brood chamber, The'Small' Branchiopod Orders a space between the body and the carapace. Egg clutch size typically varies with the size of the The 'small' branchiopods comprise the species, from one or two eggs in the smallest of Cladocera - those animals loosely termed 'water species up to tens (or hundreds) of eggs in the fleas' and comprising the Anomopoda and largest of species. Live young are usualiy borne Ctenopoda, which are predominantly filter which have the same appearance as the adult. feeders, and two predatory orders, the Growth is by moulting. Under conditions of Onychopoda and Haplopoda. In size they vary environmental stress, such as reduction in the from approximately 0.2mm tn Alonella to 1.Amm availability of food, over-crowding, or reduction Anostraca Lipostraca t Notostraca Kazacharthra ?G o Laevicaudata q 0 tg F Spincaudata ? -() tl og. s - (! c ! L Gyclesthridia t - I o s E Anomopoda G & ! Lo o Ctenopoda () (,o LLTl(E o o onychopoda E I FO t! ? I s Haplopoda I .i5 tt (J Frc. 1 Current phylogeny of the Branchiopoda [after Olssen]. An introduction to the branchiopod crustaceans 681 in photoperiod, males are produced asexually families. Anomopods have a bivalve carap^ce which fertilise haploid eggs in the brood that protects the trunk and limbs of which there chamber. The diploid egg undergoes several ce1l are five or six pairs, of variable shape and size. division cycles after which development is The head is protected by a head-shield, which is arrested (diapause). These resting '.eggs' are usually well-developed (Fig.Z). In most resistant to freezrng and drying and are further circumstances, the Anomopoda are the most protected by an ephippial case, formed from a common order of cladocerans, and include the thickened part of the carapace. Most ephippia genera Dapbnia, Chydorws and Bosmina. sink and attach to the substrate; those of Daphnia tend to float where they may be Ctenopoda ingested by birds or fish as an aid to dispersal. Ephippia may survive for several years or The Ctenopoda (Fig.3) are distinct from the Anomopoda having head-shields decades; development of the embryo is in not and always stimulated by water, increasing day length and having six pairs of trunk limbs which are high oxygen concentrations. In the Haplopoda, similar in shape although the 6'h pair is reduced however, the eggs hatch into nauplius larvae, in size. There are only two families; the Sididae rather than the miniature adults seen in other with 50 described species in 8 genera and Cladocera. Holopediidae with one genus and two species. Anomopoda Onychopoda The Anomopoda is the largest Order within the The Onychopoda (Fig.4) are all predatory Cladocera characterised Branchiopoda, with about 560 species in 10 and are by a much- reduced carapace leaving the limbs uncovered and typically large heads of which the eye occupies the major portion. They are very Frc. 3 Ctenopod cladoceran; Sid.a ctystalline \X/idespread but not particularly common; occurs in Frc. 2 Amonopod cladoceran; Simocepbalus aetulus larger lowland lakes, attached to the underside or stems Commonly found associated with vegetation. Grizedale of aquatic plants. Virginia 'Water, Surrey, UK. Body Forest, Cumbria, UK. Body length 1.6 mm. length 2.95 mm. 682 Pnrrrp M. Gnrevps Frc.,l Onychophorna cladoceran; Bythotrephes longimanus A predatorv member of the plankton of largcr lakes. Coniston rVateq Cumbria, UK. Body length 2.4 mm excluding caudal spine. Frc. 5 Haplopod cladoceran; Leptodora kindtii The most hyaline non- marine organism, found in larger lakes. Very rsvg i.,h. south and east. Coniston lffateq Cun-rbia, UK. Bod,v length 9.7 mm. mobile animals, rapidly searching for, and in plankton collections it is only detectcd by the grasping, prey. There are three families and a water currents created by its swimming motion. total ol ll described species. The species is planktonic, usually restricted to larger lakes, although the author has found Haplopoda individuals in both the Liverpool and Manchester canals, and Rousselet reported the There is only one genus and species within the species as present on two occasions in the Haplopoda. Leptodora bindtii (Figure 5) differs Regent's Cana1, London 16]. from other 'water fleas' in having a very elongated body, an elongated head with a single The'Large' Branchiopod Orders large complex eye consisting of approximately 500 specialised, radially arranged ommatidia. The '1arge' branchiopods - fairy and brine Leptodora is predatory and is reputedly the shrimps, tadpole shrimps and clam or seed most hyaline (transparent) non-marine animal; shrimps - occupy onlv waters where fish cannot An introdwction to tbe branchiopod crustaceans 683 survive (although there are reports of mitigated by large branchiopods in two ways. In co-existence of the tadpole shrimp Lepidwrus some species egg hatching when wetted is arcticus with fish in some deep Norwegian delayed, with hatching taking around