| First stage: very transparent, with red chromatophores, very little yellow or blue in the colouring; at the tip of each antenna and antennule is a small red chromatophore, and at the base of each of the third maxillipeds and first pereiopods is a large red chromatophore; about the mouth
and internal organs there is a little general red colour; brownish red chromatophores down the endopodites of the pereiopods and the second and third maxillipeds, and one large red chromatophore at the base of the telson.The larva has a length of about 6 mm. from the tip of the rostrum to the tip of the telson; carapace, exclusive of the rostrum, is about one third the length of the abdomen; dorsally the carapace has a small rounded prominence close behind the base of the rostrum, and another slightly rounded part near the posterior edge; the rostrum is slender, spiniform, without dentides, about three quarters the length of the carapace, and projects horizontally or slightly downwards; the abdomen, composed of six well defined segments, is generally angularly bent in the neighbourhood of the third segment but may be held horizontally, or even (if the larva is walking on the bottom) be bent upwards; the telson is distinct from the sixth segment, is slightly emarginated distally and bears 14 densely plumose setae fairly evenly paced around the end; the spines are graduated in length, the innermost and outermost being the
shortest; between the spines a row of fine setae is visible extending from nearthe bottom of the emargination to the base of the sixth spine from the middle; at the proximal end of the telson the buds of the uropods may be seen showing through the transparent cuticle; the compound eyes are quite immobile, forming two large expansions immediately in front of the carapace; they are contiguous in the middle and extend laterally somewhat beyond the sides of the carapace; the simple eye or ocellus is to be seen as a small dark spot situated between the compound eyes; the first antenna or antennule has a simple tubular stem bearing a small conical segment tipped by two long setae and two short, and a small projection carrying a long plumose seta; the second antenna has a simple basal portion slightly divided into two parts; the scale or squame reaches about to the end of the first antenna, has no trace of segmentation, and bears eight long and three short densely plumose setae; the flagellum is about half as long again as the scale; it consists of a peduncular part of three segments, the proximal one being only lightly indicated, and a long undivided styliform joint tipped by a plumose seta and a short strong spine; mandibles have no palps and the molar and incisor processes are not very distinct; the two mandibles differ somewhat in shape; the incisor process of the right mandible bears two small teeth at the tip, and, between this and the truncated molar part, there are three small teeth; the incisor process of the left mandible bears four teeth, two of which are very small, and there are two small teeth between this and the molar process; the first maxilla consists of three lobes, the first two being coxopodite
and basipodite respectively and the third the endopodite; the coxopodite has a stout spine near the base and five plumose setae at the tip; the basipodite is tipped with eleven short stout spines, arranged in two rows; the endopodite bears five setae, four plumose and one simple; the second, maxilla suggests the adult form, although there is only a slight expansion of the exopodite; the two proximal lobes, coxopodite and basipodite, are each divided into two lobules, and fringed with plumose setae of varying size; the endopodite bears nine plumose setae; the exopodite is an oval lamella almost as big as all the remaining lobes together and fringed with simple fine setae; at the proximal edge there is the beginning of that expansion which is so conspicuous in the adult second maxilla; the first maxiilliped is more pediform than the maxillae; the basal part, or protopodite, is only faintly divided into two parts and is fringed with both simple and plumose setae; the endopodite is slender, somewhat pediform, and unsegmented and bears seven or eight simple setae; the exopodite is a slender ramus, about twice as long as the endopodite, and provided with twelve sparsely plumose setae; at the base of the protopodite is the epipodite, shaped like a flat, curved bar; the second maxilliped is larger than the first, but similar in shape; the endopodite is not jointed but five divisions are indicated; there is no
epipodite; the third maxilliped is only a little larger than the second but has a much bigger endopodite, this consists of five joints, and is more cylindrical than in the first two maxillipeds; the exopodite is similar to that of the second maxilliped; there is no epipodite; the first pereiopod is smaller than the third maxilliped but similar in shape except that there is no distinct joint between the first and second segments, and no setae on the exopodite; neither this nor any of the pereiopods has any trace of an epipodite; the second pereiopod is similar to the first except that the endopodite is a little longer, there is a distinct joint between its first two segments and the fourth or propodal joint is slightly extended to form the beginning of a claw; the third pereiopod has no exopodite and is essentially adult in shape except that it has no epipodite; the fourth and fifth pereiopods are verysimilar to the third; there are no pleopods visible at this stage but the larva swims fairly rapidly by means of the exopodites of the maxillipeds and pereiopods, or backwards by sudden flexions of the abdomen. Second stage: about 8 mm long and has a colouring similar to that of the first stage; carapace has a pair of supraocular spines; rostrum is little changed, but the ocellus beneath it is situated in a fleshy lobe; eyes are stalked and somewhat pyriform in shape; telson now bears eight pairs of spines, and