ux (2 Veas 1. we, 
Bull. nat. Hist. Mus. Lond. (Zool.) 67(2):169-182 
\ 
Issued 29 November 2001 

A review of the genus Erenna Bedot, 1904 
(Siphonophora, Physonectae) 

P.R. PUGH 
Southampton Oceanography Centre, Empress Dock, Southampton SO14 3ZH 
SYNOPSIS. 

The status of the poorly known physonect genus Erenna is reviewed in the light of the collection, by submersibles, 
of specimens in excellent condition. The few previous descriptions had been based on only the tentacles, or on other parts in poor 
condition. Two species have been described, E. richardi Bedot, 1904 and E. bedoti Lens & van Riemsdijk, 1908, and there has 
been some debate as to whether they are conspecific or not. It is concluded here that they are conspecific. Two further Erenna 
species, E. laciniata sp.nov. and E. cornuta sp.nov., are described, together with a third, closely related species, Parerenna 
emilyae sp.nov. The distinctiveness of their tentilla, with uncoiled hypertophied cnidobands, and the nectophores with a basic 
ridge pattern and a muscle-free zone at the apex of the nectosac, is considered sufficient to warrant the transference of these 
species into a new physonect family, the Erennidae. 
INTRODUCTION 
Very little is known about the physonect genus Erenna, and speci- 
mens have rarely been identified. In fact, the first species, E. 
richardi Bedot, 1904, was originally described from only six tenta- 
cles found attached to the rope of a fish trap brought up from a depth 
of 5310 m somewhere between Portugal and the Azores. However, 
these tentacles bore highly distinctive tentilla of a type not previ- 
ously known for any siphonophore, with uncoiled, hypertrophied 
cnidobands (stinging bands), and with the gastrodermal walls of the 
gastrovascular cavity packed with dark granules. Bedot (1904) 
made a detailed histological study of these tentilla and suggested 
that they probably belonged to a physonect siphonophore. 
A second species, Erenna bedoti Lens & van Riemsdijk, 1908, 
was described from a denuded specimen collected during the Siboga 
Expedition. From the fragmented material, with many appendages 
containing black pigmentation, Lens and van Riemsdijk (1908) 
deduced that the species was a physonect siphonophore, and they 
assigned it to the family Forskaliidae. Although they could compare 
only the tentacles and tentilla with Bedot’s (1904) material, they 
reasoned that their material could be referred to a different species 
because the free end of the cnidoband, on the more developed 
tentilla in their material, lay proximally, whereas it was distal in E. 
richardi. However, most subsequent authors have considered E. 
bedoti to be conspecific with E. richardi. 
Bigelow (1911, p. 271) mentioned another specimen of Erenna 
richardi, in poor condition: “In fact the condition is so bad that it is 
impossible to state whether or not it is specifically identical with the 
‘Siboga’ example. Nor, for that matter, is it clear whether the latter 
is distinct from Bedot’s E. richardi.’. However, he, like Lens and 
van Riemsdijk (1908), considered that its closest relatives were the 
forskaliids. Moser (1925) described a further specimen collected in 
the Bay of Biscay, which consisted of only a poorly preserved 
siphosome. She noted that the gastrozooids appeared not to have a 
pedicle (stalk), and that their gastrodermal lining contained black 
granules. On the basis of the structure of the gastrozooids and 
tentacles she considered that it could not be a forskaliid siphonophore 
and she likened it to a bathyphysid (Order Cystonectae), but noted 
that the latter lacked nectophores. 
Tentacles, with characteristic tentilla were collected, in the north- 
east Atlantic on two further occasions (Leloup, 1936), but then no 
© The Natural History Museum, 2001 
further specimens of Erenna species were recorded until Totton 
(1965) found three more. These were all in poor condition, but 
sufficient for the mature nectophores and bracts to be described and 
illustrated for the first time. The apex of the nectosac of the large, 
flattened nectophores was found to be muscle-free; and the radial 
canals could have more or less well-developed ‘horn’ canals ascend- 
ing into the mesogloea. The bracts were said to have two pairs of 
lateral processes. 
Margulis (1969) added to the description of the nectophores of 
Erenna richardi, noting that there were two small processes on the 
ventral side of the thrust block (the central region that abuts the 
stem) and that ‘horn’ canals were not always present on the lateral 
radial canals. In a later paper (Margulis, 1977) she described this 
specimen in more detail and concluded, from the shape of the mature 
tentilla, that it could be referred to Erenna richardi. However, she 
then briefly discussed possible differences from Lens and van 
Riemsdijk’s (1908) specimen and concluded that E. bedoti was also 
a valid species. Margulis (1990) used these differences to describe a 
further specimen of E. bedoti collected in the southern Pacific. 
Recently, other specimens of E. richardi have been briefly described 
and/or recorded (Pugh, 1975; Musayeva, 1976; Alvarifo, 1980; 
Leloup, 1980; Daniel, 1985). 
In recent years, specimens of Erenna species have been collected 
by the submersibles Johnson-Sea-Link (JSL) I and II, and these are 
here used to give a more detailed description of E. richardi, together 
with descriptions of two other, previously undescribed, species that 
can be referred to the same genus. In addition, another JSL speci- 
men, that is closely related to the genus Erenna, will be described. 
The taxonomic status of these species is discussed below and it is 
concluded that they should be separated off into a new family. The 
validity of E. bedoti also is discussed. 
Family ERENNIDAE fam. nov. 
DIAGNOSIS. Physonect siphonophores best characterised by their 
uncoiled tentilla bearing a hypertrophied cnidoband with nematocysts 
of three types: large anisorhizas and two types of smaller ones (? 
haplonemes). Terminal process devoid of nematocysts. Nectophores 
with basic ridge pattern of apico-, infra- and vertical laterals; with 
apical muscle-free zone on nectosac; radial canals straight or slightly 
curved. Ostium, without mouth plate, opening basally. 
