Peltidium nayarit Suárez-Morales & Jarquín-González, 2013

Figs 1, 2, 3

Material examined.

• Four adult females, two specimens mounted on glycerin sealed with acrylic varnish for optical stereo microscope observation and two specimens used for scanning electron microscopy • Two adult females collected at Punta Norte, San Benedicto Island, Revillagigedo National Park, Mexico (19 ° 20 ' 10 " N, 110 ° 47 ' 58 " W); 18 April 2023, 16: 10 h, zooplankton sample collected near surface <2 m depth; collector Jaime Gómez-Gutierrez • One adult female collected at Punta Sureste, Clarion Island, Revillagigedo National Park, Mexico (18 ° 20 ' 50 " N, 114 ° 41 ' 39 " W); 21 April 2023, 18: 47 h, zooplankton sample collected near surface <2 m depth; collector Jaime Gómez-Gutierrez • One adult female collected at Piedra Caleta, Clarion Island, Revillagigedo National Park, Mexico (18 ° 22 ' 17 " N, 114 ° 41 ' 35 " W); 23 April 2023, 18: 47 h, zooplankton sample collected near surface <2 m depth; collector Jaime Gómez-Gutierrez. Standardized abundance of P. nayarit was typically low (average 9.7 ind. / 1000 m 3, range 7.2–12.5 ind. / 1000 m 3), found in three positive sampling stations out of a total of 10 zooplankton sampling stations.

New locality.

San Benedicto and Clarion islands, Revillagigedo National Park, Mexico.

Complementary description.

We describe only the observed morphological differences and details not included in the original description of Peltidium nayarit reported in Suárez-Morales and Jarquín-González (2013).

Copepods with dark reddish-pink coloration (Fig. 1 A). Specimens measure on average 0.8 mm total length and 0.5 mm width (Fig. 1 B, C). Free endopodal segment with outer row of long spinules, armed with one spine and two lateral setae plus seven distal setal elements, four of them being articulated stout setae. The same element is ornamented with inner pectinate margin (Fig. 2 A, B). Antenna. Coxa small, allobasis with short abexopodal seta and longitudinal patch of spinules on outer margin. Exopod two-segmented, elongated, first segment with short slender seta, second segment bearing three setae distally, distal margin with row of short spinules. One exopodal seta modified, with regular pectinate ornamentation along both margins (Suárez-Morales and Jarquín-González 2013, Fig. 2 C). The pectinate ornamentation of the distal margin of the antenna was not shown in the original description of P. nayarit (Suárez-Morales and Jarquín-González 2013).

Leg 1 (Fig. 2 D). Coxa elongate, ornamented with single row of small spinules on inner and outer margins, plus single short seta on inner middle part of segment. Basis wide, inner margin and part of outer margin ornamented with spinules. Inner distal basipodal seta reaching distal margin of first endopodal segment. Outer basipodal seta reaching distal end of basis. Exopod three-segmented, second exopodal segment longest, about 1.5 times as long as first segment, with patch of minute spinules on outer distal margin. Two exopodal claws on distal position of third exopodal segment; outer claw half as long as inner claw. Endopod two-segmented, shorter than exopod. Endopodal segments wide, globose (sensu Wells 2007), ornamented with rows of short setule along the inner and outer margins. Terminal elements include a spine ornamented with distal row of minute spinules and two equally long slender setae. First endopodite segment with an inner seta; second endopodite segment with an inner seta and two equally long slender terminal setae, the inner seta bears a pectinate fringe on its inner margin (Fig. 2 C, D).

Remarks.

In the original description of P. nayarit (Suárez-Morales and Jarquín-González 2013, fig. 2 C) the margin of the endopodite with the pectinate fringe on its inner margin was not described (Fig. 2 C, D).

Leg 5 (Fig. 3). This is the amendment of the original description exopod and baseoendopod separated. Baseoendopod with two pores bearing single inner seta; external seta long, borne on elongate cylindrical lobe of baseoendopod reaching half the length of exopodal lobe; exopodite slender, with one pore and with 5 setal elements (I – V) (sensu Wells 2007), two inserted on inner margin (I, II), and three (III – V) distally; elements I – III represented by stout, distally pinnate setae, elements IV and V possess equally long slender setae; in the specimens from the Revillagigedo Islands, the unique pinnate element observed is element III, and elements I and II were spiniform (Fig. 2 E).

According to Suárez-Morales and Jarquín-González (2013), P. nayarit shares some diagnostic morphological characters with P. speciosum Thompson & Scott, 1903, including leg 5 with a very similar armature and structure except for a relatively robust exopodal segment (length / width ratio = 3.7 vs. 4.2 in P. nayarit) and a shorter outer baseoendopodal seta, reaching to about half the length of exopodal seta V (Nicholls 1941, see fig. 8). These morphological features differ from P. nayarit, in which the same seta almost reaches the distal end of seta V (Suárez-Morales and Jarquín-González 2013, fig. 3). However, we observed remarkable morphological differences with the original description, because the III element of the exopodite of the specimens of the present study bear only pinnate element and elements I and II were spiniform, while in specimens of P. nayarit from the Nayarit coast elements I – III have setae.