Monstrilla barbata Suárez-Morales & Gasca-Serrano, 1992

Monstrilla barbata Suárez-Morales & Gasca-Serrano, 1992 View in CoL

Figs 1 View Figure 1 , 2 View Figure 2 , 3 View Figure 3

Type material.

Holotype • adult female, undissected, deposited in the collection of Crustacea, U. S, National Museum of Natural History, Smithsonian Institution. USNM 251756 About USNM . GoogleMaps

Type locality.

Bahia de la Ascension   GoogleMaps , central part of eastern Yucatan Peninsula coast ( 19°47.00'N, 87°33.20'W). Depth 1.5 m. Date of collection 6 September, 1991.

Description of adult female holotype.

Total body length measured from forehead to posterior margin of anal somite: 1.82 mm. Cephalothorax 0.947 mm long, representing ~ 52.1 % of total body length. Antennules moderately divergent, representing 16.6 % of total body length and 31.5 % of cephalothorax length. Oral papilla small, located anteriorly, ~ 26 % posteriorly on ventral surface of cephalothorax (Fig. 1 A, C View Figure 1 ). Eyes represented by relatively small medial cup and two larger, weakly pigmented lateral cups (Fig. 2 A View Figure 2 , mec, lec). Forehead flat, corrugate, with two large sensilla and field of small cuticular papillae extending to most of cephalic area, including ventral and dorsal surfaces (Fig. 2 A, B View Figure 2 ). Ventral surface of cephalic area bearing: 1) single pair of nipple-like cuticular processes between antennule bases and oral papilla, 2) ventral surface with coarsely corrugate medial keel-like protuberance (Fig. 2 B View Figure 2 ) visible in lateral view of the whole specimen (Fig. 1 C View Figure 1 , arrowhead); 3) pale pattern of cuticular wrinkles and minute papillae present adjacent to these structures (Fig. 2 A View Figure 2 ).

Antennules (Fig. 2 D View Figure 2 ) 0.34 mm long, almost 17 % of total body length; antennules 4 - segmented; segments 1–4 clearly divided. Following antennule armature nomenclature by Grygier and Ohtsuka (1995), first segment with short, spiniform element 1; second segment carrying long spiniform elements 2 v 1-3 and 2 d 1, 2, dorsal seta IId long; third segment with short, spiniform element 3 and IIIv; elements IIId and IIIv setiform, slender; fourth segment with reduced armature including proximal spiniform element 4 d 1, flexible setae IVd, IV v, and slender ventral aesthetasc 4 aes. Fourth segment carrying short spiniform elements 4 v 1-3, setiform elements IVd, IVv, Vm, Vv, Vd, spiniform element 5, three setae of the “ b ” group inserted on the outer distal margin (b 1, b 2, b 3, b 6), and reduced apical elements 6 1 and 6 2.

First pedigerous somite incorporated into cephalothorax; this and succeeding three free pedigerous somites each bearing pair of biramous swimming legs. Pedigerous somites 2–4 together accounting for 26 % of total body length in dorsal view. Intercoxal sclerites of legs 1–4 subrectangular, without ornamentation on surface or along distal margin. Basis of legs articulating with rectangular coxa along diagonal line. Basis with thin, simple lateral basipodal seta on legs 1, 2, and 4; on leg 3, this seta thicker, lightly setulate, and 4 × longer than on other legs (Fig. 3 C – F View Figure 3 , bs). Endopods and exopods of swimming legs 1–4 tri-articulate (Fig. 3 C – F View Figure 3 ). Ramus setae all lightly and biserially plumose except for spiniform outer setae on exopodal segments 1 and 3, and inner seta of first exopodal segment, all these being short and slender. Outer apical exopodal seta of swimming legs 1–4 with outer margin smooth, inner margin lightly setose. Armature formula as (not provided in original description):

Basis Endopod Exopod:

leg 1 1-0 0-1; 0-1; 1, 2, 2 I- 1; 0-1; I, 2, 2

legs 2–4 1-0 0-1; 0-1; 1, 2, 2 I- 1; 0-1; I, 1, 2, 3

Fifth legs biramous. Outer lobe represented by subrectangular exopodal lobe armed with three setae, outermost seta lightly pinnate, being longer, slightly wider than adjacent two exopodal setae; innermost exopodal seta lightly shorter, narrower. Inner endopodal lobe reduced, drop-like, arising proximally from inner margin of exopodal lobe, armed with short, slender apical seta (Fig. 3 B View Figure 3 ).

Urosome consisting of four somites: fifth pedigerous somite, genital double-somite, one free postgenital somite, and short anal somite (Fig. 3 B View Figure 3 ). Genital somite with pair of lateral protuberances on distal 1 / 2 visible in frontal and ventral views (Fig. 1 B View Figure 1 , plp; Fig. 3 B View Figure 3 , arrowheads). Ventral surface of genital somite forming enlarged base of cylindrical shaft with distal genital lappets. Relative length of urosomites, from proximal to distal as: 40: 35: 16.25: 8.76. Caudal rami subquadrate, symmetrical, weakly divergent, ~ 1.1 × longer than wide, each ramus bearing six setae (I – IV), seta VI being shortest (Fig. 3 B View Figure 3 ).

Male. Unknown.

Remarks.

There are several characters of this species that were not properly described in its original description in 1992. The holotype habitus was originally provided in dorsal view; I was able to add both ventral and lateral views. The armature of the antennules was largely incomplete and at least one setal element (element 1 sensu Grygier and Ohtsuka 1995) was erroneously illustrated in the original drawings ( Suárez-Morales and Gasca-Serrano 1992: fig. 1 b). The setal elements present in the holotype specimen are identified, illustrated, and labelled in this redescription, thus allowing a more accurate comparisons among the Caribbean species of Monstrilla . Also, the coarse forehead surface noticed in the re-examination was not mentioned or illustrated by Suárez-Morales and Gasca-Serrano (1992); the same is true for the eye cups, which were originally described as present and moderately developed; it was possible now to provide more details about their relative size and pigmentation, recognizing the lateral and medial cups. The cephalic integumental ornamentations were not typically deemed relevant in the taxonomy of monstrilloid copepods, but they can aid to separate species ( Cruz Lopes da Rosa et al. 2021). In this redescription of M. barbata , I was able to provide new data on the cephalic ventral ornamentation, which includes fields of papillae and wrinkles, a pair of slender sensilla, a pair of nipple-like processes, and details of the medial keel-like corrugate antero-ventral process that is distinctive of the species ( Suárez-Morales and Gasca-Serrano 1992). Also, the swimming legs 1–4 were not illustrated in the original description, but drawings of these legs are newly provided in this redescription.

This species was originally compared with M. longicornis Thompson, 1890 and M. lata Desai & Bal, 1963 based on sharing a bilobed fifth leg carrying four setae. Its fifth leg was also compared with that of M. reticulata Davis, 1949 . The most distinctive character of M. barbata is the beard-like protuberant medial process and was considered unique among species of Monstrilla ( Suárez-Morales and Gasca-Serrano 1992) , but this structure was compared recently with those of other Monstrilla species described after M. barbata , like M. pustulata Suarez-Morales & Dias, 2001 from Brazil, and M. brevicornis Isaac, 1974 from Java (see Suárez-Morales and McKinnon 2025). A further comparison of M. barbata ’ s fifth leg with Australian congeneric species was presented by Suárez-Morales and McKinnon (2025). The presence of paired lateral protuberances on the genital double-somite of M. barbata was also mentioned by Suárez-Morales and Gasca-Serrano (1992) as another distinctive character of this species and is documented in this paper.