At this time, four additional species, unreported by Wilson [1932], can be added to the list of those species to be found within the limits of the bay. These are Acartia tonsa Dana, Cyclops vernalis Fischer, Diaptomus spatulocrenatus Pearse, and Paracalanus crassirostris Dahl var. nudus nov. The specimens from which identifications were made were collected by means of Clarke-Bumpus nets, in use on the motor ship "Mahatru.

Davis, Charles C.

English

Aquatic Commons

BOARD OF NATURAL RESOURCES 
State of Maryland 
Department of Research and Education 
On Four Species of Copepoda New to 
Chesapeake Bay, with a Description 
of a New Variety of Paracalanas .r, ( ,  
CHARLES C. DAVIS 
January, 1944 
Publication No. 61 
Chesapeake Biological Laboratory 
Solomons TsIand, MaryIand 
State of Maryland 
DEPARTMENT OF RESEARCH AND EDUCATION 
Commissioners: 
E. N. Cory, Chairman ..............,.... . ..................................................................... -- l e g  Park 
R. R. Bassett  -.,..-.,,.,,...................~................-....................~..-........-....-......~..-.-.......~.,...v............. CrisfieZd 
. BerthoIf ....,..... . u...,...........-.-.....,.,..-.-..M..-. ,".-...-....-.....--,s-......-... yes tmins ter  
Julian D. Corrington ................................................................................ - C h e s t e r t o m  
B. H. Willier ,,., ............. . ..................................................................................... Baltimore 
Dkector : 
R. V. 'Pr~jtltt.~ .,.. ..................-....-...-.-......--.-..*... S~o~omons Island 
State Weather Service : " 
/ 
................. J. R. W e e k s ,  B. E., Sta te  Meteorologist ................................................... Baltimore 
Chesapeake Biological Leborat ory : 
G .  I?. Bleaven, M .  A., Biologist I ,  Oyster Investigations, Resident Manager 
E. Eugene Cronin, M .  S., Biologist 11, Grab .lnvastigations 
R. 6. Hammer, M.  S., Biologist I I ,  Fisherg Investigations. I n  eh.arge of 
Hatcheries 
'Harvey Mister, Captain, Fish CuEt'~krist 
Marcella E. Cassady, Secretary 
R. A. Olson, Ph. D., Biologist II.  I n  charge of Hgdrography and Pollutioa 
(Ac t i ve  Duty, U .  S. Naval Reserve) 
Dorothy C. Morse, M. S., Assistant Chemist 
Richard E. Tiller, M. S., Biologist 11, F i s h e m  Investigations 
WilIis L. Tressler, Ph. D., Planktologist. A s s i s t m t  Professor of  Zoology, 
Universitg of Maryland 
R. V. T m i t t ,  Ph. D., Biologist 
O N  FOUR SPECIES OF COPEPODA NEW TO CHESA- 
PEAKE BAY, WITH A DESCRIPTION OF A 
NEW VARIETY OF PARACALANUS 
CRASSIROSTRIS DAHL 
Wilson (1932) l has r2eported forty-three spccies of Copepoda from 
Ch'esapeake Bay, or from its very mouth. At this time, four addition'al 
speciles, unreportled by Wilson, can be added to the list of those species 
to b'e found within thle limits of the bay. These are Acartia tonsa 
Dana, Cyclops vernalis Fischer, Diaptomus spatulocrenatus Pearse, and 
Paracalanus crassirostris Dahl var. nudus nov. T h e  speci~mens from 
which the identifications were made were collected by means of Clarke- 
Bumpus nets, in use on the motor ship "Mahatru." Must of the 
specimens were collected during the regular hydrography cruise from 
the Chesapeake Bioclogical Laboratory, in August, 1942, but #some were 
obtained on special cruises at other times, especially during th'e winter 
months of 1942-1 943. 
Acartia tonsa Dana, 1848,3 was present in nearly all the plankton 
samples (examined, but it was not found in the samples taken off Perry- 
ville, at the very head of the bay, where the water is completely firesh. 
It oocurred, however, off Ho.we.11 Poinl at the mouth of thie Sassafras 
River in water where the chlorinity amounted to 0.4 per millle only. 
It was also founld at the hydrsographic station off Cape Charlles City, 
Virginia, wh'eve the chlorini ty conditions approached those of the 
ocean, as well as at all (of the intervening stations. It  was usually 
present in large numbers, as a rule bleing the dominant animal form of 
