| First stage: both dorsal and ventral denticles present on the rostrum, twenty-four setae on the telson, very long, jointed antennal flagellum; colouring is very bright and conspicuous, but there are no definite chromatophores; whole cephalothorax is a bright orange-red, as are the anterior parts of the eyes, the last four joints of the endopodites of the third, fourth and fifth pereiopods, and the base of the telson; base of the exopodite of the third maxilliped is pale pink and the flagellum of the antenna is all brown; otherwise the appendages and abdomen are quite colourless; as the larva usually swims backwards, trailing the antennal flagella, the transparent abdomen is almost invisible, and the effect is that of a bright red copepod with two very long egg sacs; larva is 10 mm from the tip of the rostrum to the tip of the telson; rostrum slopes abruptly upward above the eyes, and bears five subequal dorsal spines and three similar ventral spines; eye and antennule both resemble those of a first stage P. danae; stem is definitely divided into two parts and bears a strong spine at the base of the flagellum; scale is oblong linear, tapers distally to end in a sharp dentiform projection, and is fringed with long plumose setae; antennal flagellum is longer than the whole body, and is segmented throughout its length; these flagellae are pigmented some time before the remainder of the larva, and, in eggs that are near hatching, they lie curled back and around the larva like two notes of interrogation, giving a very peculiar appearance to the egg; two mandibles have the same arrangement of denticles, thus differing from those of the Pandalus larvae; incisor process is not distinct, there being five denticles fairly evenly spaced above the triturated molar part; maxillae are all similar to those of a first stage P. danae except for the presence of a few more setae; three maxillipeds and all the pereiopods except the second and third are very similar to those of a first stage P. platyceros, but for a few more setae; second pereiopod differs in being much less chelate than in P. platyceros and the third pereiopod in having no exopodite; all the thoracic appendages tend to be very long and thin; buds of pleurobranchiae are present at the bases of the first four pereiopods; abdomen is somewhat peculiar in the relative lengths of the different
segments; first five segments are all about the same length, the fifth being slightly the longest, but the sixth segment is as long as all the other five put together; abdomen is usually bent at the fourth and fifth segments instead of at the third; all pleopods are present as simple or slightly bilobed buds; telson is distinctly separated from the sixth segment and is very wide at the end; bears twenty-four plumose setae. Second stage: the colouring of this larva in general is similar to that of the first stage larva, but it is more restricted to definite chromatophores on the ventral surface
of the cephalothorax, the first two segments of the abdomen, and the tail fan; length is about 13 mm; a supra-ocular spine over each stalked eye; rostrum does not curve up as abruptly as in the first stage and there are 3 to 4 small dorsal spines at the base, six dorsal spines halfway to the tip,
and 3 to 4 small ventral spines; antennule is similar to that of a second stage P. danae except that the outer flagellum is a little longer and bears four clumps of "olfactory" setae; antenna is practically adult in all respects; mouth parts and pereiopods are not greatly changed although the two first segments of the endopodite of the third maxilliped have fused, all exopodites bear setae, and the claw on the second pereiopod is better developed; proportional lengths of the abdominal segments are more normal than in the first stage; pleopods are bilobed but not jointed or setose; telson is very little changed except that the enclosed uropods are longer, and the setae are more equal in length. Third stage: except for the tail fan this larva closely resembles that of the second stage; 16 mm long; rostrum is a little longer and has 8 dorsal spines between the eyes and the tip, 1 small dorsal spine near the tip, and 5-6 small ventral spines, besides the 3-4 small dorsal spines at the base which were present in the
last stage; both flagellae of the antennule are a little longer and the slender terminal portion of the outer flagellum is beginning to appear; proximal expansion of the exopodite on the second maxilla is developing; a slight tendency towards a claw at the tip of the first pereiopod; each of the third maxilliped and the first four pereiopods has the bud of a mastigobranchia on the
protopodite; pleurobranchiae are larger and lobulated; pleopods are distinctly biramous, but joints are still not well marked and there are no setae. In the tail fan the uropods are free; telson is still broader towards the tip, and has 10 pairs of terminal setae and 2 pairs of lateral setae. Fifth stage: length is 30 mml; rostrum has 15 dorsal spines including one near the tip, and 10 ventral spines; flagellate of the antennule are growing rapidly as would be expected considering their length in the adult; outer flagellum has ten clumps of "olfactory" setae on the stout proximal
portion, and the thin distal part is well developed and jointed; inner flagellum is a little shorter than the outer, and is segmented; antenna, mandibles and first maxilla are little changed; second maxilla is similar to that of a sixth stage P. borealis, except that the exopodite is rather larger proportionately; exopodite of the second maxilliped is bilobed; merus of the third maxilliped is slightly flattened and expanded, and has many setae on the endopodite, but is still essentially very little altered; first pereiopod has the ischium slightly expanded and the claw at the
tip is in the adult vestigial condition; second pereiopods are very slightly unequal in length and have a few secondary annulations in their carpopodites; other pereiopods are only changed in length; mastigobranchiae are still all rather small, and it may be noted that they are not quite as well developed in the adult as they are in P. danae; all pleurobranchiae are well developed, all arthrobranchiae are present as minute buds, but there is no trace of a podobranchia; segments, pleurae, and pleopods of the abdomen are practically adult in shape; tail fan has now seven pairs of terminal setae, all slightly plumose, and six pairs of simple lateral spines; adult telson is not quite like that of P. danae. |