Biology of Finfish and Shellfish (2+1)

4.12.8. Protozoea I

MTL: 0.88 mm (0.88-0.91 mm); MCL: 0.42 mm

Carapace anteriorly rounded, with median notch, frontal organs present as rounded protuberances, ocellus of nauplius persists, developing compound eyes covered with carapace, body divisible into 3 parts, carapace covered anterior region, 6 segmented thorax in middle and posterior unsegmented abdomen; newly hatched protozoea with a swelling in anterior part of the abdomen which is replaced in advanced protozoea I by 5 somites resulting in lengthening of abdomen last abdominal somite and telson not separated by a movable joint, each lobe of caudal furca with 7 setae, outermost seta originates from dorsolateral aspect of furca and is dorsally disposed.

A1 3 segmented, basal segment with 5 sub segments, middle segment with 3 setae and distal segment with 2 setae of which one is long, about twice length of A1 peduncle and 2 aesthaetes, a spike-like setal rudiment present on distal inner margin of terminal segment; A2 biramous, endopod 2 segmented and exopod 10 segmented, 1st segment of endopod with 4 plumose setae of which 2 are placed together near inner distal margin of 1st joint, distal segment with 5 plumose setae of which inner one is smallest, exopod with 11 plumoce setae along inner and distal margin and 2 small setae on outer margin; Md flattened, without exopod and endopod, incisor process with 2 or 3 teeth and molar with transverse rows of smaller grinding teeth 1 free standing tooth present between molar and incisor process; Mx1 with unsegmented protopod having 2 lobes, proximal with 7 and distal with 4 setae, some setae stout and distally spinose, exopod small, knob like with 4 long feathery setae, endopod 3 segmented, distal segment carries 5 long plumose setae, basal and middle segments carry 3 and 2plumose setae respectively; Mx2 with protopod having 5 lobes on inner margin, 1st lobe with 7 or 8 setae, 2nd and 3rd with 4 setae and 4th and 5th with 3 setae respectively, exopod knob-like, with 5 long feathery setae, endopod 4 segmented, terminal segment with 3 long setae distally, the other 3 segments each with 2 long setae on inner margin; Mxp1 biramous, longer than Mx2, protopod 2 jointed, coxa with 4 to 5 and basis with 12 setae along inner margin, exopod unsegmented, carrying 7 plumose setae, 4 along outer margin, 2 terminal and one sub terminal on inner margin, endopod 4 segmented, 1st, 2nd, 3rd and 4th segments carry 3, 1, 2 and 5 long plumose setae respectively; Mxp2 shorter than Mxp1, protopod 2 segmented, coxa with 2 and basis with 5 setae along inner margin, exopod unsegmented, with 6 plumose setae; 3 along outer margin, 2 terminal and one sub terminal on inner margin, endopod 4 segmented, carrying 2, 1, 2, and 5 plumose setae on segments 1, 2, 3 and 4 respectively. Duration of this sub stage was 24 to 48 hours.