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[Annelida] Trochochaeta revison and Spionid fertilization biology

Vasily Radashevsky via annelida%40net.bio.net (by radashevsky from gmail.com)
Wed Aug 29 04:20:00 EST 2018


Dear Annelideans,

 

Please find below information about two papers that have just been
published. They are not Open access publications and the PDFs can be
requested from me or the co-authors.

 

Radashevsky, V.I., Rizzo, A.E. & Peixoto, A.J.M. (2018a) First record of
Trochochaeta japonica (Annelida: Spionidae) in Brazil with identification
key to species of the genus. Zootaxa, 4462 (4), 566–578.

                http://dx.doi.org/10.11646/zootaxa.4462.4.8

Abstract: Polychaetes of the spionid genus Trochochaeta occur mainly in the
northern hemisphere, including North and Central America. In South America,
they have been reported only from the northeast region of Brazil – Sergipe
and Paraíba – despite numerous biological investigations around the
continent. In 2006, a dense population (up to 7000 individuals per square
meter) of Trochochaeta was discovered in the estuary of Santos, São Paulo,
Brazil, hosting the busiest container sea port in Latin America, and in
2008, one Trochochaeta specimen was found in Camamu Bay, Bahia. We identify
these worms as Trochochaeta japonica Imajima, 1989 and describe and
illustrate their morphology. This is the first record of the species from
outside of its type locality in Honshu, Japan. It might have been introduced
to the estuary of Santos as larvae in ballast water of ocean-going vessels.
We review the systematics of Trochochaeta and provide an identification key
to 12 currently recognized species.

 

 

The latter paper, however, has a URL providing 50 days' free access to the
PDF. Anyone clicking on this link before October 14, 2018 will be taken
directly to the final version of your article on ScienceDirect, which they
are welcome to read or download. No sign up, registration or fees are
required.

 

 <https://authors.elsevier.com/a/1XckM3SCZM7wxF>
https://authors.elsevier.com/a/1XckM3SCZM7wxF

 

Radashevsky, V.I., Yurchenko, O.V. & Alexandrova, Y.N. (2018b) Fine
structure of the gametes and spermiogenesis in Spiophanes uschakowi
(Annelida: Spionidae) from the Sea of Japan, with comments on fertilization
biology in broadcast-spawning spionids. Micron, 115 (1), 32–40.

                http://dx.doi.org/10.1016/j.micron.2018.08.005

Abstract: Spiophanes uschakowi is a common polychaete living in tubes in
sandy sediments in shallow waters of the Sea of Japan. Females and males
release their gametes into the water where fertilization and holopelagic,
planktotrophic larval development occur. In females, oogenesis is
intraovarian: vitellogenesis occurs when the oocytes grow in paired ovaries
attached to genital blood vessels in fertile segments. The developed oocytes
are accumulated in the coelomic cavity prior to spawning. The newly released
oocytes are lentiform, 185–200 µm in diameter, with honey-combed envelopes
5–7 µm thick. Each oocyte has 41–49 cortical alveoli regularly arranged in a
peripheral circle, a nucleus 80–83 µm in diameter, and a single nucleolus
about 30 µm in diameter. In males, spermatogonia proliferate in testes and
the rest of spermatogenesis occurs in the coelomic cavity. During
spermiogenesis, the acrosomal vesicle migrates from the posterior to the
anterior part of the spermatid. The spermatozoa are ect-aquasperm with a
plate-like acrosome 0.58 ± 0.06 µm thick and 2.14 ± 0.13 µm in diameter,
barrel-shaped nucleus 2.23 ± 0.13 µm long and 3.18 ± 0.13 µm in diameter,
short midpiece 0.93 ± 0.09 µm long with five spherical mitochondria, two
centrioles and one small lipid droplet, and a flagellum 62–63 µm long with 9
× 2 + 2 organization of microtubules. The acrosome is a complex
heterogeneous structure with 4–6 subspherical apical bodies, and numerous
small branched basal cisternae. The anterior end of the nucleus is truncate,
while its posterior end has wide shallow depressions accommodating the
mitochondria. The centrioles are situated in the center of the midpiece
between mitochondria and oriented obliquely to each other. The structure of
the gametes of broadcast-spawning spionids is reviewed and the roles of
surface granules in species-specific attraction of sperm toward eggs by
releasing chemical signals (sperm chemotaxis), and cortical alveoli as a
place of penetration of spermatozoa into oocytes (micropyle) are suggested.
The lentiform oocytes of Spiophanes spp. are unique among Spionidae by their
shape, while spermatozoa are unique by their plate-like acrosomes.

 



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