Taxonomic report on some monstrilloids (Copepoda, Monstrilloida) from southeast Mexico with the description of a new species of M onstrilla Author Suárez-Morales, E. Author Escamilla, J. B. text Journal of Natural History 2001 2001-12-30 35 10 1433 1445 journal article 10.1080/002229301317067629 1464-5262 A90176A5-234A-4415-B5B6-159CF141E324 Monstrilla humesi Suárez-Morales sp. nov. (gures 3, 4) M aterial ex amined H ol ot ype: one adult female, undissected, ethanol preserved. Laguna de Chelem , Yucatan , Mexico . 22 September 1987 . Deposited in The Natural History Museum , London , registered under catalogue number 2000.1257 . T ype locality Laguna de Chelem , northern coast of Yucatan Peninsula, Mexico (21ss19.35¾ N; 89ss49.10¾ W). Water column. D epth: 1.2 m . Description Female (gures 3, 4). Total body length of described specimen 0.75 mm ; cephalothorax 0.37 mm long, representing about 50% of total (gures 3A,C, 4A). Oral papilla not prominent, located medially about 23% of ventral margin from anterior end of cephalothorax (gure 3A). Cephalic region wide in dorsal view, about as wide as posterior part of cephalothorax, moderately constricted at level of ocelli. Ventral ocellus absent. Dorsal ocelli present; pigment cups relatively large, poorly developed, relatively widely separated from each other by gap equal to diameter of ocellus; ocelli pigmented on inner parts only, rounded in dorsal view (gure 4B). Low, rounded protuberance with two sensilla located on forehead between antennular bases, visible in dorsal view (gure 4B). Antennules relatively long, 0.18 mm , representing about 27% of total body length, and c. 53% of cephalothorax length. Antennules four-segmented, but purported segments 2–4 partially fused. Segments armed with 0–I; 1–V; 2–I; 6–IX–2aes setae (Arabic numbers), spines or spiniform setae (Roman numbers), and aesthetascs (aes), respectively. In terms of pattern described by Grygier and Ohtsuka (1995) for female monstrilloid antennular armature, expected setae and spines on rst (1), second (2d,2v, IId), and third (3,IIIv,d) purported segments all present. Only 1–3 1–2 two elements absent in fourth segment (4v, b) from both antennules. Setae b 1 5 1–3 unbranched. Length ratio of antennular segments, from proximal to distal, 17.1:30.8:15.4:36.7 (5100) (gure 3B). F irst pedigerous thoracic somite incorporated into cephalothorax. Pedigerous somites 2–4 accounting for 24.1% of total length in dorsal view. These four pedigers each bearing pair of well developed swimming legs, all with three-segmented rami and with same armament pattern, except for leg 1 exopod (gures 3D,E). Exopods longer than endopods in all cases. Coxae of each pair unarmed, joined by intercoxal F ig. 3. M onstrilla humesi n.sp. Adult female holotype . Laguna de Chelem: (A) habitus, ventral view; (B) left antennule, dorsal view; (C) habitus, dorsal view; (D) left rst swimming leg; (E) left third swimming leg showing long basipodal outer seta; (F) outer apical exopodal seta of third leg. F ig. 4. M onstrilla humesi n.sp. Adult female holotype . Launa de Chelem: (A) habitus, lateral view; (B) anterior end of head, dorsal view; (C) caudal rami, ventral view; (D) fth pedigerous somite with legs 5, and genital double somite with ovigerous spines, ventral view; (E) same structures, lateral view. sclerite as long as wide. Basis separated from coxa by diagonal articulation. Outer margin of basis of swimming legs 1, 2, and 4 with small, thin seta; seta on basis of leg 3 approximately three times larger than in the other legs, naked (gure 3E). Outer distal corner of rst and third exopodal segments of legs 1–4 each with short spine 20–30% as long as bearing segment. All natatory setae lightly and biserially plumose except for seta on outer distal corner of third exopodal segments of legs 1–4, this being naked along inner side, but bearing row of small denticles along outer margin (gure 3F). Armament formula of swimming legs as follows: basis exopodite endopodite