the enclosed uropods are longer and show through the integument more distinctly than in the first stage; antennule has a three jointed stem somewhat expanded at the base; outer flagellum has three groups of "olfactory" setae; in the antenna the scale is well fringed with setae and approaching the adult shape, and the flagellum is longer and jointed throughout its length; there has been no very essential change in the mouth parts; first maxilliped has a bilobed epipodite approaching the adult shape; second maxilliped has more distinct joints of the endopodite; first and second pereiopod have exopodites fringed with plumose setae; first pereiopod has the propodite slightly expanded to suggest a claw; claw at the tip of the second pereiopod is better developed than in the first stage; at the base of each of the five pereiopods there is now a gill, a pleurobranchia. Third stage: about 9 mm long and except for the tail fan, is not very different from the second stage; rostrum is longer and sometimes has two or three minute dorsal teeth at the base; pleura are beginning to develop on the abdominal segments, but there is still no sign of pleopods; flagellae of the two pairs of antennae are longer proportionately; endopodite of the second maxilliiped, has four distinct joints, and an epipodite has appeared as a small bud on the protopodite; otherwise the mouth parts show no important change; pereiopods are also little changed except in size, and the development of the claw on the second pereiopod; gills at their bases are faintly lobulated; uropols are free and well provided with plumose setae; ttelson is triangular in shape; it still bears eight pairs of spines, but only five are at the end, the other three
being much smaller and situated on the sides. Fourth stage: much bigger than third stage, averaging 12 mm in length; rostrum has 8 to 10 small dorsal spines close together, and frequently
another near the acute tip; 3 to 5 small vertical spines; eyes are rather dilated distally; outer flagellum of the antennule has six groups of "olfactory" setae, and the tip is a little drawn out, beginning the slender terminal portion; antenna is almost adult in all respects except length of flagellum; paragnatha have now appeared as two little lobes under the oral aperture fringed with small setae; proximal expansion of the exopodite of the second marilla extends to the base of the appendage, and the whole exopodite is fringed with plumose setae; third maxilliped's first and second segments of the endopodite have fused together, and there is the bud of the mastigobranchia; in the first pereiopod the dactylopodite is getting smaller; claw at the tip of the second pereiopod is now sufficiently developed to be used and the right leg is slightly longer than the left; each pereiopod except the fifth has a rudimentary mastigobranchia on the protopodite; pleopods have appeared as small buds, simple or slightly cleft in the middle, but with no distinct rami or joints; epimeral plates are present on the first five abdominal segments; uropods have both rami well developed and as long as the telson; sides of the telson are nearly paralle; its spines are similar to those of a third stage telson except that they have almost ceased to be plumose. Fifth stage: superficially similar to the fourth, except that it is a little
bigger, averaging 14 mm in length; rostrum is well developed; 10 to 12 dorsal spines (of which 2 or 3 are on the carapace and 1 near the acute tip) and 4 or 5 ventral spines, all much larger than in the fourth stage; secondary "ocellus" has appeared on the eye as a small dark spot at the
base of the facetted portion; epipodite of the second maxilliped is bilobed and the mastigobranchia on the third maxilliped is a curved bar with small setae on one side, but otherwise there is no important change in the mouth parts; claw at the tip of the first pereiopod is getting smaller, but is still much more distinct than in the adult; in the second pereiopod, the difference in lengths of the two is more marked, but they are otherwise not much altered; mastigobranchiae on the first four pereiopods are similar to those of the third maxilliped; pleurobranchiae are almost adult in shape; pleopod are still somewhat rudimentary, but quite distinct from those of the fourth stagel; definitely biramous, but have no joints or setae; epimeral ptates are well developed; ttelson now narrows slightly towards the tip, but is otherwise little changed. Sixth stage: almost adult in character and is very difierent to the fifth stage; about 17 mm long; carapace lacks supra-orbital spines; rostrum is essentially adult; antennute has not altered much, although both flagellae are longer and jointed, and the slender tip of the outer flagellum is quite distinct; absence of setae on the palp, the mandibles are completely adult with two distinct processes and a palp; in the remaining appendages it will be convenient to note the traces of larval condition still remaining, rather than their assumption of adult form; basipodite of the first maxilliped not as much expanded as in the adult, the exopodite is not jointed, and the
whole is still rather undeveloped; second maxilliped has still no podobranchia; third maxilliped has a remnant of the exopodite, and the arthrobranchiae are only small buds; first pereiopod has a remnant of the exopodite and only the bud of the arthrobranchia, this is further true of the second pereiopod while the third and fourth also have the arthrobranchiae just appearing; second pereiopod is moreover undeveloped in that the two legs are still not as long in proportion to the body as in the adult, nor with as many subdivisions of the carpopodite; pleopods are definitely biramous, but there are still no distinct joints and only one or two setae on each ramus; telson is not quite as narrow at the tip as in the adult, and the second, third, and fourth pairs of setae have not quite disappeared though they are reduced to slender threads. |