Streblospio gynobranchiata, a new spionid polychaete species (Annelida: Polychaeta) from Florida and the Gulf of Mexico with an analysis of phylogenetic relationships within the genus Streblospio

14 Pages·1998·5 MB·English

by  Stanley A Rice

PROCEEDINGS OF THE BIOLOGICAL SOCIETY OFWASHINGTON
lll(3):694-707. 1998.
Streblospio gynobranchiata, a new spionid polychaete species
(Annelida: Polychaeta) from Florida and the Gulf of Mexico with an
analysis of phylogenetic relationships within the genus Streblospio
Stanley A. Rice and Lisa A. Levin
(SAR) Department of Biology, University of Tampa, Tampa, Florida 33606 U.S.A.; (LAL)
Marine Life Research Group, Scripps Institution of Oceanography,
La JoUa, California 92093-0218 U.S.A.
—
Abstract. Streblospio gynobranchiata, anew species ofspionidpolychaete,
is described from Florida and the GulfofMexico. This species is distinguished
by the presence of strap-like branchiae, beneath which larvae are brooded, in
the genital body region of the females. Data from experimental crosses con-
ducted in the laboratory are presented that indicate incipient reproductive iso-
lation between S. gynobranchiata from Florida and S. benedicti from North
Carolina and California. The spermatophores produced by males of S. gyno-
branchiata and S. benedicti are described for the first time. Morphological,
developmental, and reproductive characteristics are used in combination to con-
struct a cladogram that suggests possible phylogenetic relationships between
known species in the genus Streblospio.
Genus Streblospio Webster, 1879 1989. Paratypes: 17 males (USNM
— 178824), 8 females (USNM 178823), same
Diagnosis. The genus Streblospio was
collection data as holotype.
established by Webster (1879) based upon
material from New Jersey. Distinguishing Additional material prepared for scan-
features of the genus include: conical, ning electron mic—roscopy (SEM): Stub #1
(USNM 178825) 4 anterior ends, collect-
rounded prostomium with 2-4 pairs ofeyes
ed 22 Jun 1987, Hillsborough River, Tam-
and with or without a small nuchal tentacle;
pa, Florida, at the University of Tampa,
peristomium fused with the first setiger and depth 2 m, muddy sand; Stub #2 (USNM
forming a U-shaped envelope around the
178826)—2 adults, collected 23 Mar 1987,
pofropsatlopmsiaunmdlaotnerealplayiranodfvbenrtarnaclhliya;eonoenptahier same a—s Stub #1; Stub #3 (USNM
178827) 4 anterior ends, collected 4 Aug
peristomium; a dorsal collar across the dor-
sum of setiger 2; notosetae all capillary, (19U8S8,NMsam1e78c8ol2l8.)d—at4a aasntheorlioortypeen;dsS,tusbam#5e
neurosetae include capillaries, multidentate coll. data as Stub #3; Stub #7 (USNM
hooded hooks and ventral sabre setae; and
178829)—4 adults, coll. 26 Mar 1987,
pygidium simple, with ventral lappets or
same coll. data as holotype; Stub #8
without appendages.
(USNM 178830)—5 adult females, coll. 2
Streblospio gynobranchiata, new species MStauyb #1998(7,USsNaMme1c7o8ll8.31d)at—a5 aasdulhtosl,otsyapmee;
Fi—gs. 1-13 coll. dat—a as Stub #8; Stub #10 (USNM
Type material. Holotype: adult female 178832) 6 adults, same coll. data as Stub
(USNM 178822), length 8.4 mm, Tampa #8; Stub #11 (USNM 178833)—3 adults,
Bay, Florida; Courtney Campbell Cause- coll. 1 Apr 1987, same coll. data as holo-
way (west): depth 1 m, muddy sand, 27 Jul type.
VOLUME NUMBER
111, 3 695
Figs. 1-4. Streblospio gynobranchiata, new species (USNM 178830): 1, whole female with characteristic
brood structures; 2, posterior dorsal portion of female showing strap-like brood structures; 3, lateral view of
brood structures in female; 4, dorsal view ofmost anteriorbrood structures and notosetae. Scales = 200 \ymfor
1; 100 ixm for 2, 3.
