Journal of the Marine Biological Association of the United Kingdom, page i of 3.    ?2008 Marine Biological Association of the United Kingdom 
doi:io.ioi7/Soo253i54o8ooi288 Printed in the United Kingdom 
Protohydra leuckarti near Plymouth 
C.C. KILVINGTON^, A.G. COLLINS^, I.A. KOSEVICH^, S.V. PYATAEVA^ AND E.A. ROBSON"^ 
'6 Fisher Road, Stoke, Plymouth, PL2 3BB, UK, ^National Systematics Laboratory of the NCAA Fisheries Service, National Museum 
of Natural History, MRC-153, Smithsonian Institution, PC Box 37012, Washington, DC 20013-7012, USA, 'Department of 
Invertebrate Zoology, Faculty of Biology, MV Lomonosov Moscow State University, Moscow 119991, Russia, ''School of Biological 
Sciences, AMS Building, University of Reading, Reading, RG6 6AJ, UK 
A new location for Protohydra leuckarti is reported near Plymouth at Millbrook Lake (Tamar Estuary). To place this finding 
in context, notes follow on a familiar habitat of this species in the White Sea, and on the general ecology and distribution of 
Protohydra and its enigmatic phylogeny. 
Keywords: Hydrozoa, Protohydra leuckarti, Plymouth, meiofauna, phylogeny 
Submitted 19 October 2007; accepted 23 November 2007 
Published records of the solitary hydrozoan Protohydra leuck- 
arti Greeff 1870 in the Plymouth area refer only to the River 
Tavy at Bere Ferrers and the estuary of the River Plym at 
Chelson Meadow (Baker, 1912; Hickson, 1920; Lebour, 
1930; Marine Biological Association of the United Kingdom, 
1957). Its presence at Millbrook Lake, a shallow creek near 
the mouth of the River Tamar, is reported in this preliminary 
note. It was found by C.C.K. during the period March 1970 to 
February 1971 while sampling estuarine oligochaetes, and was 
still present at this site in June 2007 (National Grid Reference 
SX 4401 5245)- 
The surface sediment consists mainly of silt with small 
amounts of sand and is relatively firm when exposed. At 
high water marine conditions obtain, with the salinity of 
standing water in depressions at low tide, up to 35.45 ppm 
(determined by silver nitrate titration). After heavy rain, 
lower saUnities were recorded (10.40-24.20 ppm). 
In 1970-1971 the meiofauna was sampled at regular 
monthly intervals from a 5 m^ fixed quadrat situated at 
about mid-tide level, by means of a simple coring device. 
Sediment samples were taken to a depth of 10 cm using a 
clear plastic tube (internal diameter 3.1 cm) with a piston 
for expelling the core. A 10 cm length of core was cut into 
2 cm sections as it was extruded. Ten cores were taken at 
random within the quadrat, furnishing 50 samples which 
were preserved within 4 h of collection by adding 4% formal- 
dehyde solution containing 0.2% rose Bengal. The meiofauna 
was extracted later by stirring gently with tap water, giving a 
suspension that was washed into a small sieve (250 |xm). 
The residue was sorted in a flat glass dish under a stereobino- 
cular microscope, and specimens stored in 70% ethanol (see 
Hulings & Gray (1971) in Fenchel, 1978). 
The meiofauna was dominated numerically by small 
worms: polychaetes {Manayunkia aestuarina Bourne and 
Streblospio shrubsoli Buchanan), and oligochaetes in smaller 
numbers    (mainly    Tubificoides    (=Peloscolex)    benedeni 
Corresponding authors: 
C.C. Kilvington and E.A. Robson 
Email: e.a.robson@reading.ac.uk 
Udekem). Nematodes and copepods, upon which P. leuckarti 
often feeds (Help & Smol, 1976) were less numerous. 
Preserved P. leuckarti were approximately 1 mm long and 
deeply stained with rose Bengal. They were all in the top sec- 
tions of cores (at 0-2 cm depth): see Table 1. In the course of 
12 months 94 polyps were found in 1.8 1 of sediment. 
The presence of P. leuckarti at this site was confirmed in 
June 2007 by a field excursion. Surface mud was collected at 
the same samphng station or next to it (10 separate samples, 
total volume 1.2 1). Suspensions of mud in seawater were fil- 
tered on a 250-|jLm sieve which retained sand grains together 
with strands of filamentous green alga {Enteromorpha sp.). 
This material was allowed to stand in Petri dishes and scruti- 
nized at intervals under a stereobinocular microscope. Over a 
24 h period five living polyps were found. They were identified 
by observing nematocysts under the microscope with the help 
of Dr Carina Ostman. All were from a 300 ml sample collected 
within 25 m of the original site where the mud was firmer, 
possibly due to a slightly higher sand content. No other 
polyps were found, suggesting that P. leuckarti may be 
unevenly distributed over small areas (see also Table 1). 
