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Proc. Arthropod. Embryol. Soc. Jpn. 48, 59–60 (2017)Ⓒ 2017 Arthropodan Embryological Society of Japan
ISSN 1341–1527

Preliminary Notes on the Life History of a Pycnogonid, Ammothella
biunguiculata (Pycnogonida, Ammotheidae): Comparison between thePopulations of Izu and Kii Peninsulas*1,*2
Yuichi MOCHIZUKI1–3) and Katsumi MIYAZAKI1, 4)
Department of Zoology, Division of Biological Science, Graduate School of Science, Kyoto University, Kyoto 606–8502, Japan
Seto Marine Biological Laboratory, Field Science Education and Research Center, Kyoto University, Wakayama 649–2211, Japan3)
Kyushu Environmental Evaluation Association, Fukuoka 813–0004, Japan
4)
Department of Environmental Science, Faculty of Science, Niigata University, Niigata 950–2181, Japan
E-mail: miyazaki@env.sc.niigata-u.ac.jp (KM)
1)
2)

Ammothella biunguiculata is a pycnogonid species
belonging to the family Ammotheidae and inhabiting shallow
water in Sagami Bay and southward in Japan. They have beenrecorded also in the Mediterranean Sea (original description),
the Pacific coast of North America, Hawaii, Korea, Australia
and Madagascar, and considered to be pantemperate (Child,1987). Miyazaki (2002a, 2002b) reported the endoparasitic
larval forms of A. biunguiculata in an actinian, Entacmaea
actinostoloides (synonymized to E. quadricolor after Dunn(1981) and Yanagi (2006)) in the population of Shimoda, Izu
Peninsula. In the population of Shirahama, Kii Peninsula,
however, the larvae were found as free-living (Miyazaki,2002b). In the present study, we conducted the monthly
samplings in Shimoda and Shirahama to compare the life
history between the two populations.
For the population of Izu Peninsula (Izu population),
specimens of E. quadricolor were collected monthly (n = 10–20) from tide pools at the tip of Noroshi-Zaki point near theShimoda Marine Research Center, University of Tsukuba
from May 2012 to June 2013 excepting October, December,and March due to a typhoon or a stormy weather. The parasitic
pycnogonids were extracted from the dissected actinians, andthe developmental stages, the body length and the number ofpycnogonids per host were recorded. We also collected freeliving individuals under the boulders of the same location inJuly, August, September, December 2012 and January 2013.
For the population in Kii Peninsula (Kii population), themonthly collection of free-living A. biunguiculata (n = about100) was conducted from intertidal zone near the Seto Marine
Biological Laboratory, Kyoto University, from May 2012 toJuly 2013. Collected specimens were observed in the same
way as those of the Izu population. The ratio of ovigerousmales (adult males with fertilized eggs or embryos on theirovigers) and of adult females with mature oocytes in theirpedal ovaries was also recorded. Most specimens of the Kii

population were released to their habitats after examination.
We collected several specimens of Entacmaea actinians fromthe same locality of the Kii population, but no pycnogonids
could be found. Some fixed specimens of both populations
were stained with a chitin-specific fluorescent dye, Uvitex 2B(Polysciences) followed by Yoshinaga et al. (2010) to enhance
the segmentation pattern on trunk and legs which wasessential to decide the postembryonic stages.
From the Izu population, we sampled 629 pycnogonid
specimens from 182 actinians in total. We could divide 11
postembryonic stages from protonymphon (hatching larvae)
to adult in this population (Mochizuki and Miyazaki, in press).
There were parasitic larvae from second to tenth (subadult)
instar on host actinians, but no adults. The first instar wascollected only from the free-living ovigerous males. From Julyto August, the number of parasitic larvae per host was very
low, and in September, no larvae were found. The number hada peak at January, and then decreased again in the next spring
season. The second instar occurred only in November andJanuary, which showed the period of recruitment of parasitic
larvae to the host actinians. These newly larvae should havebeen fertilized in summer season. Free-living adults as wellas ninth and tenth instars were collected from July to January.
Ovigerous males were recorded only in December andJanuary. Considering the period of the occurrence of ovigerous
males and of the parasitic larval recruitment, there are twopossibilities about the reproductive period of the Izu
population. One is that the breeding period continues fromsummer to winter, and the other is that it occurs twice a year,
summer and winter. As the sampling duration of the freeliving individuals was limited, further discussion isimpracticable.
From the Kii population, we sampled 1511 specimens intotal. Protonymphon larvae (first instar) clinging the ovigersof adult males and free-living individuals from sixth instar to*1 Abstract of paper read at the 49th Annual Meeting of the Arthropodan Embryological Society of Japan, June 7–8, 2013 (Tsukuba-san, Ibaraki)*2 This article, which was accepted in 2013 and should have been published in 2014, was printed in 2017 being much delayed due to various circumstances.

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adult were collected, but no larvae from second to fifth instars
could be found from this population. We found some specimens
in the postembryonic stage apparently between the eighthand ninth of the Izu population, and thus the Kii populationshows at least 12 instars. The youngest (= sixth) instar first
appeared in January. Adults occurred throughout the year, andpredominated from September to December. Ovigerous
males appeared between October and May, which showed thereproductive period. The ratio of their number had a peak inDecember exceeding 80%. The fluctuation of the ratio of adultfemales with mature oocytes showed a similar pattern to thatof the ovigerous males. Considering these fluctuation
patterns and the reproductive period, the Kii population
apparently has an annual life cycle. Collecting of larvae before
sixth instar is necessary to complete the life history in thispopulation.
There are some remarkable differences on life history
between the Izu and the Kii populations of A. biunguiculata
such as the mode of larval life (endoparasitism or free-living),
the presumed number of postembryonic stages, and thereproductive period. In addition, we have found a distinct
difference in the spinning spines at larval chelifores(Mochizuki and Miyazaki, unpublished data). These
differences suggest that the two populations represent twodifferent species though we could not detect any differencesin adult morphology. Another possibility is that the differencein the larval spinning spines is a case of adaptive phenotypic
plasticity reflecting their modes of life. Further phylogenetic
study is required to resolve the problem.

Krapp for his useful comments on the early version ofmanuscript. The present study was carried out in part as a
joint-research (No. 25–18) in Japanese Association for Marine
Biology (JAMBIO).
References
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Miyazaki, K. (2002a) Occurrence of juvenile forms of a pycnogonid,Ammothella biunguiculata (Pycnogonida, Ammotheidae) in anactinian, Entacmaea actinostoloides (Anthozoa, Stichodactylidae).
Proceedings of the Arthropodan Embryological Society of Japan, 37,43–44.
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endoparasitictoanactinian

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Acknowledgments: We are grateful to Mr. Y. Tsuchiya andMr. Y. Yamada, the Shimoda Marine Research Center (SMRC),
University of Tsukuba, for their assistance for the collection ofactinians. We also express our sincere thanks to Dr. FranzDevelopment of a sensitive method for the detection of young
larvae of the parasitic pycnogonid Nymphonella tapetis in Manila
clam Ruditapes philippinarum. Fish Pathology, 46, 38–41.