Biology of Finfish and Shellfish

4.12.11. Mysis I

MTL: 3.36 mm (3.07-3.65 mm); MCL: 1.17 mm (1.12-1.26 mm).

Larvae assume more or less a shrimp like appearance in this stage, rostrum long and curved extending beyond eye, devoid of rostral spines, supraorbital prominent, a small spine present at anteroventral angle of carapace, hepatic spine well developed, carapace covers thoracic region completely and thoracic appendages are well developed; posterolateral spines persist on 5th and 6th abdominal segments, dorsal spines present on posterior margin of 4th, 5th and 6th abdominal segments, in some specimens on 3rd segment also, in rare cases even the 1st and 2nd abdominal segments possess a dorsal spine; minute pieopod buds seen on 1st five abdominal segments; 6^th abdominal segment develops a ventromedian curved spine at junction withtelson,ventrolateral spines on posterior end retained; telson broader distaliy with a median notch, each lobe bearing 2 lateral and 6 terminal setae, cleft extends to level half way between origin of outermost and penultimate pair of setae.

A1 with 3 segmented peduncle, I st segment longest with a ventromedian serrated spine, base of this segment swollen due to developing statocyst and carries 2 short plumose setae, numerous setae occur along appendage, distal segment carries 2 unsegmented rudiments offlagellae, inner one small and knob like carrying 1 very long and another short seta at its apex, outer flagellum carries on distal margin 3 setae and 4 aesthaetes; A2 with endopod unsegmented carrying 3 terminal setae, one proximal seta on inner margin and 2 small setae near a very small knob-like projection on inner side distaliy, exopod unsegmented, leaf like, with a distolateral seta on outer margin and II setae on distal and inner lateral margin; Md asymmetrical, with 7 free standing teeth in left Md and 3 in right Md, molar part shows a number of hard ridges bearing small teeth; Mx1, proximal segment of protopod with 8 setae; Mx2 with exopod enlarged to form scaphognathite carrying 10 plumose setae, proximal one being long and thick; Mxp1 with some setae on inner side of protopod longer and stouter, setae on coxa reduced to 5, exopod with 12 plumose setae, one seta each added to outer margin of 1st and 2nd segments of endopod: Mxp2 with 7 setae on basis of protopod, exopod as long as endopod carrying only 6 setae, 4 apical and 2 subapical, endopod 4 segmented, first 2 segments carry 1 seta on the outer side, terminal segment with 5 setae; Mxp3 well developed, protopod with 3 setae on basis, coxa without seta, endopod 5 segmented, terminal segment with 1 short and 5 long setae, 1st, 2nd and 4th segments each with 2 setae, 3rd segment naked, exopod as long as endopod carrying 4 apical and 3-4 subapical plumose setae; P considerably enlarged and their exopods serve as main swimming organs; PI, P2 and P3 almost identical, endopod segmentation indistinct, developing chelae with 5 long slender setae, exopod twice length of endopod with 4 apical and 3-4 subapical plumose setae; P4 and P5 almost identical, endopod unsegmented, half size of exopod, and bears 4 long setae apically, exopod with 4 long apical and 2 subapical setae uropods well developed, protopod with a large posteroventral spine, exopod with a prominent posterolateral spine followed by a short nonplumose seta and about 15 plumose setae along distal and inner margin, endopod with 14 plumose setae along inner and distolateral margin. Duration of this sub stage was 48 to 72 hours.