the plankton, and for this reason it is  ema ark able that its presence in 
the Chesapeake Bay plankton had previously been overlooked. In 
certain tows taken in water in deep stagnant holes, on the othleir hand, 
where the oxygen contlent was very low, there w'ere few specimens, 
and those that were present were frequently in poor condilion, and 
were ,evidently exarnp1,es that had died in the superficial, oxygen-rich 
water, and driftled down into the lower reaches. T h e  species was 
sometimes (during the winter months) found together with A. clausi 
Giesbrecht. Wilson had reported A. clausi as the most abundant 
copepud speciles in the bay, while he did not mention the presence of 
A. tonsa. However, A. tonsa was always the more common of the two 
in the tows whose contents are ~urnrnari~zed here. 
1 Wilson, C. B. 1932. The Copepod Crustaceans of Chesapeake Bay. Proc. U. S. Nat. 
Mus., Vol. SO, Art. 15, pp. 1-54. 
2 Giesbrecht, W. 1892. Systematik und Faunistik der pelagischen Copepoden des Golfee 
von Neapel und der angrenzenden Meeres. R. +F~iedi%rrde+ and Sohn, Berlin. Pp. 508, 511, 
518-521; p1. 30, figs. 7, 24 ,34; pl. 43, figs 6, 10. 
A. tonsn is easily 'distinguishable from A. clausi by the presence of 
well developed r~s t r a l  filaments, which are entirely lacking in clausi, 
as wlell as by the structure of the fifth legs. The  terminal (second) 
segment of thle female fifith leg in clausi tapers smoothly to a point, 
whereas in tonsa, thfe segment bears coarse teeth about two-thirds of 
the distance from thfe ptdximal border, distal to which the segment 
suddenly decreases in width anld tapers to a point as a hair-like process. 
Thle easle with which the two species can be distinguished after la mini- 
mum of ldisslection makes it unlikely that Wilson was mistaken in his 
identiification. The  apparent change in the dominant copepod species 
w'ould indi~at~e ,  an important ecological evolution in the Chesapeake 
Bay over the course of brily a few years. 
Cyclops uernalis Fiscber, 1853,"as founfd only in the strictly fresh 
water off Stump Point at Perxyville, Maryland, on August 27, 1942. 
This is just outside the mouth of the Susquehanna River, and at the 
very head of thle bay. The samples that were available for analysis by 
Wilson were not taken. north of the mouth of the Patapsco River, 
where thle water is considerably brackish. 
Diaptornus spatulocrenatus Pearse, 1906,4 is another strictly fresh 
watler species that occurred only at the Stump Point hydrographic 
station, on August 127, 1942. 
Paracalanus+ cmssirostris Dahl, 1894 var. nudus  nov. was found at 
the following statisns, all near the middle of the bay: off Cape Charles 
City, off Wolf Trap Light, off the 'Great Wicomico River, off Point-No- 
Point, off Cove Point, and off the southern tip of Tilghman's Island. 
These statilons were, all occupied in August, 1942. P. crassirostris is 
notleworthy as the ,smallest known species of Calanoid copepod. Fe- . 
males occurred rather consistently in the tows examined from the 
lower portion of thle bay, but always in small numbers. No male 
specimens were encountleued. The tows all were taken, however, with 
a silk net of coarse (No. 6) mesh, and thus no true picture of the 
distribution or abundanlce of this small species was obtained, since 
most examplles passed through the net uncaptured. 
Diagnosis of variety nudus  nov.: Other authors describing P. 
crassirostris have made no attempt to rlecognize distinct varieties, and 
laicking specimens from other lscaliti~es, it will not be possible to 
accomplish this task at this time either, beyond a description of the 
Chesapeake variety. Chesapeake specimens differ from all others that 
have been described having a less well developed spiny armature on 
the posterior faces of the rami of the swimming legs, and hence the 
variety was nam'ed nudus.  The> second leg is entirely naked in this 
xtespect, which is true of no other specimens in which the slecond leg 
has been described. 
3 Gurney, Robert. 1933. British Fresh-Water Copepoda. Vol. 3. Cyclopoida. Ray Society, 
