Female (figs. 51-64).

Overall length 3.0-5.2 mm, composed of two types of individual, contracted forms (3.0 mm-3.9 mm) in which the second, third and fourth thoracic segments overlap each other slightly (see Plate A figs 1-2) and extended forms (4.3 mm-5.2 mm) in which the second, third and fourth thoracic segments are not overlapped to any extent and may be separated by a short neck (see Plate A figs. 3-5). Of 19 individuals, 10 were contracted, the other nine extended, see Graph 1 below.

Graph 1

Cephalothorax subovate, width four-fifths length (1.3 mm-1.45 mm × 1.1 mm-1.2 mm), separated from the second thoracic segment in extended specimens by a short neck (ca 0.2 mm × 0.7 mm).

Second thoracic segment, length half width (0.75 mm-1.05 mm × 1.6 mm-1.85 mm), anterior angled broadly rounded, posterior angles less broadly rounded, segment widest posteriorly, narrowing by almost one-third anteriorly, separated from third thoracic segment in extended specimens by a short neck (ca 0.07 mm × 1.2 mm).

Third thoracic segment subrectangular, length two-fifths width (0.7 mm-0.9 mm × 1.6 mm-1.9 mm), angles rounded, narrowing very slightly anteriorly, separated from fourth thoracic segment in extended specimens by a short neck (ca 0.06 mm × 1.0 mm).

Fourth thoracic segment subrectangular, length half width (0.65 mm-0.8 mm × 1.4 mm-1.7 mm), angles rounded, anterior angles slightly more broadly rounded than posterior.

Fifth thoracic segment, length three-quarters width (0.45 mm-0.75 mm × 0.75 mm-0.9 mm), anterior margins sublinear, lateral and posterior margins united in a somewhat irregular entire curve.

Genital segment, length half width (0.3 mm-0.35 mm × 0.6 mm-0.7 mm), lateral margins rounded.

First abdominal segment subrectangular, length one-third width (0.07 mm-0.13 mm × 0.33 mm-0.40 mm), narrowing slightly posteriorly.

Second abdominal segment disc-shaped, length one-third width (0.06 mm-0.12 mm × 0.29 mm-0.32 mm).

Third abdominal segment subrectangular, length two-thirds width (0.18 mm-0.21 mm × 0.27 mm-0.35 mm), posterior angles slightly rounded, the caudal laminae borne laterally on posterior margin.

Caudal laminae subovate, width one-third length (0.20 mm-0.25 mm × 0.07 mm-0.10 mm), with six spines on distal margin, the innermost and the two outermost being very small.

Egg strings missing or damaged in all specimens so that total length could not be reliably measured.

First antenna apparently of twelve segments, their proportionate lengths being given by the following ratio—16:8:2:4:2:4:2:3:3:2:5:7; all segments subrectangular, distal segment rounded distally; first segment length twice width; second segment as long as wide, with two setae on distal margin and six setae on outer margin; third segment length half width, with one seta on distal margin; fourth segment length two-thirds width, with four setae on or near outer distal angle; fifth segment, length two-fifths width, with one seta on outer distal angle; sixth segment, length three-quarters width, with one seta on outer distal angle; seventh segment, length half width; eighth segment length two-thirds width, with one seta near outer distal angle; ninth segment length three-quarters width, with one seta on outer distal angle; tenth segment as long as wide, with one seta on outer distal angle; eleventh segment width two-thirds length, with one seta on outer distal angle; twelfth segment width two-fifths length, with about eight setae distally and four setae placed more proximally.

Second antenna of four segments, first and third segments subequal in length, second and terminal segments two-thirds this length; first segment subrectangular, width half length; second segment subrectangular, width two-thirds length with a few to 39 very small spines on inner distal area; third segment subrectangular, width one-third length with two to 21 very small spines in rows and patches: terminal segment, basal width one-third length, narrowing rapidly from the base to terminate in a sharp point distally, sharply curved into a claw, with three small spines near the base, one on a raised boss.

Mouth tube 0.3 mm in length, basal width two-thirds length, narrowing gradually to two-fifths this width distally, distal margin irregularly rounded.

