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Some New Zealand Parasitic Copepoda of the Family Anthosomidae



Female (figs. 78-89)

Overall length 11.2mm - 16.1 mm (14.1 mm).

Cephalothorax three-quarters as wide as long (7.4 mm - 10.2 mm × 5.7 mm - 7.3 mm), subovate, widest posteriorly, the margin entire except for a shallow groove one-sixth distance from anterior margin, which is associated with a ridge running across dorsum of cephalothorax, dorsum otherwise smooth. Posterior margin of cephalothorax overlying remaining thoracic segments and anterior part of genital segment.

Second thoracic segment disc-like, five times as wide as long (2.3 mm - 2.7 mm × 0.4 mm - 0.8 mm), with a pair of broad, flattened, dorsal plates, one-fifth length of page 24

Anthosoma crassum (Abildgaard, 1794) female: fig. 78: dorsal view, specimen unusually extended so that genital segment is visible; fig. 79: lateral view, specimen with post-cephalothoracic region normally flexed; fig. 80: ventral view; fig. 81: first antenna; fig. 82: second antenna, two distal segments; fig. 83: mandibular palp; fig. 84: mouth tube, dorsolateral view; fig. 85: maxilla; fig. 86: maxilla, detail of distal part of second segment; fig. 87: maxilliped; fig. 88: juvenile female, lateral view; fig. 89: maxilla of juvenile female, detail of distal part of second segment.

page 25 body, each as wide as the carapace, overlapping in the midline and curved down around the body laterally; these plates have the same membranous structure as the basipods of the pereiopods and are similar to them in texture.

Third thoracic segment similar to second but slightly longer and narrower (1.9 mm - 2.4 mm × 0.5 mm - 1.2 mm), and lacking plates.

Fourth thoracic segment difficult to discern. Shiino (1955, p.54) states that it is fused with the genital segment. Lewis (1966, p.69) says it is indistinctly fused and similar to two preceding segments although partly or completely covered by the swollen genital segment. In the specimens I have examined it appears to be very reduced and totally concealed by the genital segment in dorsal view although there is a small subtriangular area ventral to the anterior part of the genital segment indicating the position of this segment.

Genital segment subovate, width two-thirds length (4.7 mm - 7.7 mm × 3.8 mm - 4.7 mm), with a slight narrowing at its midpoint.

Abdomen, length half width (0.6 mm - 1.0 mm × 1.3 mm - 1.6 mm) narrowing slightly posteriorly, with caudal rami on posterolateral angles.

Caudal rami subovate, width four-tenths length (1.4 mm - 1.8 mm × 0.45 mm - 0.75 mm), with scattered very small spines irregularly over surface.

Egg string 35 mm - 68 mm in length.

First antenna of six segments, third and fourth segments subequal in length, otherwise segments becoming shorter distally so that distal segment is one-quarter basal segment length, basal segment partially divided by a groove running medially and proximally along the outer margin; second and third segments each with single setae, distal segment with several very small setae.

Second antenna of four segments, proximal half capable of being withdrawn into carapace (as noted by Lewis, 1966, p.70) the proximal half a flexible membrane, first and third segments subequal in length, second segment a little shorter, distal segment one-third length of third segment, claw-like, sharply curved, closing against a projection near midpoint of third segment.

Associated with the bases of the antennae is a suboval, chitinised structure (1.2 mm × 1.1 mm) which projects, lappet-like, beyond the cephalothorax. Lewis (1966, p.72) suggests that these may be homologous with the adhesion pads of pandarids and the processes of trebiids, euryphorids and caligids which are found in an approximately analogous position.

Mouth tube 2.0 mm in length, 0.9 mm in basal width, rounded distally.

Mandibular palp biramous, exopod one-segmented, one-quarter endopod length, borne on an extension of the basipod, with three small spines distally; endopod subtriangular in cross section, basal width two-fifths length, narrowing almost to a point distally, with two setae two-fifths segment length borne distally.

