28
THE BIOLOQY OF EUPHAUSIIDS
lb. Thoracic legs unequally developed, one or two of the anterior pairs of
legs being greatly elongate.
6a. Second and third pairs of thoracic legs greatly elongated.
6b. Second pair of thoracic legs greatly elongated.
Tessarabrachion Hansen
7a. Second pair of thoracic legs rather strong, the last two segments
Thysanobsa Brandt (in part)
7b. Second pair of thoracic legs very slender, filiform, naked, with
Nematoscelis G. 0. Sars
armed with spiniform bristles on both margins.
only a tuft of apical bristles.
6c. Third pair of thoracic legs greatly elongated.
8a. Third pair of thoracic legs slender, naked with a tuft of serrated
apical bristles.
Nematobrachion Calman
8b. Third pair of thoracic legs with penultimate segment dilated, and
forming, together with the last one, a kind of prehensile hand.
Photophores are present in the eyes, a t the bases of the seventh
pair of thoracic legs, and in the first abdominal segment only.
Stylocheiron G . 0. Sars
Genus Thysanopoda
Species of Thysanopoda can be identified by the combined use of
the following key and the descriptions of Sheard (1942, 1953), Brinton
(1953)) Boden (1954)) Boden et al. (1955)) and Boden and Brinton
(1957). These species are difficult t o identify and reference should be
made t o the appropriate figures and descriptions in the cited papers.
la. Carapace without a distinct cervical groove. Sixth abdominal segment
These
longer than the fifth.
2a. Lateral denticle(s) present on inferior margin of carapace.
denticles are often very small.
3a. One or more abdominal segments armed with dorsal spine.
4a. Dorsal spine on third abdominal segment only; fourth and
fifth slightly produced. No spine at base of rostrum. Single
lateral denticle on carapace
. . ..
monacantha
4b. Dorsal spine on fourth and fifth abdominal segments only;
sixth abdominal segment only slightly larger than fifth.
cristata
40. Dorsal spines on third, fourth, fifth and sixth abdominal
segments ; spine a t base of rostrum. Two lateral denticles on
carapace . . .. .. .. ..
tricuspidata
THE BIOLOQY OF EUPHAUSIIDS
lb. Thoracic legs unequally developed, one or two of the anterior pairs of
legs being greatly elongate.
6a. Second and third pairs of thoracic legs greatly elongated.
6b. Second pair of thoracic legs greatly elongated.
Tessarabrachion Hansen
7a. Second pair of thoracic legs rather strong, the last two segments
Thysanobsa Brandt (in part)
7b. Second pair of thoracic legs very slender, filiform, naked, with
Nematoscelis G. 0. Sars
armed with spiniform bristles on both margins.
only a tuft of apical bristles.
6c. Third pair of thoracic legs greatly elongated.
8a. Third pair of thoracic legs slender, naked with a tuft of serrated
apical bristles.
Nematobrachion Calman
8b. Third pair of thoracic legs with penultimate segment dilated, and
forming, together with the last one, a kind of prehensile hand.
Photophores are present in the eyes, a t the bases of the seventh
pair of thoracic legs, and in the first abdominal segment only.
Stylocheiron G . 0. Sars
Genus Thysanopoda
Species of Thysanopoda can be identified by the combined use of
the following key and the descriptions of Sheard (1942, 1953), Brinton
(1953)) Boden (1954)) Boden et al. (1955)) and Boden and Brinton
(1957). These species are difficult t o identify and reference should be
made t o the appropriate figures and descriptions in the cited papers.
la. Carapace without a distinct cervical groove. Sixth abdominal segment
These
longer than the fifth.
2a. Lateral denticle(s) present on inferior margin of carapace.
denticles are often very small.
3a. One or more abdominal segments armed with dorsal spine.
4a. Dorsal spine on third abdominal segment only; fourth and
fifth slightly produced. No spine at base of rostrum. Single
lateral denticle on carapace
. . ..
monacantha
4b. Dorsal spine on fourth and fifth abdominal segments only;
sixth abdominal segment only slightly larger than fifth.
cristata
40. Dorsal spines on third, fourth, fifth and sixth abdominal
segments ; spine a t base of rostrum. Two lateral denticles on
carapace . . .. .. .. ..
tricuspidata