Megalomma Johansson, 1925 (Polychaeta: Sabellidae) from America and other world-wide localities, and phylogenetic relationships within the genus 2861
Author
Tovar-Hernández, María Ana
Author
Carrera-Parra, Luis F.
text
Zootaxa
2011
2011-04-29
2861
1
1
71
https://biotaxa.org/Zootaxa/article/view/zootaxa.2861.1.1
journal article
10.11646/zootaxa.2861.1.1
11755334
5286352
Megalomma coloratum
(
Chamberlin, 1919
)
Figures 7A–L
,
8A
,
9A–S
,
10A–B
,
28B
,
29B
Potamilla clara
Chamberlin, 1919: 20
.
Potamilla colorata
Chamberlin, 1919: 21
.
Megalomma coloratum
.— Knight-Jones, 1997: 318,
Figs 2M–T
.—
Tovar-Hernández
et al.
2009: 326–327
,
Figs 2c, g
,
3e–f
,
4f– g
.
Type material examined.
[
MCZ
]
2173,
holotype
of
Potamilla colorata
Chamberlin, 1919
,
California, Laguna
Beach
, low tide,
Coll. W. A. Hilton
, incomplete (last posterior abdominal segments are missing).
[
MCZ
]
2171
,
holotype
of
Potamilla clara
Chamberlin, 1919
(
Fig. 15C, E, I
),
California, Laguna
Beach
, low tide,
Coll. W. A. Hilton
, complete but broken in anterior abdomen
.
Additional material examined.
[
ECOSUR
]
Baja California
Norte,
México
, Ensenada, Playa las Rosas,
July 30, 1987
, Coll.
SISV
(11 specs,
one female
). Villa las Rosas,
March 06, 2004
(2 specs). Bahía de Todos Santos, Coll.
SISV
(3 specs).
Baja California Sur
,
México
, La Paz,
CICIMAR
,
March 01, 2004
, Coll.
PSS
,
50 cm
, on basaltic rock (3 specs).
Sinaloa
,
México
, Mazatlán, Playa Cerritos, Facultad de Ciencias del Mar,
February 27, 2004
, on rock oyster covered with red and green algae,
4 m
, Coll. Esteban (7 specs,
1 juvenile
,
one female
);
February 22, 2004
,
12 m
(10 specs).
Nayarit
,
México
, Islas Marías,
November 02, 1979
, Coll.
SISV
(
1 spec.
).
Nayarit
, North of Bucerias,
March 09, 2008
,
20° 45’ 44.7’’ N
105° 21’ 28.6’’W
, Coll
PSS
, in oyster,
OH-P
0293 (
1 spec
).
Nayarit
, La Cruz de Huanacaxtle, Vallarta Garden,
February 23, 2008
,
20° 45’ 4.3’’ N
,
105° 22’ 25.7’’ W
, Coll
PSS
, in coralline rock,
OH-P
0294 (
1 spec
).
Nayarit
, La Cruz de Huanacaxtle, Vallarta Garden,
February 23, 2008
,
20° 45’ 4.3’’ N
,
105° 22’ 25.7’’ W
, Coll
PSS
, in coralline rock,
OH-P
0295 (
1 spec
).
Nayarit
, North of Bucerias,
March 09, 2008
,
20° 45’ 44.7’’ N
,
105° 21’ 28.6’’ W
, Coll
PSS
, in oyster,
OH-P
0296 (
1 spec
).
Nayarit
, North of Bucerias,
March 09, 2008
,
20° 45’ 44.7’’ N
,
105° 21’ 28.6’’ W
, Coll
PSS
, in oyster,
OH-P
0299 (
1 spec
).
[
EMU
]
Baja California Sur
,
México
, Playa el Tesoro,
EMU
–4464, Coll. LIB,
July 17, 1996
(
1 spec.
).
Sinaloa
,
México
, Mazatlán port,
EMU
8914–8953, 2009, on metallic buoys,
50 cm
depth, Station 1:
23º 12’ 13’’ N
,
106º 24’ 31.4’’ W
, Sta. 1–I (
1 spec.
), Sta. 1–
III
(
1 spec.
), Sta. 1–IV (3 specs), Sta. 1–
V
(2 specs), Sta. 1–
VI
(5 specs), Sta. 1–VII (8 specs), Sta. 1–VIII (4 specs), Sta. 1–IX (
1 spec.
