19Proc. Arthropod. Embryol. Soc. Jpn. 52, 19–21 (2019)Ⓒ 2019 Arthropodan Embryological Society of Japan
ISSN 1341–1527[SHORT COMMUNICATION]

Outline of the Life History and Postembryonic Development in a
Pycnogonid, Nymphopsis muscosa (Pycnogonida, Ammotheidae) atIzu Oshima Island, Japan
Katsumi MIYAZAKI1) and Osamu HOSHINO2)
Department of Environmental Science, Faculty of Science, Niigata University, 8050 Ikarashi 2-no-cho, Niigata 950–2181, Japan
Diving Service Chap, 118–2 Okata Shinkai, Oshima, Tokyo 100–0102, Japan
E-mail: miyazaki@env.sc.niigata-u.ac.jp (KM)1)
2)

Pycnogonids, or sea spiders are a small group of marine
arthropods usually classified in the class Pycnogonida.
A recent comprehensive review of the developmental
pathways of pycnogonids (Brenneis et al., 2017) disclosedthat the accumulation of information on the life history
and postembryonic development of pycnogonids was still
incomplete.
Nymphopsis muscosa Loman, 1908 is an ammotheid
pycnogonid recorded from Malaysia to Sagami Bay at 12 to 300
meters depth (Nakamura and Child, 1991), and more recently
also from Papua New Guinea and Vanuatu [datasets from OBIS(Ocean Biogeographic Information System)]. In the present
study, the authors outline the life history and postembryonicstages of N. muscosa based on semi-monthly collections and/or underwater observations.
Specimens at various postembryonic stages werecollected and photographed by one of the authors (OH) during
scuba activities from 20–30 m depth off Akinohama-Beach, Izu
Oshima (Fig. 1). Sampling sites were about 100–150 m distantfrom the shore entry point. These sites were visited several
days in every month from April 2017 to March 2018 except for
November when the sites were temporarily covered by mudlike contamination. In total 112 specimens were collected byhand. Many specimens were photographed underwater by aNikon D810 with a close-up lens, INON UCL-67 or Nauticam
SMC-1. All specimens were found on the hydroids, Dentithecahertwigi and Plumularia sp. (all months), or D. habereri coveredby a zoanthid, Parazoanthus gracilis (from December to March).

Fig. 1 Sampling locality of Nymphopsis muscosa specimens examined. Asterisk indicates the location of Akinohama-Beach.

20K. MIYAZAKI AND O. HOSHINOTable 1 Appendicular article number and morphological features in each stage of Nymphopsis muscosa.
StageABCDEFGHI
Adult

app1(ch)
33
3
3
33
3
3
3
3

app2(pa)lalalalala33
569

app3(ov)
la−
−
−−−
−
lt
rs
10

Appendages
wl1
wl2−
−
lb
7999999−−−lb
799
999wl3

wl4−
−
−
−
lb
799
99−
−
−
−
−
lb
7999

Morphological features
la: in same size and proportion

wl1: femur and 1st tibia undivided; tarsus and propodus undivided
wl2: same as wl1 of Stage D
wl3: same as wl1 of Stage D
wl4: same as wl1 of Stage D
wl length: 1=2=3>4
wl length: 1=2=3=4, genital pores absent
genital pores present

app: appendage, ch: chelifore, la: larval appendage, lb: limb bud, lt: low tubercle, ov: oviger, pa: palp, rs: rod-shaped, wl: walking leg.

Specimens at various stages of postembryonic development
were found clinging firmly to the hydroids by their chelifores
and later also by walking legs following their appearance.
Collected specimens were observed under stereoscopicor biological light microscope, and nine postembryonic stages(Stage A–I) were distinguished based on the article numbersof each appendage and other morphological features (Table1). The size and the proportion of the “Stage A” specimens
correspond closely to the previous figures by Loman (1908)
and to SEM photographs by Nakamura (1987) of the hatchinglarvae (protonymphon larvae) of N. muscosa. Compared withthe previous studies on the postembryonic development inother ammotheids (Morgan, 1891; Okuda, 1940; Gillespie andBain, 2006; Mochizuki and Miyazaki, 2017), the incomplete
number of palp articles and the still non-articled ovigers at“Stage I” suggest further one or more stages before reaching
adult stage. The type of hatching larvae (protonymphonlarvae), the pattern of walking leg development (sequential),and its mode of life (parasitic on hydroids) show that the modeof postembryonic development in N. mucosa corresponds tothe “Type 1” of Brenneis et al. (2017). This type of development
is widely reported not only in the Ammotheidae but also in
the families Endeidae, Nymphonidae and the Pycnogonidae(Brenneis et al., 2017).
In N. muscosa, the newly developed walking legs are
made up of seven articles in the Stages D to G (Table 1).
The fourth article subsequently divides to form the femur
and the first tibia, and the sixth article to form the tarsus andthe propodus. The nine-articled leg is then complete. This
progressive pattern of walking leg development is completely
concordant with that shown in the genus Tanystylum (Morgan,1891; Gillespie and Bain, 2006).
The various developmental stages were easily observedin close-up photographs. The monthly data provided a goodoutline of the life history of N. muscosa over a twelve-month
period (Table 2). Three cycles from the earliest to the latest
developmental stages are suggested a year in the Izu-Oshima
population during the period (April to March). Significantly,
no adult specimens were collected during the present study.
There is no reported association between adult N. muscosa andhydroids (Loman, 1908, 1911; Stock, 1953, 1954; Utinomi, 1959;

Table 2 Nymphopsis muscosa collected in each month.
MonthA2B
11C
11DStageEFGHIApril 2017
May101June
11July11 1022August
14September
1153October☆
November
No data (no dives).
December☆
January 2018
☆ ☆
February
215March☆ ☆ ☆
☆: developmental stage identified by close-up photographs.

AdultNakamura, 1987), suggesting that specimens would leave their
host hydroids prior to maturity and reproduce elsewhere.
Adults may move unexpected distances far away, as the adultwalking legs of N. muscosa are provided with numerous longspine-like projections, which would enhance their ability torise into the water column utilizing a strong kicking action
thereby to be carried by the tides while remaining suspended.
Acknowledgments: The authors thank Dr. Masakazu
Aoki of Tohoku University for his providing an opportunity tostart the present study. Thanks are also due to Dr. David A.
Staples of Museum Victoria, Australia, for the English editing,Dr. Hiroshi Namikawa of National Museum of Nature andScience, Tokyo for the identification of host hydroids, and Dr.
Yoshie Takahashi of Hokurei Junior and Senior High School for
providing some literature.
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