Mandibular palp biramous, rami placed on a subrectangular base; outer ramus subrectangular, width one-third length, with one long and two short setae distally; inner ramus subrectangular, width two-fifths length, with two long setae distally.

Maxilla of two segments, segments subequal in length, first segment subrectangular, width half length; second segment width one-third length, rounded distally, with two processes distally, each one-quarter length of segment, outer process width three-quarters length, rounded distally, distal half covered in stout spines, inner process width two-fifths length, narrowing distally, with rows of small sharp spines on inner and outer margins, segment also bears a tuft of long cilia just proximal to the bases page 18 of these processes, and a group of small spines on outer margin near base of outer process.

Maxilliped subchelate, of two segments; first segment basal width half length, narrowing to half this width distally, with a blunt spine or process on inner margin near base; second segment basal width one-quarter length, narrowing gradually to a sharp point distally, segment a smooth curve, with two small spines on inner margin, the first one-quarter distance from base, the second three-fifths distance from base, the more distal spine with a small hair arising at its midpoint.

First pereiopod biramous, the basipod of two subrectangular segments, the second narrower and shorter than the first; exopod of two segments, first segment width half length, a little narrower at the base, inner distal angle expanded to increase width by one half, expansion rounded and covered in short stout spines, distal half of outer margin covered in very short spines, one spine and one very short spine on distal margin beside outer distal angle, inner margin covered in very long cilia; second segment one-third length of first, width three-quarters length, distal angles rounded, inner margin with about seven very small spines, distal margin with three long spines; basal segment of endopod two-thirds length of second segment of exopod, length two-thirds width, with a long plumose seta at outer proximal angle, and with two large processes on distal margin, each twice length of segment, the innermost, width two-fifths length, has very short spines on the rounded distal and inner distal region of margin, the outer process, which may be second segment of endopod, is rounded distally, basal width half length, slightly narrower distally, with a small spine on outer margin one-third distance from base, and a group of very short spines on and near distal margin.

Second pereiopod biramous. each ramus of two segments; basipod of two subrectangular segments, the second shorter and narrower than the first, larger than those of the first pereiopod; first segment of exopod as long as wide, inner margin two-sevenths length of curved outer margin, with a large spine on outer distal angle, a spine on inner distal angle, and a row of very short spines on distal margin near outer distal angle; second segment two-fifths length of first, as long as wide, rounded distally, with six to eight spines on distal margin, one of which may be significantly smaller than the rest, most spines about half length of segment; endopod subequal in length to exopod, first segment subrectangular, length half width, with very large spines on outer and inner distal angles, and a row of very small spines on distal margin near outer distal angle; second segment two-thirds length of first, as long as wide, rounded distally, with five or six spines on distal margin, one of which may be significantly smaller than the rest.

Third pereiopod biramous, each ramus of two segments, the basipod and segments similar in shape and size to those of second pereiopod, the first segment of exopod with a large spine on outer and inner distal angles, and a row of small spines on distal half of outer margin, distal margin of exopod second segment with six or seven spines, of which none to three may be significantly smaller than the rest, first segment of endopod with a large spine on inner distal angle and a slightly shorter spine on outer distal angle, second endopod segment with four spines on distal margin of which one may be significantly shorter than the rest.

Fourth pereiopod similar in form to second, but a little smaller; endopod first segment armed as in second pereiopod, second segment with six to eight small spines on distal margin; first endopod segment armed as in second pereiopod except that spines on distal angles are a little smaller, second endopod segment with three to six spines on distal margin.

Nemesis robusta (van Beneden, 1851) from Alopias vulpinus. Male—fig. 65: dorsal view; fig. 66: anterior, lateral view; fig. 67: first antenna; fig. 68: second antenna; fig. 69: mandible and mandibular palp; fig 70: mouth tube; fig. 71: maxilla; fig. 72: maxilliped; fig. 73: first pereiopod; fig. 74: second pereiopod; fig. 75: third pereiopod; fig. 76: fourth pereiopod; fig. 77: caudal lamina.

Fifth pereiopod of one segment, small, subrectangular, width two-thirds length, with three setae on distal margin.

Male (figs. 65-77).

Overall length 3.3 mm-3.7 mm, with no evidence in this sample of the contractile powers possessed by the female.

