Material

From gills of Cheilodactylus macropterus: One female collected by the author from Somes Island, Wellington Harbour, 28 April, 1961.

Description

Female (figs. 51-63).

Overall length 3.82 mm.

Cephalothorax subovate, width two-thirds length (1.22 mm × 0.86 mm), anterior and posterior margins sublinear, lateral margins entire convex curves, anterior margin half cephalothorax width, posterior margin three-quarters cephalothorax width; antennae carried laterally on an anterior area one-quarter cephalothorax length, half cephalothorax width posteriorly, slightly narrower anteriorly, distinguished by very faint grooves; cephalothorax without lateral expansions.

Second and third thoracic segments fused, distinguishable by a dorsal and lateral transverse groove, combined length two-thirds width, width of second segment four-fifths width of third (combined length 0.81 mm, width of second thoracic segment 1.04 mm, width of third thoracic segment 1.24 mm); two poorly developed dorsal plates which are rounded laterally, cover much of the dorsum of each segment; page 17

Aethon garricki n.sp. female: fig. 51: dorsal view; fig. 52: lateral view; fig. 53: ventral view; fig. 54: first antenna; fig. 55: second antenna; fig. 56: mouth tube and mandibular palp; fig. 57: maxilla; fig. 58: maxilliped; fig. 59: first pereiopod; fig. 60; second pereiopod; fig. 61: fourth pereiopod; fig. 62: genital segment, abdomen and caudal laminae; fig. 63: caudal lamina.

page 18 lateral margins of these segments are extended in wing like projections which increase width of segments by up to one-third the extensions rounded anteriorly, extended posterolaterally for a distance equal to half length of combined second and third thoracic segments, this extension narrowing rapidly and ending in a blunt point, this extension well separated from the plate of the fourth thoracic segment.

Fourth thoracic segment, including plate, subovate, anterior margin sublinear, width two-thirds length (1.96 mm × 1.36 mm), lateral margins forming an entire curve with posterior margin except that posterior margin has a median convex invagination, one-ninth segment length, one-fifth segment width. The segment is entirely covered by the plate in dorsal view and the single specimen was not dissected so that the segment itself was not seen.

Genital segment subrectangular, slightly swollen posteriorly, length three-quarters width (0.33 mm × 0.46 mm).

Abdomen subcircular, length four-fifths width (0.32 mm × 0.39 mm), caudal laminae borne posteroventrally.

Caudal laminae width two-fifths length (0.12 mm × 0.05 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 indorsal 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 two small setae on outer margin, fourth segment width half length, with one long and one short seta on outer margin, fifth segment as wide as long, with one small seta on outer margin, sixth segment as wide as long, with one small and one large seta on outer distal angle, seventh segment rounded distally, width three-quarters length, with one small seta on outer margin and six setae on distal margin.

Second antenna of two segments, subchelate; first segment, basal width two-thirds 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-third of distance from base.

Mouth tube small (0.2 mm in length), sharply pointed distally.

Mandibular palp, with two rami on a flattened subrectangular base; outer ramus, width one-third length, rounded distally, with two small and one large setae distally; inner ramus half length of outer, width two-thirds length, rounded distally, with one seta distally.

Maxilla of two segments, segments subequal in length; first segment, basal width two-fifths length, narrowing slightly distally, distal margin rounded; second segment basal width one-seventh length, narrowing gradually distally except that distal seventh narrows suddenly; a small process, half length of narrowed distal region is situated on inner margin at base of this region.

Maxilliped of two segments, subchelate; first segment, basal width half length, narrowing slightly distally, distal margin rounded, with a small spine one-third of distance from base; second segment basal width two-fifths length, narrowing gradually to a distal point, sharply curved over distal half.

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 half length, with five flattened spines on distal margin; endopod subtriangular, subequal in length to exopod, basal width half length, distal apex bearing a spine.

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, 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, half 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; endopod with a sharply curved section near outer margin, the inner portion lying flat against egg strings, the outer portion turned ventrally, to form a shallow ridge which lies parallel to the exopod, endopod if flattened would be subrectangular, width one-quarter 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 withouter 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 two-fifths length, rounded distally, bent so as to be directed posterolaterally, then posteriorly, with a small seta on a well developed projection near distal margin.

Discussion

A. garricki can be separated from A. quadratus Krøyer 1836 and A. percis (Thomson, 1889) by the lateral margins of the cephalothorax which are entire curves, without the well developed lateral lobes found in the other species.