—
Other material examined. Massachu- the subtidal estuarine sediments of the
setts: Provincetown, coll. H. E. Webster, Hillsborough River adjacent to the Univer-
type (USNM 415), 6 specimens + 3 frag- sity of Tampa—in downtown Tampa.
ments; San Francisco Bay, Berkeley Beach, Etymology. The specific name, gyno-
coll. O. Hartman, 27 Jul 1934, (USNM branchiata, refers to the branchiate brood
20220) 8 paratypes; New Jersey, Little Egg structures found in mature females of this
Inlet, coll. 17 Apr 1972, (USNM 71677) 8 species. The prefix is from the Greek, gyne,
specimens, (USNM 71678) 22 spe—cimens; meaning woman or female plus the suffix
SEM preparations: B—ox #7, Stub #4 1 an- from the Greek, branchia, refering to
terior end. Stub #6 3 anterior ends, coll. "gills." —
Bogue Sound, North Carolina, coll. L. Lev- Description. Prostomium elongate
in; Cultured material: Sebastian River, Flor- and rounded anteriorly, flanked laterally
ida, 29 Mar 1993; Copano Bay, Texas, 18 by peristomial ridges leading to ventral
Oct 1983; Godineaux, Trinidad 3 Apr 1984; mouth. One pair ofpalps located lateral to
Ballast Point, Tampa Bay, Florida 6 Jun prostomium and median to peristomial
1984. — ridges. Palps short; about same length as
Distribution. Streblospio gynobran- adjacent branchiae and densely ciliated on
chiata has been collected from the east and frontal surfaces (Figs. 1, 5). One pair of
west coasts ofFlorida, Texas, and Trinidad. thick, ciliated branchiae insertedjust pos-
The type locality is Tampa Bay, Florida in terior to palps. These branchiae with dis-
696 PROCEEDINGS OFTHE BIOLOGICAL SOCIETY OF WASHINGTON
tal digitiform appendage terminally (Fig. erally between noto- and neuropodium and
6). Small conical nuchal tentacle present extending dorsally as thin digitiform ap-
between branchiae (Fig. 7). Nuchal ten- pendage resembling a branchium. Devel-
tacle difficult to see without removing oping larvae loosely held between branchi-
branchiae. ae by brooding females. Posterior to bran-
Notopodium of setiger 1 with 1-3 cap- chiate region on females are dorsal, seg-
illary setae and no postsetal lobe (Fig. 5). mentally arranged extensions of epidermis
First neuropodium with 3-6 capillary setae forming branched, ciliated appendages in
and flap-like postsetal lobe. Second noto- rows between left and right notopodia (Fig.
podium with 6-12 capillary setae and 9). Three orfourofthese extensionspresent
broad, postsetal lobe continuous withdorsal on posterior setigers to near end of body.
hood thatextends across dorsumconnecting Cilia on these epidermal extensions ar-
left and right notopodia. Anterior margin of ranged in discrete tufts.
hood flares upward and forms opening into Males of Streblospio gynobranchiata
dorsal pouch that extends posteriorly to end produce spermatophores in laboratory cul-
of third setiger (Fig. 5). Second neuropo- tures in the presence or absence offemales.
dium with 6-8 capillary setae and broad These spermatophores are composed of a
flap-like postsetal lobe. Notopodia of fe- sickle-shaped proximal piece and a distal
males situated along lateral sides of body sperm ball (Fig. 11). The proximal piece is
anterior to branchiate region but shifted divided into two regions: a thick coarsely
mm
dorsally throughout branchiate region (se- granular region (0.28 long and 0.12
mm
tigers 20-35) and on posterior setigers. No- wide) further from the sperm ball and
mm
tosetae in branchiate and posterior body a curved, conical, tapering region (0.24
mm
regions longer than anterior notosetae. No- long and 0.08 wide at widest point)
topodial lobes flap-like through anterior leading to and attached to the sperm ball.
one-half of body, becoming digitiform and The former, thickregion has a groove down
shifted dorsally toward posterior. Neurose- one side that ends at the junction between
tae capillary in setigers 1-6. Ventralmost it and the conical region (Figs. 11, 13). The
capillary seta in neuropodia 3-6 stouter conical region is smoother than the thick
mm
than others and curving ventrally under region. The sperm ball measures 0.51
body. Neuropodial hooded hooks and sabre in diameter and is spherical in shape (Fig.
