KNIGHT: STAGES OF THYSANOPODA TRICVSPIDATA 



Maxilliped (Figure 8c) with 5 setae on me- 

 dial margin of coxa; there is no other change 

 in setation. 



No rudiment of the second thoracic appendage 

 was observed. 



Uropod (Figure 8d) biramous; protopod with 

 stout ventral spine; exopod produced into pos- 

 terolateral spine and bearing 7 plumose setae 

 around posterior and medial margins, the seta 

 near posterolateral spine is relatively small; en- 

 dopod with 5 distal plumose setae, 1 seta is sit- 

 uated submarginally and projects dorsally, 



IDENTIFICATION OF 

 EARLY STAGES 



The morphological evidence on which the 

 identification of the larval series is based may 

 be summarized as follows: 1) the nauplius II 

 is linked to the metanauplius by dissection of the 

 spinose carapace of the metanauplius from well- 

 developed nauplii; 2) the metanauplius and ca- 

 lyptopes I-III are related by the setation of 

 mouthparts, particularly the endopods of max- 

 illule and maxilla; 3) the third calyptopis is 

 identified with the larva described by Sars 

 (1885) by the long and slender body, the dis- 

 tinctive 7-facetted eyes, and the setation of the 

 exopod and 1-segmented endopod of the max- 

 illule which bear 3 setae each. 



There is additional evidence to support the 

 identification of the metanauplius in the way in 

 which the observed distribution of the larva cor- 

 responds with that of T. tricuspidata in the In- 

 dian Ocean as shown in Figure 9, and in the oc- 

 currence of the larvae within the range of T. 

 tricuspidata in the Pacific. 



DISCUSSION 



The only description of T. tricuspidata larvae 

 found which deals with the calyptopis stages is 

 that of Sars (1885); other authors referring 

 to larvae of the species (i.e., Tattersall, 1936; 

 : Gurney, 1947; Lebour, 1950; Pillai, 1957) dis- 

 cuss the furcilia stages only. Sars provides some 

 details of setation with his general descriptions 



I and figures the mandible, maxillule, maxilla, and 

 maxilliped of the third calyptopis (1885, Plate 



21, Figures 13-16). The mouthparts of the ca- 

 lyptopis III described in this study agree with 

 those figured by Sars in the dentition of left 

 mandible, in segmentation and setation of endo- 

 pod and exopod of maxillule, in rudimentary ex- 

 opod of maxilla, and in setation of exopod and 

 terminal segment of endopod of maxilliped. The 

 carapace of Sars' calyptopis III appears to be 

 indented medially on the posterior margin rather 

 than pointed as in calyptopis II, but it is not fig- 

 ured with a lateral denticle. 



The descriptions of larvae of other species of 

 the genus Thysanopoda are also almost entirely 

 limited to the furcilia phase; only two excep- 

 tions were found. Einarsson (1945) described 

 the calyptopes II and III of T. acutifrons and 

 Lebour (1950) the calyptopis III of T. cristata, 

 but figures of the appendages and the details 

 of setation are not given. 



The described larvae of T. acutifrons are 

 larger than those of T. tricuspidata in equivalent 

 stages; calyptopes II and III measure 3.4 and 

 3.8 mm in total length respectively while T. tri- 

 cuspidata averages 2.6 and 3.1 mm (Sars' spec- 

 imens measured 2.5 and 3.5 mm) . The carapace 

 of the third calyptopis of T. acutifrons is like 

 that of the second calyptopis with "character- 

 istic pointed end," and the lateral denticle is 

 sometimes discernible although very small. 

 Einarsson notes that the maxillule has a palp 

 of 2 segments and an inner lobe with 7 bristles. 

 Frost (1939) figures the appendages of the first 

 furcilia of T. aciitifrons showing the maxillule 

 with 6 setae on the endopod and 4 setae on the 

 exopod, and the endopod of the maxilla with 3 

 setae. This setation is probably also found on 

 the calyptopis III of the species she describes. 

 [Einarsson (1945) suggested that, based on the 

 shape of the eye. Frost's larvae may instead be- 

 long to T. microphthahna; he notes, however, 

 that the species are otherwise alike in develop- 

 ment.] 



Lebour (1950) describes and figures the car- 

 apace of the calyptopis III of T. cristata as long 

 and "pointed behind," noting that the larva 

 closely resembles the calyptopis III of T. acuti- 

 frons described by Einarsson. It is also very 

 large, measuring 4.2 mm in length. Gurney 

 (1947). in his description of the first furcilia 



65 



