Complete Larval Development of the Red Frog Crab Ranina Ranina (Crustacea, Decapoda, Raninidae) Reared in the Laboratory*1, 2

Nippon Suisan Gakkaishi56(4), 577-589(1990) Complete Larval Development of the Red Frog Crab Ranina ranina (Crustacea, Decapoda, Raninidae) Reared in the Laboratory*1, 2

MegumiMinagawa*3 (ReceivedJune 27, 1989)

The complete larval development of the red frog crab Ranina ranina under laboratory conditions is described and illustrated. Zoeal characters of this species are compared with previously reported ones, and morphological differences of megalopas in the family Raninidae are discussed. This species is proved to have 7 or 8 zoeal instars and one meaglopal instar. Morphological differences among individuals in the same instar were observed from instar VI, in which two dif- ferent features were observed on mandibular palp and the endopod of 3rd maxillipeds. Of the 7th instar zoeas about 19% showed that several body parts, such as antennular peduncle, 2nd maxilliped and pleopods, were morphologically advanced, like the 8th instar zoeas. It is so-called accelerated development, because they seem to metamorphose directly to megalopas by omitting instar VIII.

The red frog crab Ranina ranina is found on females with eyed eggs were caught from off sandy bottom of the vast Indo-West Pacific region. Hachijo Island with traps and put in 500-liter In Japan, it is one of the large and edible crabs tank with filtered sea water. Rearing methods found around southern Honshu. In spite of and foods for larvae were already described.5) commercial importance, information on their The water temperature was 26.1-29.9•Ž and the early life history are so limited and the complete specific gravity was 1.023-1.026. The molted larval development is not known. zoeas, which were easily distinguished from others In addition to the newly hatched zoea1,2) and by body size and body color, were moved to new the last stage one3), Sakai4) presented the de- containers. tailed morphological description of the 1st to the 8th zoeas reared in the laboratory. However, Observation of Morphology there is not any morphological data about the Within a few days after molting, 5-10 larvae of megalopas and the juveniles so far. I succeeded each instar and 2 specimens for juvenile crabs in rearing newly hatched zoeas up to the juveniles were fixed with 5 % formalin and later preserved in the laboratory. In this paper the morphology in 70% ethanol. After measuring several body

of the megalopa and the juvenile of Ranina ranina parts, larvae were dyed in Crorazol Black E are first described, as well as that of the zoeal solution6) for 12 to 24 hours for observation of stages, giving the special attention to the ac- morphology. celerated development. To make the description short and simple, special expressions were adopted as shown in Materials and Methods Table 1. Several abbreviations are also used; VIIA is the 7th instar zoeas with ordinary number Rearing the Larvae of segmentations of appendages, which molted to Larvae were reared from July to September, the 8th instar zoeas, while VIIB is those with 1985 to 1987 at Hachijo Branch, the Tokyo advanced morphology of segmentations. M7 Metropolitan Fisheries Experiment Station, means the megalopas molted directly from the Tokyo but those reared in 1986 were mainly used VIIB zoeas, which were distinguished from the for observation of morphology. Ovigerous ,megalopas (M8) from the 8th instar zoeas, CL *1 Partly presented at the annual meeting of the Japanese Society of Scientific Fisheries, Tokyo, 1987. *2 Studies on the rearing of larvae of the red frog crab , Ranina ranina-III. *3 Hachijo Branch , Tokyo Metropolitan Fisheries Experiment Station, Hachijojima, Tokyo 100-15, Japan (皆川恵:東京都水産試験場八丈分場). Table 1. Special expressions adopted on the number of setae of several appendages of R. ranina larvae

