Two new species of the interstitial genus Parvocythere (Crustacea, Ostracoda, Cytheroidea) from Japan: an example of morphological variation

Abstract

Two new species of the interstitial ostracod genus Parvocythere, Parvocythere gottwaldi sp. n. and Parvocythere gracilis sp. n., are herein described. Although these two new species are clearly distinguishable by certain morphological differences in elements of the male copulatory organ, and the carapace, they share the following simplified characters of the appendages and male copulatory organ: antennular fourth podomere with no suture; reduced claws on the distal end of antenna; and asymmetric male copulatory organ. The morphological differences among known and new Parvocythere species suggest that the species of this genus can be classified into two groups by the presence/absence of the suture on the antennular fourth podomere. The “Group S” is characterised by the presence of the antennular suture, and all species of this group have a two-clawed antenna and symmetric male copulatory organ, characters which are generally seen in cytheroid ostracods. The species belonging to “Group N” are characterised by the absence of the suture, regarded as a pedomorphic character, show the following characters: two clawed or one clawed antenna, and symmetric or asymmetric male copulatory organ. The morphological variation within Group N includes reductive characters regarded as an adaptation to the narrow spaces of the interstitial environment of a sandy beach. These intrageneric morphological variations of the exclusively interstitial genus Parvocythere suggest the possibilities that Group N might be derived from Group S, and that some adaptive characters to an interstitial environment could have developed after the colonisation of these environments.

Molecular phylogeny of interstitial Polycopidae ostracods (Crustacea) and descriptions of a new genus and four new species

“…Marine interstitial ostracods were first reported by Klie (), who described three new polycopid species from ‘amphioxus sand’ and shell gravel in Helgoland, Germany. Like other interstitial animals, these ostracods often show specialized morphological characters (Hartmann, ; Maddocks, ; Gottwald, ; Higashi & Tsukagoshi, ), e.g. they are much smaller than their surface‐dwelling relatives (Danielopol & Bonaduce, ; Yamada & Tanaka, ) and have reduced or absent eyes (Kaji & Tsukagoshi, ).…”

Revised Morphological Characteristics of Species of Two Ostracod Genera Loxoconcha Sars, 1866 (Loxoconchidae) and Xestoleberis Sars, 1866 (Xestoleberididae)

“…However, observation of plural individuals of the species L. pulchra showed this species carries ve adductor muscle scars, in which the top one was divided into two (Appendix 2.13). This character may be a mutation phenomenon that was already mentioned by several authors (e. g., Higashi and Tsukagoshi 2012). It also can be regarded as apomorphy in Loxoconcha.…”

Added Morphological Characteristics of Muscle Scars, Maxillula and Mandible of Two Ostracod Genera Loxoconcha (Loxoconchidae) and Xestoleberis (Xestoleberididae)

“…7, M). This character may be a mutation phenomenon that was already mentioned in the species of Parvocythere by Higashi & Tsukagoshi (2012), of Eucypris by Schön et al (2000), of Darwinulidae by Van Doninck et al (2004). It also can be regarded as apomorphy in Loxoconcha.…”