Order Lophogastrida Key

Key: Order Lophogastrida

Phylum Arthropoda
Subphylum Crustacea
Class Malacostraca
Subclass Eumalacostraca
Superorder Peracarida

Key written by Dave Cowles (based on Literature References) Note: Not all these species have been found in the Pacific Northwest. Those marked with a single asterisk have been found off the U.S. continental west coast, and those with two asterisks have been found off the Pacific Northwest coast.

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Lower taxonomic level Main Page Alphabetic Index Systematic Index Glossary

1a Rostrum blunt. Scale of second antenna with apical suture, and outer margin has no spines. Telson is entire. 4th pereopod is a gnathopod. Abdominal segments lack pleural plates. Family Eucopiidae

1b Rostrum plate-like, or elongated and triangular in cross-section (photo). Scale of second antenna with or without apical suture. Second pereopod is a gnathopod (although it may look like the other pereopods). Pleural plates well-developed on abdominal segments. 2

2a Carapace well-developed, anterior margin has spines. Rostrum elongated, triangular in cross-section. Scale of second antenna with or without apical suture. Exopod of uropod is divided by a suture near the apex. 3 Family Gnathophausiidae
(or the Gnathophausid section of
family Lophogastridae)

2b Carapace large. Rostrum plate-like. Second antenna does not have an apical suture. Exopod of uropod is not divided by a suture near the apex Family Lophogastridae

3a Antennal scale small, whole, without a distinctly isolated distal part separated from the proximal part by a more or less well-developed articulation. External margin of antennal scale serrated, with 3-9 spines. Dactyls of thoracopods 3-8 elongated, lanceolate, with 8-10 spines along nearly the entire length of the inner margin. Pleural plates of the sixth abdominal segment knitted together ventrally to form an indivisible plate with a deep cleft at the distal end (Genus Neognathophausia) 10

3b Antennal scale large, with a distinctly isolated distal part separated from the proximal part by a more or less well-developed articulation. Distal end of antennal scale smooth, with 1 large spine on the external margin, or with 1-4 small spines. Dactyls of thoracopods 3-8 widened, lanceolate, with 3 spines only on the distal part of the inner margin and 1 spine in the middle of the inner margin. Pleural plates of the sixth abdominal segment not knitted together ventrally (Genus Gnathophausia) 4

4a Keel along ventrolateral margin of carapace does not curve dorsally near the posterior end of the carapace. The mid-dorsal keel of the carapace is interrupted. No strong keel along the dorsolateral margin of carapace. 5

4b Keel along ventrolateral margin of carapace curves dorsally as it approaches the posterior end of the carapace. There is no spine at the posteroventral margin of the carapace. The mid-dorsal keel of the carapace is not interrupted nor serrated. No spines on the mid-dorsal keel of the abdominal segments, or only small, posteriorly-directed spines. Usually have a keel along the dorsolateral margin of the carapace. 6

5a Keel along ventrolateral margin of carapace ends in a spine at the posteroventral margin of the carapace. The mid-dorsal keel of the carapace is sharply serrated. The mid-dorsal keel on the abdomen has large spines projecting posterodorsally. *Gnathophausia gracilis

5b Posteroventral margin of carapace has no spine. The mid-dorsal keel of the carapace is not serrated. Abdominal segments are rounded dorsally, with no mid-dorsal keel. *Gnathophausia childressi

6a Two spines on each side of the anterior pleura of the sixth abdominal segment. Antennal spine missing or very small. Large, triangular branchiostegal spine. Spine on antennal scale projects well beyond the end of the scale and is serrated on both sides Gnathophausia longispina

6b Only one spine on each side of the anterior pleura of the sixth abdominal segment. Have a distinct antennal spine. No branchiostegal spine, and the branchiostegal lobe of the carapace is usually rounded. Spine on antennal scale barely projects past the end of the scale, if at all. 7

7a Carapace has a keel along the dorsolateral margin 8

7b Carapace does not have a dorsolateral keel. The branchiostegal lobe of the carapace may be rounded or angular, but has no spine. Abdominal segments have no dorsal keel but do have a small posterior triangular projection. Posteroventral margin of pleura of abdominal segments 1-5 pointed. Gnathophausia elegans

