ERENNA REVISION 

Fig. 1  Erenna richardi. Image from in situ video of JSL II Dive 1456 
specimen; approximately 70-80 cm in length. 
states of development, and several nectophoral buds, remained with 
the JSL II 1456 specimen. They were flattened, and measured up to 
32 mm in length, 33 mm in width and 10 mm in height. The large 
axial wings tapered toward their apices (Fig. 2A aw). Mature 
nectophore had relatively large thrust block (Fig. 2C tb) with a broad 
U-shaped indentation apically. On its ventral surface there were two 
small conical protuberances (Fig. 2C cp). However, on the younger 
nectophores, the thrust block was small and had no protuberances 
(Fig. 3). 
The prominent main ridge system consisted of pairs of apico- 
(Fig. 2A ral) and infra-laterals (Fig. 2B ril), which united close to 
the apex of each axial wing; and a pair of vertical laterals (Fig. 2B 
rvl) that connected the apico-laterals with the infra-laterals; al- 
though in some nectophores the junction with the latter was weak 


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and difficult to discern. Apico-laterals branched close to the ostium, 
with each branch reaching the latter. In addition to these ridges at 
least two pairs of incomplete lateral ridges passed obliquely down 
the lateral facet in the basal half of the nectophore. Often these were 
difficult to discern without staining, but were also described by 
Margulis (1977), who noted 2-3 pairs of them. 
Ostial opening basal with no obvious mouth plate. On each side of 
the ostium there were prominent lateral protuberances on which lay 
strips of distinctive epidermal cells. A much smaller triangular patch 
also was present dorsally. In addition, there was a small patch of 
such cells on each side of the nectophore, at about the mid-height of, 
and basal to, the vertical lateral ridges. All these patches of epider- 
mal cells are believed to be sites of bioluminescence. 
T-shaped nectosac (Fig. 2B n) with a distinct muscle-free area 
across the whole of its apical region. Pallial canal (Fig. 2A pa) was 
relatively short, running from the base of the thrust block over onto 
the ventral surface and ending just beyond the point of origin of the 
pedicular canal (Fig. 2B ped). On the nectosac the pedicular canal 
typically gave rise to all four radial canals, although occasionally 
there was a slight asymmetry in the arrangement. All four radial 
canals were straight. Laterals pass out, through the muscle-free 
zone, toward the lateral margins of the nectosac. Typically, before 
reaching the latter, they became thickened and could have small 
protuberances, or spikes extending up from them. These thickenings 
were particularly prominent on the youngest nectophores. All the 
canals had brown, but originally black, pigment in their gastrodermal 
walls. 
SIPHOSOME. As the in situ video (see Fig. 1) showed, the sipho- 
some was tightly contracted, and possibly, as in Agalma okeni 
Eschscholtz, 1825 and Frillagalma vityazi Daniel, 1966 (see Pugh, 
1998), this was its permanent state. 
BRACT. (Fig. 4). Two types of bract were present; the first long, up 
to 50 mm, and narrow (Fig. 4A); the second shorter and broader (Fig. 
4B, C). Both possessed a pair of prominent, lateral cusps. These 
Fig. 2 Erenna richardi. A. upper and B. lower views of mature nectophore. C. detail of folded back thrust block. Scale bar 5 mm. aw axial wing; cp 
conical protuberance: n nectosac; pa pallial canal; ped pedicular canal; ral, ril, rvl apico-, infra- and vertical lateral ridges; tb thrust block. 
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