Monstrilla parki, Suárez-Morales & P.M.B, 2025

Monstrilla parki sp. nov.

urn:lsid:zoobank.org:act:44543675-34ED-413E-A277-C623662ECE67

( Figs 48 View FIGURE 48 , 49 View FIGURE 49 )

Material examined. Adult male holotype undissected, mounted on slide in glycerine, (ECO-CHZ-12541).

Type locality. Davies Reef , Queensland, Australia (19°7.340’ S, 146°53.024’ E), coll. on 15 October 1985 GoogleMaps .

Diagnosis. Male monstrilloid with cephalothorax relatively short, robust, more than half of total body length (58%); anterior margin with weakly produced, smooth and flat forehead. Urosome relatively short, about 15% of total body length. Oral cone cylindrical, wide-based, moderately protuberant. Preoral surface with medial pore cluster, single pair of nipple-like integumental processes, and few integumental wrinkles. Antennules 5-segmented, geniculate between fourth and fifth segments; second segment longest; fifth segment with reduced setation including two slender, simple setae, one on outer margin and one on inner margin plus strong apical spines (6 1,2). Fifth pedigerous somite with ventral swelling carrying well-developed pair of globose protuberances armed with long, biserially setulated seta representing fifth leg, barely reaching beyond posterior margin of caudal rami. Genital somite carrying large, strongly protuberant genital complex with short bulging shaft and pair of rhomboid, divergent genital lappets ornamented with spinule rows on outer margin. Caudal rami armed with 5 caudal setae; setae III and IV unmodified.

Description of male holotype. Body relatively robust, margins of cephalothorax straight. Total body length 1.47 mm in dorsal view. Cephalothorax 58% of total body length, with flat, smooth forehead ( Fig. 49D View FIGURE 49 ) except for few integumental wrinkles. Preoral anteroventral surface with pair of large medial pore clusters between antennule bases (mpc in Fig. 49D View FIGURE 49 ); pores surrounded by patches of integumental wrinkles (iw in Fig. 49D View FIGURE 49 ); with single pair of nipple-like processes on ventral surface (nlp in Fig. 49D View FIGURE 49 ). Oral cone wide-based, weakly protuberant (oc in Fig.49D View FIGURE 49 ), located at 30% of way back along ventral surface of cephalothorax ( Fig. 45A View FIGURE 45 ). Eyes pigmented, represented by two lateral cups and medial ventral cup at anterior end of cephalothorax, medial cup slightly larger than lateral cups (mec, lec in Fig. 46A View FIGURE 46 ).

Urosome relatively robust, short ( Fig. 48B, C View FIGURE 48 ), about 15% of total body length, comprising fifth pedigerous somite, genital somite, one free somite, preanal and anal somites. Relative length of urosomites, from proximal to distal: 31.1: 21.4: 17.1: 13.4: 17.2 = 100. Fifth pedigerous somite longest, with ventral expansion bearing pair of globose fifth leg protopods (arrowheads in Fig. 48B, C View FIGURE 48 ), armed with long seta reaching beyond distal margin of caudal rami ( Fig. 48B View FIGURE 48 ). Genital somite carrying genital complex ventrally. Succeeding preanal and anal somites with smooth lateral and dorsal surfaces; anal somite carrying pair of caudal rami. Genital complex arising from ventral surface of genital somite ( Fig. 48C View FIGURE 48 ), with short thick shaft with smooth lateral margins; shaft expanded into globose structure branching distally into pair of leaf-shaped, symmetrical genital lappets, divergent in ventral view ( Fig. 48B, D, E View FIGURE 48 , GL in Fig. 49B View FIGURE 49 ). Lappets joined by weak medial notch (arrowheads in Fig. 48D, E View FIGURE 48 ) and ornamented with spinule rows along outer margin ( Fig. 48D, E View FIGURE 48 ). Caudal rami armed with 5 caudal setae subequal in length and width, one seta broken off in holotype.

