Cyerce willetteorum, Moreno & Rico & Middlebrooks & Medrano & Valdés & Krug, 2024

Moreno, Karina, Rico, Diane M., Middlebrooks, Michael, Medrano, Sabrina, Valdés, Ángel A. & Krug, Patrick J., 2024, A cryptic radiation of Caribbean sea slugs revealed by integrative analysis: Cyerce ‘ antillensis’ (Sacoglossa: Caliphyllidae) is six distinct species, Zoological Journal of the Linnean Society 200 (4), pp. 940-979 : 968-970

Cyerce willetteorum sp.nov.

( Figs 1–3 , 5 , 8F , 17 )

ZooBank registration: lsid:zoobank. org:act: B2309FF2-4BF7-4317-BE5F-5398AB298F30

Type material

Holotype: Stirrup Cay , Bahamas, July 2001, 2 mm preserved length ( LACM 3844 ; isolate 07Stir01).

Range

Great Stirrup Cay, Bahamas (present study).

Description

External morphology: No photograph was taken of the live specimen, hence no description of external morphology is possible at this time.

Internal morphology: Radula of holotype (LACM 3844, isolate 07Stir01) with six teeth on ascending limb and seven teeth on descending limb ( Fig. 17A ). Teeth shallow, bent at an angle of 18°, tapering to pointed tip; 97 µm in length ( Fig. 17B ). Row of nine denticles along each cutting edge, irregular in shape and width; narrow at base, widening to a curved edge, ≤ 2.5 μm wide. Denticles narrower, more rectangular near tip ( Fig. 17B ). Partial ascus with four pre-radular teeth ( Fig. 17C ).

Penis with curved, wide stylet, narrowing gradually from embedded base, 120 µm long; oval opening at wide tip ( Fig. 8F ).

Ecology

Collected from Pe. capitatus .

Etymology

Named in joint honour of Dr Demian Willette, who contributed specimens to this work and helped P.J.K. to initiate studies of sacoglossan biodiversity, and his brother Darian Willette, a devoted naturalist lost at too young an age.

Remarks

Only a single exemplar of C. willetteorum was sampled over the 15-year duration of this study of Western Atlantic sacoglossans. However, the lone specimen was supported as a distinct species by all methods of molecular species delimitation. Although the external morphology could not be described at this time, the penial stylet was distinct from the other complex members, less curved and shorter than C. nicholasi but more curved and longer than any other newly described species. The radular denticles were also distinctive, with an irregular shape and curved edge not observed in any other species. Given the genetic support for the holotype as a separate species and the distinctive characteristics of the internal anatomy, we elected to name the species to clarify the diversity of the Caribbean Cyerce spp. and to facilitate future studies of the biology of this rare taxon.

This was the only species collected from Pe. capitatus , although C. cf. cristallina associates transiently with Pe. capitatus at night (M. Charteris, unpublished data). Algal congeners Pe. dumetosus and Pe. lamourouxii were used as hosts by four other complex members and have thicker filaments than Pe. capitatus on the ‘shaving brush’ portion of the algal thallus. However, extensive collections of Pe. capitatus made elsewhere in the Caribbean did not yield specimens of Cyerce , leaving it unclear whether Pe. capitatus is a preferred host of C. willetteorum or was merely the more locally abundant Penicillus sp. at the type locality. Further study is needed to understand the basis of host specificity within the C. antillensis complex.

Figures

Figure 1. Western Atlantic sampling sites; for more details, see Table 1. Top panel shows southern Florida peninsula and eastern Caribbean; bottom panel shows expanded view of inset box.

Figure 2. Consensus phylogenetic tree for Cyerce and Sohgenia based on maximum likelihood (ML) analysis of three concatenated loci. Percentages corresponding to significant bootstrap support are given below branches, and posterior probabilities from Bayesian inference (BI) analysis are shown in bold above branches. Capital letters label three key supported nodes. Haplotypes are coded by date–location–specimen number on terminals. Results of four species delimitation analyses are indicated by vertical bars; horizontal shaded bars enclose specimens grouped as species entities by all methods.

Figure 3. Histogram of pairwise Tamura–Nei (TrN)-corrected COI distances, showing barcoding gap; white bars denote intraspecific distances and black bars interspecific distances, based on automated barcode gap discovery (ABGD) and assemble species by automatic partitioning (ASAP) analyses.

Figure 5. Haplotype network of phased histone 3 alleles colour-coded by candidate species, with the size of each circle denoting the frequency of the sampled allele. A small black dot indicates an unsampled allele. Each bar crossing a line denotes one nucleotide substitution.

Figure 8. Stained and mounted penial stylets of Cyerce species from the Western Atlantic. Black arrow indicates stylet.A, Cyerce nicholasi, isolate 10Bim03. B, Cyerce piercei, isolate KM66. C, Cyerce ellingsonorum, isolate 06Jam05. D, Cyerce antillensis, isolate 10Bim01.E, Cyerce browneveorum, isolate 09Gei01.F, Cyerce willetteorum, isolate 07Stir01.G, Cyerce cf. cristallina, isolate B101.

Figure 17. Cyerce willetteorum, radular scanning electron micrographs of LACM 3844 (isolate 07Stir01). A, complete radula, with ascus. B, close-up view of tissue-free teeth from descending limb, showing irregularly shaped denticles.C, close-up view of ascus.