MODULE 9: ADVANCED IDENTIFICATION OF MISCELLANEOUS TAXA INCLUDING CRUSTACEA - BY TERRY GLEDHILL AND IAN WALLACE Introduction to this module To include: Crustacea (with tips on the identification of zooplankton), freshwater arachnids, Bryozoa, Lepidoptera and Megaloptera and Neuroptera. This module provides guidance on the very important groups of Crustacean arthropods and also serves as a “catch- all” for some small, but fascinating invertebrate groups which do not warrant modules of their own. These are i) the water spiders and their relatives the freshwater mites (a large group which to date are difficult to identify, but which might prove important in water quality terms in the future, ii) the moss animals or Bryozoa, iii) the moths with aquatic larvae, iv) the alderflies, aquatic lacewings and spongeflies (N.B. alderflies were covered in module 2 and will only be given a brief mention here). As with the other modules, there are mandatory exercises which will be marked by your tutor. You can submit them by printing out this workbook and filling in the appropriate spaces by hand (but please add your name to the front of the workbook), or you can use the template appended to the introductory part and send completed exercises by email. Completion of this module will give you the Advanced Level for identification of miscellaneous taxa including Crustacea. Module 9: Version 2, December 2010 (Terry Gledhill and Ian Wallace) Page 2 of 68 SECTION 1: CRUSTACEA For this section you’ll need a copy of the following FBA Keys: British Freshwater Crustacea Malacostraca: a key with ecological notes (Gledhill et al., 1993); British Freshwater Cladocera (Scourfield & Harding, 1966); A Key to the British Freshwater Cyclopoid and Calanoid Copepods (Harding & Smith, 1974). The freshwater crustacean fauna of Britain and Ireland can be split into various groups: the small (often microscopic) planktonic and sometimes benthic cladoceran and copepod water fleas and seed shrimps and the larger fairy, brine and tadpole shrimps. With the exception of the bathynellids which are c. 1mm long, the other major group comprises the larger crustaceans (Malacostraca), which includes the mysid shrimps, amphipod shrimps, water hog lice, crabs and crayfish. Some particular features that may be useful for separating these groups are: 1) Size 2) Shape 3) If alive, swimming movement 4) Colour and patterning In places, pointers will be given to identification features. These are not definitive, but may be helpful when looking at some specimens. It is helpful to view specimens alive where possible, and observe their movement and colour (for example, when separating the families of freshwater shrimp Gammaridae and Crangonyctidae, the former tend to be pinkish when alive and crawl or scuttle on their sides, whilst the latter are more transparent with a bluish tinge and tend to ‘walk’ in an upright position). If looking at preserved specimens under the microscope, make sure that they are completely covered by a layer of water or preservation fluid to prevent reflections which can produce artefacts. Depending on the preservative used, colours may be leached or misrepresented, and therefore are not a reliable character in preserved specimens. Module 9: Version 2, December 2010 (Terry Gledhill and Ian Wallace) Page 3 of 68 SECTION 1: CONTINUED 1.1 Other Crustacea Fairy shrimps, brine shrimps, tadpole shrimps, and cladoceran water fleas (Class BRANCHIOPODA) • There are four small orders: Conchostraca (clam shrimps – now split into three separate orders: Cyclestherida, Laevicaudata, Spinicaudata - which will not be covered any further in this module as they are not found wild here); Anostraca (fairy shrimps); Notostraca (tadpole shrimps) and Entomostraca (cladoceran water fleas) Fairy shrimps • One species: Chirocephalus diaphanus • Pointers to identification: eleven pairs of thoracic limbs (maximum length 35mm); swims with appendages uppermost and back acting as a keel; eyes are usually fairly large and carried on stalks; transparent body which often has brightly coloured parts (tips of limbs and tail may have a reddish hue) (see Fig. 1.1.1) Fig. 1.1.1 Fairy shrimp • Only found in shallow, temporary pools e.g. in the New Forest Module 9: Version 2, December 2010 (Terry Gledhill and Ian Wallace) Page 4 of 68 SECTION 1: CONTINUED Brine shrimps • One species: Artemia salina • Pointers to identification: resembles Chirocephalus but much smaller (maximum length 15mm) (see Fig. 1.1.2) • Rare, found in brackish water bodies (a) (b) Fig. 1.1.2 (a) Adult brine shrimps swimming, (b) juvenile brine shrimp (reproduced from Natural History of the British Entomostraca, Ray Society) Tadpole shrimps • One species: Triops cancriformis • Pointers to identification: broad oval carapace (maximum length 40mm) with two long tapering tails and many pairs of limbs which they use for swimming, although these may be hidden under the carapace (see Fig. 1.1.3) • Found in small, shallow, muddy temporary pools, rare in British Fig. 1.1.3 Tadpole shrimp Isles