), Sta. 1–X (
1 spec.
). Station 2:
23º 12’ 13’’ N
,
106º 24’ 30.1’’ W
, Sta. 2–I (
1 spec.
), Sta. 2–II (2 specs), Sta. 2–
III
(8 specs), Sta. 2–IV (11 specs), Sta. 2–
V
(20 specs), Sta. 2–VII (2 specs). Sta. 3:
23º 11’ 48.7’’ N
,
106º 24’ 31’’ W
, Sta. 3–I (3 specs), Sta. 3–II (3 specs), Sta. 3–IV (7 specs), Sta. 3–
V
(9 specs), Sta. 3–
VI
(8 specs), Sta. 3–VII (14 specs), Sta. 3–VIII (3 specs), Sta. 3–IX (
1 spec.
), Sta. 3–X (
2 spec.
), Sta. 3–XII (
1 spec.
). Sta. 4:
23º 11’ 31.1’’ N
,
106º 24’ 43.9’’ W
, Sta. 4–I (
1 spec.
), Sta. 4–II (
1 spec.
), Sta. 4–IV (2 specs), Sta. 4–
V
(15 specs), Sta. 4–
VI
(
1 spec.
), Sta. 4–VII (4 specs). Sta. 5:
23º 11’ 8.9’’ N
,
106º 24’ 55.8’’ W
, Sta. 5–I (5 specs), Sta. 5–II (9 specs), Sta. 5–
III
(3 specs), Sta. 5–IV (
1 spec.
), Sta. 5–
V
(10 specs), Sta. 5–
VI
(
5 spec.
), Sta. 5–VII (12 specs), Sta. 5–VIII (7 specs), Sta. 5–XII (5 specs).
Nayarit
,
México
, Punta Raza,
EMU
–5113, Coll. LIB,
April 11, 1996
, coralline algae (
1 spec.
);
EMU
–5114 (
1 spec.
).
[
LACM
–
AHF
]
California
,
USA
, Point Dume, St. 404, POIDUM, SubID 4246,
34.00867º N
,
118.79386º W
, Coll. Marine Pollution Studies Lab/Moss Landing Marine Laboratories, Invasive Species Survey,
July 16, 2007
, low rocky intertidal, lots of
Chondrachanthus
, some
Codium
,
Ulva
, tunicates, anemones, small laminarians and coralline mats (8 specs). Point Dume, Sta. 404,
MLML
– 155, 1
DORG
471, 1
R
–C–1, SB ¼, 0471, Coll. Marine Pollution Studies Lab/Moss Landing Marine Laboratories, Invasive Species Survey,
January 22, 2005
, low rocky intertidal (36 specs). Point Dume, Sta. 404,
MLML
–155, 1
DORG
249, SR–2, Coll. Marine Pollution Studies Lab/Moss Landing Marine Laboratories, Invasive Species Survey,
April 05, 2005
, 5.4 m (30 specs). Velero
III
, 003488, Sta. 1139–40,
33º 50’ 30’’ N
,
118º 24’ 15’’ W
, off Redondo Beach,
3 m
, sand (
1 spec.
).
Sinaloa
,
México
, Mazatlán, F3363,
N 15196
, n 10118, reef 3.2 km N of Mazatlán, Colls E. Yale & Dawson,
June 7, 1952
, among algal clumps (3 specs).
FIGURE 7
.
Megalomma coloratum
(
Chamberlin, 1919
)
. A) Body, lateral view; B) thorax, lateral view; C) glandular ridge on chaetiger 3 as indicated with arrow; D) thorax, ventral view; E) branchial crown and thorax, dorsal view; F) ventralmost radiole; G) dorsalmost radiolar eye; H) eye from 5
th
dorsal radiole; I) abdominal tori; J–L) pygidiums. A–L) Specimens from Mazatlán, México, ECOSUR. Scale bars: A, E) 10 mm; B–D) 3 mm; F–H) 0.3 mm; I–L) 3 mm.
Diagnosis.
Eyes in dorsalmost and fifth dorsal radioles (spherical); dorsal margin of collar fused to faecal groove; a glandular ring on segment 3; thoracic chaetae
Type
C; abdominal chaetae broadly hooded.
