Material

On the gills of Latridopsis ciliaris (moki)—three females from Ngaraunga, Wellington, collected by W. Heaphy on 7 August, 1951 (Dominion Museum collection).

Description

Female (figs. 64-77).

Overall length 4.45 mm - 4.71 mm.

Cephalothorax, length nine-tenths width (1.25 mm - 1.33 mm × 1.36 mm - 1.46 mm) anterior and posterior margins sublinear, antennae carried laterally on an anterior page 20 area which is two-fifths cephalothorax length, one-quarter cephalothorax width, and which is marked off laterally by shallow grooves, and extends anteriorly a little beyond remainder of anterior margin of cephalothorax, anterior margin of anterior area very slightly curved; anterior quarter and posterior three-quarters of lateral margin expanded as two rounded lateral lobes, the anterior one directed laterally, posterior one directed anterolaterally.

Second and third thoracic segments fused, the junction between them marked by a transverse groove running dorsally and laterally, second segment nine-tenths width of third, overall length six-tenths width of third (second segment width 1.12 mm - 1.41 mm, third segment width 1.31 mm - 1.61 mm. overall length 0.77 mm - 0.85 mm); the combined segments are extended laterally as wing-like projections, which may increase width of segment by up to two-fifths, lateral margins sublinear, anterior angles rounded, posterior angles extended posterolaterally for a distance equal to two-fifths segment length, free margins slightly serrate.

Fourth thoracic segment including plate, width nine-tenths length (2.32 mm - 2.61 mm × 2.17 mm - 2.46 mm), subovate, with slightly developed blunt posterolateral angles, posterior margin divided into two entire curves by a median concave invagination which is one-tenth segment length, one-eighth segment width, margin of plate slightly serrated. Fourth segment completely covered by plate, a little narrower than plate, but less than one-third its length (0.6 mm).

Genital segment subovate, length three-fifths width (0.39 mm × 0.65 mm).

Abdomen subcircular, as long as wide (0.56 mm × 0.55 mm), caudal laminae carried posteroventrally.

Caudal laminae very small, length twice width (0.18 mm × 0.09 mm), subtriangular, lateral margins irregular, with a lateral projection one-quarter distance from base, one-fifth as long as lamina, a little wider than long, and tipped with a sharp spine; lamina with a further sharp spine at the distal apex, and a further spine on medial margin near the apex.

Egg strings long, complexly coiled and hidden in dorsal view by the plate of the fourth thoracic segment, in ventral view by the third pereiopods.

First antenna of seven subrectangular segments, ratio of lengths from the basal segment outwards being approximately 3:3:2:3:1:1:1; first segment width two-thirds length, second segment width four-sevenths length, with three setae on outer margin, third segment as wide as long, with three setae on outer margin, fourth segment width half length, with five setae on outer margin, fifth segment as wide as long, sixth segment as wide as long, with two long setae on outer distal angle and one small seta on distal margin, seventh segment rounded distally, width three-quarters length, with one small seta on outer margin and six setae distally.

Second antenna of two segments, subchelate; first segment, basal width half length, narrowing to three-quarters this width distally, curved, with a stout spine on inner margin near base; second segment, basal width half length, narrowing steadily to a sharp point distally, strongly curved, with a stout spine near inner margin one-quarter of distance from base.

Month tube small (0.25 mm in length), sharply pointed distally.

Mandibular palp, with two rami on a flattened subrectangular base; outer ramus width two-fifths length, rounded distally, with one long and one short seta distally; inner ramus half length of outer, width two-thirds length, rounded distally.

Maxilla of two segments, segments subequal in length; first segment basal width two-fifths length, narrowing slightly distally, distal margin rounded; second segment page 21

Aethon morelandi n. sp. female: fig. 64: dorsal view; fig. 65; lateral view; fig. 66: ventral view; fig. 67: first antenna; fig. 68: second antenna; fig. 69: mouth tube and mandibular palp; fig. 70: maxilla; fig. 71: tip of maxilla; fig. 72: maxilliped; fig. 73: first pereiopod (dorsal view); fig. 74: second pereiopod; fig. 75: fourth pereiopod; fig. 76: genital segment, abdomen and caudal laminae; fig. 77: caudal lamina.

page 22 basal width one-fifth length, narrowing gradually distally except that distal one-fifth narrows suddenly and bears two longitudinal rows of small spines reaching almost to the slightly blunted tip, with two flattened spines lying transversely at distal end of rows; a small process, one-third length of narrowed distal region, width half length, is situated near inner margin one-third distance from tip, and bears two setae distally, the larger seta subequal in length to process, the other a little smaller.

Maxilliped of two segments, subchelate; first segment, basal width two-thirds length, narrowing slightly distally, distal margin rounded; second segment basal width half length, narrowing gradually to a distal point, sharply curved over distal two-thirds.

First pereiopod biramous, each ramus of one segment; basipod swollen, subsemicircular, length two-thirds width, with one small spine medial to endopod and another on a raised boss lateral to exopod; exopod subovate, subequal in length to basipod, width two-thirds length, with five flattened spines on distal margin; endopod subtriangular, subequal in length to exopod, basal width half length, without spine, but spine may have been lost.

Second pereiopod biramous, the rami fused to the basipod, length including rami more than twice length of first pereiopod, as long as basal width, narrowing steadily distally, to end in a sharp point, the terminal section presumed to include the endopod, distal portion curving sharply medially and posteriorly away from the body, inner margin with a well developed subtriangular expansion one-third distance from base which is tipped with a flattened disc-shaped process, and a process on outer margin two-thirds distance from base is assumed to be the reduced exopod; exopod one-quarter length of combined basipod and endopod, basal width half length, narrowing gradually for three-quarters its length then more suddenly to one-third basal width, tip rounded.

Third pereiopod very large, two-thirds length of body, biramous, the rami lamellar, directed posteriorly and separate but fused with base which is one-fifth length of subequal rami; exopod a flattened subsemiovate lamella, basal width two-thirds length, narrowing slightly distally, distal margin rounded, hiding the egg strings in lateral view; the endopod is folded almost into a right angle in cross section, the inner portion lying flat against egg strings, the outer portion turned ventrally, involving one-quarter width of endopod distally, less proximally, the ventrally turned portion lying almost parallel to exopod, endopod if flattened would be subrectangular, width one-third length, posterior angles rounded.

Fourth pereiopod biramous, total length half total length of third pereiopod, rami fused with basipod which is one-quarter length of exopod and narrows towards its base so that its lateral margins form entire curves with outer margin of exopod and inner margin of endopod; exopod one-quarter as wide at the base as long, narrowing and rounded distally, outer margin a convex curve, inner margin sublinear, with a very small spine on a raised boss on outer margin near junction with basipod; endopod three-quarters exopod length, width at midpoint half length, narrowed slightly proximally, more narrowed distally, rounded distally, outer margin an entire curve, inner margin sublinear.

Fifth pereiopod borne near midpoint of genital segment lateral margin, almost as long as genital segment, width half length, rounded distally, bent into a right angle, directed laterally, then posteriorly, with a small seta on a raised boss near distal margin.

Discussion

A. morelandi can be separated from A. garricki since its cephalothorax possesses lateral lobes which are lacking in the latter. A. morelandi lacks the well developed page 23neck round in A. quadratus and also has the posterior lateral lobe of the cephalothorax less well developed.

A. morelandi most closely resembles A. percis but can be distinguished from it by the anterior lobe of the cephalothorax which projects laterally, not posterolaterally as in A. percis, and by the posterior margin of the fourth thoracic segment plate which is not as strongly curved as in A. percis and has more clearly defined posterolateral angles.