setae beginning on setiger 7 and continuing 12). The dimensions of the spermatophore
to end ofbody (Figs. 8, 10). Hooded hooks components vary with the size ofthe worm
accompanied by 1-3 small anterior capil- producing them, with larger worms releas-
lary setae to near end of body. Single in- ing larger spermatophores. In cross-section,
ferior sabre seta present in each neuropo- the material making up the thick and coni-
dium from setiger 7 to end of body (Fig. cal regions ofthe spermatophore appears to
8). Hooded hooks number 2-4 in setiger 7 be composed of fibrous material of un-
to 6-8 near end of body; each hook with known composition. The sperm ball is sur-
three or four pairs ofsmall teeth in addition rounded by a thin layer of this fibrous ma-
to main unpaired tooth (Fig. 10). Neuro- terial. Only mature sperm are found inside
podial lobes flap-like on setigers 1-6, de- the sperm ball. These sperm are oriented
creasing in size posteriorly. parallel to each other and closely packed
Brood structures present on females from inside the sperm ball with their tails ex-
about setiger 20 to about 35 (24-35 in ho- tending in a single direction. In fresh sper-
lotype), small in anterior and posterior matophores, the sperm tails have a refrin-
regions, reaching maximum size in middle gent color in reflected light and move in
of range (Figs. 1-4). Largest pouches com- slow synchronous beating motions. Sper-
posed ofbroad semicircular fold arising lat- matophores ofthe same general structure as
VOLUME NUMBER
111, 3 697
H
^^H
M^
^ ^^^
f^. 1
feg
1
^^^B
^- ^^
^^^^^91 Bs^wfc^^'1
Figs. 5-10. Streblospio gynobranchiata, new species (5, 9, USNM 178829; 6, USNM 178831; 7, USNM
178828; 8, 10, USNM 178830): 5, lateral view of anterior end with branchia (B), palp (P), and hood (arrow)
visible; 6, distal tip of branchium showing finger-like extension (arrow): 7, lateral view of anterior end with
right palp and branchium removed to expose the nuchal antenna (arrow); 8, lateral view of posterior setigers
showing hooded hooks (H) and sabre setae (S), sabre setae are ventral to the hooded hooks; 9, dorsal view of
female posterior to brood structures showing segmental epidermal extensions with tufts of cilia; 10, hooded
hooks from posterior setiger showing pairs ofsmall teeth distal to the main tooth. Scales =100 |xm for 5; 50
|xm for 6, 7; 25 |xm for 8, 9; 5 (xm for 10.
698 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
Figs. 11-13. Streblospiogynobranchiata, new species: 11, whole spermatophore asreleasedbymale; arrows
indicate region enlarged in Fig. 13; 12, sperm ball attached to end of spermatophore; 13, central portion of
spermatophore (region between arrows in Fig. 11) showing central groove and texture ofmaterial ofspermato-
phore. Scales = 100 |xm for 11; 25 |xm for 12, 13.
—
described above were produced in labora- Biology. Streblospio gynobranchiata
tory cultures of S. benedicti from North is found in estuarine to marine conditions
Carolina and Los Angeles. The mature in shallow-water sediment. Worms may
sperm of S. gynobranchiata are greatly form dense assemblages of tubes in
elongate with a mean head length (nucleus stressed or disturbed habitats. Larval de-
plus acrosome) of 41.15 |xm (n = 150). velopment is planktotrophic with brood-
VOLUME NUMBER
111, 3 699
ing to the three-setiger stage followed by tions were shown to be interfertile but fe-
release into the plankton and settlement at males from interpopulational crossestended
about 9-12 setigers. Females that are to produce larvae characteristic of their
forced to leave their tubes while brooding original population. The production of dif-
may drop their embryos prematurely. ferent larval types was not affected by tem-
Male worms produce spermatophores (de- perature or food availability in populations
scribed above) that are incorporated into of S. benedicti from North Carolina (Levin
ventrally located seminal receptacles in & Creed 1986), although S. benedicti from
the females. Site offertilization and trans- Narragansett Bay increased brood sizes in
port of mature oocytes into brood struc- response to elevated nutrient levels in me-
tures have n—ot been observed. socosm studies (Levin 1986). The demo-
Remarks. In Webster's (1879) original graphic consequences ofplanktotrophy ver-
description of Streblospio benedicti, ref- sus lecithotrophy in S. benedicti have been
erence is made to the genital pouches in addressed by Levin, et al. (1987), Levin &
females: "On one specimen the middle Huggett (1990) and Levin & Bridges
third ofthe dorsum was covered by a very (1994). A genetic basis for this polymor-
thin, transparent, raised membrane." phism in S. benedicti was demonstrated by
(Webster 1879: 121). Webster (1879) did Levin et al. (1991).
