Common Seahorse vs Compact Stonewort

Hippocampus kuda compared with Nitella tenuissima

Key Differences

Common Seahorse is Vulnerable while Compact Stonewort is Extinct.

Taxonomic Classification

Rank	Common Seahorse	Compact Stonewort
Kingdom	Animalia (Animals)	Plantae (Plants)
Phylum	Chordata (Chordates)	Charophyta (Charophyta)
Class	Actinopterygii (Ray-finned Fish)	Charophyceae (Charophyceae)
Order	Perciformes (Perch-like Fish)	Charales (Charales)
Family	Pomacentridae (Clownfish & Damselfish)	Characeae
Genus	Amphiprion (Clownfish)	Nitella
Species	Hippocampus kuda	Nitella tenuissima

Conservation Status

Common Seahorse

VU — Vulnerable

Trend: Decreasing ↓

Compact Stonewort

EX — Extinct

Physical Characteristics

Attribute	Common Seahorse	Compact Stonewort
Diet	Carnivore	—
Average Lifespan	5 years	—
Average Length	17 cm	—
Average Weight	10 g	—

Habitat & Geographic Range

Common Seahorse

Habitat

Found across multiple habitat types including tropical and subtropical moist broadleaf forests, tropical and subtropical dry broadleaf forests, and tropical and subtropical grasslands and savannas, among 7 distinct biome types. Populations are also found in montane and highland environments at higher elevations.

Range

Distributed across Australia, India, Indonesia, Japan, and Philippines. Currently classified as Vulnerable on the IUCN Red List, this species faces significant conservation challenges across its range.

Compact Stonewort

Habitat

Native to Asia and Europe and North America, inhabiting ecosystems characteristic of the region.

Range

Distributed across Brazil, Norway, Sweden, Taiwan, and United States.

Common Seahorse

The common seahorse is found in tropical and temperate waters. Males carry and deliver the babies.

Compact Stonewort

<em>Nitella tenuissima</em>, a stonewort formerly found in fresh and brackish water habitats, was a member of the charophyte family Characeae — the algal lineage most closely related to land plants. Historical records document its occurrence across Brazil, Norway, Sweden, Taiwan, and the United States, where it inhabited clear, oligotrophic lakes, ponds, and slow-flowing water bodies with low nutrient levels. Like other Nitella species, it was a delicate, translucent, submerged aquatic plant lacking the calcium carbonate encrustation of related genera, forming low-growing mats on soft sediments in well-illuminated shallow water. The species played a role in aquatic ecosystems by stabilising lake sediments, contributing to water clarity, and providing microhabitat for invertebrates and small aquatic organisms. <em>Nitella tenuissima</em> is classified as Extinct by the IUCN, having not been recorded from any of its former localities despite targeted searches. The primary causes of its extinction are believed to be widespread eutrophication of freshwater habitats driven by agricultural nutrient runoff and sewage discharge, which eliminated the clear, nutrient-poor conditions on which the species depended. The loss of this stonewort is emblematic of the broader decline of freshwater charophyte diversity across the Northern Hemisphere. Biological traits including historical morphological measurements and reproductive parameters are documented only in sparse historical herbarium specimens and early botanical literature.