Module 9: Version 2, December 2010 (Terry Gledhill and Ian Wallace) Page 5 of 68 SECTION 1: CONTINUED Cladoceran water fleas • There are many genera, families and species • Pointers to identification: the characteristics used for identification include antennal length and segments, carapace shape (maximum length c. or below 4mm) and markings (see Fig. 1.1.4). Refer to FBA key to take identification further • Many species are truly planktonic, but several families crawl and are associated with vegetation • Predaceous cladocera can be longer than 10mm, but these are truly planktonic, very transparent, elongated with a residual carapace, and are only found in lakes Fig. 1.1.4 Cladoceran water flea Seed shrimps (Class OSTRACODA) • Around 90 species • Pointers to identification: Valve shape can be used as a pointer, but identification of genera requires dissection; do not confuse with small bivalve molluscs. The body is enclosed in an oval carapace made up of two halves, which may look like a bivalve shell (fairly transparent when they are alive), but they have jointed Fig. 1.1.5 Seed shrimp limbs and other appendages, which bivalves do not have. These appendages may not be immediately visible, or only partially showing (see Fig. 1.1.5) Module 9: Version 2, December 2010 (Terry Gledhill and Ian Wallace) Page 6 of 68 SECTION 1: CONTINUED • They are generally associated with the substratum, although they can be found in the plankton. They are found in both rivers and stillwaters, and in large numbers in interstitial spaces, but you are not likely to find many in standard net samples, though occasionally can be hugely abundant in benthic sweeps from silty substrata • They may go through a 1mm mesh although Gigantocypris grows to over 1mm long • Tips on preservation: • Do not preserve in concentrated ethanol, methanol or formalin, as these can cause the shells to decalcify • In order to preserve with open valves and show appendages use 70-80% alcohol, to preserve with closed valves (best for observing overall shape) use a solution of glycerine in 80-90% alcohol (Bronshtein, 1988) • The British key “Freshwater Ostracods” by P.A. Henderson, (1990, Linnean Society) has been out of print for some time but can be obtained as CD ROM (Pisces Conservation Ltd, July 2002) Ref: Z. S. Bronshtein (1988) Fresh-water Ostracoda A. A. Balkema, Rotterdam Module 9: Version 2, December 2010 (Terry Gledhill and Ian Wallace) Page 7 of 68 EXERCISE 1 Find an example of a cladoceran water flea and an ostracod in your samples, and note down (and draw) the morphological differences between the two Mark = / 10 Module 9: Version 2, December 2010 (Terry Gledhill and Ian Wallace) Page 8 of 68 SECTION 1: CONTINUED Copepod water fleas (Class COPEPODA) • There are three orders which share some common characteristics: Cyclopoidea; Calanoidea; Harpacticoidea. They all have five pairs of limbs, a single median eyespot, and can be planktonic or benthic, and many would pass through a 1mm mesh. In all three groups the characteristics used for identification include appendages and spines on different legs. Take care when examining organisms, as egg sacs may be dislodged from some of the individuals, so try to look at more than one. Refer to FBA key to take identification further for calanoids and cyclopoids (FBA key only covers females). Order Cyclopoidea • There are a number of genera, and depending on the authority, a variable number of species (~50) • Pointers to identification: tear drop shaped body and antennae which are not longer than the length of the body; segments of appendages are important for identification; females have two egg sacs (see Fig. 1.1.6) • They are found throughout the whole water column, some near the substratum and some in the Fig. 1.1.6 Cyclopoid copepod plankton, in both rivers and stillwaters Order Calanoidea • Fourteen species (FBA key) • Pointers to identification: Antennae much longer than length of whole body; females have a single egg sac (See Fig. 1.1.7) Fig. 1.1.7 Calanoid copepod • Generally planktonic and only found in lakes (this group is mostly marine, with only remnant species in freshwaters) Module 9: Version 2, December 2010 (Terry Gledhill and Ian Wallace) Page 9 of 68 SECTION 1: CONTINUED Order Harpacticoidea • Around 40 species • Pointers to identification: slim, elongate body shape with somewhat parallel sides and reduced antennae; will usually go through a standard 1mm pond net mesh (see Fig. 1.1.8) • Benthic and found in interstitial spaces, found in both rivers and stillwaters Fig. 1.1.8 Harpacticoid copepod Fish lice (Class BRANCHIURA) – one family • Three species: Argulus coregoni and Argulus foliaceus are both native; Argulus japonicus has been recorded in exotic fish, but is very rare • All are ectoparasites which drop off and swim in the plankton to find another fish host and therefore may be found in net samples • Pointers to identification: the species can be distinguished by tail shape: Argulus coregoni – abdominal lobes (extensions from the back of the body) (see Fig.