not use the term "pouches" to describe Buchanan (1890) described a species,
these female structures; however, exami- Streblospio shrubsolii (originally Hekater-
nation of worms from Little Egg Inlet, obranchus shrubsolii) from Sheppey, En-
New Jersey (USNM 71678) revealed
gland, that differed from S. benedicti by
brood pouches on females similar to those lacking a median nuchal tentacle (conical
typically seen in worms from North Car-
papilla or cirrus) on the first segment, lack-
olina and California. Webster (1879) did
ing the conical dorsal cirri on posterior se-
not mention what have been called "sabre
tigers, and lacking thoracic nephridia. Ad-
setae" in the neuropodium from setiger 7
ditional features ofS. shrubsolii that distin-
to the end of the body nor did he describe
the pairs of small teeth located above the guish it from S. benedicti include: the first
main tooth on neuropodial hooded hooks. appearance of hooded hooks on setiger 8;
He refers to the hooded hook morphology the apparent lack of ventral sabre setae; the
as: ". they have four terminal teeth, the two-lobed dorsal hood on setiger 2; and the
. . 2 rows of small teeth on hooded hooks.
outer one being shortest ..." (Webster
1879: 121). Examination of the material Subsequent examinations ofthis species re-
from New Jersey (USNM 71678) by SEM vealed differences in egg diameter, location
revealed that sabre setae begin in setiger of the first gametogenic setiger, larval de-
7 and continue to near the end ofthe body velopment, brood structures on females,
and that the neuropodial hooded hooks and isozyme frequencies. According to Ca-
have 3 or 4 pairs of small teeth in addition zaux (1985) and our unpublished observa-
to the main unpaired tooth. The morpho- tions (LAL), S. shrubsolii from France ex-
logical and reproductive characteristics of hibit mature ova 200-230 |xm in diameter,
the species in the genus Streblospio are with one large larvabroodedbetweentrans-
summarized in Table 1. verse ridges on each segment. Development
Levin (1984) reported that Streblospio is direct in this species. In an examination
benedicti displayed different patterns oflar- of four enzyme systems (PHI, MDG-2,
val development over its range with some ADH, and IDH), individuals ofStreblospio
populations producing lecithotrophic larvae shrubsolii (n = 12) were fixed for com-
and others producing planktotrophic larvae. pletely different isozymes than plankto-
Planktotrophic and lecithotrophic popula- trophic individuals (n = 8-70) and leci-
700 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
—
Table 1. Morphological and reproductive characteristics ofdescribed species ofStreblospio.
Streblospio
Streblospio Streblospio benedicti
Streblospio benedicti shrubsolii japonica
gynobranchiala Webster Buchanan Imajima
Character newspecies 1879 1890 1990
Body length (mm) 8.4 6-12 6-10 7
No. of segments 70 70 48 48
Pairs ofeyes 2-3 2-3 2-A 2
Nuchal antenna on 1st segment present present absent present
Branchial pairs 1 1 1 1
Start ofhooded hooks (setiger) 7 6/7/8/9 8 7
No. hooks per ramus
anterior 3^ 3-5 2-3 5-6
posterior 8-10 8-12 5 ?
