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The Larvae of Some Species of Pandalidae (Decapoda) By THE LARVAE OF SOME SPECIES OF PANDALIDAE (DECAPODA) BY R. B. PIKE 1) AND D. I. WILLIAMSON 2) INTRODUCTION There are many cases in the literature of larvae which have been ascribed to the wrong species and several such cases concern the Pandalidae. Thus larvae described by Sars (1900) as "Pandalus boreali.r" and "P. bonnieri" were shown by Lebour (1930) to be the larvae of Caridion gordoni (Bate) and C. Jteveni Lebour respectively, and larvae which Stephensen (1912, 1916) named ""Pandalus propinqtlu/' and uSpirontocaris-larva No. 4" were later found to be stages in the development of P. boreali.r Krbyer (described by Berkeley, 1930). In his account of the Decapoda of the Godthaab Expedition, Stephensen (1935) corrected his former misidentifications and described another larva as "'Pandalus pro pinquu.r ( ? ) ". In the present paper we describe larvae of P. propinquus G. O. Sars from labora- tory hatchings and they differ appreciably from the larvae ascribed to this species by Stephensen (1935). They closely resemble "Spiro?ztocari.r-larva No. 5" (Ste- phensen, 1916, 1935) and also show only very small differences from the larvae of Dichelo pandalus bonnieri (Caullery), which are re-described below. The oppor- tunity is also taken in this paper to give more complete descriptions than have hitherto been available of the larval development of Pandalus montagui Leach and of Pandalina breviro.rtri.r (Rathke) and to summarise our present knowledge of pandalid larvae. The larvae described were obtained from laboratory hatchings at the Marine Station, Millport, and the Marine Biological Station, Port Erin, and from plankton collected in the Firth of Clyde and the Irish Sea. The approximate mean length (from the tip of the rostrum to the posterior margin of the telson, excluding the telson spines) is given for each stage described; the range in length encountered was usually about ± 15% of this mean. The terms "zoea" and "megalopa" are used as defined by D. I. Williamson (1957). Yellow chromatophores are indi- cated in the figures by stippling; all other chromatophores shown were red or orange. The generic groupings of De Man (1920) and Holthuis (1955) are employed. 1) Work done at The Marine Station, Millport, Scotland; present address: Fisheries Laboratory, 27 Wingfield Street, Wellington, New Zealand. 2) Marine Biological Station, Port Erin, Isle of Man, British Isles. 266 Pandalina brevirostris (Rathke) (fig. i ) Sars, 1900: 27, pl. 8 figs. 3, 4 (stage V, as "6th stage"); H. C. Williamson, 1915: 366, fig. 48 (after Sars, 1900); Lebour, 1940: 243, fig. 3 (stage I); Gurney, 1942: 206, fig. 72 (stage I); D. I. Williamson, 1957: 3, fig. 25 (head of stage IV); Bourdillon-Casanova,1960: 29, fig. 3 a-h (last zoea and megalopa). Laboratory hatchings of this species have been obtained at the Marine Station, Millport, in April and in June, but the larvae have not developed beyond stage II. The last zoeal stage (from plankton) has moulted to the megalopa in the Port Erin laboratory. All zoeal stages and the megalopa have been obtained from plankton from both the Firth of Clyde and the Irish Sea between April and September, and the following descriptions are based on these planktonic specimens. - Zoeal stages. Material from the Firth of Clyde and the Irish Sea suggests that P. brevirostris usually passes through 7 zoeal stages in these regions, but not all specimens fall clearly into one of these stages and it seems likely that some pass through 8 or 9 stages, which is the total number suggested by Lebour (1940) and by Bourdillon-Casanova ( 1960) . There is a definite rostrum in all stages but it is considerably shorter than in most pandalid larvae and never extends beyond about the middle of the antennular peduncle. It bears dorsal teeth in the later zoeal stages but the first ventral tooth does not appear until the megalopa stage. Some specimens in all stages have two small denticles on the carapace margin behind each pterygostomian spine, but these denticles were absent in about half the larvae examined. The carapace shows both anterior and posterior dorsal tubercles (dorsal organs). The 6th abdominal somite bears a blunt spine at the base of each uropod from stage III and a ventral (anal) spine from stage IV, but there are no other abdominal spines or denticles. Chromatophores are distributed as shown in fig. lA, with others (not shown) in the mouth region. Most of the chromatophores have both red and yellow com- ponents but those on the 3rd abdominal somite are predominantly yellow. In later stages there is a chromatophore on the posterior side of each eye-stalk in addition to that on the anterior side, the endopods of the peraeopods each bear several chromatophores and there is one on each ramus of the uropods as well as a pair in the posterior half of the telson. A chromatophore is sometimes present on each antennal scale and in the later stages additional chromatophores may occur on the head and on the 5th and 6th abdominal somites. - Stage I (fig. 1 A, B). Length about 1.9 mm. The slender rostrum projects to about the middle of the antennular peduncle. The inner ramus of the antennule is represented by a plumose seta and the outer ramus by a single segment termin- ating in 3 aesthetascs and a seta. The endopod of the antenna is about 2/3 as long as the scale, excluding spines and setae in both cases. The endopod terminates in a slender serrated spine and a long plumose seta, with the spine nearer the mid line. The scale bears 11marginal setae, of which 2 occur on the outer margin, and the tip consists of 4 free segments. There is a ventral spine at the base of the antennal endopod and an outer seta arises from the base of the maxil- .
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