London. Pp. 198-210, figures 1598-1625. 
4 Pearse, A. S. 1906. Fresh water Copepoda of Massachusetts. Amer. Nat., Val. 40, 
pg. 246, figures 6-9. 
Dahl's (1894) description of P. crassirostris is very short an'd doles 
not describ'e the species in much 'etail. Ch,esapeake specimens differ 
fr'om his in that the second segment of thle fifth l'eg is much longer 
in poportion to the first segment. 
Scott's (1894) ~ p e c i m e n s ,  which he d~escrib~eld as P. pygrnaeus 
(Claus) , are similar tso those !of Chesapeake Bay, but the exopod of the 
second antenna is only half the length of the 'endoped instlead of the 
rami being subdequal as in n u d u s .  In additilon to having more spines 
on thje posterior faces of the second, third and fourth legs, Scott's 
specimens are provided with serrate outer margins on the second and 
third segments of the outer ramus, whereas these are present in n u d u s  
only on the third segment. The  furcal rami of Scott's specimens we 
relativiely shorter than in nudus .  
Chesapeake specimens differ from those describesd by Gurn~ey (192'7) ' 
in several characteristics. Thqe last two segments of thle first antenna 
of n u d z ~ s  are equal in length, where in Gurney's specimens thle last 
segment is longer than the peiiultimate in the ratio of 21 to 16. Alsoi 
in Gurney's specimens thle first antennae reach the furcal rami, where 
in n u d u s  thley reach only to the middle of the uros~ome. Th'e second 
segment of the fifth leg is relatively short?; in Gurney's . . specimens. 
A description of the salient [eat-ures of Ch.esapeake4emale specimens 
follo'ws: - c 
B o d y  (Plate I, figures 1 and 4) . Length 0.476-0.567 mm. T h e  
proportional parts of the body are duch .as described and figured by 
other authors. Scott, however, figured .the furcal rami relatively 
shortler. The rostrum (Plate I, figures 2. and 6) , as is ~h~aracte~ristic of 
th.e species, is short and thick, and the two branchtes are not filamentous. 
, 
First a n t e n n a  (Plate I, figure 5) .  These are sufficiently long to 
reach about th.e middle of the urtosomle: This agrees with previous 
descriptions except that of Gurnley, who says they rleach the furcal rami. 
Each antenna clonsists of twenty-four segments, of which the last two 
,are equal in length (Gurney reported the last segment as longer than 
th'e penultimate in thle ratio of 21 to 16) . 
Second a n t e n n a  (Plate 11, figure 1) .  The rami are approximately 
equal in length, in contrast to the specimens reported by Scott, in 
wh,ilch thle exopod was described as only onme-half th'e length of the 
endopod. The  endopod in Chesapeake specimens consists of seven 
segments. 
M a n d i b l e  (Platie I, figures 7 and 8). The  masticatory portion is 
provided terminally and subterminally with numerous small teeth, 
5 Dahl, F. 1894. Die Copepodenfauna des hnteren Amazonas. Ber. Naturf. Ges. Freiburg, 
Vol. 8, pg. 21, figs. 27-28. 
1 6 Scott, T,. 1894. Report on Entomostraca from the Gulf of Guinea, collected by John 
Rattray, B. Sc. Trans. Linn. Soc. Lond., Ser. 2, .Val. 6, Pt. 1, pg. 27, pl. 1, figs. 1-8. 
7 Gurney, Robert. 1927. Report on the Crustacea, Copepoda and Cl+docera of the Plankton. 
Trans. 2001. Soc., Pt. 2, 1927, pg. 144, figs. 16B; 17. . * 
arranged in a complicated manner. On the inn'er corner there is a 
large double tooth, giving the whole masticatory' portion a very dif- 
ferent appearance than in that d P. pawus (Claus). The  palp is 
small and the rami are approximately equal in length. 
First maxilla (Plate I, figure 10). Typical of thle genus. The  
first inn,er lobe bears nine heavy setae. The endopod consists of five 
segments. 
Second maxilla (Plate I, figure 9 ) .  There are six segments, T h e  
first segment blears two inlner lobes, each of which has two hleavy setae. 
The  second segment bears three such lobes, the first with three, the 
second and third with two setae. The third segment has one inner 
lobe and it bears three setae, one of which is shorter and stouter than 