Maxilla of two segments, first segment three-quarters length of second, subrectangular, two-thirds as wide as long; second segment one-fifth as wide as long, with two parallel flanges near outer margin, for three-fifths segment length, terminating on an outer spur-like projection of outer margin, distal fifth of segment rounded, with longitudinal striations, and a longitudinal semicircular denticulate ridge running longitudinally around it, associated with a further semicircular denticulate ridge around outer portion of its base. these denticulate ridges are derived from rows of spines clearly seen in juvenile specimens, in which this distal portion of segment is smaller, narrower and more pointed distally.

page 26

Anthosoma crassum (Abildgaard, 1794) male. fig. 90: dorsal view, specimen mechanically extended; fig. 91: lateral view, specimen naturally flexed; fig. 92: ventral view; fig. 93: first antenna; fig. 94: second antenna, two distal segments; fig. 95: mouth tube; fig. 96: mandibular palp; fig. 97: maxilla; fig. 98: maxilliped: fig. 99: rami of first pereiopod; fig. 100: rami of second pereiopod; fig. 101: juvenile male.

page 27

Maxilliped of two segments, basal segment, two-thirds as wide as long, somewhat rounded distally, outer margin rounded, inner margin swollen medially and proximally, the second claw-like segment closing against and between these swellings; second segment two-thirds length of first, basal width half length, pointed distally, moderately curved.

First second and third pereiopods with basipod greatly enlarged and flattened, in each case overlapping in the ventral midline, and extending laterally to hide much of the genital segment in lateral view, the second pereiopod partly overlying the plates on the second thoracic segment, and these plates partly overlying the basipod of the third pereiopod which extends further around the body than do the other two; the basipods of the pereiopods and the plates of the second segment between them envelope much of the body, hiding from view the three thoracic segments and much of the genital segment; first and second pereiopods each with a mediodistal notch, in the apex of which are faint signs of degenerate rami, third pereiopod which no notch and no signs of rami.

Male (figs. 90-101)

Overall length 9.0 mm - 16.7 mm (smaller specimens may be less mature males).

Carapace similar in form to that of female, two-thirds as wide as long (5.2 mm - 9.5 mm × 4.0 mm - 7.3 mm).

Second thoracic segment disc-shaped, length one-third width (0.6 mm - 1.4 mm × 2.8 mm - 3.5 mm), lacking the dorsal plates found in the female.

Third thoracic segment similar in form to second, length half width (1.1 mm - 2.5 mm × 1.9 mm - 4.3 mm).

Genital segment subrectangular, angles rounded, slightly wider anteriorly, a little longer than wide (2.0 mm - 3.3 mm × 1.5 mm - 3.2 mm), with two plate-like ventral extensions of posterior margin covering much of ventral surface of abdomen, the extensions separated by a narrow V-shaped sinus; two small semicircular projections from the base of these extensions could perhaps be degenerate fifth pereiopods.

Abdomen subrectangular, two-thirds as long as wide (0.4 mm - 1.2 mm × 0.8 mm - 1.8 mm), the caudal rami carried on posterolateral angles.

Caudal rami of similar form to those in female, width one-third length (0.9 mm - 1.8 mm × 0.3 mm - 0.7 mm).

Appendages as in female, except that in the first and second pereiopods the notch in the basipod is shallow and the degenerate rami are slightly better developed; in the first pereiopod each ramus is of one segment, lying against margin of pereiopod, each subrectangular, endopod slightly narrowed distally, each with several small spines and one broader spine along outer and distal margins; rami of second pereiopod more complex, exopod subcircular, with two setae and one heavy spine distally, the spine with pigmentation over distal half, the whole ramus almost hidden by a thin hood extending around it from the basipod, endopod similar to rami on first pereiopod but broader.

Juvenile specimens (female, fig. 88, male, fig. 101) very similar to adults, but can be recognized by their smaller size, their relatively smaller genital segment and the nature of the maxilla (see above).