Hymenodora gracilis

How to Distinguish from Similar Species: Hymenodora frontalis has a longer rostrum which extends up to or beyond the distal end of the antennal peduncle. H. glacialis has no podobranch on the epipodite of maxilliped 2 and has no V-shaped groove on the side of the carapace.

Bathypelagic

Depth Range: Bathypelagic

This is a true shrimp from the family Oplophoridae, which lives in deep midwater offshore. True shrimp have the second abdominal epimera overlapping that of segment 1 and 2. Family Oplophoridae is almost entirely midwater, has exopodites on its pereopods, and pereopods 1 and 2 are longer and more stout than the others. Hymenodora are deepliving, non-vertically migrating species that have almost no pigment in their small eyes, giving them a golden color, and usually have very soft exoskeletons. None of their abdominal segments has a median dorsal ridge. H. gracilis has a short rostrum which extends only slightly beyond the cornea of the eye, maxilliped 2 has a podobranch and an epipod, and the side of the carapace has a V-shaped groove with the apex directed ventrally. It has a groove passing upward and backward from the middle of the hepatic groove but no groove converging toward the first from the supra-branchial groove. The telson has 4 pairs of dorsolateral spines. Unlike the other Oplophorids, which tend to be dark red in deepliving species and half red in vertical migrators, the color of Hymenodora is orange-red, darker on carapace and on eggs. Maximum length:

"This species is apparently somewhat smaller than H. glacialis, and is distinguished by its more slender form and longer and more slender rostrum, which is prolonged in a slender, unarmed tip, reaching as far forward as the tips of the eyes. The antennal scale is apparently considerably narrower. In the only specimen in which the tip of the telson is perfect, the male from station 2036, it is armed with only four spines, there being only two between the long lateral spines. The most remarkable difference, however, is the first gnathopods, which, as already remarked, bear distinct podobranchiæ. In the larger specimens these branchiæ are conspicuous and composed of several lamellæ each, being nearly as large in proportion to the size of the animal as in Meningodora mollis; but in some of the smaller specimens they are represented by only on or two small lamellæ attached near the base of the epipod, and are very easily overlooked. There are well developed podobranchiæ at the bases of the first gnathopods in all the species of the allied genera known to me, Acanthephyra, Ephyrina, Notostomus, and Meningodora, and I had regarded their absence as one of the best generic characters of Hymenodora, but their occurrence and variability in a species so very closely allied to the typical species of the genus shows that they are not always of generic importance. The two species of Hymenodora still differ, however, from the species of the allied genera above-named in the form of the protognath of the second maxilla and in the number of segments in the endopod of the maxilliped, characters which, for the present at least, may be regarded as of generic value."

H. glacialis

H. glacilis

Catalogue number……………………………………..

………….

5456

7874

7158

Station…………………………………………………

Faröe

2099

2182

2036

Sex………………………………………………….....

♂

♀

♂

♂

Length from tip of rostrum to tip of telson……………

70

54+

55

43

Length of carapax, including rostrum…………………

23.0

19.0

18.0

13.0

Length of rostrum……………………………………..

3.0

2.5

3.0

2.3

Height of carapax……………………………………..

………….

10.0

8.4

6.8

Breadth of carapax…………………………………….

………….

………….

7.3

5.5

Length of eye-stalk and eye…………………………...

3.0

2.3

2.5

2.0

Greatest diameter of eye………………………………

1.0

0.8

0.8

0.6

Length of antennal scale………………………………

9.0

………….

6+

5.7

Breadth of antennal scale……………………………...

3.1

2.4

2.0

1.5

Length of first peræopod……………………………...

18.0

………….

11.5

10.0

Length of chela………………………………………..

4.9

………….

3.1

2.5

Breadth of chela……………………………………….

0.7

………….

0.7

0.5

Length of dactylus…………………………………….

2.0

………….

1.1

1.0

Length of second peræopod…………………………..

………….

………….

11.5

10.0

Length of chela………………………………………..

………….

………….

3.1

2.5

Breadth of chela……………………………………….

………….

………….

0.7

0.4

Length of dactylus…………………………………….

………….

………….

1.1

0.9

Length of third peræopod……………………………..

………….

………….

3.2

14.0

Length of propodus……………………………………

………….

………….

0.5

3.5

Length of dactylus…………………………………….

………….

………….

1.2

1.3

Length of fourth peræopod……………………………

………….

………….

………….

16.0

Length of propodus……………………………………

………….

………….

………….

4.3

Length of dactylus…………………………………….

………….

………….

………….

1.9

Length of fifth peræopod……….……………………..

………….

………….

21.0

13.0

Length of propodus………………………..…………..

………….

………….

6.3

3.6

Length of dactylus………………………………….....

………….

………….

2.6

0.6

Length of sixth somite of pleon……………………….

8.3

7.5

16.0

6.5

Height of sixth somite of pleon……………………….

4.0

3.5

4.6

2.8

Length of telson………………………………………

14.5

8+

0.8

7.8

Length of inner lamella of uropod…………………….

10.1

………….

7.5

5.8

Breadth of inner lamella of uropod……………………

2.0

………….

3.3

1.1

Length of outer lamella of uropod……………………

11.5

………….

10.5

6.5

Breadth of outer lamella of uropod……………………

2.7

………….

………….

1.3

(Smith 1886)

Distribution: south of Mozambique Channel (30S, 48E) .

Known from seamounts and knolls