8a Abdominal segments have a small dorsal ridge and small, posteriorly-directed spines. Posteroventral margin of pleura of abdominal segments 1-5 pointed. Branchiostegal lobe of carapace is rounded 9

8b Abdominal segments have no dorsal ridge nor dorsal spines. Posteroventral margin of pleura of abdominal segments 1-5 rounded. Branchiostegal lobes of carapace somewhat angular Gnathophausia affinis

9a Anterolateral shoulder of carapace is rounded. Carapace is not sharply constricted anteriorly. Branchiostegal lobes of carapace are moderate *Gnathophausia zoea

9b Carapace suddenly constricts anteriorly, and anterolateral shoulder of carapace is distinctly angular in front of the dorsolateral ridge. The branchiostegal lobes of the carapace are greatly expanded Gnathophausia scapularis

10a Both the anterior and posterior ventral lobes of the pleural plates of abdominal segments 2-5 are pointed (spiniform). The antennal scale is ovate or subovate, with a sharply pointed apex **Neognathophausia ingens

10b The anterior ventral lobe of the pleural plates of abdominal segments 2-5 is small and rounded, while the posterior ventral lobe is pointed (spiniform). The antennal scale is lanceolate or sublanceolate, tapering to a sharp spiniform point **Neognathophausia gigas

References used for key:

Boltovskoy, D. (ed), 2006. Zooplankton of the South Atlantic Ocean. A taxonomic reference work with identification guides and spatial distribution patterns. ETI Bioinformatics (CD-ROM). www.eti.uva.nl

Casanova, Jean-Paul, 1996. Gnathophausia childressi, new species, a mysid from deep near-bottom waters off California, with remarks on the mouthparts of the genus Gnathophausia. Journal of Crustacean Biology 16:1 192-200

Clarke, W.D., 1962. The genus Gnathophausia (Mysidacea, Crustacea), its systematics and distribution in the Pacific Ocean. Ph.D. thesis, University of California, San Diego, Ca. 251 pp.

Kathman, R.D., W.C. Austin, J.C. Saltman, and J.D. Fulton, 1986. Identification manual to the Mysidacea and Euphausiacea of the Northeast Pacific. Canadian Special Publication of Fisheries and Aquatic Sciences 93. ISBN 0-660-12096-8

Meland, Kenneth. Mysidacea: Families, Subfamilies, and Tribes. Crustacea.net

Pequegnat, Linda H., 1965. The bathypelagic mysid Gnathophausia (Crustacea) and its distribution in the eastern Pacific Ocean. Pacific Science 19:4 399-421

Petryshov, V.V., 1992. Notes on mysid systematics (Crustacea, Mysidacea) of Arctic and the north-western Pacific. Zoologichesky Zhurnal 71:10 47-58

Taxonomic Levels Represented in This Key:

Gnathophausia childressi
Gnathophausia gracilis
Gnathophausia longispina
Neognathophausia gigas
Neognathophausia ingens

Page created by Dave Cowles, 2006
Edited by:

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Lower taxonomic level	Main Page	Alphabetic Index	Systematic Index	Glossary