the others. Th'e other three segments are very short and bear one 
to three setae each. 
Maxilliped (Plate 11, figure 2) .  Typical of the genus. 
First leg (Plate 11, figures 5 and 6). Each segment of th<e exopod 
bears a marginal spine on the outer distal corner, while thle third seg- 
ment has a second such spine about midway on the segment. T h e  
second exopod segment bears one and thte third four inn'er set*. T h e  
first segment of the endopod bears one inner seta, while the second 
bears two setae on the inner margin and two terminally. 
Second leg (Plate 11, figure 8) . Thiere are nlo spinules on the pos- 
terior faces of the rami. In this, Chesapeake specimens differ from 
a11 oth'er descrilbd specimens s f  the species. Thlere are four serrations 
on  the outer margin of the third segment of the dexopod, proximal to  
the first marginal spine of the segment. In Scott's specimens, the see 
ond e x o p d  segment also bears similar serrations. 
Third  leg (Plate 11, figure 4) . There is a curved row of about seven 
small spinules on the postlerior face of the middle segment of the 
endopod, these constituting the only armatme 'of this kind to be found 
on  any of the legs. This differentiates th'e Chesapeake specimens from 
all other described specimens. In addition to the spinules, ther'e is a 
row of fine hairs near thie *sutler distal corner of the same segment. 
'The third cexopod segment bears six to sewn fine serrati'ons on the 
outer margin proximal to the first marginal spine. In Scott's speci- 
mens, thle second ,exopod segment also bears such serr'ations. 
Fourth leg (Plate 11, figures 8, 9 and lo) .  The rami are propor- 
tionatlely narrower than in the othler legs. There is nso armature on 
the posterior faces of thde rami, (except that there is a row of fin'e hairs 
on  the outler distal corner of the second endopod segment. The outer 
border of the third exopod segmnent, proximal to thle first marginal 
spine, bears eight to nin'e fine serrations. In Scott's specimens, the 
second e x o p d  segment also bears such serrations. 
Fifth leg (Plate 11, figure 3 ) -  The proximal of the two segments is 
considerably swollen and bears no armature. The  distal segmlent is 
about one and one-half times the length of the other, and bears 
terminally a small spine on the outer distal corner and a longer spine 
on  the Snner distal corner. Both of these spines are simple, and rela- 
tively thick lcompared to their length. The proportitonal llength of 
the two segments agrees with the description of Scott, but differs from 
those of Dahl and Gurney. 
Acknowled~gment, with deep appreciation, is made of the critical 
review given th'e manuscript by Dr. R. E. Coker, Unilversity of North 
Carolina, and of the helpful advice of Dr. Waldo Schmitt, U. S. 
National Museum. 
PLATE I 
Figure 1. Whole animal, dorsal view. x 90. 
Figure 2. Rostrum and anterior portion of head, ventral view. x 190. 
Figure 3. Right furcal ramus, ventral view. x 390. 
Figure 4. Whole animal, lateral view. x 90. 
Figure 5. First antenna. x 190. 
Figure 6. Rostrum and anterior portion of head, Iaterd view. x190. 
Figure 7. Masticatory portion of mandible. x 390. 
Figure 8. Palp of mandible. x 390. 
Figure 9. Second maxilla. x 390. 
Figure 10. First maxilla. x 390. 
PLATE I 
PLATE I1 
Figure 1. Second antenna. x 390. 
Figure 2. Maxilliped. x 390. 
Figure 3. Fifth leg. x 390. 
Figure 4. Endopod of third lleg. x 390. 
Figure 5. Endopod of first leg. x 390. 
Figure 6. First leg (endopod witbout ,its setae &awn). x 390. 
Figure 7. Sleoond leg. x390. 
Figure 8. Third segment of the exopad of the fourth leg. x 390. 
Figure 9. Endopod of fourth leg. x 390. 
Figure 10. Fourth leg. x 390. 



On four species of Copepoda new to Chesapeake Bay, with a description of a new variety of Paracalanus crassirostris Dahl

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On four species of Copepoda new to Chesapeake Bay, with a description of a new variety of Paracalanus crassirostris Dahl

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