The author (I.A.K.) who found the live specimens is fam- 
iliar with P. leuckarti and its habitat in the vicinity of the 
White Sea Biological Station of Moscow State University, 
at 66?34'N 33?o6'E (see Bozhenova et at., 1989; Stepanjants, 
1989). It is found there in muddy sand in the middle part of 
the intertidal zone (estimated proportion of sand at least 
80%; grains of medium size). The location is marked by the 
presence of Arenicola marina, Macoma baltica and sometimes 
Mya arenaria. The characteristic meiofauna consists of har- 
pacticoid copepods, nematodes, small gastropods (Hydrobia 
sp.), oligochaetes and polychaetes. The salinity is on average 
18-24 ppm and may fall to ~5 ppm. Seawater temperatures 
range from 12-14?C (summer) to below zero (winter). The 
White Sea polyps are usually observed adhering to organic 
particles by the basal peduncle but they can move interstitiaUy 
by peristalsis. They readily catch and engulf prey (e.g. nema- 
todes). In summer, the surface sediment of an area 20 x 
20 cm may contain 10-20 polyps, among which it is not 
uncommon to find individuals undergoing transverse fission. 
Protohydra leuckarti was first recorded in the White Sea at 
Seldjanaya Bay, an intertidal brackish habitat near a small 
C.C. KILVINGTON ET AL. 
Table i. Protohydra leuckarti in intertidal mud samples from MiUbrook 
Lake (all found at depth 0-2 cm). 
Date Number per 10 cores 
1970 
March 
April 
May 
June 
July 
August 
September 
October 
November 
December 
1971 
January 
February 
Total 
Nil 
Nil 
1 
Nil 
26 
29 
6 
7 
16 
94 
Stream, consisting of muddy sand (Stepanjants, 1989; 
Anokhin, 2001; and personal communications). 
The ecology and distribution of P. leuckarti are considered 
by Mclntyre (1969) and Fenchel (1978) in general reviews of 
meiobenthos. Protohydra leuckarti appears almost cosmopoli- 
tain in its distribution (e.g. Omer-Cooper, 1964; Clausen, 
1971; Anokhin, 2001; Schuchert, 2006; Sergeeva, 2006). It is 
recorded from a wide range of brackish marine sediments. It 
is euryhaline and tolerates pollution and low oxygenation. 
Its habitat preferences differ from those of cnidarian psammo- 
fauna (Teissier (1950) in Delamare-DebouttevOle, i960; 
Swedmark, 1964; Stepanjants, 1989). It occupies the top 
layer of sand or muddy sand, usually with detritus or else a 
surface diatom layer. In common with other vermiform inter- 
stitial species its robust burrowing behaviour and adhesive 
ability ensure survival. 
The population ecology of P. leuckarti has been studied by 
Muus (1966, 1967), Help (1971) and Help & Smol (1976). It 
feeds voraciously on copepods, nematodes or small poly- 
chaetes, capturing passing prey by means of nematocysts. 
Protohydra leuckarti is a top predator and influences the 
structure of prey populations (Heip, 1977). In favourable con- 
ditions it multipUes asexually (Muus (1967) records up to 20/ 
cm^). In contrast, the life cycle oi Protohydra remains largely 
unknown. Several authors have described gonads (ovaries 
with a single large oocyte, or testes) and although sexual indi- 
viduals are not uncommon, fertilization and the course of 
embryonic development have not yet been observed 
(Nyholm, 1951; Muus, 1966). 
Protohydra has an evolutionary history that is shrouded in 
mystery. Its simple form makes it very challenging to infer its 
relationship to other hydrozoans. Nevertheless, Protohydra 
has traditionally been classified (in its own family 
Protohydridae) close to Hydridae (e.g. Naumov, i960; 
Bouillon, 1985; Schaefer, 1996). Hydridae contains species of 
Hydra, which have made such excellent model organisms 
that more is known about their biology (from development 
to genomes) than that of any other cnidarians. If 
Protohydridae were shown to be the sister group of 
Hydridae, it would make an important point of comparison 
when assessing the generality of features studied in Hydra. 
However, Petersen (1990) noted that Protohydra could con- 
ceivably share an ancestry with any number of different 
groups of capitate hydrozoans, given its relative lack of char- 
acters. More recently, Stepanjants et al. (2000) suggested that 
Protohydra and Hydra may have independent origins from 
within Corymorphidae. Molecular data have since confirmed 
a close relationship between representatives of 
Corymorphidae and Hydridae, in the clade dubbed 
Aplanulata (CoUins et al, 2005, 2006). Genetic data extracted 
from our new samples oi Protohydra should allow the shroud 
to be lifted so that we might see a bit into the past of this fas- 
cinating animal. 
ACKNOWLEDGEMENTS 
The Marine Biological Association of the United Kingdom is 
thanked for providing laboratory space and facilities. C.C.K. 
thanks Dr P.E. Gibbs, Dr E.G. Southward and Dr E.D.S. 
Corner for their help. Dr S.D. Stepanjants kindly furnished 
Russian texts with English translations. 
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Correspondence should be addressed to: 
C.C. Kilvington 
6 Fisher Road 
Stoke 
Plymouth 
PL2 3BB 
UK 
emaU: e.a.robson@reading.ac.uk