1a	Rostrum blunt. Scale of second antenna with apical suture, and outer margin has no spines. Telson is entire. 4th pereopod is a gnathopod. Abdominal segments lack pleural plates.	Family Eucopiidae
1b	Rostrum plate-like, or elongated and triangular in cross-section (photo). Scale of second antenna with or without apical suture. Second pereopod is a gnathopod (although it may look like the other pereopods). Pleural plates well-developed on abdominal segments.	2
2a	Carapace well-developed, anterior margin has spines. Rostrum elongated, triangular in cross-section. Scale of second antenna with or without apical suture. Exopod of uropod is divided by a suture near the apex.	3 Family Gnathophausiidae (or the Gnathophausid section of family Lophogastridae)
2b	Carapace large. Rostrum plate-like. Second antenna does not have an apical suture. Exopod of uropod is not divided by a suture near the apex	Family Lophogastridae
3a	Antennal scale small, whole, without a distinctly isolated distal part separated from the proximal part by a more or less well-developed articulation. External margin of antennal scale serrated, with 3-9 spines. Dactyls of thoracopods 3-8 elongated, lanceolate, with 8-10 spines along nearly the entire length of the inner margin. Pleural plates of the sixth abdominal segment knitted together ventrally to form an indivisible plate with a deep cleft at the distal end (Genus Neognathophausia)	10
3b	Antennal scale large, with a distinctly isolated distal part separated from the proximal part by a more or less well-developed articulation. Distal end of antennal scale smooth, with 1 large spine on the external margin, or with 1-4 small spines. Dactyls of thoracopods 3-8 widened, lanceolate, with 3 spines only on the distal part of the inner margin and 1 spine in the middle of the inner margin. Pleural plates of the sixth abdominal segment not knitted together ventrally (Genus Gnathophausia)	4
4a	Keel along ventrolateral margin of carapace does not curve dorsally near the posterior end of the carapace. The mid-dorsal keel of the carapace is interrupted. No strong keel along the dorsolateral margin of carapace.	5
4b	Keel along ventrolateral margin of carapace curves dorsally as it approaches the posterior end of the carapace. There is no spine at the posteroventral margin of the carapace. The mid-dorsal keel of the carapace is not interrupted nor serrated. No spines on the mid-dorsal keel of the abdominal segments, or only small, posteriorly-directed spines. Usually have a keel along the dorsolateral margin of the carapace.	6
5a	Keel along ventrolateral margin of carapace ends in a spine at the posteroventral margin of the carapace. The mid-dorsal keel of the carapace is sharply serrated. The mid-dorsal keel on the abdomen has large spines projecting posterodorsally.	*Gnathophausia gracilis
5b	Posteroventral margin of carapace has no spine. The mid-dorsal keel of the carapace is not serrated. Abdominal segments are rounded dorsally, with no mid-dorsal keel.	*Gnathophausia childressi
6a	Two spines on each side of the anterior pleura of the sixth abdominal segment. Antennal spine missing or very small. Large, triangular branchiostegal spine. Spine on antennal scale projects well beyond the end of the scale and is serrated on both sides	Gnathophausia longispina
6b	Only one spine on each side of the anterior pleura of the sixth abdominal segment. Have a distinct antennal spine. No branchiostegal spine, and the branchiostegal lobe of the carapace is usually rounded. Spine on antennal scale barely projects past the end of the scale, if at all.	7
7a	Carapace has a keel along the dorsolateral margin	8
7b	Carapace does not have a dorsolateral keel. The branchiostegal lobe of the carapace may be rounded or angular, but has no spine. Abdominal segments have no dorsal keel but do have a small posterior triangular projection. Posteroventral margin of pleura of abdominal segments 1-5 pointed.	Gnathophausia elegans
8a	Abdominal segments have a small dorsal ridge and small, posteriorly-directed spines. Posteroventral margin of pleura of abdominal segments 1-5 pointed. Branchiostegal lobe of carapace is rounded	9
8b	Abdominal segments have no dorsal ridge nor dorsal spines. Posteroventral margin of pleura of abdominal segments 1-5 rounded. Branchiostegal lobes of carapace somewhat angular	Gnathophausia affinis
9a	Anterolateral shoulder of carapace is rounded. Carapace is not sharply constricted anteriorly. Branchiostegal lobes of carapace are moderate	*Gnathophausia zoea
9b	Carapace suddenly constricts anteriorly, and anterolateral shoulder of carapace is distinctly angular in front of the dorsolateral ridge. The branchiostegal lobes of the carapace are greatly expanded	Gnathophausia scapularis
10a	Both the anterior and posterior ventral lobes of the pleural plates of abdominal segments 2-5 are pointed (spiniform). The antennal scale is ovate or subovate, with a sharply pointed apex	**Neognathophausia ingens
10b	The anterior ventral lobe of the pleural plates of abdominal segments 2-5 is small and rounded, while the posterior ventral lobe is pointed (spiniform). The antennal scale is lanceolate or sublanceolate, tapering to a sharp spiniform point	**Neognathophausia gigas