C. oppositus Walker Immatures

Fourth instar larva: medium sized larvae, generally of bathophilus-type, but in all forms, except f. 'edwardi', showing some degree of development of the lateral projections (less than 200 µm).  Anterior ventral tubules with an elbow bend, generally slightly longer than the slightly curved posterior pair (ant 0.32-1.4; post 0.28-1.4 mm).  Longer hooks of anterior parapods without teeth.
Gular region slightly darkened, some degree of darkening of the frontoclypeus.
Mentum with 4th laterals slightly reduced (type I-II), c2 teeth usually well developed, c1 relatively narrow (type (IIA-III).
Ventromentum with about 33 - 42 striae.
Premandible with outer tooth well developed and relatively blunt, sometimes almost equally as broad as the inner tooth but variable between populations, PE ratio from 1.2-2.5, both teeth about equally long.
Basal segment of antenna about 3.0-3.7 times as long as wide, AR 1.48-2.13.
Third inner tooth of mandible reasonably well developed (type II), and about 13-19 striae on inner surface near base.

Cytology:  4 polytene chromosomes with the pseudothummi arm combination AE, BF, CD, G.
Arm G with subterminal nucleolus, and generally unpaired at the distal end.  There are two visible Balbiani rings (BRs), a large one near the nucleolus (presumably BR2), and a smaller one near the distal end (BR3).  The relative position of the BRs differs in the other two known sequences of arm G.  BR1 appears to have been split, as in situ hybridization of cloned spIa gene (from BR1) to arm G shows localization to two places, one about the middle of the arm and the other very near the distal end, but no BR develops at either site.  BR4 also does not develop, but cloned ssp160 hybridizes at the edge of the nucleolar region, between the nucleolus and BR2.
There is also a nucleolus in arm F at about group 19.
Polymorphic in all arms.
All forms have the same basic chromosome complement, but different dominant sequences and different sets of polymorphic inversions, as well as different see MD variants:
f. connori:  A2 (& A3)(males only), A5 (both sexes); B2 (& B1); C2; D1 & D2; E2; F1; G1.
f. oppositus:  A1 & A2; B1 (& B2); C2 (& C1); D1 & D2; E2 (& occasional E1); F1; and G1:  sequences in arms C and D may appear sex linked.
f. tyleri:  now considered a separate species, see C. 'tyleri'.
f. whitei:  A5 & A4 with some A1 & A2; B2 & B1; C1 & C2, but also other less frequent sequences; D1, D2 & some D3; E2 (& rare E1); F1 & some F2 or F3; G1 (& G2, G3);  sequences in arms A (A4), C, D, F and G may appear sex linked in different populations.  These populations with different sex determiner (MD) locations appear to show some degree of differentiation of sequences present.
f. 'edwardi':  A4, inversion of B2 (puff very near 4 distinctive bands), inv. of C1, ausD1, E1, F1, possibly G3.
Occasional hybridization between eastern forms may lead to introgression of sequences between forms (e.g. E1 in forms oppositus and whitei).
The sequence oppA4 requires two inversion steps from the other sequences in this arm, but is a single inversion step from the New Zealand forA2.  The same sequence as oppA4 is also common in New Zealand.

oppA1:    1a-e, 7-4, 12a-c, 3i-f, 9-8, 11-10, 2c-1f, 3e-2d, 13-19
oppA2:    1a-e, 7-4, 12a-c, 3i-f, 9-8, 2d-3e, 1f-2c, 10-11, 13-19
oppA3:    1a-e, 7-5, 11-10, 2c-1f, 3e-2d, 8-9, 3f-i, 12c-a, 4a-d, 13-19
oppA4:    1a-e, 11-10, 2c-1f, 3e-2d, 8-9, 3f-i, 12c-a, 4-7, 13-19                                       (from A2)
oppA5:    1a-e, 9-8, 2d-3e, 1f-2c, 10-11, 15-13, 7-4, 12a-c, 3i-f, 16-19                         (complex from A4)
oppB1:    A large puff, with dark bands (groups 7-8) proximally,is developed near the middle of the arm.
oppB2:    Large puff, with the dark bands on the distal side (groups 8-7), is towards the distal end of the arm.
oppC1:    Typical groups, 3-4, about one third from distal end.    as C1 of New Zealand species C. novaezelandiae and C. 'thermarum'
oppC2:    Inversion of most of the arm, taking groups 3-4 to a proximal location
oppC3:    A small distal inversion of C1, with one break in groups 3-4.
oppC4:
oppC5:
oppC6:
oppD1:    1-2, 16-13, 9a-e, 3d-a, 10d-12, 18-17,10c-a, 3e-8, 19-24                         (from ausD1 by Inv 9-12 & 18-8)
oppD2:    1-2, 4-3e, 10a-c, 17-18, 12-10d, 3a-d, 9e-a, 13-16, 19-24
oppD3:    1-2, 16-15c, 8-3e, 10a-c, 17-18, 12-10d, 3a-d, 9e-a,13-15b, 19-24
oppD4:    1-2, 16-14h, 19c-a, 8-3e, 10a-c, 17-18, 12-10d, 3a-d, 9e-a, 13-14g, 19d-24                        (rare)
oppD5:    not in C. oppositus, now tylD3
oppD6:    1-2, 16-13, 9a-e, 3d-a, 10d-12, 18, 6-3e, 10a-c, 17, 7-8, 19-24
oppD7:    1-2, 16-15d, 18, 12-10d, 3a-d, 9e-a, 13-15c, 17,10c-a, 3e-8, 19-24
oppE1:    1-3e, 10b-3f, 10c-13                                                                                                  as halophilus, etc.
oppE2:    1-2d, 7g-10b, 3e-2e, 7f-3f, 10c-13
oppF1:    1-2a, 10-2b, 11-23
oppF2:    1-2a, 10-6c, 15g-11, 2b-6b, 15d-23
oppF3:    1-2a, 10-2c, 15c-11a, 2b, 15d-23
oppG1:    Subterminal nucleolus with a nearby BR and another BR near the distal end. Most common sequence.
oppG2:    Inversion of about middle half of the arm, beween the two BRs.
oppG3:    Smaller simple inversion of G1 within the limits of G2.

f. 'edwardi':  Don Edward described larvae of C. oppositus from Lake Gwellup, near Perth, Western Australia.  This should also be considered a separate species (see under C. 'edwardi')

Basic drawn chromosome maps according to the Australian standard, with some photographs, provided by Martin (1969a).  The sequences of arms A, E and F according to the Keyl system are given by Wülker, Dévai & Dévai (1989).  Nucleoli and location of C-bands studied by Lentzios & Stocker (1979) and Lentzios et al. (1980).

Pupa:  f. whitei:  Length about 7.3 mm (6.5-8.1) in female, about 7.2 mm (6.7-7.7) in male.
About 73 (54-89) recurved hooks on second segment in females, about 66 (40-71) in males; about 185 (158-200) filaments on swim fin in female, about 164 (148 - 188) in males.
Caudolateral spur of segment VIII normally with only one spine, but may be 2 in males and up to 4 in females, as is common in the species of the oppositus-group.

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Modified: 19 April 2020
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