“Aenigmathura lactanea, n. gen. n. sp.
Eyes poorly developed, weakly pigmented, though usually discernible. As other species in the same tubes have heavy pigment in the eyes, the poor pigmentation is presumably representative of the living condition and not an effect of storage in spirit.
The peraeon segments bear scattered setae marginally on either side. Segments 4 to 7 have dorso-lateral keels and these are slight. Shallow dorsal pits occur anteriorally on segments 4, 5 and 6. Segment 7 is shorter than the other peraeon segments but not so markedly as in Accaltithura. The pleon is relatively short—about the same length as segment 6. The pleon sutures distinct laterally but variably so dorsally, whore they are never discernible in the.mid-dorsal line.
The telson is broadly rounded and slightly less than the pleon in length. Dorsally it is convex, ventrally slightly concave. The margin is smooth and clothed in dense fine setae. Two rows of longer setae originate dorso-laterally inside the margin. Apically there are four pairs of long setae originating on the margin except for the central pair, which originate a little way forward on the dorsal surface. There is a single largemedian statocyst proximally.
Antenna I swollen in the male and of about 18 joints. In the female it is normal and the flagellum is four to five jointed. Antenna II has a flagellum of three or four joints in both sexes. There is a groove overhung by an expansion in the basal segment in which antenna I normally lies.
The mandibular pale has the first and third joints subequal and the third joint bears a comb of setae. The second joint is markedly larger than the others.
The maxillipeds is 4-jointed; the second joint is prolonged distally reaching barely beyond the base of the fourth joint.
Pereiopods 1-3 are sub-chelate with a basal tooth to each palm. Pereiopod 1 has a convexly arched palm in the female and young males, but almost straight in the adult male. There is a row of spinules along the ungnis, the palm and the basal tooth, and on either side a row of long setae laterally to the palm, and a long seta at the distal base of the basal tooth.
Pereiopods 2 and 3 have convex palms strongly arched in the female—less so or almost straight in the male. The female has a small distal tooth en the palm of pereiopods 2 and 3 but this structure is represented in the mole only by a very slight swelling. The spines on the basal tooth of pereiopods 2 and 3 are much stouter in the female than in the male.
Pereiopods 4 to 7 have rather short and stout joints, the fifth of which very slightly under-rides the 6th.
Pleopod I is somewhat indurated but not strongly operculiform. Pleopods broad and squat. The inner ramus of pleopod I only half as broad as the outer—in the remaining pleopods the inner ramus is at least three-quarters as broad as the outer. The male stylet is a simple rod.
There is no marked inner projection on the base of the uropod which is lined with long ciliate setae on the outer side and the distal half of the inner margin. The exopod is very slightly arched over the telson and both it and the endopod with the base of the uropod are somewhat splayed—forming an open cu-shaped tail fan. The endopod of the uropod is less than half the length of the base, and projects slightly beyond the end of the telson. Its margin is lined with non-ciliate setae—those on the inner margin being only half as long as those on the outer. The female has four pairs of oostegites—which enclose about 36 ova. No pigment could be discerned apart from the faint darkening of the eyes. The preserved specimens are creamy in colour.
In many respects, the genus is intermediate between Accalathura Barnard and Leptanthura Sass.
As in the Accalathura, the maxilliped is 4-jointed. The prolongation of the second joint reaches nearly to the distal end of the fourth in Accalathura, whereas in Aenignathura it projects scarcely beyond the base of segment four. In these two genera also the third joint of the mandibular palp is subequal to the first. But the second joint is not much larger than the others in the case of Accalathura whereas this joint is markedly elongated in Aenignathura. Although Accalathura has the basal tooth or lobe at the base of the palm of pereiopod 1 it lacks the similar teeth which Aenigmathura has on pereiopods 2 and 3.
The swollen first antenna of the male is common to Aenigmathura and Leptanthura but not to Accalathura; but in Leptanthura it is densely clothed in short setae; whereas the specimens of Aenigmathura have the swollen flagellar portion almost bare. The flagellum of the female first antenna is not so rudimentary in Aenigmathura as in Leptanthura as at least three and sometimes four joints can definitely be made out.
The flagellum of the second antenna, the feeble eyes, the large statocyst, the elongate second joint of the mandibular palp and the under-riding of segment 6 by segment 5 in pereiopods 4-7 and the relative sizes of the telson to the pleon are common to Aenigmathura and Leptanthura. But another difference occurs in the third joint of the mandibular palp which has a comb of setae in Aenigmathura but none in Leptanthura. A most important difference is the presence of a 3-jointed maxilliped in Leptanthura. It is 4-jointed in Aenigmathura.
33 specimens.
♂ 2.0 cm., 1.8 cm.. 1.8 cm.. 1.7 cm., 1.7 cm., 0.9 cm. ♀ ovigerous
1.8 cm.. 1.4 cm.. 1.2 cm. 9 1.1 cm., 0.9 em. December.
1929.
♀1.6 cm., 1.45 cm., 1.45 cm., 1.• cm. January, 1930.
♂1.3 cm., 0.5 cm. 9 0.7 cm. February, 1930.
♂1.3 cm., 1.1 cm. 9 ovigerous 2.0 cm., 1.5 cm.
♀1.7 cm. 1mm. 1.3 cm., 1.1 cm., 1.1 cm., 0.55 cm., 0.3 cm.
February, 1931.
♀1.8 m.--16062/05.
♂1.2 cm. ♀ovigerous 1.0 cm. ♀1.5 cm., 1.3 cm. January, 1937.”
(Thomson, 1951: 5-8)