Cephalothorax as in female, width three-quarters length (1.25 mm-1.32 mm × 1.00 mm-1.04 mm).

Second thoracic segment length three-fifths width (0.61 mm-0.66 mm × 1.07 mm-1.18 mm), narrowing slightly posteriorly and anteriorly, lateral margins rounded.

Third thoracic segment similar in shape to second but smaller, length two-fifths width (0.41 mm-0.47 mm × 1.06 mm-1.08 mm).

Fourth thoracic segment similar in shape to third, length two-fifths width (0.39 mm-0.47 mm × 0.94 mm-1.0 mm).

Genital segment subovate, anterior and posterior margins sublinear, a little wider than long (0.76 mm-0.80 mm × 0.81 mm-0.91 mm).

First abdominal segment, length three-quarters width (0.27 mm-0.34 mm × 0.43 mm-0.45 mm), lateral margins rounded.

Second abdominal segment subrectangular, angles rounded, length one-third to two-thirds width (0.11 mm-0.24 mm × 0.31 mm-0.33 mm).

Third abdominal segment subrectangular, angles rounded, length two-fifths width (0.10 mm-0.12 mm × 0.26 mm-0.27 mm).

Fourth abdominal segment subrectangular, angles rounded, length three-fifths width (0.14 mm-0.17 mm × 0.24 mm-0.26 mm).

Caudal laminae subovate, anterior margin sublinear, width two-fifths length (0.25 mm-0.28 mm × 0.10 mm-0.11 mm), with three long plumose setae on posterior margin, two smaller setae just medial to these, three small setae just lateral to these, and a row of short cilia near base of outer margin.

First antenna of twelve segments, the proportionate lengths of these segments being given by the following ratio—14:9:4:4:2:3:3:4:4:4:6:8; all segments subrectangular, distal margin of terminal segment rounded; first segment width two-thirds length; second segment width three-quarters length, with three setae placed widely apart on distal margin, and a further six setae proximal to these; third segment length half width, with two setae on distal margin; fourth segment length two-thirds width, with four setae on or near distal margin; fifth segment length half width, with one seta on distal margin; sixth segment length two-thirds width, with one seta on distal margin; seventh to tenth segments as long as wide, the seventh with one seta on distal margin, the others with two setae on distal margin; eleventh segment width half length, with one seta on distal margin; twelfth segment width two-sevenths length, with seven setae on or near distal margin, and one seta proximal to these.

Second antenna, Mouth tube, Mandibular palp, Maxilla and maxilliped as in female.

First pereiopod as in female except that second segment of exopod has small spines on outer margin instead of inner, and first segment of endopod bears three processes, all rounded distally, two of which are twice length of first segment, the other two-thirds their length, all have groups of small spines on and near their distal margins, and in addition the two longer processes have one and two larger spines respectively; the larger process with two spines is a little wider distally than the process with one spine and probably represents the second segment of the endopod.

Second pereiopod biramous, each ramus of two segments; basipod two segmented, second segment narrower and shorter than first; first segment of exopod width three-quarters length, inner margin one-third length of outer, outer margin curved, with a long plumose seta on inner distal angle, a well developed spine on outer distal angle, and a row of very short spines just proximal to the outer distal angle; second segment subovate, proximal margin sublinear, width three-quarters length, with four long setae on inner part of distal margin and four spines on outer part of distal margin; endopod a little shorter than exopod, first segment length four-fifths width, subrectangular, outer margin curved, with a well developed spine on outer distal angle, a long seta on inner distal angle, and a row of short spines along distal margin; second segment half as long again as first, width two-thirds length, distal margin rounded, with six long setae on distal margin.

Third pereiopod similar to second except as follows: rami are a little shorter, first segment of basipod bears a plumose seta on inner distal angle, distal margin of second segment of exopod bears five setae and three spines and distal margin of second segment of endopod bears five normal setae and one very stout seta.

Fourth periopod very similar to third except as follows: rami are a little larger, endopod has rows of cilia along outer margins of both segments, and lacks the row of spines along the distal margin of the first segment, and distal margin of second endopod segment has only five setae which are all normal.