Dorsal collar one piece one piece 2 lobes one piece
Brood structures branchiate pouches transverse, mid-seg- ?
mental ridges
First saber seta 7 7 ? 3
Rows ofsmall teeth on hooded 3-A 3-4 2 5 pairs
hooks
Pygidium simple simple or lobed simple 2 lappets
Egg diameter (ixm) 70-90 70-90 (plankto- 200-230 ?
trophic)
100-220 (lecitho-
trophic)
Larval development planktotrophic planktotrophic and Direct ?
lecithotrophic
Larval swimming setae yes yes (planktotrophic) no ?
no (lecithotrophic)
Number oflarvae per brood 100-200 200-400 (plankto- 7 ?
trophic)
30-70 (lecitho-
trophic)
Sperm head length (|xm) 41.15 47.81 9 7
thotrophic individuals (n = 10-60) of S. the other species, as well as a differentmor-
benedicti. phology of the egg envelope (K. Eckelbar-
Studies of oogenesis in Streblospio have ger, pers. comm.). These differences sug-
revealed differences in yolk bodies that ap- gest interspecific divergence in female ga-
pear to vary with species and developmen- mete morphology similar to that reported
tal mode. The size ofyolk granules and rel- for sibling species of Capitella (Eckelbar-
&
ative proportion of heterosynthetically-de- ger Grassle 1983).
rived yolk differs between planktotrophic Horst (1909) described an additional spe-
and lecithotrophic forms of S. benedicti cies of Streblospio (5. dekhuyzeni) from
(Eckelbarger 1980, 1986). Prehminary ul- Zuide Zee, France that had two types of
trastructural studies suggest that average capillary notosetae and more hooded hooks
yolk body diameter in S. shrubsolii (6.8 per ramus than S. shrubsolii. These differ-
jjtm) is greater than that in S. gynobran- ences were minor enough to lead most tax-
chiata (3.2 |xm) from Fort Pierce, or from onomists to consider S. dekhuyzeni and S.
&
planktotrophic (2.6-3.2 |xm) or lecitho- shrubsolii synonyms (Fonseca-Genevois
trophic (3.2-5.3 |xm) S. benedicti. The ma- Cazaux 1987).
ture egg of S. shrubsolii contains large Hartman (1936) described Streblospiolu-
quantities of lipid droplets not evident in tincola from several locations along the
VOLUME NUMBER
111, 3 701
central California coast. She (pg. 46) con- from Los Angeles. The location of the first
sidered this new species to differ from 5". gametogenic setiger in males of S. gyno-
benedicti in having a "... much smaller branchiata (15.66 ± 9.98, n = 35) is not
ventral peristomial fold, and its much larger significantly different from that of plank-
prostomium." Streblospio lutincola was lat- totrophs of S. benedicti from Fort Pierce
er synonymized with S. benedicti (Hartman (9.0 ± 2.28, n = 6).
1944). In females of Streblospio gynobranchia-
Foster (1971) proposed a synonymy of ta, the location of the first gametogenic se-
all previously described species making the tiger is significantly different from that of
genus Streblospio monotypic. In a note at S. benedicti (planktotrophs and lecitho-
the end of her treatment of the genus (pg. trophs), and S. shrubsolii (Table 2). In ad-
115), she mentions a population of Streb- dition, the percent gametogenic setigers, the
lospio collected from Maracaibo estuary location ofthe first brood structure, and the
that has branchiate brood structures in fe- total number of brood structures is signifi-
males. This appears to be the first mention cantly different between S. gynobranchiata
of S. gynobranchiata in the literature. and S. benedicti (Table 2).
While Streblospio gynobranchiata gen- Reproductive isolation has been reported
erally possesses a more southerly distri- between Streblospio gynobranchiata from
bution than the other described species of Tampa Bay, Florida and S. benedicti from
Streblospio, it has been reported in the North Carolina and from Los Angeles, Cal-
same geographical regions as S. benedicti. ifornia (Rice 1991). Experimental crosses
For example, lecithotrophic 5". benedicti between populations were undertaken with
have been collected from Big Slough in worms that had been raised in isolation un-
Aransas Bay, Texas and 5". gynobranchia- til sexual maturity then paired with a mate
ta from an attached estuarine system, Co- from an exotic population (experimental) or
pano Bay, Texas. Planktotrophic S. bene- from the same population (control) and
dicti from Fort Pierce, Florida were col- monitored for production of larvae. Fe-
lected within a few km of the Sebastian males from unsuccessful interpopulational
River system where S. gynobranchiata crosses were subsequently paired with
occurs. It is unknown whether these pat- males from their own population to ensure
terns of distribution are natural or the.re- female fertility. In 28 reciprocal crosses be-
sult of anthropogenic transport since tween Tampa Bay and North Carolina
Streblospio may be transported in ship worms, 26 crosses produced no offspring
ballast water from one location to another (see Rice 1991, table 11). In six crosses be-
(Carlton 1975). tween Tampa Bay females and Los Angeles
Imajima (1990) described a new subspe- males, no offspring were produced.