Antennules 0.67 mm long, almost 45% of total body length, 5-segmented; segments 1–2 clearly divided, second segment longest ( Fig. 48A View FIGURE 48 ), partly fused with succeeding third segment; segments 3–4 fused, intersegmental division marked by constriction ( Fig. 48A View FIGURE 48 ). Following nomenclature by Grygier & Ohtsuka (1995), first segment unarmed, second segment carrying relatively short spiniform elements 2v 1–3 and smooth setiform element IId, third segment with short, spiniform element 3 and smooth elements IIIv and IIId ( Fig. 49A View FIGURE 49 ), fourth segment armature including short, spiniform elements 4v 1–3 and aesthetasc 4aes on proximal half, distal half with reduced armature including spiniform element 5 and setiform elements Vv and Vd ( Fig. 48A View FIGURE 48 ), with small, rounded integumental window adjacent to insertion of elements 4v 1–3 (asterisk in Fig. 48A View FIGURE 48 ); geniculation between fourth and fifth segments; fifth segment with reduced armature. Following Huys et al.’s (2007) nomenclature for the setation of the male antennulary fifth segment, outer margin with slender unbranched elements 5 and 6 and spiniform apical elements 1 and 2 ( Fig. 48F, G View FIGURE 48 ), inner margin with short element C on medial position.

Swimming legs 1–4 as in M. huysi sp. nov. Armature of swimming legs 1–4:

Leg Basis Endopod Exopod

1 1-0 0-1; 0-1;1-2-2 I-1; 0-1; I-2-2

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

Remarks. The male of M. parki sp. nov. can be included in the genus Monstrilla by the possession of (1) two urosomites between the genital somite and the anal somite; (2) the structure of its genital complex that is typical for the genus, in this case, type II (Suárez-Morales 2000); (3) the presence of well-developed paired fifth legs; (4) the possession of 4–6 caudal setae in both sexes, and (5) branched antennulary setae sometimes present. This combination of characters is unique among the known genera of monstrilloids ( Grygier & Ohtsuka 2008, Suárez-Morales & McKinnon 2014, Jeon et al. 2018).

Monstrilla parki sp. nov. belongs to a recently recognized species group related to M. conjunctiva that includes at least three species: (1) M. wandelii Stephensen, 1913 originally described from a female collected in Greenland; (2) specimens designated by Park (1967) as the males of M. wandelii (a decision likely based on Giesbrecht’s (1902) illustrations but deemed inaccurate by Suárez-Morales (2022) who argued that this male likely represents an undescribed species), (3) t M. conjunctiva and (4) M. mahahualensis . This group of species, currently known from males only, shares several distinctive characters including: (1) antennulary segmentation with first segment unarmed, (2) antennulary segments 3–4 fused, with a constriction marking the intersegmental division, (3) similar structure of the genitalia, with divergent, leaf-like genital lappets, (4) fifth leg represented by a single seta arising ventrally from pair of ventral bulb-like protopods on the fifth pediger, the fifth leg seta is of variable length ( Suárez-Morales 2022), and (5) the presence of one or more integumental windows on putative antennulary segments 3 and 4 ( Suárez-Morales, 2022, figs.1C, E, F, 2B).

The absence of a fifth caudal seta is reported in our holotype specimen, with only 4 setae observed ( Fig. 49C View FIGURE 49 ). Only four caudal setae was reported by Stephensen (1913) in the Greenland female and he illustrated a reduced caudal seta II, clearly narrower and shorter than the other setae ( Stephensen, 1913, pl. VI). This caudal seta structure was previously observed in M. conjunctiva ( Giesbrecht 1902) . This modification is clearly present in the Australian member of this group, M. parki sp. nov. (asterisk II in Fig. 49C View FIGURE 49 ). The same caudal seta reduction was illustrated for M. mahahualensis ( Suárez-Morales 2022, fig.2F). Consequently, the presence of four caudal setae including a reduced seta II can be added to the morphological features of the M. conjunctiva species-group.