FIGURE 8.
Scanning electronic micrographs of body and caruncle. A) Lateral view of
Megalomma coloratum
(
Chamberlin, 1919
)
from Mazatlán, México, ECOSUR; B–C) lateral and dorsal views of caruncle of
Megalomma lobiferum
(
Ehlers, 1887
)
from Ria Lagartos, México, ECOSUR. Scale bars: A) 1 mm, B–C) 0.2 mm.
Description.
Branchial crown length 2.94±0.77 mm (
n
= 100; 1.1–
5 mm
), as long as thorax (
Figs 7A
,
8A
,
9A
), with 15±2 pairs of radioles (
n
= 100; 8–21 pairs). Branchial lobes semi-circular (
Fig. 9E
). Radiolar bases olive green. Radioles with several narrow red or purple bands distributed over outer and lateral radiole margins and adjacent pinnules, each band occupies a space of 4–6 pairs of pinnules. Outer surfaces of radioles quadrangular basally, rounded distally. Sub-distal compound eyes spherical, present in dorsalmost pair of radioles (23%, n= 100) or dorsalmost and fifth dorsal radioles (77%, n= 100) (
Figs 7G
,
9N
). Eyes from fifth dorsalmost radiolar pair smaller than dorsalmost ones (
Figs 7H
,
9O–P
). Dorsalmost pair of radioles rigid, erect and longer than other radioles (
Figs 7E
,
9B
); ommatidia purple with minute small, white lens; and epithelium near to tip wider than posterior epithelium (
Fig. 9N
). All radioles with short tips (
Fig. 7F
). Dorsal collar margins square, fused to faecal groove, forming broad gap (
Figs 7C, E
,
9B–C
). Dorsal lappets absent. Dorsal pockets present (
Figs 7B–C
,
9B–C
). Epithelium of dorsal pockets translucent and very narrow, as a membrane (
Fig. 7E
). Ventral lappets rounded, not overlapped, as long as ventral shield of collar (
Figs 7D
,
9H–I
). Anterior peristomial ring not exposed. Lateral collar margins of collar covering base of radioles (
Figs 7B–C
,
9A
). Mouth located in middle of anterior peristomial ring. Two small patches of nuchal organs presented near mouth and two horns of basal lateral skeleton (
Fig. 9E
). Dorsal lips red colored, erect, triangular about 1/4 length of branchial crown, with mid-rib (
Fig. 9D
). Dorsal pinnular appendages present. Ventral lips about one quarter the length of dorsal lips, broadly rounded (
Fig. 9D
). Ventral sacs present. Caruncle and keel absent. Body plump, cylindrical, (
Figs 7A
,
8A
) green olive or pale with ventral shields cream colored and white spots surrounding the lateral sides of the faecal groove and dispersing in all thoracic dorsal epithelium. A whitish glandular ring on segment 3 (
Fig. 7C
). Total thorax-abdomen length 13.41±5.16 mm (
n
= 100; 4.1–
28 mm
) (
25 mm
holotype
), and maximum width 2.04±0.56 mm (
n
= 100; 0.8–3.8 mm) (2.2 mm
holotype
) throughout most of thorax. Thorax with 8±1 segments (
n
= 100; 4–8 segments). Thoracic tori longest on chaetigers 2–3. Tori in chaetigers 2–3 occupy the entire distance between notopodia and ventral shield margins (
Figs 7B
,
8A
), contacting shields (
Figs 7D
,
8A
). Notopodial fascicles with superior group of elongate, narrowly hooded chaetae (
Fig. 9J
); an inferior group of chaetae Type C (
Figs 9K
,
28B
). Thoracic uncini with main fang surmounted by 8–10 rows of numerous minute teeth (
Fig. 29B
), handles 1.5x length of main fang; not extending beyond base of shaft of companion chaetae (
Fig. 9R–S
). Companion chaetae with teardrop-shaped membranes (
Figs 9R–S
,
29B
). Tori slightly shorter than those on chaetiger 7 (
Figs 7I
,
8A
). Abdominal segments 42±7 (
n
= 100; 28–64 segments) (
43 holotype
). Abdominal chaetae broadly hooded (
Fig. 9L–M
); chaetae in posterior row longer than those in anterior row. Abdominal uncini with main fang surmounted by 8–10 rows of numerous minute teeth (
Fig. 9G
). Pygidium broadly rounded (
Figs 7J
,
8A
), sometimes forming two or three lobes (
Fig. 7L
). Three groups of 4–5 red pygidial eyespots, each unequalsized (
Fig. 7J–K
). Tubes covered with fine sand grains, and brown algae incrustrating.