cies {Streblospio benedicti japonicd) from In a separate series of experimental
the Yatsu tidelands, Japan. This new form crosses, we were able to successfully cross
differs from S. benedicti in having ventral Streblospio gynobranchiata from Copano
sabre setae beginning on setiger 3 and by Bay, Texas with lecithotrophic S. benedicti
having 5 pairs of small teeth in addition to from Big Slough, Texas. We also found lar-
the main unpaired tooth on the hooded val production in limited crosses between
hooks. females of S. gynobranchiata from Tampa
The mean length ofthe sperm (acrosome Bay and males (planktotrophic) of S. be-
+ nucleus + middlepiece) from spermato- nedicti from Tar Landing, North Carolina,
phores is significantly different {P < 0.001) indicating that reproductive isolation be-
between Streblospio gynobranchiata (41.15 tween these two (or more) species is not
|xm ± 4.22, n = 150) from Tampa Bay and complete.
S. benedicti (47.81 jim ± 2.83, n = 150) In an experimental cross between one
1
702 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
—
Table 2. Reproductive characteristics ofmature females ofStreblospio species. Underlinedmean values are
not significantly different (P > 0.05).
S. benedicti S. benedicti Analysisof
Characteristic (planktotrophs) (lecithotrophs) 5.gynobranchiata S. shrubsolii Variance
Total setigers
mean 47.8 45.0 46.6 51.3 F = 1.502
std. dev. 6.4 10.7 11.8 6.5 P = 0.2146
number 68 97 79 6
First gametogenic setiger
mean 10.5 12.7 7.7 19 F = 217.2
std. dev. 1.1 1.3 2.0 1.1 P = 0.0001
number 7 80 78 6
% gametogenic setigers
—
mean 38.3 34.6 45.4 — F = 12.7
std. dev. 8.7 6.8 8.7 — P = 0.0001
number 6 18 61
First pouch/branchium —
mean 21.2 21.6 20.0 — F = 7.46
std. dev. 2.2 1.9 3.6 — P = 0.0007
number 69 94 66
Total pouches/paired branchiae
M —
mean 9^ 14.5 — F = 16.97
std. dev. 2.7 2.7- 11.5 — P = 0.0001
number 69 92 66
male of S. gynobranchiata from Copano At present, there appear to be at least
Bay, Texas and one female of 5'. shrubsolii four species ofStreblospio that can be dis-
from Sully Island, Wales, larvae were pro- tinguished based upon morphological
duced after 12 days butwere misshapen and characteristics (Table 1). Streblospio gy-
did not survive. In two experimental cross- nobranchiata differs from S. benedicti in
es between males of S. gynobranchiata its more southern distribution, the pres-
from Trinidad and planktotrophic females ence of branchiate brood structures on fe-
ofS. benedicti from North Carolina, no lar- males, the presence ofposterior dorsal cil-
vae were produced. These results suggest iated appendages in females, gamete dis-
that reproductive isolation is incipient be- tribution in females, and mature sperm di-
tween S. gynobranchiata and S. benedicti mensions. Streblospio gynobranchiata
and between S. gynobranchiata and S. differs from S. shrubsolii in the distribu-
shrubsolii. Reproductive compatibility be- tion of hooded hooks (beginning on setig-
tween populations is generally considered er 7 in the former species and setiger 8 in
to be a pleisiomorphic characteristic, the latter), the incomplete dorsal collar in
whereas loss of reproductive potential be- the latter species, and the absence of a
tween closely related taxa can be consid- prostomial nuchal tentacle in the latter
ered an apomorphic characteristic. Consid- species. Streblospio gynobranchiata dif-
ering the degree of morphological differ- fers from S. benedictijaponica in the dis-
entiation (Tables 1, 2) in addition to the dif- tribution of ventral sabre setae (beginning
ferences in geographic range and on setiger 3 in the latter species) and in
reproductive isolation, it seem certain that the number of paired small teeth on the
S. gynobranchiata represents anew anddis- hooded hooks [see Ohwada & Nishino
tinct species. (1991) for a discussion of variability in
VOLUME 111, NUMBER 3 703
this character]. In addition to the differ- four equally parsimonious trees. In the con-