and CW are carapace length and carapace width, 2 setae at distal end. respectively. The size of each instar zoea is Antennal exopod with 6 setae; 1 spine on distal shown with a mean CL with range in parentheses, margin of proximal segment. Endopod bud and and in megalopas and juvenile crabs mean CW with 1 long seta. with range is added. Mandible without pale. Maxillule with 7:6:5; palp 2-segmented. Results Maxilla with 3:3:5:4/5/6; paip without segmentation. Newly hatched zoeas showed apparent pho- First maxilliped with 1/9/3:2:1:2:5; endopod totaxis, always swimming actively in reverse 5-segmented; exopod with 0:4. condition, directing the rostrum downward. Second maxilliped with 0/4/3:1:1; endopod Zoeas sometimes bit one another on the dorsal 3-segmented; exopod with 0:4. carapace spine from instar III. Third maxilliped, pereopods, pleopods and There were two dark orange stripes, one on uropod absent. the rostrum and the other on the dorsal carapace Telson not demarcated, with 6:0. spine in instar I and these stripes were divided into two lines in the later instars. In megalopas Second instar zoea (Fig. 2) orange pigments were present on eye stalks, the Age 4 to 10 days. CL 1.39 (1.29-1.46) mm. edge of carapace, the back of abdomen and Eye stalked. pereopods. Megalopas and juvenile crabs showed Antennule with 4 aesthetascs. a similar habit to the adults to conceal themselves Antennal exopod with 13 to 16 setae; endopod into bottom sand. still bud. Maxillule with 10:8-9:5. First instar zoea (Fig. 1) Maxilla with 4:3-4:5-6:5-6/6/14-15. Age hatching to 5 days. CL 1.04 (0.98-1.12) First maxilliped with 1/10/7:3:2:2:3; exopod mm. with 0:10-11. Carapace with spinules on entire margin. Second maxilliped not changed but exopod Rostrum and dorsal carapace spine long with with 0:11-14. spinules. Lateral carapace spines large with Bud of 3rd maxilliped and 1st to 5th pereopods spinules on outer margin. Eye sessile. present near 2nd maxilliped. Antennular rod simple with 3 aesthetascs and Pleopods and uropod absent. Fig. 1. First instar zoea of the red frog crab Ranina ranina. A: animal in lateral view, B: antennule, C: antenna, D: mandible, E: maxillule, F: maxilla, G: 1st maxilliped, H: 2nd maxilliped, I: telson.

Fig. 2. Second instar zoea of the red frog crab Ranina ranina. All explanations are the same as shown in Fig. 1.

Telson with 10: 6. exopod with 1:15-16. Exopod of 2nd maxilliped with 1:15-18. Third instar zoea (Fig. 3) Third maxilliped still bud; 1st pereopod larger Age 8-17 days. CL 1.86 (1.68-2.00) mm. but not bilobed. Antennule with 2 tiers of aesthetascs; distal Pleopods absent. and proximal tiers with 5-6 and 2 aesthetascs, Uropod with 5-8 marginal setae. respectively. Telson demarcated, with 14-16:7-10. Antennal exopod with 21-26 setae; endopod elongated. Fourth instar zoea (Fig. 4) Maxillule with 16:9-10:6. Age 12-21 days. CL 2.40 (2.22-2.60) mm. Maxilla with 5:4:6-7:7-8/6/22-26. Antennule with 3 tiers; distal 2 tiers with 4 First maxilliped with 2/15/10:6:4:2:3; or 5 aesthetascs and proximal tier with 2 aes- Fig. 3. Third instar zoea of the red frog crab Ranina ranina. A: animal in lateral view, B: antennule, C: antenna, D: mandible, E: maxillule, F: maxilla, G: 1st maxilliped, H: 2nd maxilliped, I: telson and uropod.