FIGURE 9
.
Megalomma coloratum
(
Chamberlin, 1919
)
. A) Body, lateral view; B) branchial crown, dorsal view; C) thorax, dorsal view; D) dorsal and ventral lips; E) peristomium, frontal view; F) oocytes; G) abdominal uncinus; H–I) thorax, ventral views; J) superior thoracic narrowly hooded chaeta; K) inferior thoracic chaeta type C; L–M) abdominal broadly hooded chaetae; N) dorsalmost radiolar eyes; O–P) eyes from from 5
th
dorsal radiole in adult and juvenile stages, respectively; Q) ventral radiole; R–S) thoracic uncini and companion chaetae. A–S) Specimens from Mazatlán, México, ECOSUR. Abbreviations:
bls
basal lateral skeleton;
d
dorsum;
dl
dorsal lip;
ep
epithelium;
no
nuchal organ;
rs
radiolar skeleton;
v
ventrum;
vl
ventral lip. Scale bars: A–E, H–I) 1 mm; F) 15 µm; G, J–M, R–S) 20 µm; N) 125 µm.
GAMETES: From
100 specimens
selected from southern Gulf of
California
, 91% were sexually mature (32% males, 59% females) and 9% unripe. Gametes in mature females are distributed mostly from first abdominal chaetiger to the posterior abdomen, visible through the epithelium between notopodium and neuropodium. Ovogenesis is continuous throughout the entire year, except for November (no specimens were found) and asynchronous as indicated by change in shape (rounded to polygonal) (
Fig. 9F
), the appearance of the cytoplasm and oocyte size: 103.8±45.27 µm (
n
= 72; 30–180 µm). In males, sperm is distributed from median to posterior abdomen. Sperm morphology was described in
Tovar-Hernández
et al
. (2009)
. Based on branchial crown and body colour,
M. coloratum
does not show sexual dimorphism.
SPECIMEN VARIATION: Among specimens from Southern Gulf of
California
, the number of radiolar eyes was found to vary. The most common condition is the presence of two pairs of eyes in dorsalmost and fifth dorsalmost radioles (77%,
n
= 100) while eyes only present in dorsalmost radioles is less common (23%,
n
= 100). In the phylogenetic analysis presented here, this character (character 3) was scored as state 5, i.e. eyes only in dorsalmost and fifth dorsal radioles, as this was the most common distribution.
GROWTH: The relationship between the body length (y) and the number of abdominal segments (x) is described by the power function y= 0.0086x
1.9528
(r= 0.786, p<0.001,
n
= 100) indicating a continuous growth in
M. coloratum
(
Fig. 10A
). Body length (x) was significantly correlated with the branchial crown length (y) and is described by the power function y= 0.6629x
0.5775
(r= 0.837, p<0.001,
n
= 100) (
Fig. 10B
).
BARCODE: Nucleotide sequences between 433–616 bp of the section of COI gene used for barcoding were obtained from
four specimens
, two from
La Cruz de Huanacaxtle
,
Nayarit
,
Mexican Pacific
(
ECOSUR
OH-P0294
,
ECOSUR
OH-P0295
) and two from
North of Bucerias
,
Nayarit
,
Mexican Pacific
(
ECOSUR
OH-P0296
,
ECOSUR
OH-P0299
). The averange evolutionary divergence over the four sequence pairs was 0.9
%.
Remarks.
Chamberlin in 1919 described
Potamilla clara
and
P. colorata
from low tide in
Laguna
Beach,
California
. Original descriptions of both species are brief, do not include diagnostic characters and lack illustrations.
Hartman (1938)
stated that the
type
of
P. clara
is a
Megalomma
and has affinities with
M. roulei
(Gravier)
. Later, in the catalogue of the polychaetes of the world,
Hartman (1959)
listed the
type
of
Potamilla colorata
as
Megalomma
sp.
