FISHERY BULLETIN: VOL. 76. NO. 4 



M. subrugosa (White 1847). Rayner did not note 

 any substages or skipped stages in the five instars 

 he descritjed for the two species, and was not cer- 

 tain whether additional stages followed. By anal- 

 ogy with M. rugosa [as M. bamffica] he thought it 

 possible that the next stage would be postlarval. In 

 this he was probably correct, but it seems strange 

 in retrospect that Rayner did not attach impor- 

 tance to the well-developed pleopods on the larvae 

 before him, a feature by which he earlier charac- 

 terized the fifth zoeal stage. These appendages in 

 other galatheid larvae are quite obviously de- 

 veloped at stage V (see Lebour, Sars, Boyd and 

 Johnson, and others), and Sars (1889) even drew 

 attention to them when describing his "last zoeal 

 stage." 



Intercalation of substages, however, is known in 

 the genus Pleuroncodes, as was specifically discus- 

 sed by Boyd and Johnson ( 1963) in the larvae of P. 

 planipes Stimpson 1860.^ Five zoeal stages had 

 been initially noted in this species (Boyd 1960), 

 but a sixth stage, apparently unnatural and not 

 known to occur in the plankton, could be induced 

 in the laboratory. Boyd and Johnson thought this 

 stage was due to the presence of penicillin pills or 

 to the CaCOg buffer in the pills, used to control 

 bacterial growth in the cultures. These authors 

 also stated that numerical stage IV could be sub- 

 divided into a complex of from four to nine sub- 

 stages, each represented by a molt, all without 

 pleopods, but otherwise morphologically similar 

 to each other. Although no sequential substages 

 were skipped (e.g., a molt from substage IVa to 

 IVh), one or more substages could be omitted ter- 

 minally, with a subsequent molt to the morpholog- 

 ically discrete stage V, which possessed pleopods 

 (Boyd 1960). Boyd and Johnson suggested that in 

 P. planipes the number of substages in stage IV 

 was probably influenced by temperature, with 

 higher culture temperatures (e.g., 16°-20°C) pro- 

 ducing faster development but causing more sub- 

 stages to occur before the molt to stage V. They 

 noted, however, that other factors such as food 

 supply or crowding of larvae might also exert an 

 effect on the number of substage instars, but ne- 

 glected to consider the possibility that the large 

 number of induced substages in stage IV might 

 also be due to the use of antibiotics in the cultures, 

 as suggested by Fagetti and Campodonico ( 1971 ). 



^'Both Stimpson (1860) in his original description of Pleuron- 

 codes planipes and Haig (1955) have suggested that the species 

 may prove to be only a northern Pacific form of the Chilean P. 

 Monodon. 



786 



Figure 2. — Galathea rostrata, zoeal stages in lateral and dorsal 

 view: (A, a) First zoea; (B, b) second zoea; (C, c) third zoea; (D, d) 

 fourth zoea (regular); (E, e) fifth zoea. Scale line equals 1.0 mm. 



The Chilean congener, Pleuroncodes monodon 

 Milne Edwards 1837, also was found to have inter- 

 calated substages (Fagetti and Campodonico 

 1971). At 15°C, substage IVa-d were followed by a 

 molt to stage V, possessing pleopods; at 20°C a fifth 

 substage (IVe) was attained instead of zoeal stage 

 V. Whether stage IVe would be followed by ecdy- 

 sial stage V is not known because all larvae in 

 stage IVe died. However, the lack of pleopods in 

 stage IVe implies that stage V should occur, with 

 pleopods, before the molt to megalopa takes place. 

 Whether such substages occur in the plankton is 

 conjectural , but they certainly would present some 

 difficulty in separation because of their great simi- 

 larity to each other in samples collected from the 

 plankton. 



Abbreviated larval development is also known 

 to occur in at least two galatheids. Sars ( 1889), in 

 describing the prezoel, "first" and "last" zoeal 

 stages of Munidopsis tridentata from Norwegian 

 waters suspected that development time was 

 shorter than that seen in Galathea , but came to no 

 conclusion as to the total number of stages. He 

 commented on the remarkably advanced features 

 exhibited in the early zoea, an observation later 

 supported by Samuelsen (1972). Samuelsen de- 

 termined that only three zoeal stages exist for M. 

 tridentata and further suggested that the 

 megalopal stage followed stage III because the 

 latter stage was in the same relative state of de- 

 velopment as some fourth zoeae which preceded 

 the megalopae in other galatheids. Samuelsen 

 noted that the presence of a mandibular palp, 

 pleopod primordia, antennular aesthetascs, an- 

 tennal setae, and scaphognathite setae in the 

 early zoeal stages were all advanced features usu- 

 ally restricted to later zoeae in other galatheid 

 larvae. The relatively nonsetose feeding append- 

 ages and endopodites of the natatory appendages 

 indicate that the larvae may not feed, although 

 they can swim well. 



Al-Kholy (1959) described and figured larvae 

 attributed to a "Galathea sp." which apparently 

 developed through only three zoeal stages. How- 

 ever, no methodology was given, nor indication as 

 to whether the larvae were cultured in the 

 laboratory or collected from the plankton. It is 

 doubtful whether the species will ever be identi- 