Fig. 4. Fourth instar zoea of the red frog crab Ranina ranina. All explanations are the same as shown in Fig. 3. thetascs. First maxilliped with 2-3/16-19/11-13:7-9: Antennal exopod with 30-33 setae; endopod 6-7: 2: 4; exopod with 3:17-19. one-third of exopod in length but still not sub- Exopod of 2nd maxilliped with 3:21-23. divided. Third maxilliped elongated but not subdivided. Maxillule with 17-19:12-13:7. Pereopods elongated. Maxilla with 7:4:8-9:9-11/7/35-38. Pleopod bud present on 2nd to 5th abdominal Fig. 5. Fifth instar zoea of the red frog crab Ranina ranina. A: animal in lateral view , B: antennule, C: antenna, D: mandible, E: maxillule, F: maxilla, G: 1st maxilliped, H: 2nd maxilliped, I: 3rd maxilliped and 1st to 5th pereopods , J : telson and uropod.

Fig. 6. Sixth instar zoea of the red frog crab Ranina ranina. A: animal in lateral view, B: antennule, C: antenna, D: mandible, E: maxillule, F: maxilla, G: 1st maxilliped, H: 2nd maxilliped, I: 3rd maxilliped, J: 1st to 5th pereopods, K: 1st pleopod, L: telson and uropod. Arrows show another distinct segmentation in some individuals. somites. Antennule with 4 tiers of aesthetascs; each tier Uropod with 12-16 setae . with 5-7, 4-6, 4-7 and 3 aesthetascs, respectively Telson with 16-25:10-12. from distal end. Inner ramus present as bud. Antennal exopod with 36-40 setae; endopod Fifth instar zoea (Fig. 5) still without segmentation. Age 16-26 days , CL 3.04 (2.83-3.25) mm. Mandibular palp present as bud. Fig. 7. Seventh instar zoea of the red frog crab Ranina ranina. A: animal in lateral view, B: antennule, C: antenna, D: mandible, E: maxillule, F: maxilla, G: 1st maxilliped, H: 2nd maxilliped, I: 3rd maxilliped, J: 1st pereopod, K: 1st pleopod, L: telson and uropod. Arrows show another distinct segmentation in some individuals.

Maxillule with 23-28/17-20/6-8. 2-3/4-5/3:1:1-2:1, but in some individuals Maxilla with 10-13:5-6:9-11:12-15/7-10/ distal segmentation indistinct. Exopod with 8-10: 50-56. 29-32. First maxilliped with 5-8121-31/14-18:10-11: Exopod of 3rd maxilliped simple; endopod 5-9:3-4:3-6; exopod with 5-7:21-24. 2-segmented on middle, with 1 or 2 more indis- Second maxilliped with 2-4/4/3:1:1; exopod tinct segmentations. with 6-8:25-27. First pereopod 5-segmented; 2nd to 5th per- Exopod of 3rd maxilliped present. eopods usually 4-segmented or 5-segmented in First pereopod bilobed; segmentation of all some individuals. pereopods indistinct. Pleopods without segmentation; endopod Pleopods still bud. present as bud. Uropod with 21-24 setae. Uropod with 28-32 setae. Telson with 20-25:13-16. Telson with 21-27:18-21.

Sixth instar zoea (Fig. 6) Seventh instar zoea (Fig, 7) Age 20-33 days. CL 3.88 (3.61-4.10) mm. Age 24-39 days. CL 4.76 (4.39-5.17) mm in Antennule with 5 tiers of aesthetascs; distal 4 VIIA and 5.56 (5.17-6.05) mm in VTIB. tiers with 5-7 aesthetascs and a proximal one with There were two morphological types, VIIA and 4-6 aesthetascs; peduncle demarcated with one VIIB. Main differences between them were indistinct segmentation on middle. completeness of segmentation. Characters of Antennal exopod with 43-47 setae; endopod VIIB were almost the same as those of 8th instar with one indistinct segment on middle. zoeas (Table 2). Mandibular palp elongated with 1 seta or Antennule with 6 tiers of aesthetascs; each tier without any setae, and in some individuals 2- with 5-7 aesthetascs but proximal tier with 2 or 3 segmented. aesthetascs; peduncle 3-segmented. Maxillule with 31-32/22-28/9-11. Antennal exopod with 47-54 setae; endopod Maxilla with 14-16:7-11:11-14:14-20/11-14/ 3-segmented, reaching distal two-thirds of exopod; 73-84. middle segment of endopod indistinct in VIIA but First maxilliped with 7-12/32-34/17-24:13-15: distict in VIIB. 8-11:3-4:7-8; exopod with 8-10:28-29. Mandibular palp 2-segmented in VIIA and Endopod of 2nd maxilliped 4-segmented, with 3-segmented in VTIB, both with 1 or 2 setae at Table 2. Main differences in setae and segments of several appendages among the 7th (VII A •E VIIB) and the 8th instar zoeas of R. ranina Fig. 8. Eighth instar zoea of the red frog crab Ranina ranina. A: animal in lateral view, B: antennule, C: antenna, D: mandible, E: maxillule, F: maxilla, G: 1st maxilliped, H: 2nd maxilliped, I: 3rd maxilliped, J: 1st pereopod, K: 1st pleopod, L: telson and uropod, M: abdomen.