Hartman (1969)
recorded
M. roulei
from Corona del Mar, southern
California
, but her diagnosis is a translation of original description by
Gravier (1908a)
, illustrations were redrawn from
Gravier (1909)
and her materials were not located at LACM in order to confirm identification. At the end of her diagnosis (pp. 710) Hartman stated that “The record from
California
may refer to
Megalomma pigmentum
, if it is shown that the oculate radioles have short, instead of long free tips”. Later, in 1995, Knight-Jones labeled the
type
of
P. colorata
as “this is not synonymous with
M. roulei
but a good species of
Megalomma
”. Knight-Jones (1997) synonymized
M. clara
with
M. modestum
(
de Quatrefages, 1866
)
and provided a redescription for
M. coloratum
. In this study, the synonymy between
M. clara
with
M. modestum
proposed by Knight-Jones is not supported since both species have distinguishable features (see remarks on
M. modestum
) and
M. roulei
is declared as
insertae sedis
(see remarks on
M. roulei
). Based on examination of both
types
(
M. clara
and
M. coloratum
), these constitute the same species. Apparently, pigmentation was the only feature used by Chamberlin to describe the taxa as different species. Individuals of
M. coloratum
from Mazatlán show some variation in body color: some bodies are olive green, others pale, and radioles have narrow red or purple bands distributed over outer and lateral radiole margins.
FIGURE 10
. Relationships between biometrical features in
Megalomma coloratum
(
Chamberlin, 1919
)
.
As stated above, original descriptions of
M
.
clara
and
M. coloratum
both are brief, do not include diagnostic characters and lack illustrations. Both species names were simultaneously published by
Chamberlin (1919)
:
M. clara
on page 20 and
M. coloratum
on page 21. We follow the recommendations of article 23.9 (and subsequents) of the International Code of
Zoological Nomenclature (1999)
to consider
M. clara
as a
nomen oblitum
and
M. coloratum
as a
nomen protectum
since the last name has been widely used in the literature. Furthermore, the
type
material of
M. coloratum
was characterized and illustrated by Knight-Jones (1997) and
Tovar-Hernández
et al
. (2009)
provided a complete description of the morphological features including some reproductive characters.
The most distinctive character separating
M. coloratum
from other species from the tropical Eastern Pacific (
M. carunculata
,
M. circumspectum
,
M. gesae
,
M. pacifici
and
M. pigmentum
) is the presence of a dorsal, broad whitish glandular ring on segment 3. On the other hand,
M. cinctum
from
Taiwan
has two glandular rings on segments 2 and 3 respectively, but in
M. cinctum
the branchial crown is shorter than the thorax (as long as thorax in
M. coloratum
) and the radiolar tips are short dorsally, increasing gradually towards ventral radioles (all short in
M. coloratum
).
The specimens reviewed here agree with the description provided by Knight-Jones (1997) for the type of
M. coloratum
, described from
Laguna
Beach (
California
) except that the type has just one pair of subdistal eyes in the dorsalmost radioles. All adult specimens reviewed here, have eyes in dorsalmost and fifth dorsalmost radioles (77%,
n
= 100) while in juveniles, eyes are only present in dorsalmost radioles (23%,
n
= 100). This variation is not surprising since as
Fitzhugh (2003)
pointed out, there exists variation in the number of radiolar eyes in
paratypes
of
M. cinctum
, although the most common condition is the presence of only one pair of eyes on the dorsalmost radioles. For
M. interrupta
,
Capa and Murray (2009)
recorded the presence of eyes only in dorsalmost and lateral radioles, but the eyes in lateral radioles can be absent entirely from some specimens.
Information on the reproductive biology of species of
Megalomma
is scarce, but in
M. coloratum
and in
M. vesiculosum
,
M. bioculatum
and
M.
carunculata
gonochorism and gametes distributed in abdominal segments seems to be a pattern.
Megalomma coloratum
is native in the Californian Province, known from Mazatlán and southern
California
(
USA
) from intertidal and shallow waters (
12 m
). In the Mazatlán port (
México
) it is a very common hull fouling species, found on floating docks, metal buoys, and also on rock oysters covered with red and green algae. On metal buoys it reaches densities about 4–80 ind/m
2
.