Mysidium (Mysidium) rickettsi Harrison & Bowman, 1987

Wittmann, Karl J. & Wirtz, Peter, 2019, Revision of the amphiamerican genus Mysidium Dana, 1852 (Crustacea: Mysida: Mysidae), with descriptions of two new species and the establishment of two new subgenera, European Journal of Taxonomy 495, pp. 1-48 : 23-25

Mysidium (Mysidium) rickettsi Harrison & Bowman, 1987

Mysidium rickettsi Harrison & Bowman, 1987: 674 –678, figs 1–3.

Mysidium rickettsi – Ferrari 2001: table 1 (in taxa list). — Ortiz 2001: 100. — Escobar-Briones 2002: 304. — Price 2004: 65 (in checklist). — Price et al. 2009: 232. — Gómez-Gutiérrez et al. 2014: 1027, table 3. — Ortiz et al. 2017a: table 1; 2017b: 78. — Ortiz & Lalana 2018: 80.

Mysidium reckettsi – Gómez-Gutiérrez et al. 2014: 1009 (invalid spelling variant).

Mysidium ricketsi – Gómez-Gutiérrez et al. 2014: 1024 (invalid spelling variant).

Material examined

None.

Type locality

Gulf of California, Punta Marcial, 25.5167° N, 111.0167° W ( Harrison & Bowman 1987).

Revised definition

Adapted to the scheme in Table 2 by using published data ( Harrison & Bowman 1987; Ortiz et al. 2017b) on adults of both sexes: all features diagnosed above for genus and subgenus Mysidium Dana, 1852 , with the reservation that the detailed structure of the setae on the merus of thoracic endopod 3 is unknown. Cornea calotte-shaped in dorsal view, its diameter 2.1 times as long as terminal segment of antennular trunk. Eyestalks smooth. Rostrum round-triangular, not extending beyond eyestalks.Appendix masculina obscurely bilobate, all along inner margins fringed by large setae; its length 1.5 times terminal segment of antennular trunk. Length of antennal scale four times maximum width; scale reaching well beyond antennular trunk. Median segment of mandibular palp with setae all along inner margin, whereas setae lacking on outer margin. Carpopropodus with two segments in thoracic endopods 1–2, 7–8, versus three segments in endopods 3–6. Basal segment is 0.6 times total length of carpopropodus of endopod 3. Male pleopod 1 stout, allusively bilobate. Sympod of male pleopod 4 without endite. Its exopod with basal

segment occupying 58% total length. Endopod reduced to lobe with = 11% sympod length; apically with one long seta and more proximally six additional, smaller setae. Uropodal endopod 0.6–0.7 times as long as exopod. Telson linguiform, tapering posteriorly, length 1.9 times maximum width near basis; lateral margins slightly convex, almost straight; terminal margin clearly convex, well rounded. Proximal half of lateral margins smooth, distal half with dense series of 30–37 short, blunt or pointed spines on each side; lateral margins each with about 19 spines, terminal margin with about 24 spines.

Distribution and habitat

East Pacific coast of Mexico: Gulf of California, Islas Tres Marías, 21–26° N. Occurring in shallow, coastal marine waters where it forms dense epibenthic swarms ( Gómez-Gutiérrez et. al. 2014). Also collected with night light at surface and from fish stomachs ( Harrison & Bowman 1987; Ortiz et al. 2017b).

Tables

Table 2. Diagnostic characters of the species of Mysidium Dana, 1852.

		M. gracile	M. integrum	M. cubanense	M. rubroculatum	M. triangulare	M. rickettsi 1, 2	M. pumae 2	M. columbiae	M. antillarum	M. iliffei 3
Cornea diameter is (x)–times 1.7–3.2 length of terminal segment of an- tennular trunk in dorsal view			1.6–2.4	2.6–4.1	1.9–2.9	1.7–2.5	2.1	1.5	1.5–2.0	1.4–1.7	1.5
Total numbers of setae on and close to medio-terminal exten- sion of male antennular trunk (Fig. 1B)		7–9	4–6	4–6	4–5	6–10	?	?	2–4	2–3	?
Its largest seta is (x)–times length 0.9–1.4			0.3–0.5	0.2–0.4	0.1–0.3	0.1–0.3	?	?	0.1–0.2	0.1	?
of mediodistal extension	of male
antennular trunk
Appendix masculina is (x)–times 1.6–2.7			1.1–2.5	1.1–2.3	1.3–2.0	1.5–2.0	1.5	2.0–2.2	2.0–3.3	2.2–3.9	?
length of terminal segment	of an-
tennular trunk
Antennal scale extends	beyond	yes	yes	yes	yes	yes	yes	yes	yes	yes	no
antennular trunk
Antennal scale length	is (x)–	4–6	4–5	4–6	4–5	5–7	4	6	7–8	7–11	6
times maximum width
Median segment of mandibular		yes	yes	yes	yes	yes	no	yes	yes	yes	?
palp with setae on outer margin
About evenly rounded (1), mod-		1	1	1	2	1	?	?	3	3	?
erately unevenly rounded (2)
or distally angular (3) hump on
outer face of terminal segment of
maxillula
Carpopropodus of third thoracic		3	3	3	3	3	3	2	3	3	3
endopod (n)–segmented
Basal segment is (x)–times total		0.5	0.5	0.5	0.5	0.4–0.5	0.6	0.8	0.5	0.5	0.4
length of carpopropodus of third
thoracic endopod
Numbers of serrated setae along		0	0	0	0	0	?	0	2–6	2–7	?
merus of third thoracic endopod
First pleopod rod-like (1) versus		1–2	2	2	1	2	1–2	1	1	1	?
bilobate (2)
Medial margin of third male		1	1	1	1	1	1	2	2	2	?
pleopod with widening (1) versus
projecting endite (2)
Sympod of fourth male pleopod:		0–1	0–1	0–1	0–1	0–1	0	0	2	0–1	?
without endite (0), with endite re-
duced to indistinct projection or
widening (1), with strong endite
(2)
Sympod of fourth male pleopod		0	0	0	0	0	0	0	3–6	3–7	?
with (n) setae on rostral face
Exopod of fourth male pleopod		4	4	4	4	4	4	4	3	3	?
(n)–segmented
Basal segment is (x)–times total 0.6–0.7			0.5–0.6	0.5–0.6	0.5–0.6	0.6	0.6	0.5	0.6–0.7	0.7	?
length of exopod of fourth male
pleopod
Penultimate segment of exopod		1	1	1	1	1	1	2	1	1	?
of fourth male pleopod with entire
(1) versus bifid (2) modified seta
Endopod of fourth male pleopod 0.1–0.2			0.1–0.2	0.1–0.2	0.1–0.2	0.1–0.2	= 0.1	= 0.2	0.3–0.5	0.3–0.4	?
is (x)–times length of sympod