distal end. Eighth instar zoea (Fig. 8) Maxillule with 30-39/22-27/10-13 in VIIA and Age 28-45 days. CL 5.70 (5.17-6.34) mm. 31-38/25-33/10-12 in VIIB. Antennule with 6 or 7 tiers of aesthetascs; each Maxilla with 13-16: 7-9: 11-15:16-22/11-15/ with 5-7 aesthetascs; endopod 1 seta at distal end; 87-108 in VIIA and 14-19:8-10:11-15:18-23/ peduncle 3-segmented. 11-17/104-118 in VIIB. Antennal endopod 3-segmented and three- First maxilliped with 11-15/41-47/18-27:13- fourths of or almost equal to exopod in length. 17: 10-13:3-5:7-9 in VIIA and 10-15/39-51/ Exopod with 53-58 setae. 22-23:15-20:9-13:4-7:8-10 in VIIB; exopod Mandibular palp 3-segmented with 2 setae at with 9-12:30-32 in VIIA and 10-11:27-31 in distal end. VIIB. Maxillule with 40-44/32-35/11-13. Second maxilliped with 2-8/4-6/2-3:1-2:2: Maxilla with 18-20:10-13:15-18:22-24/12- 1-2 in VIIA and 9-17/5-8/2:1-2:2-4:2:1 in 18/114-121. VIIB; endopod 4-segmented in VIIA but 5-seg- First maxilliped with 11-15/49-51/23-27:15- mented in VIIB; exopod with 9-12:32-36 in 22:12-14:4-5:8-10; exopod with 10-11:28-31. VIIA and 11-13:31-36 in VIIB. Endopod of 2nd maxilliped 5-segmented with Endopod of 3rd maxilliped 4-segmented in 11-14/7-10/1-2:2:2-3:1-2: 1; exopod with 11- VIIA and 5-segmented in VIIB, with 1-3 setae at 13:33-37. distal end; exopod simple. Endopod of 3rd maxilliped 5-segmented and 2 Pereopods 5-segmented in VIIA and 6-seg- setae at distal end of dactylus; exopod simple. mented in VIIB. Pereopods 6-segmented; segmentation between Pleopods indistinctly 2-segmented or without basis and ischium not clear. segmentation in VIIA but distinctly 2-segmented in Pleopods 2-segmented. VIIB. Uropod with 40-43 setae. Uropod with 33-40 setae in VIIA and 38-40 in Telson with 22-26:20-24. VIIB. Telson with 21-22:21-23 in VIIA and 21-24: Megalopa (Fig. 9) 19-24 in VIIB. Age 36-62 days. M7: CL 7.91 (7.03-8.79) mm Fig. 9. Megalopa of the red frog crab Ranina ranina. A: animal in dorsal view, B: animal in lateral view, C: antennule, D: antenna, E: mandible, F: maxillule, G: maxilla, H: 1st maxilliped, I: 2nd maxilliped, J: 3rd maxilliped, K: 1st pereopod, L: 5th pereopod, M: 1st pleopod, N: telson and uropod.