In M. parki sp. nov., the integumental windows are small and difficult to observe and it further differs from the other species of this group by: (1) fifth leg seta barely reaching beyond the posterior margin of the caudal rami. In both M. conjunctiva ( Giesbrecht 1902, fig. XII.3, 4) and M. wandelii (sensu Park 1967, fig. 2C, D), the leg 5 setae are relatively short, not reaching the distal margin of the caudal rami. The length of the fifth leg seta of M. parki sp. nov. presents an intermediate condition between M. wandelii and M. conjunctiva , and that of M. mahahualensis ; (2) these species share the absence of antennulary element 1 (sensu Grygier & Ohtsuka 1995) on the first segment, but the armature of the antennulary segments has some additional differences among these species, particularly of the fifth segment. In M. wandelii , M. conjunctiva , and M. mahahualensis , the armature includes 8 elements, i.e., 5 setae, 2 spines (1, 2), and the apical aesthetasc AE2 (sensu Huys et al. 2007), whereas the armature is relatively reduced in M. parki sp. nov., comprising only six elements, 3 setae, 2 spines (1, 2) and aesthetasc AE2; (3) the apical spiniform elements 1 and 2 are equally long in M. wandelii and the element 1/element 2 length ratio is 0.66 in M. mahahualensis and 0.4 in both M. conjunctiva and M. parki sp. nov., and (4) the previous members of the M. conjunctiva species group share a type II male genitalia, distinguished by the presence of a smooth, rounded medial protrusion instead of a notch in the same position, different from the weak medial incision observed in M. parki sp. nov. ( Fig. 48D, E View FIGURE 48 ). Lappets are widely divergent, probably resulting from a strong development and anterior projection of the broad medial protuberance between them. The new species also differs from these congeners by details of the leaf-like genital lappets, which are distally acute in M. conjunctiva ( Giesbrecht 1902, fig. 12.3), subchelate and smooth in M. wandelii , and simple, conical and ornamented with rows of spinules in M. mahahualensis ( Suárez-Morales 2022, fig. 3A, B). In M. parki sp. nov., the spinule ornamentation is not restricted to the inner margin of lappets as in M. mahahualensis ( Suárez-Morales 2022, fig. 3A, B), but covers its entire distal half ( Fig. 48D, E View FIGURE 48 ). In M. wandelii the ornamentation of the lappets was not described by Stephensen (1913) or by Park (1967), but they are chela-like, bifurcate structures ( Park 1967, fig. 2C). Based on our comparative analysis, we propose M. parki sp. nov. as a new species of Monstrilla belonging to the M. conjunctiva group now comprise four species. It is interesting to note that the geographic distribution of this group is very wide, including Subarctic and Antarctic areas, the tropical Atlantic, and now Australia. According to Suárez-Morales (2022), a fifth species from the Western Caribbean is yet to be described.

Etymology. The species name is an eponym in recognition to the taxonomical work of the Korean copepodologist Dr. Taisoo Park, mainly on the pelagic Calanoida , but also on the Monstrilloida , including his observations on M. wandelii from Canada.

Genus Sarsimonstrillus gen. nov.

urn:lsid:zoobank.org:act:EA079F86-67DB-4219-A4B0-686632DA2313

Type species. Sarsimonstrillus pseudoantennulatus gen. et sp. nov., by original designation.

Generic diagnosis (based on the female of S. pseudantennulatus gen. nov., sp. nov.). Large (> 3.0 mm body length), female monstrilloid with typical shape and body tagmosis; cephalothorax 55% of total body length, anterior 1/3 of cephalothorax with integumental wrinkles on dorsal, lateral, and ventral surfaces. Antennule thick, 4-segmented, fourth segment longest, with reduced setation pattern. Anterior end of cephalothorax with ventral triangular process in medial position, between antennule bases. Prefrontal area dorsal to antennulary insertion carrying pair of large uniramous processes arising from wide bases tapering into slender horn-like processes with acute points giving the appearance of a second pair of antennules. Urosome 3-segmented, including partially fused genital double-somite. Caudal rami with 5 caudal setae; setae III–V modified, proximally thickened.

Type locality. Port Phillip Bay , Black Rock, Victoria, Australia (37°58.066’ S, 145°.2705’ E) .

Etymology. The name prefix Sars recognizes Georg Ossian Sars, the eminent Norwegian copepodologist (1837–1927) for his relevant, solid contributions to the knowledge and classification of the Monstrilloida . The genus suffix, using the masculine ending “us”, denotes its affinity to Monstrilla , from which it stemmed. Gender is masculine.

Remarks. Despite the basic affinities between the new genus Sarsimonstrillus gen. nov. and Monstrilla , the most conspicuous morphological character to distinguish between these two genera is the large pair of preantennulary processes arising from the anteriormost dorsal surface of the cephalothorax. No other monstrilloid genus or species possess similar paired anteriorly directed structures. It is combined with a primitive 3+2 exopodalendopodal setation pattern of the fifth leg and three proximally thickened caudal setae, a character shared by several species of Monstrilla , but in these instances only two setae (III and IV) are thickened vs. three (III, IV, and V) in Sarsimonstrillus gen. nov. In our opinion, the unique combination of characters mentioned above clearly diverges from the pattern exhibited by any other known genus of the Monstrilloida and we consider these differences enough to propose a new genus.