ences in standard morphological charac- sensus tree derived from these four trees,
teristics between S. gynobranchiata and Streblospio benedicti is grouped as the most
the other described species in the genus, plesiomorphic member ofa clade including
there are also differences in gamete mor- Aurospio dibranchiata, Orthoprionospio cir-
phology, gamete distribution (Table 2), riformia, Paraprionospio pinnata, Prion-
modes of larval development, and repro- ospio banyulensis, Prionospio steensrtupi,
ductive compatibility. — and Laubieriellus grasslei. Sigvaldadottiret
Phylogenetic relationships. The four al. (1997) point out that many characteris-
species of Streblospio were analyzed for tics of spionid genera are missing or incor-
phylogenetic relationships using the cladis- rectly reported in the literature and that res-
tic programs, MacClade 3.01 (Maddison & olution of spionid phylogeny will likely re-
Maddison 1992) and PAUP 3.1.1 (Swofford quire re-examination of species and devel-
1993). A character matrix consisting of 16 opment of new characters. Incomplete
morphological and reproductive character- literature reports and polymorphic charac-
istics was constructed from literature re- ters within species hampered resolution in
ports and personal observations (Appendix the present study also. Four characters are
1). All characters were unweighted and coded as missing in the Streblospio data
unordered. The three most parsimonious matrix for S. benedictijaponica since these
trees found via an exhaustive search (Fig. four characters were not included in the de-
14A, B, C) all consist of 30 steps (consis- scription of the species by Imajima (1990).
tency index = 0.933, retention index = Knowledge ofthese characters would likely
0.714) and were rooted using Paraprio- help to resolve the polytomy in the Stre-
nospio pinnata and Spiophanes kroyeri as blospio consensus tree.
the designated outgroups. The strictconsen- The study of variation within the genus
sus tree (Fig. 14D) groups S. gynobran- Streblospio emphasizes the value of con-
chiata and S. benedicti as a clade with S. sidering reproductive characters along
benedictijaponica and S. shrubsaliijoining with standard morphological traits when
as a polytomy. More information is needed distinguishing traits within a polychaete
concerning the characteristics ofthese latter genus. Eckelbarger and Grassle (1984)
two species in order to resolve this node. A demonstrated a similar situation in which
bootstrap analysis of 100 replicates in sibling species of Capitella are distin-
PAUP using tree-bisection-reconnection guished primarily by reproductive fea-
branch swapping, MULPARS activated, tures. Characters such as strap-like bran-
zero-length branches collapsed, and multi- chiae in the genital region of females, the
state characters interpreted as polymor- position and number of gametogenic se-
phism, resulted in the values listed on the tigers, and mature sperm dimensions dis-
branches in Fig. 14D. tinguish S. gynobranchiata from other
Sigvaldadottir et al. (1997) presented a species ofStreblospio (Table 1). In mature
cladistic analysis of the genera within the specimens, reproductive characters like
Spionidae based upon 25 morphological brood structures are more readily ob-
characters. Analysis of generic characteris- served than setal or ciliation patterns. Un-
tics, including variation between species fortunately, immature specimens of dif-
within a genus, resulted in a large number ferent species of Streblospio appear sim-
of most parsimonious trees (13305) and ilar in overt morphology and care must be
contributed little to our understanding of taken with identification in regions where
spionid relations. A second analysis using more than one species is likely to occur
only type species as generic representatives (e.g., southern USA, Europe). We expect
produced more informative results with that additional sibling species ofStreblos-