Table 3. Morphological differences in the number of setae between two types of megalopas, M7 and M8. of R. ranina

CW 5.76 (5.06-6,66) mm M8: CL 8.44 (7.42-9.27) Carapace long anteriorly and smooth without mm CW 6.10 (5.00-6.71) mm. teeth and spinules. There was little clear difference in morphology Rostrum triangular, with blunt apex. between M7 and M8 , except for the number of Eye stalked, 3-segmented but immovable. setae (Table 3). Antennular peduncle 3-segmented; inner ramus Fig. 10. First instar juvenile crab of the red frog crab Ranina ranina. A: animal in dorsal view, B: eyes, C: antennule, D: antenna, E: mandible, F: maxillule, G: maxilla, H: 1st maxilliped, I: 2nd maxilliped, J: 3rd maxilliped, K: 1st pereopod, L: 1st pleopod, M: uropod, N: 5th and 6th abdominal sornites and telson.

3-segmented with 9-10:4-5:0 setae respectively with 28-32 setae and 4-5 spines in M7 and 34-38 from distal end; outer ramus 8-9 segmented with setae and 5-7 spines in M8. 1 long seta at distal end. More than 9 aesthetascs Endopod of 3rd maxilliped 5-segmented; distal on 2nd to 6th or 7th segments. 3 segments small with 8-14, 24-32 and 11-15 setae Antennal peduncle 2-segmented; flagellum 8- in M7 and 12-17, 24-30 and 16-17 setae in M8 on segmented with 2-4 setae on each segment but dactylus to carpus; merus and ischium with long proximal one without any setae; exopod rounded and short setae on outer and inner margins. with 40-43 setae in M7 and 49-63 in M8. Exopod bilobed with 80-90 setae in M7 and 84-92 Mandibular pale 3-segmented with 15-16:1-2: setae in M8. 0 setae from distal segment in M7 and 15-20:2-3: Pereopods 7-segmented but segmentation be- 0 in M8. tween basis and ischium obscure. First pereopod Maxillule with 43-54:31-35:12-14 in M7 and with 6 or 7 teeth on cutting edge of immovable 55-72:45-60:11-16 in M8. finger. Fifth pereopod with 4 aesthetascs at tip Maxilla with 30-38:16-20:23-24:37-40/4 or of dactylus, and on outer margin near tip and more/228-257 in M7 and 34-44:17-22:23-27: inner margin, 26-29 aesthetascs in M7 and 30-33 38-43/4 or more/249-278 in M8. aesthetascs in M8 totally. Endopod of 1st maxilliped without segmenta- First to 4th pleopods with 48-52, 48-50, 38-44 tion and with 39-57 in M7 and 47-74 setae in M8; and 34-37 setae in M7 and 52, 49-52, 45-47 and segmentation of exopod indistinct with 20-25 in 39-42 setae in M8, respectively. M7 and 24-25 setae in M8. Uropod with 49-54:8-15 setae in M7 and 50- Endopod of 2nd maxilliped 5-segmented; 54:10-15 setae in M8 on distal and proximal distal 3 segments small with 7-11, 6-9 and 5-7 segments. setae in M7 and 8-11, 8-11 and 6-9 setae in M8 Telson rounded, with 3-8 setae. from dactylus to carpus. Exopod 2-segmented; no setae on distal segment, and proximal segment Table 4. Morphological differences of reared larvae of the red frog crab Ranina ranina

First instar juvenile crab (Fig. 10) Second to 5th pereopods similar to one another Age more than 53 days. CL 10.99 (10.76-11.21) mm in shape and size. CW 8.18 (8.03-8.33) mm. Pleopods and uropods atrophied and marginal Body light orange. Carapace covered entirely setae disappeared. with tubercles on dorsal surface. Rostrum Posterior margin of telson rounded, without triangular. Three postorbital teeth on anterola- setae. teral margin of carapace; uroposterior teeth with a small tooth on their inner margin. Many Discussions setae on the lateral margin of carapace. Eye stalk 3-segmented and retractable into Morphology orbit. Rice and Ingle3) reported the terminal zoea of Inner antennular ramus 4-segmented with 5-8, R. ranina based on plankton samples. The 2-4, 2-3 and 1 setae from distal to proximal seg- carapace length of this zoea estimated from the ments. Outer ramus 9-segmented with 2, 3, and figure (Fig. 1) is 7.1 mm. It was rather larger but 3 setae on distal 3 segments and with 6 tiers of agree closely with the present 8th instar zoeas, aesthetascs on distal 2nd to 7th segments. except for the endopod of 2nd maxilliped. It Antennal flagellum 7-segmented with 1-4 setae was incompletely composed of 4 segments, which on each segment, except for proximal segment were already seen at instar VII in this study. without setae. The general morphology of the zoea given by Mandibular pale 3-segmented with 11-15, 1-2 Sakai4) agreed well with those in the present study. and 0 setae on distal to proximal segments. Sakai's larvae, however, showed inferior growth Maxillule with 61-63:50-52:12-17. to that in the present study after instar VI.5) Maxilla with 36-38:32:24-25:43-44/11/368- Moreover, in Sakai's4) larvae the development of 453. segmentation of appendages and the appearance Endopod of 1st maxilliped without segmenta- of some appendage buds were delayed after instar tion and with 44-50 setae on distal part and 46-52 IV as shown in Table 4. setae on central part. Exopod unsegmented, Morphological differences were not recognized with 38-45 long and 63-86 short setae. at instar I to V, but appeared among individuals Endopod of 2nd maxilliped 5-segmented; after instar VI. Some larger individuals of the distal 3 segments with 11-14, 11-14 and 12-16 7th instar zoeas molted directly to megalopas by setae from distal end. Exopod 2-segmented. bypassing instar VIII.5) These larger 7th instar Endopod of 3rd maxiiliped 5-segmented; dac- zoeas had almost the same morphology as that of tylus with 18-20 setae; merus and carpus flat- the 8th instar zoeas on the segmentation such as tened and large, with long setae on outer margin on endopods of 2nd and 3rd maxillipeds. On the and short setae on inner margin. Exopod with other hand, segmentation of appendages did not 41 long setae and 54 short setae. differ between megalopas molted from instar VIII Segmentation between basis and ischium of all and those from instar VII, though with more setae pereopods obscure. First pereopod with 1 tooth in the former ones. There seem to be two ways to on outer margin of dactylus near articulation; 4 metamorphose in this species; one is the ordinary teeth on inner margin and 1 large tooth on outer way, having 8 zoeal instars, and the other is the margin of propodus. accelerated way, in which the megalopas metamorphose from the 7th instar zoeas having advanced ment in Brachyura have been reported.3,17-24) morphology on segmentation of appendages. Like other many brachyuran crabs reported,17,19- The megalopas of the raninids were reported on 21,24)the present species also showed the number Raninoides benedicti,7) Lyreidus tridentatus ,8,9) of zoeal molting variation of only one instar. Raninoides sp.2) and other unidentified ran- In accelerated development, two types can be inids.10,11) Megalopa of L, tridentatus differs included, i, e, skipped and combinatorial staging. from the present species by the following char- Skipped staging, in which some instars are omit- acters: 1) the rostrum is sharper in L. tridentatus ted, is reported in Anomura25-27) and Na- than in R. ranina, 2) the dactylus of 2nd to 4th tantia.28,29) Combinatorial staging, in which pereopods are narrower in L. tridentatus than in certain stage exhibits a combination of characters R. ranina, and 3) inner antennular ramus is 5- from succeeding instar, is found in Natantia,30,31) segmented in L. tridentatus while 3-segmented in Anomura32)and Brachyura.17) In the blue crab, R. ranina. Callinectessapidus, both stagings occur in the same Main features of megalopa of R. benedicti rearing group.18) In the present study the larvae compared with those of R. ranina are as follows: 1) showed combinatorial staging after instar VI. the carapace is shorter in R. benedicti than in R. Of the 7th instar zoeas 19% omitted instar VIII ranina, 2) the rostrum is sharper in R. benedicti and metamorphosed to the megalopas. They than in R. ranina, 3) the triangular lateral spines showed the similar morphology to the 8th instar at the base of rostrum are present in R. benedicti zoeas, and consequently, these advanced 7th while entirely absent in R. ranina, and 4) 1st to instar zoeas are considered to have completed 3rd pereopods have triangular spines on the inner their zoeal development one instar earlier. margin of ischium and merus, and the dactylus of Gore12) described that "if the majority of 2nd and 3rd pereopods are armed with strong larvae in a species undergo N stages, but some serrated spines along the inner edge in R. benedicti few pass through N-1 in completing their de- while no such spines are in R. ranina. velopment, then accelerated development is Describing a very similar megalopa from the occurring". However, the "majority" in larvae Indian Ocean to that of Raninoides benedicti, of R. ranina varies under laboratory conditions. Rice2) remarked that Raninoides hendersoni and In one experiment, only 2 % of the 7th instar zoeas R. serratifrons were equally likely to be the parent molted to instar VIII and then metamorphosedto of the megalopa. A main difference between this megalopas, but the remains metamorphosed megalopa and those of R. ranina other than 1)-3) directly to megalopas (unpublished data). The described in the features of R. benedicti is that 2nd number of larval instars in R. ranina may often and 3rd pereopods have a spine on the outer fluctuate under various biotic and abiotic condi- margin of the merus in Raninoides sp. while no tions. Detailed morphological studies on each such spines in R. ranina. individual are necessary to classify the larval Chace and Barnish10) considered that their development and a field survey is also neededto unidentified raninid megalopa might be referable clarify how the larvae develop in nature. to the genus Ranilia as well as a specimen recorded from the Gulf of Guinea by Monod.11) Both, Aknowledgements however, have a long and blunt rostrum, by which they can be distinguished from the megalopas of I am indebted to the followings: Associate the present species. Professor K. Hayashi, Shimonoseki University of Fisheries, for his reading and criticizingthe Developmental Types manuscript; Professor F. Takashima, Tokyo It is well known that the number of molting University of Fisheries, for his making helpful until metamorphosis within a species is not always inspection; Research Associate A. Ohno, Tokyo consistent in many species under laboratory Universty of Fisheries, for his giving me the in- conditions12,13') and also indicated on plankton formation of literature; Mr. K. Ishikawa, ex- samples.14-16) Gore12) mainly classified larval manager of Hachijo Branch, the Tokyo Metropol- development into regular and irregular develop- itan Fisheries Experiment Station and Mr. K. ment, and assigned subcategories of accelerated, Nishimura, manager of the same station for delayed and sporadic development to irregular their giving me a chance to study: Ms. H. Iwasaki development. Several cases of irregular develop- for helping rearing the larvae. 15) H. Kurata: Bull. Hokkaido Reg. Fish. Res. References Lab., 28, 23-34 (1964). 1) H. Aikawa: Rec. Oceanogr. Wks. Japan, 12, 16) H. Kurata: Bull. Hokkaido Reg. Fish. Res. Lab., 117-118 (1941). 29, 66-70 (1964). 2) A. L. Rice: Bull. Br. Mus. Nat. Hist. (Zool.), 17) R. H. Gore, C. L. V. Dover, and K. A. Wilson: 21,1-24 (1970). J. Crust. 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Nippon Suisan Gakkaishi : Formerly Bull. Japan: Soc. Sci. Fish.